1.1

1.2

1.2.1

1.2.1.1

1.2.1.2

1.2.1.3

1.2.1.4

1.2.1.5

1.2.2

1.2.2.1

1.2.2.2

1.2.2.3

1.2.3

1.2.3.1

1.2.3.2

1.2.3.3

1.3

1.3.1

1.3.1.1

1.3.1.2

1.3.1.3

1.3.1.4

1.3.2

1.3.2.1

1.3.2.2

1.3.2.3

1.3.3

1.3.3.1

1.4

1.4.1

1.4.1.1

1.4.1.2

1.4.1.3

1.4.2

1.4.2.1

1.4.2.2

1.4.2.3

1.5

1.5.1

TableofContentsIntroduction

Unit1.GetStarted

Lesson1:BuildYourFirstApp

1.1:InstallAndroidStudioandRunHelloWorld

1.2A:MakeYourFirstInteractiveUI

1.2B:UsingLayouts

1.3:WorkingwithTextViewElements

1.4:LearningAboutAvailableResources

Lesson2:Activities

2.1:CreateandStartActivities

2.2:ActivityLifecycleandState

2.3:ActivitiesandImplicitIntents

Lesson3:Testing,Debugging,andUsingSupportLibraries

3.1:UsingtheDebugger

3.2:TestingyourApp

3.3:UsingSupportLibraries

Unit2.UserExperience

Lesson4:UserInteraction

4.1:UsingKeyboards,InputControls,Alerts,andPickers

4.2:UsinganOptionsMenuandRadioButtons

4.3:UsingtheAppBarandTabsforNavigation

4.4:CreatingaRecyclerView

Lesson5:DelightfulUserExperience

5.1:Drawables,Styles,andThemes

5.2:MaterialDesign:Lists,Cards,andColors

5.3:SupportingLandscape,MultipleScreenSizes,andLocalization

Lesson6:TestingyourUI

6.1:UsingEspressotoTestYourUI

Unit3.WorkingintheBackground

Lesson7:BackgroundTasks

7.1:CreateanAsyncTask

7.2:ConnecttotheInternetwithAsyncTaskandAsyncTaskLoader

7.3:BroadcastReceivers

Lesson8:Triggering,Scheduling,andOptimizingBackgroundTasks

8.1:Notifications

8.2:AlarmManager

8.3:JobScheduler

Unit4.AllAboutData

Lesson9:PreferencesandSettings

2

1.5.1.1

1.5.1.2

1.5.2

1.5.2.1

1.5.2.2

1.5.3

1.5.3.1

1.5.3.2

1.5.3.3

1.5.4

1.5.4.1

1.6

1.6.1

1.6.2

1.6.3

1.6.4

1.6.5

1.6.6

1.7

9.1:SharedPreferences

9.2:AddingSettingstoanApp

Lesson10:StoringDataUsingSQLite

10.1A:SQLiteDatabase

10.1B:SearchingaSQLiteDatabase

Lesson11:SharingDatawithContentProviders

11.1A:ImplementingaMinimalistContentProvider

11.1B:AddingaContentProvidertoYourDatabase

11.1C:SharingContentwithOtherApps

Lesson12:LoadingDataUsingLoaders

12.1:LoadingandDisplayingFetchedData

Appendix:Homework

HomeworkLesson1

HomeworkLesson2

HomeworkLessons3,4

HomeworkLessons5,6

HomeworkLessons7,8

HomeworkLessons9,10,11

Appendix:Utilities

3

AndroidDeveloperFundamentalsCourse–PracticalsAndroidDeveloperFundamentalsisatrainingcoursecreatedbytheGoogleDeveloperTrainingteam.YoulearnbasicAndroidprogrammingconceptsandbuildavarietyofapps,startingwithHelloWorldandworkingyourwayuptoappsthatusecontentprovidersandloaders.

AndroidDeveloperFundamentalspreparesyoutotaketheexamfortheAssociateAndroidDeveloperCertification.

Thiscourseisintendedtobetaughtinaclassroom,butallthematerialsareonline,soifyouliketolearnbyyourself,goahead!

PrerequisitesAndroidDeveloperFundamentalsisintendedfornewandexperienceddeveloperswhoalreadyhaveJavaprogrammingexperienceandnowwanttolearntobuildAndroidapps.

CoursematerialsThecoursematerialsinclude:

Thispracticalworkbook,whichguidesyouthroughcreatingAndroidappstopracticeandperfecttheskillsyou'relearningAconceptreference:AndroidDeveloperFundamentalsCourse—ConceptsSlidedecks(foroptionalusebyinstructors)Videosoflectures(forreferencebyinstructorsandstudents)

Whattopicsarecovered?

AndroidDeveloperFundamentalsincludesfiveteachingunits,whicharedescribedinWhatdoesthecoursecover?

DevelopedbytheGoogleDeveloperTrainingTeam

Introduction

4

Lastupdated:February2017

ThisworkislicensedunderaCreativeCommonsAttribution-NonCommercial4.0InternationalLicense

Introduction

5

1.1:InstallAndroidStudioandRunHelloWorldContents:

WhatyoushouldalreadyKNOWWhatyouwillNEEDWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.InstallAndroidStudioTask2:Create"HelloWorld"appTask3:ExploretheprojectstructureandlayoutTask4:CreateavirtualdeviceTask5:RunyourapponanemulatorTask6.AddlogstatementstoyourappTask7:ExploretheAndroidManifest.xmlfileTask8.Explorethebuild.gradlefileTask9.RunyourapponadeviceCodingchallengeSummaryRelatedconceptsLearnmore

Welcometothepracticalexercises.Youwilllearnto:

InstallAndroidStudio,theAndroiddevelopmentenvironment.LearnabouttheAndroiddevelopmentprocess.CreateandrunyourfirstAndroidHelloWorldapponanemulatorandonaphysicaldevice.Addloggingtoyourappfordebuggingpurposes.

WhatyoushouldalreadyKNOWForthispracticalyoushouldbeableto:

Understandthegeneralsoftwaredevelopmentprocessforobject-orientedapplicationsusinganIDE(IntegratedDevelopmentEnvironment).Demonstratethatyouhaveatleast1-3yearsofexperienceinobject-orientedprogramming,withsomeofitfocusedontheJavaprogramminglanguage.(Thesepracticalswillnotexplainobject-orientedprogrammingortheJavalanguage.)

WhatyouwillNEEDForthesepracticals,youwillneed:

AMac,Windows,orLinuxcomputer.SeethebottomoftheAndroidStudiodownloadpageforup-to-datesystemrequirements.InternetaccessoranalternativewayofloadingthelatestAndroidStudioandJavainstallationsontoyourcomputer.

WhatyouwillLEARNYouwilllearnto:

InstallandusetheAndroidIDE.

Introduction

6

UnderstandthedevelopmentprocessforbuildingAndroidapps.CreateanAndroidprojectfromabasicapptemplate.

WhatyouwillDOInstalltheAndroidStudiodevelopmentenvironment.Createaanemulator(virtualdevice)torunyourapponyourcomputer.CreateandruntheHelloWorldapponthevirtualandphysicaldevices.Exploretheprojectlayout.Generateandviewlogstatementsfromyourapp.ExploretheAndroidManifest.xmlfile.

AppOverviewAfteryousuccessfullyinstalltheAndroidStudioIDE,youwillcreate,fromatemplate,anewAndroidprojectforthe'HelloWorld'app.Thissimpleappdisplaysthestring"HelloWorld"onthescreenoftheAndroidvirtualorphysicaldevice.

Here'swhatthefinishedappwilllooklike:

Introduction

7

Introduction

8

Task1.InstallAndroidStudioAndroidStudioisGoogle'sIDEforAndroidapps.AndroidStudiogivesyouanadvancedcodeeditorandasetofapptemplates.Inaddition,itcontainstoolsfordevelopment,debugging,testing,andperformancethatmakeitfasterandeasiertodevelopapps.Youcantestyourappswithalargerangeofpreconfiguredemulatorsoronyourownmobiledevice,andbuildproductionAPKsforpublication.

Note:AndroidStudioiscontinuallybeingimproved.Forthelatestinformationonsystemrequirementsandinstallationinstructions,refertothedocumentationatdeveloper.android.com.TogetupandrunningwithAndroidStudio:

YoumayneedtoinstalltheJavaDevelopmentKit-Java7orbetter.InstallAndroidStudio

AndroidStudioisavailableforWindows,Mac,andLinuxcomputers.Theinstallationissimilarforallplatforms.Anydifferenceswillbenotedinthesectionsbelow.

1.1.InstallingtheJavaDevelopmentKit

1. Onyourcomputer,openaterminalwindow.2. Typejava-version

Theoutputincludesaline:

Java(™)SERuntimeEnvironment(build1.X.0_05-b13)

Xistheversionnumbertolookat.

Ifthisis7orgreater,youcanmoveontoinstallingAndroidStudio.IfyouseeaJavaSEversionisbelow7orifJavaisnotinstalled,youneedtoinstallthelatestversionoftheJavaSEdevelopmentkitbeforeinstallingAndroidStudio.

TodownloadtheJavaStandardEdition()DevelopmentKit(JDK):

1. GototheOracleJavaSEdownloadspage.2. ClicktheJavaSEDownloadsicontoopentheJavaSEDevelopmentKit8Downloadspage.3. IntheboxforthelatestJavaSEDevelopmentkit,youneedtoaccepttheLicenseAgreementinordertoproceed.

Thendownloadtheversionappropriateforthecomputeryouaredevelopingon.Important:Donotgotothedemosandsamples(themenuslookverysimilar,somakesuretoreadtheheadingatthetop).

4. Installthedevelopmentkit.OncetheinstallationoftheJDKiscompleted—itshouldonlytakeafewminutes—youcanconfirmit'scorrectbycheckingtheJavaversionfromthecommandline.

5. OpenaterminalwindowandenterTypejava-versionagaintoverifythatinstallationhasbeensuccessful.6. SettheJAVA_HOMEenvironmentvariabletotheinstallationdirectoryoftheJDK.

Windows:

1. SetJAVA_HOMEtotheinstallationlocation.2. Start>ControlPanel>System>AdvancedSystemSettings>EnvironmentVariablesSystemVariables>New

Variablename:JAVA_HOMEVariablevalue:C:\ProgramFiles\Java\jdk1.7.0_80(orwhateverversionyourinstallationis!)

3. Ifthevariablealreadyexists,updateittothisversionoftheJDK.4. VerifyyourJAVA_HOMEvariablefromacmd.exeterminal:echo%JAVA_HOME%

Seealso:https://docs.oracle.com/cd/E19182-01/820-7851/inst_cli_jdk_javahome_t/

Mac:

Introduction

9

1. OpenTerminal.2. ConfirmyouhaveJDKbytyping"whichjava".3. CheckthatyouhavetheneededversionofJava,bytyping"java-version".4. SetJAVA_HOMEusingthiscommandinTerminal:exportJAVA_HOME=`whichjava`5. enterecho$JAVA_HOMEtoconfirmthepath.

Linux:

See:https://docs.oracle.com/cd/E19182-01/820-7851/inst_cli_jdk_javahome_t/

Important:Don'tinstallAndroidStudiountilaftertheJavaJDKisinstalled.WithoutaworkingcopyofJava,therestoftheprocesswillnotwork.Ifyoucan'tgetthedownloadtowork,lookforerrormessages,andsearchonlinetofindasolution.BasicTroubleshooting:

ThereisnoUI,ControlPanel,orStartupiconassociatedwiththeJDK.VerifythatyouhavecorrectlyinstalledtheJDKbygoingtothedirectorywhereyouinstalledit.ToidentifywheretheJDKis,,lookatyourPATHvariableand/orsearchyourcomputerforthe"jdk"directoryorthe"java"or"javac"executable.

1.2.InstallingAndroidStudio1. NavigatetotheAndroiddeveloperssiteandfollowtheinstructionstodownloadandinstallAndroidStudio.

Acceptthedefaultconfigurationsforallsteps.Makesurethatallcomponentsareselectedforinstallation.

2. Afterfinishingtheinstall,theSetupWizardwilldownloadandinstallsomeadditionalcomponents.Bepatient,thismighttakesometimedependingonyourInternetspeed,andsomeofthestepsmayseemredundant.

3. Whenthedownloadcompletes,AndroidStudiowillstart,andyouarereadytocreateyourfirstproject.Troubleshooting:Ifyourunintoproblemswithyourinstallation,checkthelatestdocumentation,programmingforums,orgethelpfromyouinstructors.

Task2:Create"HelloWorld"appInthistask,youwillimplementthe"HelloWorld"apptoverifythatAndroidstudioiscorrectlyinstalledandlearnthebasicsofdevelopingwithAndroidStudio.

2.1Createthe"HelloWorld"app1. LaunchAndroidStudioifitisnotalreadyopened.2. InthemainWelcometoAndroidStudiowindow,click"StartanewAndroidStudioproject".3. IntheNewProjectwindow,giveyourapplicationanApplicationName,suchas"HelloWorld".4. VerifytheProjectlocation,orchooseadifferentdirectoryforstoringyourproject.5. ChooseauniqueCompanyDomain.

AppspublishedtotheGooglePlayStoremusthaveauniquepackagename.Sincedomainsareunique,prependingyourapp'snamewithyouroryourcompany'sdomainnameisgoingtoresultinauniquepackagename.Ifyouarenotplanningtopublishyourapp,youcanacceptthedefaultexampledomain.Beawarethatchangingthepackagenameofyourapplaterisextrawork.

6. VerifythatthedefaultProjectlocationiswhereyouwanttostoreyourHelloWorldappandotherAndroidStudioprojects,orchangeittoyourpreferreddirectory.ClickNext.

7. OntheTargetAndroidDevicesscreen,"PhoneandTablet"shouldbeselected.AndyoushouldensurethatAPI15:Android4.0.3IceCreamSandwichissetastheMinimumSDK.(Fixthisifnecessary.)

Atthewritingofthisbook,choosingthisAPIlevelmakesyour"HelloWorld"appcompatiblewith97%ofAndroiddevicesactiveontheGooglePlayStore.Thesearethesettingsusedbytheexamplesinthisbook.

8. ClickNext.

Introduction

10

9. IfyourprojectrequiresadditionalcomponentsforyourchosentargetSDK,AndroidStudiowillinstallthemautomatically.ClickNext.

10. CustomizetheActivitywindow.Everyappneedsatleastoneactivity.AnactivityrepresentsasinglescreenwithauserinterfaceandAndroidStudioprovidestemplatestohelpyougetstarted.FortheHelloWorldproject,choosethesimplesttemplate(asofthiswriting,the"EmptyActivity"projecttemplateisthesimplesttemplate)available.

11. ItisacommonpracticetocallyourmainactivityMainActivity.Thisisnotarequirement.12. MakesuretheGenerateLayoutfileboxischecked(ifvisible).13. MakesuretheBackwardsCompatibility(AppCompat)boxischecked.14. LeavetheLayoutNameasactivity_main.Itiscustomarytonamelayoutsaftertheactivitytheybelongto.Acceptthe

defaultsandclickFinish.

Afterthesesteps,AndroidStudio:

CreatesafolderforyourAndroidStudioProjects.BuildsyourprojectwithGradle(thismaytakeafewmoments).AndroidStudiousesGradleasit'sbuildsystem.SeetheConfigureyourbuilddeveloperpageformoreinformation.Opensthecodeeditorwithyourproject.Displaysatipoftheday.

AndroidStudiooffersmanykeyboardshortcuts,andreadingthetipsisagreatwaytolearnthemovertime.

TheAndroidStudiowindowshouldlooksimilartothefollowingdiagram:

Youcanlookatthehierarchyofthefilesforyourappinmultipleways.

1. ClickontheHelloWorldfoldertoexpandthehierarchyoffiles(1),2. ClickonProject(2).3. ClickontheAndroidmenu(3).4. Explorethedifferentviewoptionsforyourproject.

Note:ThisbookusestheAndroidviewoftheprojectfiles,unlessspecifiedotherwise.

Introduction

11

Task3:ExploretheprojectstructureInthispractical,youwillexplorehowtheprojectfilesareorganizedinAndroidStudio.

ThesestepsassumethatyourHelloWorldprojectstartsoutasshowninthediagramabove.

3.1ExploretheprojectstructureandlayoutIntheProject>Androidviewofyourprevioustask,therearethreetop-levelfoldersbelowyourappfolder:manifests,java,andres.

1. Expandthemanifestsfolder.

ThisfoldercontainsAndroidManifest.xml.ThisfiledescribesallofthecomponentsofyourAndroidappandisreadbytheAndroidrun-timesystemwhenyourprogramisexecuted.

2. Expandthejavafolder.AllyourJavalanguagefilesareorganizedinthisfolder.Thejavafoldercontainsthreesubfolders:

com.example.hello.helloworld(orthedomainnameyouhavespecified):Allthefilesforapackageareinafoldernamedafterthepackage.ForyourHelloWorldapplication,thereisonepackageanditonlycontainsMainActivity.java(thefileextensionmaybeomittedintheProjectview).com.example.hello.helloworld(androidTest):Thisfolderisforyourinstrumentedtests,andstartsoutwithaskeletontestfile.com.example.hello.helloworld(test):Thisfolderisforyourunittestsandstartsoutwithanautomaticallycreatedskeletonunittestfile.

3. Expandtheresfolder.Thisfoldercontainsalltheresourcesforyourapp,includingimages,layoutfiles,strings,icons,andstyling.Itincludesthesesubfolders:

drawable.Storeallyourapp'simagesinthisfolder.layout.EveryactivityhasatleastonelayoutfilethatdescribestheUIinXML.ForHelloWorld,thisfoldercontainsactivity_main.xml.mipmap.Storeyourlaunchericonsinthisfolder.Thereisasub-folderforeachsupportedscreendensity.Androidusesthescreendensity,thatis,thenumberofpixelsperinchtodeterminetherequiredimageresolution.Androidgroupsallactualscreendensitiesintogeneralizeddensities,suchasmedium(mdpi),high(hdpi),orextra-extra-extra-high(xxxhdpi).Theic_launcher.pngfoldercontainsthedefaultlaunchericonsforallthedensitiessupportedbyyourapp.values.Insteadofhardcodingvalueslikestrings,dimensions,andcolorsinyourXMLandJavafiles,itisbestpracticetodefinethemintheirrespectivevaluesfile.Thismakesiteasiertochangeandbeconsistentacrossyourapp.

4. Expandthevaluessubfolderwithintheresfolder.Itincludesthesesubfolders:colors.xml.Showsthedefaultcolorsforyourchosentheme,andyoucanaddyourowncolorsorchangethembasedonyourapp'srequirements.dimens.xml.Storethesizesofviewsandobjectsfordifferentresolutions.strings.xml.Createresourcesforallyourstrings.Thismakesiteasytotranslatethemtootherlanguages.styles.xml.Allthestylesforyourappandthemegohere.StyleshelpgiveyourappaconsistentlookforallUIelements.

3.2TheGradlebuildsystem

AndroidStudiousesGradleasitsbuildsystem.Asyouprogressthroughthesepracticals,youwilllearnmoreaboutgradleandwhatyouneedtobuildandrunyourapps.

1. ExpandtheGradleScriptsfolder.Thisfoldercontainsallthefilesneededbythebuildsystem.2. Lookforthebuild.gradle(Module:app)file.Whenyouareaddingapp-specificdependencies,suchasusingadditional

libraries,theygointothisfile.

Introduction

12

Task4:Createavirtualdevice(emulator)Inthistask,youwillusetheAndroidVirtualDevice(AVD)managertocreateavirtualdeviceoremulatorthatsimulatestheconfigurationforaparticulartypeofAndroiddevice.

UsingtheAVDManager,youdefinethehardwarecharacteristicsofadeviceanditsAPIlevel,andsaveitasavirtualdeviceconfiguration.

WhenyoustarttheAndroidemulator,itreadsaspecifiedconfigurationandcreatesanemulateddevicethatbehavesexactlylikeaphysicalversionofthatdevice,butitresidesonyourcomputer.

Why:Withvirtualdevices,youcantestyourappsondifferentdevices(tablets,phones)withdifferentAPIlevelstomakesureitlooksgoodandworksformostusers.Youdonotneedtodependonhavingaphysicaldeviceavailableforappdevelopment.

4.1CreateavirtualdeviceInordertorunanemulatoronyourcomputer,youhavetocreateaconfigurationthatdescribesthevirtualdevice.

1. InAndroidStudio,selectTools>Android>AVDManager,orclicktheAVDManagericon inthetoolbar.2. Clickthe+CreateVirtualDevice….(Ifyouhavecreatedavirtualdevicebefore,thewindowshowsallofyourexisting

devicesandthebuttonisatthebottom.)

TheSelectHardwarescreenappearsshowingalistofpreconfiguredhardwaredevices.Foreachdevice,thetableshowsitsdiagonaldisplaysize(Size),screenresolutioninpixels(Resolution),andpixeldensity(Density).

FortheNexus5device,thepixeldensityisxxhdpi,whichmeansyourappusesthelaunchericonsinthexxhdpifolderofthemipmapfolder.Likewise,yourappwilluselayoutsanddrawablesfromfoldersdefinedforthatdensityaswell.

3. ChoosetheNexus5hardwaredeviceandclickNext.4. OntheSystemImagescreen,fromtheRecommendedtab,choosewhichversionoftheAndroidsystemtorunonthe

virtualdevice.Youcanselectthelatestsystemimage.

TherearemanymoreversionsavailablethanshownintheRecommendedtab.Lookatthex86ImagesandOtherImagestabstoseethem.

5. IfaDownloadlinkisvisiblenexttoasystemimageversion,itisnotinstalledyet,andyouneedtodownloadit.Ifnecessary,clickthelinktostartthedownload,andclickFinishwhenit'sdone.

6. OnSystemImagescreen,chooseasystemimageandclickNext.7. Verifyyourconfiguration,andclickFinish.(IftheYourAndroidDevicesAVDManagerwindowstaysopen,youcan

goaheadandcloseit.)

Task5.RunyourapponanemulatorInthistask,youwillfinallyrunyourHelloWorldapp.

5.1Runyourapponanemulator

1. InAndroidStudio,selectRun>RunapporclicktheRunicon inthetoolbar.2. IntheSelectDeploymentTargetwindow,underAvailableEmulators,selectNexus5API23andclickOK.

Theemulatorstartsandbootsjustlikeaphysicaldevice.Dependingonthespeedofyourcomputer,thismaytakeawhile.Yourappbuilds,andoncetheemulatorisready,AndroidStudiowilluploadtheapptotheemulatorandrunit.

YoushouldseetheHelloWorldappasshowninthefollowingscreenshot.

Introduction

13

Introduction

14

Note:Whentestingonanemulator,itisagoodpracticetostartituponce,attheverybeginningofyoursession.Youshouldnotclosetheemulatoruntilyouaredonetestingyourapp,sothatyourappdoesn'thavetogothroughthebootprocessagain.

CodingchallengeNote:Allcodingchallengesareoptional,andarenotrequirementsforsubsequentpracticals.

Challenge:Youcanfullycustomizeyourvirtualdevices.

StudytheAVDManagerdocumentation.Createoneorseveralcustomvirtualdevices.

Youmaynoticethatnotallcombinationsofdevicesandsystemversionsworkwhenyourunyourapp.Thisisbecausenotallsystemimagescanrunonallhardwaredevices.

Task6.AddlogstatementstoyourappInthispractical,youwilladdlogstatementstoyourapp,whicharedisplayedintheloggingwindowoftheAndroidMonitor.

Why:Logmessagesareapowerfuldebuggingtoolthatyoucanusetocheckonvalues,executionpaths,andreportexceptions.

TheAndroidMonitordisplaysinformationaboutyourapp.

1. ClicktheAndroidMonitorbuttonatthebottomofAndroidStudiotoopentheAndroidMonitor.

Bydefault,thisopenstothelogcattab,whichdisplaysinformationaboutyourappasitisrunning.Ifyouaddlogstatementstoyourapp,theyareprintedhereaswell.

YoucanalsomonitortheMemory,CPU,GPU,andNetworkperformanceofyourappfromtheothertabsoftheAndroidMonitor.Thiscanbehelpfulfordebuggingandperformancetuningyourcode.

2. ThedefaultloglevelisVerbose.Inthedrop-downmenu,changethelogleveltoDebug.

Introduction

15

LogstatementsthatyouaddtoyourappcodeprintamessagespecifiedbyyouinthelogcattaboftheAndroidMonitor.Forexample:

Log.d("MainActivity","HelloWorld");

Thepartsofthemessageare:

Log–TheLogclass.APIforsendinglogmessages.d–TheLoglevel.Usedtofilterlogmessagedisplayinlogcat."d"isfordebug.Otherloglevelsare"e"forerror,"w"forwarning,and"i"forinfo."MainActivity"–Thefirstargumentisatagwhichcanbeusedtofiltermessagesinlogcat.Thisiscommonlythenameoftheactivityfromwhichthemessageoriginates.However,youcanmakethisanythingthatisusefultoyoufordebugging.

Byconvention,logtagsaredefinedasconstants:

privatestaticfinalStringLOG_TAG=MainActivity.class.getSimpleName();

"Helloworld"–Thesecondargumentistheactualmessage.

6.1Addlogstatementstoyourapp1. OpenyourHelloWorldappinAndroidstudio,andopenMainActivityfile.2. File>Settings>Editor>General>AutoImport(Mac:AndroidStudio>Preferences>Editor>General>Auto

Import).SelectallcheckboxesandsetInsertimportsonpastetoAll.Unambiguousimportsarenowaddedautomaticallytoyourfiles.Notethe"addunambiguousimportsonthefly"optionisimportantforsomeAndroidfeaturessuchasNumberFormat.Ifnotchecked,NumberFormatshowsanerror.Clickon'Apply'followedbyclickingonthe'Ok'button.

3. IntheonCreatemethod,addthefollowinglogstatement:

Log.d("MainActivity","HelloWorld");

Introduction

16

4. IftheAndroidMonitorisnotalreadyopen,clicktheAndroidMonitortabatthebottomofAndroidStudiotoopenit.(Seescreenshot.)

5. MakesurethattheLoglevelintheAndroidMonitorlogcatissettoDebugorVerbose(default).6. Runyourapp.

SolutionCode:

packagecom.example.hello.helloworld;

importandroid.os.Bundle;

importandroid.support.v7.app.AppCompatActivity;

importandroid.util.Log;

publicclassMainActivityextendsAppCompatActivity{

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

Log.d("MainActivity","HelloWorld");

}

}

OutputLogMessage

03-1812:20:23.1842983-2983/com.example.hello.helloworldD/MainActivity:HelloWorld

Codingchallenge

Introduction

17

Note:Allcodingchallengesareoptionalandarenotaprerequisiteforthenextchapter.Challenge:AcommonuseoftheLogclassistologJavaexceptionswhentheyoccurinyourprogram.TherearesomeusefulmethodsintheLogclassthatyoucanuseforthispurpose.UsetheLogclassdocumentationtofindoutwhatmethodsyoucanusetoincludeanexceptionwithalogmessage.Then,writecodeintheMainActivity.javafiletotriggerandloganexception.

Task7:ExploretheAndroidManifest.xmlfileEveryappincludesanAndroidManifestfile(AndroidManifest.xml).ThemanifestfilecontainsessentialinformationaboutyourappandpresentsthisinformationtotheAndroidruntimesystem.Androidmusthavethisinformationbeforeitcanrunanyofyourapp'scode.

InthispracticalyouwillfindandreadtheAndroidManifest.xmlfilefortheHelloWorldapp.

Why:Asyourappsaddmorefunctionalityandtheuserexperiencebecomesmoreengagingandinteractive,theAndroidManifest.xmlfilecontainsmoreandmoreinformation.Inlaterlessons,youwillmodifythisfiletoaddfeaturesandfeaturepermissions.

7.1ExploretheAndroidManifest.xmlfile1. OpenyourHelloWorldappinAndroidstudio,andinthemanifestsfolder,openAndroidManifest.xml.2. Readthefileandconsiderwhateachlineofcodeindicates.Thecodebelowisannotatedtogiveyousomehints.

Annotatedcode:

Introduction

18

<!--XMLversionandcharacterencoding-->

<?xmlversion="1.0"encoding="utf-8"?>

<!--Requiredstartingtagforthemanifest-->

<manifest

<!--Definestheandroidnamespace.Donotchange.-->

xmlns:android="http://schemas.android.com/apk/res/android"

<!--Uniquepackagenameofyourapp.Donotchangeonceappis

published.-->

package="com.example.hello.helloworld">

<!--Requiredapplicationtag-->

<application

<!--Allowtheapplicationtobebackedupandrestored.–>

android:allowBackup="true"

<!--Iconfortheapplicationasawhole,

anddefaulticonforapplicationcomponents.–>

android:icon="@mipmap/ic_launcher"

<!--User-readablefortheapplicationasawhole,

anddefaulticonforapplicationcomponents.NoticethatAndroid

Studiofirstshowstheactuallabel"HelloWorld".

Clickonit,andyouwillseethatthecodeactuallyreferstoastring

resource.Ctrl-click@string/app_nametoseewheretheresourceis

specified.Thiswillbecoveredinalaterpractical.–>

android:label="@string/app_name"

<!--Whethertheappiswillingtosupportright-to-leftlayouts.–>

android:supportsRtl="true"

<!--Defaultthemeforstylingallactivities.–>

android:theme="@style/AppTheme">

<!--Declaresanactivity.Oneisrequired.

Allactivitiesmustbedeclared,

otherwisethesystemcannotseeandrunthem.–>

<activity

<!--Nameoftheclassthatimplementstheactivity;

subclassofActivity.–>

android:name=".MainActivity">

<!--Specifiestheintentsthatthisactivitycanrespondto.–>

<intent-filter>

<!--Theactionandcategorytogetherdeterminewhat

happenswhentheactivityislaunched.–>

<!--Startactivityasthemainentrypoint.

Doesnotreceivedata.–>

<actionandroid:name="android.intent.action.MAIN"/>

<!--Startthisactivityasatop-levelactivityin

thelauncher.–>

<categoryandroid:name="android.intent.category.LAUNCHER"/>

<!--Closingtags–>

</intent-filter>

</activity>

</application>

</manifest>

CodingchallengeNote:Allcodingchallengesareoptional.Challenge:TherearemanyotherelementsthatcanbesetintheAndroidManifest.ExploretheAndroidManifestdocumentationandlearnaboutadditionalelementsintheAndroidManifest.

Task8.Explorethebuild.gradlefileAndroidStudiousesabuildsystemcalledGradle.Gradledoesincrementalbuilds,whichallowsforshorteredit-testcycles.

TolearnmoreaboutGradle,see:

GradlesiteConfigureyourbuilddeveloperdocumentation

Introduction

19

Searchtheinternetfor"gradletutorial".

Inthistask,youwillexplorethebuild.gradlefile.

Why:WhenyouaddnewlibrariestoyourAndroidproject,youmayalsohavetoupdateyourbuild.gradlefile.It'susefultoknowwhereitisanditsbasicstructure.

8.1Explorethebuild.gradle(Moduleapp)file1. Inyourprojecthierarchy,findGradleScriptsandexpandit.Thereseveralbuild.gradlefiles.Onewithdirectivesfor

yourwholeproject,andoneforeachappmodule.Themoduleforyourappiscalled"app".IntheProjectview,itisrepresentedbytheappfolderatthetop-leveloftheProjectview.

2. Openbuild.gradle(Module.app).3. Readthefileandlearnwhateachlineofcodeindicates.

Solution:

//AddAndroid-specificbuildtasks

applyplugin:'com.android.application'

//ConfigureAndroidspecificbuildoptions.

android{

//SpecifythetargetSDKversionforthebuild.

compileSdkVersion23

//Theversionofthebuildtoolstouse.

buildToolsVersion"23.0.2"

//Coresettingsandentries.Overridesmanifestsettings!

defaultConfig{

applicationId"com.example.hello.helloworld"

minSdkVersion15

targetSdkVersion23

versionCode1

versionName"1.0"

}

//Controlshowappisbuiltandpackaged.

buildTypes{

//Anothercommonoptionisdebug,whichisnotsignedbydefault.

release{

//Codeshrinker.Turnthisonforproductionalongwith

//shrinkResources.

minifyEnabledfalse

//UseProGuard,aJavaoptimizer.

proguardFilesgetDefaultProguardFile('proguard-android.txt'),'proguard-rules.pro'

}

}

}

//Thisisthepartyouaremostlikelytochangeasyoustartusing

//otherlibraries.

dependencies{

//Localbinarydependency.IncludeanyJARfileinsideapp/libs.

compilefileTree(dir:'libs',include:['*.jar'])

//Configurationforunittests.

testCompile'junit:junit:4.12'

//Remotebinarydependency.SpecifyMavencoordinatesoftheSupport

//Libraryneeded.UsetheSDKManagertodownloadandinstallsuch

//packages.

compile'com.android.support:appcompat-v7:23.2.1'

}

ForadeeperlookintoGradlecheckouttheBuildSystemOverviewandConfiguringGradleBuildsdocumentation.Therearetoolstohelpyoushrinkyourcode,removeunnecessarylibraries/resourceandevenobfuscateyourprogramtopreventunwantedreverse-engineering.AndroidStudioitselfprovidessomeusefulfeatures.Learnmoreaboutavaluableopen-sourcetoolcalledProGuard.

Task9.[Optional]Runyourapponadevice

Introduction

20

Inthisfinaltask,youwillrunyourapponaphysicalmobiledevicesuchasaphoneortablet.

Why:Youruserswillrunyourapponphysicaldevices.Youshouldalwaystestyourappsonbothvirtualandphysicaldevices.

Whatyouneed:

AnAndroiddevicesuchasaphoneortablet.AdatacabletoconnectyourAndroiddevicetoyourcomputerviatheUSBport.IfyouareusingaLinuxorWindowsOS,youmayneedtoperformadditionalstepstorunonahardwaredevice.ChecktheUsingHardwareDevicesdocumentation.OnWindows,youmayneedtoinstalltheappropriateUSBdriverforyourdevice.SeeOEMUSBDrivers.

9.1[Optional]Runyourapponadevice

ToletAndroidStudiocommunicatewithyourdevice,youmustturnonUSBDebuggingonyourAndroiddevice.ThisisenabledintheDeveloperoptionssettingsofyourdevice.Notethisisnotthesameasrootingyourdevice.

OnAndroid4.2andhigher,theDeveloperoptionsscreenishiddenbydefault.ToshowDeveloperoptionsandenableUSBDebugging:

1. Onyourdevice,openSettings>AboutphoneandtapBuildnumberseventimes.2. Returntothepreviousscreen(Settings).Developeroptionsappearsatthebottomofthelist.ClickDeveloper

options.3. ChooseUSBDebugging.

NowyoucanconnectyourdeviceandruntheappfromAndroidStudio.

1. ConnectyourdevicetoyourdevelopmentmachinewithaUSBcable.2. InAndroidStudio,atthebottomofthewindow,clicktheAndroidMonitortab.Youshouldseeyourdevicelistedinthe

top-leftdrop-downmenu.

3. ClicktheRunbutton inthetoolbar.TheSelectDeploymentTargetwindowopenswiththelistofavailableemulatorsandconnecteddevices.

4. Selectyourdevice,andclickOK.

AndroidStudioshouldinstallandrunstheapponyourdevice.

Troubleshooting

IfyouAndroidStudiodoesnotrecognizeyourdevice,trythefollowing:

Unplugandreplugyourdevice.RestartAndroidStudio.Ifyourcomputerstilldoesnotfindthedeviceordeclaresit"unauthorized":

1. Unplugthedevice.

2. Onthedevice,openSettings->DeveloperOptions.

3. TapRevokeUSBDebuggingauthorizations.

4. Reconnectthedevicetoyourcomputer.

5. Whenprompted,grantauthorizations.

YoumayneedtoinstalltheappropriateUSBdriverforyourdevice.SeetheUsingHardwareDevicesdocumentation.Checkthelatestdocumentation,programmingforums,orgethelpfromyourinstructors.

Codingchallenge

Introduction

21

Note:Allcodingchallengesareoptional.

Challenge:Nowthatyouaresetupandfamiliarwiththebasicdevelopmentworkflow,dothefollowing:

1. CreateanewprojectinAndroidStudio.2. Changethegreetingto"HappyBirthdayto"andsomeonewitharecentbirthday.3. Changethebackgroundoftheappusingabirthday-themedimage.4. Takeascreenshotofyourfinishedappandemailittosomeonewhosebirthdayyouforgot.

SummaryInthischapter,youlearnedto:

InstallAndroidStudioObtainabasicunderstandingofthedevelopmentworkflowonceyouhavelaunchedinAndroidStudio.HavebasiccomprehensionofthestructureofanAndroidappinthebuildenvironment.HaveabasicunderstandingoftheAndroidManifest,andwhatitisusedfor.Addlogstatementstothecodethatgiveyouabasictoolfordebugging.

DeploytheHelloWorldappontheAndroidemulatorand[optionally]onamobiledevice.

RelatedconceptsTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

CreateYourFirstAndroidApp

LearnmoreAndroidStudiodownloadpageHowdoIinstallJava?AndroidStudiodocumentationSupportingMultipleScreensGradleWikipediapageReadingandWritingLogs

Introduction

22

1.2A:MakeYourFirstInteractiveUIContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.Createthe"HelloToast"projectTask2:Addviewsto"HelloToast"intheLayoutEditorTask3:Editthe"HelloToast"LayoutinXMLTask4:Addon-clickhandlersforthebuttonsCodingchallengeSummaryRelatedconceptLearnmore

TheuserinterfacedisplayedonthescreenofamobileAndroiddeviceconsistsofahierarchyof"views".ViewsareAndroid'sbasicuserinterfacebuildingblocks.YouspecifytheviewsinXMLlayoutfiles.Forexample,viewscanbecomponentsthat:

displaytext(TextViewclass)allowyoutoedittext(EditTextclass)representclickablebuttons(Buttonclass)andotherinteractivecomponentscontainscrollabletext(ScrollView)andscrollableitems(RecyclerView)showimages(ImageView)containotherviewsandpositionthem(LinearLayout).popupmenusandotherinteractivecomponents.

YoucanexploretheviewhierarchyofyourappintheLayoutEditor'sComponentTreepane.

TheJavacodethatdisplaysanddrivestheuserinterfaceiscontainedinaclassthatextendsActivityandcontainsmethodstoinflateviews,thatis,taketheXMLlayoutofviewsanddisplayitonthescreen.Forexample,theMainActivityintheHelloWorldappinflatesatextviewandprintsHelloWorld.Inmorecomplexapps,anactivitymightimplementclickandothereventhandlers,requestdatafromadatabaseortheinternet,ordrawgraphicalcontent.

AndroidmakesitstraightforwardtoclearlyseparateUIelementsanddatafromeachother,andusetheactivitytobringthembacktogether.ThisseparationisanimplementationofanMVP(Model-View-Presenter)pattern.

YouwillworkwithActivitiesandViewsthroughoutthisbook.

WhatyoushouldalreadyKNOWForthispracticalyoushouldbefamiliarwith:

HowtocreateaHelloWorldappwithAndroidStudio.

WhatyouwillLEARNYouwilllearn:

HowtocreateinteractiveuserinterfacesintheLayoutEditor,inXML,andprogrammatically.Alotofnewterminology.CheckouttheVocabularywordsandconceptsglossaryforfriendlydefinitions.

Introduction

23

WhatyouwillDOInthispractical,youwill:

CreateanappandadduserinterfaceelementssuchasbuttonsintheLayoutEditor.Edittheapp'slayoutinXML.Addabuttontotheapp.Useastringresourceforthelabel.Implementaclickhandlermethodforthebuttontodisplayamessageonthescreenwhentheuserclicks.Changetheclickhandlermethodtochangethemessageshownonthescreen.

AppOverviewThe"HelloToast"appwillconsistoftwobuttonsandonetextview.Whenyouclickonthefirstbutton,itwilldisplayashortmessage,ortoast,onthescreen.Clickingonthesecondbuttonwillincreaseaclickcounter;thetotalcountofmouseclickswillbedisplayedinthetextview.

Here'swhatthefinishedappwilllooklike:

Introduction

24

Introduction

25

Task1.Createanew"HelloToast"projectInthispractical,youwilldesignandimplementaprojectforthe"HelloToast"app.

1.1.Createthe"HelloToast"project

StartAndroidStudioandcreateanewprojectwiththefollowingparameters:

Attribute Value

ApplicationName HelloToast

CompanyName com.example.androidoryourowndomain

PhoneandTabletMinimumSDK API15:Android4.0.3IceCreamSandwich

Template EmptyActivity

GenerateLayoutfilebox Checked

BackwardsCompatibilitybox Checked

SelectRun>RunapporclicktheRunicon inthetoolbartobuildandexecutetheappontheemulatororyourdevice.

Task2:Addviewsto"HelloToast"intheLayoutEditorInthistask,youwillcreateandconfigureauserinterfaceforthe"HelloToast"appbyarrangingviewUIcomponentsonthescreen.

Why:Everyappshouldstartwiththeuserexperience,eveniftheinitialimplementationisverybasic.

ViewsusedforHelloToastare:

TextView-Aviewthatdisplaystext.Button-Abuttonwithalabelthatisusuallyassociatedwithaclickhandler.LinearLayout-Aviewthatactsasacontainertoarrangeotherview.ThistypeofviewextendstheViewGroupclassandisalsocalledaviewgroup.LinearLayoutisabasicviewgroupthatarrangesitscollectionofviewsinahorizontalorverticalrow.

Introduction

26

HereisaroughsketchoftheUIyouwillbuildinthisexercise.SimpleUIsketchescanbeveryusefulfordecidingwhichviewstouseandhowtoarrangethem,especiallywhenyourlayoutsbecomemoresophisticated.

2.1ExploretheLayoutEditor

UsetheLayoutEditortocreatethelayoutoftheuserinterfaceelements,andtopreviewyourappusingdifferentdevicesandappthemes,resolutions,andorientations.

Refertothescreenshotbelowtomatch

1. Intheapp>res>layoutfolder,opentheactiviy_main.xmlfile(1).

TheAndroidStudioScreenshouldlooksimilartothescreenshotbelow.IfyouseetheXMLcodefortheUIlayout,clicktheDesigntabbelowtheComponentTree(8).

2. Usingtheannotatedscreenshotbelowasaguideline,exploretheLayoutEditor.

Introduction

27

3. Findthedifferentwaysinwhichthe"HelloWorld"string'sUIelement,aTextView,isrepresented.InthePaletteofUIelements(2)developerscancreateatextviewbydraggingitintothedesignpane.Visually,intheDesignpane(6).IntheComponentTree(7),asacomponentinahierarchyofUIelementscalledtheViewHierarchy.Thatis,viewsareorganizedintoatreehierarchyofparentsandchildren,wherechildreninheritpropertiesoftheirparents.InthePropertiespane(4),asalistofitsproperties,where"HelloToast"isthevalueofthetextpropertyoftheTextView(5).

4. Usetheselectorsabovethevirtualdevice(3)todothefollowing:

Changethethemeforyourapp.Changetherotationtolandscape.UseadifferentversionoftheSDK.Previewlayoutvariantssuchasaright-to-leftlayoutdirection.

Usethetooltipsontheiconstohelpyoudiscovertheirfunction.

5. SwitchbetweentheDesignandTexttabs(8).SomeUIchangescanonlybemadeincode,andsomearequickertoaccomplishinthevirtualdevice.

6. Whenyou'redone,undothechanges(forUIchanges,useEdit>Undoorthekeyboardshortcutfortheoperatingsystem).

SeetheAndroidStudioUserGuideforthefullAndroidStudiodocumentation.

Note:IfyougetanerroraboutamissingAppTheme,tryFile>InvalidateCaches/Restartorchooseathemethatdoesnotgeneratetheerror.Additionalhelpcanbefoundinthisstackoverflowpost.

2.2ChangetheviewgrouptoaLinearLayoutTherootoftheviewhierarchyisaviewgroup,whichasimpliedbythename,isaviewthatcontainsotherviews.

Averticallinearlayoutisoneofthemostcommonlayouts.Itissimple,fast,andalwaysagoodstartingpoint.Changetheviewgrouptoavertical,LinearLayoutasfollows:

1. IntheComponentTreepane(7inthepreviousscreenshot),findthetoporrootviewdirectlybelowtheDeviceScreen.

Introduction

28

2. ClicktheTexttab(8)toswitchtothecodeviewofthelayout.3. Inthesecondlineofthecode,changetherootviewgrouptoLinearLayout.Thesecondlineofcodenowlooks

somethinglikethis:

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

4. Makesuretheclosingtagattheendofthecodehaschangedto</LinearLayout>.Ifithasn'tchangedautomatically,changeitmanually.

5. Theandroid:layout_heightisdefinedaspartofthetemplate.Thedefaultlayoutorientationahorizontalrow.Tochangethelayouttobevertical,addthefollowingcodeinsideLinearLayout,belowandroid:layout_height.

android:orientation="vertical"

6. Fromthemenubar,select:Code>ReformatCode…

Itmaysay"Nolineschanged:codeisalreadyproperlyformatted".

7. Runthecodetomakesureitstillworks.8. SwitchbacktoDesign.9. VerifyintheComponentTreepanethatthetopelementisnowaLinearLayoutwithitsorientationattributesetto

"vertical".

SolutionCode:DependingonyourversionofAndroidStudio,yourcodewilllooksomethinglikethefollowing.

<?xmlversion="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical"

tools:context="hellotoast.android.example.com.hellotoast.MainActivity">

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="HelloWorld!"/>

</LinearLayout>

2.3AddviewstotheLinearLayoutintheLayoutEditor

InthistaskyouwilldeletethecurrentTextView(forpractice),andaddanewTextViewandtwobuttonstotheLinearLayoutasshownintheUIsketchforthistask.RefertotheUIdiagramabove,ifnecessary.

AddUIElements

1. ClicktheDesigntab(8)toshowthevirtualdevicelayout.2. ClicktheTextViewwhosetextvalueis"HelloWorld"inthevirtualdevicelayoutortheComponentTreepane(7).3. PresstheDeletekeytoremovethatTextView.4. FromthePalettepane(2),draganddropaButtonelement,aTextView,andanotherButtonelement,inthatorder,one

belowtheotherintothevirtualdevicelayout.

AdjusttheUIElements

1. Toidentifyeachviewuniquelywithinanactivity,eachviewneedsauniqueID.Andtobeofanyuse,thebuttonsneedlabelsandthetextviewneedstoshowsometext.Double-clickeachelementintheComponentTreetoseeitspropertiesandchangethetextandIDstringsasfollows:

Introduction

29

Element Text ID

Topbutton Toast button_toast

Textview 0 show_count

Bottombutton Count button_count

1. Runyourapp.

SolutionLayout:

ThereshouldbethreeViewsonyourscreen.Theywon'tmatchtheimagebelow,butaslongasyouhavethreeViewsina

verticallayout,youaredoingfine!

Challenge:ThinkofanappyoumightwantandcreateaprojectandlayoutforitusingLayoutEditor.ExploremoreofthefeaturesofLayoutEditor.Asmentionedbefore,theLayoutEditorhasarichsetoffeaturesandcodingshortcuts.ChecktheAndroidStudiodocumentationtodivedeeper.

Task3:Editthe"HelloToast"layoutinXMLInthispractical,youwilledittheXMLcodefortheHelloToastappUIlayout.Youwillalsoeditthepropertiesoftheviewsyouhavecreated.YoucanfindthepropertiescommontoallviewsintheViewclassdocumentation.

Why:WhiletheLayoutEditorisapowerfultool,somechangesareeasiertomakedirectlyintheXMLsourcecode.ItisapersonalpreferencetouseeitherthegraphicalLayoutEditororedittheXMLfiledirectly.

1. Openres/layout/activity_main.xmlinTextmode.2. InthemenubarselectCode>ReformatCode3. ExaminethecodecreatedbytheLayoutEditor.

Notethatyourcodemaynotbeanexactmatch,dependingonwhatchangesyoumadeintheLayoutEditor.Usethesamplesolutionsasguidelines.

3.1ExamineLinearLayoutpropertiesALinearLayoutisrequiredtohavetheseproperties:

layout_widthlayout_heightorientation

Introduction

30

Thelayout_widthandlayout_heightcantakeoneofthreevalues:

Thematch_parentattributeexpandstheviewtofillitsparentbywidthorheight.WhentheLinearLayoutistherootview,itexpandstothesizeoftheparentview.Thewrap_contentattributeshrinkstheviewdimensionsjustbigenoughtoencloseitscontent.(Ifthereisnocontent,theviewbecomesinvisible.)Useafixednumberofdp(deviceindependentpixels)tospecifyafixedsize,adjustedforthescreensizeofthedevice.Forexample,"16dp"means16deviceindependentpixels.

Theorientationcanbe:

horizontal:viewsarearrangedfromlefttoright.vertical:viewsarearrangedfromtoptobottom.

ChangetheLinearLayoutof"HelloToast"asfollows:

Property Value

layout_width match_parent(tofillthescreen)

layout_height match_parent(tofillthescreen)

orientation vertical

3.2Createstringresources

Insteadofhard-codingstringsintotheXMLcode,itisabestpracticetousestringresources,whichrepresentthestrings

Why:Havingthestringsinaseparatefilemakesiteasiertomanagethem,especiallyifyouusethesestringsmorethanonce.Also,stringresourcesaremandatoryfortranslatingandlocalizingyourappasyouwillcreateonestringresourcefileforeachlanguage.

1. Placethecursorontheword"Toast".2. PressAlt-Enter(Option-EnterontheMac).3. SelectExtractstringresources.4. SettheResourcenametobutton_label_toastandclickOK.(Ifyoumakeamistake,undothechangewithCtrl-Z.)

Thiscreatesastringresourceinthevalues/res/string.xmlfile,andthestringinyourcodeisreplacedwithareferencetotheresource,

@string/button_label_toast

5. Extractandnametheremainingstringsfromtheviewsasfollows:

View ResourceValue/String Resourcename

Button HelloToast! button_label_toast

TextView 0 count_initial_value

Button Count button_label_count

6. IntheProjectview,navigatetovalues/strings.xmltofindyourstrings.Now,youcaneditallyourstringsinoneplace.

3.3ResizeSimilartostrings,itisabestpracticetoextractviewdimensionsfromthemainlayoutXMLfileintoadimensionsresourcelocatedinafile.

Introduction

31

Why:Thismakesiteasiertomanagedimensions,especiallyifyouneedtoadjustyourlayoutfordifferentdeviceresolutions.Italsomakesiteasytohaveconsistentsizing,andchangethesizeofmultipleobjectsbychangingoneproperty.

Dothefollowing:

1. Lookatthedimens.xmlresourcefile.Thereshouldbevaluesforthedefaultscreenmarginsdefined.Forthedimensionsofviews,itisbetternottousehard-codedvalues,becausethatpreventsviewsfromadjustingtothescreensize.

2. Ifnecessary,changethelayout_widthofallelementsinsidetheLinearLayoutto"match_parent".

IfyouwanttousethegraphicalLayoutEditor,clickontheDesigntab,selecteachelementintheComponentTreepaneandchangethelayout:widthpropertyinthePropertiespane.IfyouwanttodirectlyedittheXMLfile,clickontheTexttab,changetheandroid:layout_widthforthefirstButton,theTextView,andthelastButton.

3. Ifnecessary,changethelayout_heightofallelementsinsidetheLinearLayoutto"wrap_content".

3.4SetcolorsandbackgroundsStylesandcolorsareadditionalpropertiesthatcanbeextractedintoresources.Allviewscanhavebackgroundsthatcanbecolorsorimages.

Why:Extractingstylesandcolorsmakesiteasytousethemconsistentlythroughouttheapp,andstraightforwardtochangeacrossallUIelements.

Experimentwiththefollowingchanges:

1. Changethetextsizeoftheshow_countTextView."sp"standsforscale-independentpixel,andlikedp,isaunitthatscaleswiththescreendensityanduser'sfontsizepreference.Itisrecommendyouusethisunitwhenspecifyingfontsizes,sotheywillbeadjustedforboththescreendensityandtheuser'spreference.

android:textSize="160sp"

2. ExtractthetextsizeoftheTextViewasadimensionresourcenamedcount_text_size,asfollows:

i. ClicktheTexttabtoshowtheXMLcode,ifyouhaven'talreadydoneso.

ii. Placethecursoron"160sp".

iii. PressAlt-Enter(Option-EnterontheMac).

iv. ClickExtractdimensionresource.

v. SettheResourcenametocount_text_size,andclickOK.(Ifyoumakeamistake,youcanundothechangewithCtrl-Z).

vi. IntheProjectview,navigatetovalues/dimens.xmltofindyourdimensions.Thedimens.xmlfileappliestoalldevices.Thedimens.xmlfileforw820dpappliesonlytodevicesthatarewiderthan820dp.

3. ChangethetextStyleoftheshow_countTextViewtobold.

android:textStyle="bold"

4. Changethetextcolorintheshow_counttextviewtotheprimarycolorofthetheme.Lookatthecolors.xmlresourcefiletoseehowtheyaredefined.

ThecolorPrimaryisoneofthepredefinedthemebasecolorsandisusedfortheappbar.Forexample,Inaproductionapp,youcouldcustomizethistofityourbrand.UsingthebasecolorsforotherUIelementscreatesauniformUI.SeeUsingtheMaterialTheme.Youwilllearnmoreaboutappthemesandmaterialdesigninalaterpractical.

Introduction

32

android:textColor="@color/colorPrimary"

5. Changethecolorofboththebuttonstotheprimarycolorofthetheme.

android:background="@color/colorPrimary"

6. Changethecolorofthetextinbothbuttonstowhite.WhiteisoneofthecolorsprovidedasanAndroidPlatformResource.SeeAccessingResources.

android:textColor="@android:color/white"

7. AddabackgroundcolortotheTextView.

android:background="#FFFF00"

8. IntheLayoutEditor(Texttab),placeyourmousecursoroverthiscolorandpressAlt-Enter(Option-EnterontheMac).

9. SelectChoosecolor,whichbringsupthecolorpicker,pickacoloryoulike,orgowiththecurrentyellow,thenclickChoose.

10. Openvalues/colors.xml.NoticethatcolorPrimarythatyouusedearlierisdefinedhere.11. Usingthecolorsinvalues/colors.xmlasanexample,addaresourcenamedmyBackgroundColorforyourbackground

color,andthenuseittosetthebackgroundofthetextview.

<colorname="myBackgroundColor">#FFF043</color>

3.5Gravityandweight

Specifyinggravityandweightpropertiesgivesyouadditionalcontroloverarrangingviewsandcontentinlinearlayouts.

1. Theandroid:layout_gravityattributespecifieshowaviewisalignedwithinitsparentView.Becausetheviewsmatchtheirparentinwidth,itisnotnecessarytosetthisexplicitly.Youcancenteraviewthatisnarrowhorizontallyinitsparent:android:layout_gravity="center_horizontal"

2. Theandroid:layout_weightattributeindicateshowmuchoftheextraspaceintheLinearLayoutwillbeallocatedtotheviewsthathavethisparameterset.Ifonlyoneviewhasthisattribute,itgetsalltheextrascreenestate.Formultiple

Introduction

33

views,thespaceispro-rated.Forexample,ifthebuttonshaveaweightof1andthetextview2,totalling4,thebuttonsget¼ofthespaceeach,andthetextviewhalf.

3. Theandroid:gravityattributespecifiesthealignmentofthecontentofaViewwithintheViewitself.Thecounteriscenteredinitsviewwith:android:gravity="center"

Dothefollowing:

1. Centerthetextinatheshow_countTextViewhorizontallyandvertically:android:gravity="center"2. Maketheshow_countTextViewadjusttothesizeofthescreen:

android:layout_weight="2"

SampleSolution:strings.xml

<resources>

<stringname="app_name">HelloToast</string>

<stringname="button_label_count">Count</string>

<stringname="button_label_toast">Toast</string>

<stringname="count_initial_value">0</string>

</resources>

SampleSolution:dimens.xml

<resources>

<!--Defaultscreenmargins,pertheAndroidDesignguidelines.-->

<dimenname="activity_horizontal_margin">16dp</dimen>

<dimenname="activity_vertical_margin">16dp</dimen>

<dimenname="count_text_size">160sp</dimen>

</resources>

SampleSolution:colors.xml

<resources>

<colorname="colorPrimary">#3F51B5</color>

<colorname="colorPrimaryDark">#303F9F</color>

<colorname="colorAccent">#FF4081</color>

<colorname="myBackgroundColor">#FFF043</color>

</resources>

SampleSolution:activity_main.xml

Introduction

34

<?xmlversion="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="hellotoast.android.example.com.hellotoast.MainActivity">

<Button

android:id="@+id/button_toast"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:text="@string/button_label_toast"

android:background="@color/colorPrimary"

android:textColor="@android:color/white"/>

<TextView

android:id="@+id/show_count"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:gravity="center"

android:text="@string/count_initial_value"

android:textSize="@dimen/count_text_size"

android:textStyle="bold"

android:textColor="@color/colorPrimary"

android:background="@color/myBackgroundColor"

android:layout_weight="2"/>

<Button

android:id="@+id/button_count"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:text="@string/button_label_count"

android:background="@color/colorPrimary"

android:textColor="@android:color/white"/>

</LinearLayout>

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterchapters.

Createanewprojectwith5views.Haveoneviewusethetop-halfofthescreen,andtheother4viewssharethebottomhalfofthescreen.UseonlyaLinearLayout,gravity,andweightstoaccomplishthis.UseanimageasthebackgroundoftheHelloToastapp.Addanimagetothedrawablefolder,thensetitasthebackgroundoftherootview.Foradeepdiveintodrawables,seetheDrawableResourcesdocumentation.

Task4:AddonClickhandlersforthebuttonsInthistask,youwilladdmethodstoyourMainActivitythatexecutewhentheuserclicksoneachbutton.

Why:Interactiveappsmustrespondtouserinput.

Toconnectauseractioninaviewtoapplicationcode,youneedtodotwothings:

Writeamethodthatperformsaspecificactionwhenauseruserclicksanon-screenbutton.Associatethismethodtotheview,sothismethodiscalledwhentheuserinteractswiththeview.

Introduction

35

4.1AddanonClickpropertytoabutton

Aclickhandlerisamethodthatisinvokedwhentheuserclicksonauserinterfaceelement.InAndroid,youcanspecifythenameoftheclickhandlermethodforeachviewintheXMLlayoutfilewiththeandroid:onClickproperty.

1. Openres/layout/activity_main.xml.2. Addthefollowingpropertytothebutton_toastbutton.

android:onClick="showToast"

3. Addthefollowingattributetothebutton_countbutton.

android:onClick="countUp"

4. Insideofactivity_main.xml,placeyourmousecursorovereachofthesemethodnames.5. PressAlt-Enter(Option-EnterontheMac),andselectCreateonClickeventhandler.6. ChoosetheMainActivityandclickOK.

ThiscreatesplaceholdermethodstubsfortheonClickmethodsinMainActivity.java.

Note:Youcanalsoaddclickhandlerstoviewsprogrammatically,whichyouwilldoinalaterpractical.WhetheryouaddclickhandlersinXMLorprogrammaticallyislargelyapersonalchoice;though,therearesituationswhereyoucanonlydoitprogrammatically.SolutionMainActivity.java:

packagehellotoast.android.example.com.hellotoast;

importandroid.support.v7.app.AppCompatActivity;

importandroid.os.Bundle;

importandroid.view.View;

publicclassMainActivityextendsAppCompatActivity{

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

}

publicvoidcountUp(Viewview){

//Whathappenswhenuserclicksonthebutton_countButtongoeshere.

}

publicvoidshowToast(Viewview){

//Whathappenswhenuserclicksonthebutton_toastButtongoeshere.

}

}

4.2ShowatoastwhentheToastbuttonisclicked

Atoastprovidessimplefeedbackaboutanoperationinasmallpopup.Itonlyfillstheamountofspacerequiredforthemessageandthecurrentactivityremainsvisibleandinteractive.Toastsprovideanotherwayforyoutotesttheinteractivityofyourapp.

InMainActivity.java,addcodetotheshowToast()methodtoshowatoastmessage.

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TocreateaninstanceofaToast,youcallthemakeText()factorymethodontheToastclass,supplyingacontext(seebelow),themessagetodisplay,andthedurationofdisplay.Youdisplaythetoastcallingshow().Thisisacommonpatternthatyoucanreusethecodeyouaregoingtowrite.

1. Getthecontextoftheapplication.

DisplayingaToastmessagerequiresacontext.Thecontextofanapplicationcontainsglobalinformationabouttheapplicationenvironment.SinceatoastdisplaysontopofthevisibleUI,thesystemneedsinformationaboutthecurrentactivity.Contextcontext=getApplicationContext();

Whenyouarealreadyinthecontextoftheactivitywhosecontextyouneed,youcanalsousethisastheshortcuttothecontext.

2. Thelengthofatoaststringcanbeeithershortorlong,andyouspecifywhichonebyusingaToastconstant.

Toast.LENGTH_LONG

Toast.LENGTH_SHORT

Theactuallengthsareabout3.5sforthelongtoastand2sfortheshorttoast.ThevaluesarespecifiedintheAndroidsourcecode.SeethisStackoverflowpostdetails.

3. CreateaninstanceoftheToastclasswiththecontext,message,andduration.Thecontextistheapplicationcontextwegotearlier.ThemessageisthestringyouwanttodisplayThedurationisoneofthepredefinedconstantsToast.LENGTH_LONGorToast.LENGTH_SHORT.

Toasttoast=Toast.makeText(context,"HelloToast",Toast.LENGTH_LONG);

4. Extractthe"HelloToast"stringintoastringresourceandcallittoast_message.

i. Placethecursoronthestring"HelloToast!".

ii. PressAlt-Enter(Option-EnterontheMac).

iii. SelectExtractstringresources.

iv. SettheResourcenametotoast_messageandclickOK.

Thiswillstore"HelloWorld"asastringresourcenametoast_messageinthestringresourcesfileres/values/string.xml.Thestringparameterinyourmethodcallisreplacedwithareferencetotheresource.

R.identifiestheparameterasaresource.stringreferencesthenameoftheXMLfilewheretheresourcesisdefined.toast_messageisthenameoftheresource.

Toasttoast=Toast.makeText(context,R.string.toast_message,duration);

5. Displaythetoast.

toast.show();

6. RunyourappandverifythetoastshowswhentheToastbuttonistapped.

Solution:

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/*

*WhentheTOASTbuttonisclicked,showatoast.

*

*@paramviewTheviewthattriggersthisonClickhandler.

*Sinceatoastalwaysshowsonthetop,viewisnotused.

**/

publicvoidshowToast(Viewview){

//Createatoastshowit.

Toasttoast=Toast.makeText(this,R.string.toast_message,Toast.LENGTH_LONG;);

toast.show();

}

4.3IncreasethecountinthetextviewwhentheCountbuttonisclickedTodisplaythecurrentcountinthetextview:

Keeptrackofthecountasitchanges.Sendtheupdatedcounttothetextviewtodisplayitontheuserinterface.

Implementthisasfollows:

1. InMainActivity.java,addaprivatemembervariablemCounttotrackthecountandstartitat0.2. InMainActivity.java,addaprivatemembervariablemShowCounttogetthereferenceoftheshow_countTextView.3. InthecountUp()method,increasethevalueofthecountvariableeachtimethebuttonisclicked.4. GetareferencetothetextviewusingtheIDyousetinthelayoutfile.

Views,likestringsanddimensions,areresourcesthatcanhaveanid.ThefindViewById()calltakestheIDofaviewasitsparameterandreturnstheview.BecausethemethodreturnsaView,youhavetocasttheresulttotheviewtypeyouexpect,inthiscase(TextView).

Inordertogetthisresourceonlyonce,useamembervariableandsetitinonCreate().

mShowCount=(TextView)findViewById(R.id.show_count);

5. Setthetextinthetextviewtothevalueofthecountvariable.

if(mShowCount!=null)

mShowCount.setText(Integer.toString(mCount));

6. RunyourapptoverifythatthecountincreaseswhentheCountbuttonispressed.

Solution:

Classdefinitionandinitializingcountvariable:

publicclassMainActivityextendsAppCompatActivity{

privateintmCount=0;

privateTextViewmShowCount;

inonCreate():

mShowCount=(TextView)findViewById(R.id.show_count);

countUpMethod:

publicvoidcountUp(Viewview){

mCount++;

if(mShowCount!=null)

mShowCount.setText(Integer.toString(mCount));

}

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Resources:

LearnmoreabouthandlingAndroidInputEvents.Contextclassdocumentation

SolutioncodeAndroidStudioproject:HelloToast

CodingchallengeNote:Allcodingchallengesareoptionalandarenotaprerequisiteforlaterchapters.

Challenge:EvenasimpleapplikeHelloToastcanbethefoundationofmanyscoringorproductorderingapps.Writeoneappthatwouldbeofusetoyou,ortryoneoftheseexamples:

Createacoffeeorderingapp.Addbuttonstochangethenumberofcoffeesordered.Calculateanddisplaythetotalprice.Createascoringappforyourfavoriteteamsport.Makethebackgroundanimagethatrepresentsthatsport.Createbuttonstocountthescoresforeachteam.

SummaryInthischapter,you:

AddedUIelementstoanappintheLayoutEditorandusingXML.MadetheUIinteractivewithbuttons.andclicklistenersAddclicklistenersthatupdateatextviewinresponsetouserinput.Displayedinformationtousersusingatoast.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

Layouts,Views,andResources

LearnmoreAllViewsaresubclassesoftheViewclassandthereforeinheritmanypropertiesoftheViewsuperclass.YoucanfindinformationonallButtonpropertiesintheButtonclassdocumentation,andalltheTextViewpropertiesintheTextViewclassdocumentation.YoucanfindinformationonalltheLinearLayoutpropertiesintheLinearLayoutclassdocumentation.TheAndroidresourcesdocumentationwilldescribeothertypesofresources.Androidcolorconstants:AndroidstandardR.colorresourcesMoreinformationaboutdpandspunitscanbefoundatSupportingDifferentDensities

DeveloperDocumentation:

AndroidStudiodocumentationVocabularywordsandconceptsglossarydeveloper.android.comLayoutsViewclassdocumentation

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deviceindependentpixelsButtonclassdocumentationTextViewclassdocumentationAndroidresourcesdocumentationCompletecodefortheHelloToastappArchitecturalPatterns(overview)

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1.2B:UsingLayoutsContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppOverviewTask1:ChangethelayouttoRelativeLayoutTask2:ChangethelayouttoConstraintLayoutTask3:CreatelayoutvariantsCodingChallengeSummaryRelatedconceptsLearnmore

WhenyoustartanAndroidStudioproject,thetemplateyouchooseprovidesabasiclayoutwithviews.Asyoulearnedinapreviouspractical,youcanlineviewsupquicklyandeasilyinalayoutusingLinearLayout,whichisaviewgroupthatalignschildviewswithinithorizontallyorvertically.

Thispracticalexplorestwootherlayoutviewgroups:

RelativeLayout:Agroupofchildviewsinwhicheachviewispositionedandalignedrelativetootherviewswithintheviewgroup.Positionsofthechildviewsaredescribedinrelationtoeachotherortotheparentviewgroup.ConstraintLayout:AlayoutsimilartoRelativeLayoutbutmoreflexible.Itgroupschildviewsusinganchorpoints(aconnectiontoanotherview),edges,andguidelinestocontrolhowviewsarepositionedrelativetootherelementsinthelayout.ConstraintLayoutwasdesignedtomakeiteasytodraganddropviewsinthelayouteditorofAndroidStudio

WhatyoushouldalreadyKNOWFromthepreviouspracticals,youshouldbeableto:

CreateaHelloWorldappwithAndroidStudio.Runanappontheemulatororadevice.ImplementaTextViewinalayoutforanapp.Createandusingstringresources.Convertlayoutdimensionstoresources.

WhatyouwillLEARNYouwilllearnto:

UsethelayouteditorinAndroidStudioPositionviewswithinaRelativeLayoutPositionviewswithinaConstraintLayoutCreatevariantsofthelayoutforlandscapeorientationandlargerdisplays

WhatyouwillDOInthispracticalyouwill:

ExperimentwithusingRelativeLayoutandConstraintLayout.

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CopyandrefactortheHelloToastapptocreatetheHelloRelativeapp.ChangetherootviewgroupinthemainlayouttobeaRelativeLayout.Rearrangetheviewsinthemainlayouttoberelativetoeachother.CopyandrefactortheHelloRelativeapptocreateHelloConstraint.ChangetherootviewgroupinthemainlayouttobeConstraintLayout.Modifythelayouttoaddconstraintstotheviews.Modifytheviewsforlayoutvariantsforlandscapeorientationandlargerdisplays.

AppOverviewTheHelloToastappinapreviouspracticalusesaLinearLayouttoarrangetheviewsintheactivitylayout,asshowninthefigurebelow.

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Inordertopracticeusingthelayouteditor,youwillcopytheHelloToastappandcallthenewcopyHelloRelative,inordertoexperimentwithaRelativeLayout.YouwillusethelayouteditortoarrangetheviewsinadifferentUIlayoutasshownbelow.

Finally,youwillmakeanothercopyoftheappandcallitHelloConstraint,andreplaceLinearLayoutwithConstraintLayout.ConstraintLayoutoffersmorevisualaidsandpositioningfeaturesinthelayouteditor.YouwillcreateanentirelydifferentUIlayout,andalsolayoutvariantsforlandscapeorientationandlargerdisplays,asshownbelow.

AndroidStudioproject:HelloToast

Task1:ChangethelayouttoRelativeLayoutARelativeLayoutisaviewgroupinginwhicheachviewispositionedandalignedrelativetootherviewswithinthegroup.Inthistask,youwillinvestigateusingRelativeLayout.

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1.1CopyandrefactortheHelloToastapp

1. CopytheHelloToastprojectfolder,renameittoHelloRelative,andrefactorit.(SeetheAppendixforinstructionsoncopyingaproject.)

2. Afterrefactoring,changethe<stringname="app_name">valueinthestrings.xmlfile(withinapp>res>values)toHelloRelative(withaspace)astheapp'sname.

1.2ChangeLinearLayouttoRelativeLayout

1. Opentheactivity_main.xmllayoutfile,andclicktheTexttabatthebottomoftheeditingpanetoseetheXMLcode.2. Changethe<LinearLayoutatthetopto<RelativeLayoutsothatthestatementlookslikethis:

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

3. Scrolldowntomakesurethattheendingtag</LinearLayout>hasalsochangedto</RelativeLayout>;ifithasn't,changeitmanually.

1.3RearrangeviewswiththeDesigntab1. ClicktheDesigntabatthebottomoftheeditingpane.2. Theeditingpaneshouldnowlooklikethefigurebelow,withthelayoutdesignanditsblueprint.Ifyouseeonlyalayout

design,oronlyablueprint,clicktheShowDesign+Blueprintbutton(#1inthefigurebelow).

3. WiththechangetoRelativeLayout,thelayouteditoralsochangedsomeoftheviewattributes.Forexample:

Thebutton_countviewfortheCOUNTbuttonisoverlayingthebutton_toastviewfortheTOASTbutton,whichiswhyyoucan'tseetheTOASTbutton.However,intheblueprint,youcanseethatthetwobuttonsareoccupying

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thesamespace.Thetoppartoftheshow_countview(showing0)isalsooverlayingtheCOUNTandTOASTbuttons.

4. Dragthebutton_countview(fortheCOUNTbutton)toanareabelowtheshow_countview(showing0),andthendragituptothebottomoftheshow_countviewuntilitsnapsintoplaceasshownbelow.Alsodragtheshow_countviewsothatthetopoftheviewsnapstothebottomofthebutton_toastviewfortheTOASTbutton.

Tip:Whenselectingaviewinthelayout,itspropertiesappearinthePropertiespaneontherightsideoftheeditingpane.ThesepropertiescorrespondtoXMLattributesintheXMLcodeforthelayout,whichyouwillexamineinthenextstep.

1.4ExaminetheXMLcodeintheTexttabFollowthesestepstoseehowtheapplooks:

1. Runtheapp.Theappworksthesamewayasbefore.TheonlydifferenceisthatthelayoutusesaRelativeLayouttopositiontheelements,ratherthanaLinearLayout.Inthenexttask,youwillchangethelayoutoftheUI.

2. Changethedeviceoremulatororientationtolandscape.Notethatthebutton_countviewdisappearsbecausethescreenlayoutdoesnotaccommodatethelandscapeorientation.Youwillfixthisprobleminasubsequenttaskinthispractical.

3. ClicktheTexttabatthebottomoftheeditingpane.4. ExaminethechangestotheXMLcodeintheeditingpaneasaresultofchangingLinearLayouttoRelativeLayout.

StartbyexaminingthesecondButton(button_count):

<Button

android:id="@+id/button_count"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_gravity="center_horizontal"

android:background="@color/colorPrimary"

android:onClick="countUp"

android:text="@string/button_label_count"

android:textColor="@android:color/white"

android:layout_below="@+id/show_count"

android:layout_centerHorizontal="true"/>

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TwonewXMLattributeswereautomaticallyaddedbythelayouteditorafteryoumovedtheButton(button_count)inthelayout:

android:layout_below="@+id/show_count"

android:layout_centerHorizontal="true"

Theandroid:layout_belowattributeplacesthebutton_countviewdirectlybelowtheshow_countview.ThisattributeisoneofseveralattributesforpositioningviewswithinaRelativeLayout—youplaceviewsinrelationtoTheXMLcodeforshow_countview,whichyoualsomovedinthelayouteditor,isnowinapositionbelowthetwobuttonsintheTextview.ThisisduetothechangefromLinearLayouttoRelativeLayout.Theshow_countviewalsonowincludesthefollowingattributes,asaresultofmovingtheviewinthelayouteditor:

android:layout_below="@+id/button_toast"

android:layout_alignParentLeft="true"

android:layout_alignParentStart="true"

Theandroid:layout_alignParentLeftalignstheviewtotheleftsideoftheRelativeLayoutparentviewgroup.Whilethisattributebyitselfisenoughtoaligntheviewtotheleftside,youmaywanttheviewtoaligntotherightsideiftheappisrunningonadevicethatisusingaright-to-leftlanguage.Thus,theandroid:layout_alignParentStartattributemakesthe"start"edgeofthisviewmatchthestartedgeoftheparent.Thestartistheleftedgeofthescreenifthepreferenceisleft-to-right,oritistherightedgeofthescreenifthepreferenceisright-to-left.

1.5RearrangeelementsintheRelativeLayout

1. ToexperimentmorewithRelativeLayout,selecttheactivity_main.xmllayoutagainforediting(ifit'snotalreadyselected),andclicktheDesigntabatthebottomoftheeditingpane.

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2. Selecttheshow_countviewinthelayoutortheComponentTree,andchangeitslayout_widthinthePropertiespaneontherightsideofthewindowtowrap_contentasshowninthefigurebelow.

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Thelayouteditordisplaysathinnershow_countviewalignedtotheleftsideoftheparentview,asshowninthefigurebelow.

3. Dragtheshow_countviewhorizontallytothecenterofthelayout.Asyoudragtheview,acenterguideappears—theview'scentershouldsnapintoplacewiththeguideasshownbelow.

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4. Selectthebutton_toastviewandchangeitslayout_widthtowrap_contentinthePropertiespane,andthenchangethelayout_widthofthebutton_countviewtowrap_content.Thelayoutshouldnowlooklikethefigurebelow.

5. Dragthebutton_countviewuptojustbelowthebutton_toastviewsothatitsnapstothebottomofthe

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button_toastview,anddragtheshow_countviewupnexttotherightedgeofthebutton_toastviewsothatitsnapstotherightedgeofthebutton.Thelayoutshouldnowlooklikethefigurebelow:

6. ClicktheTexttabatthebottomoftheeditingpane,andexaminethechangestotheXMLcodeasaresultofmovingtheviewsinthelayout:

Theshow_countviewnowusesthefollowingattributestopositionittotherightofandtheendofthebutton_toastview:

android:layout_toRightOf="@+id/button_toast"

android:layout_toEndOf="@+id/button_toast"

Thebutton_countviewnowusesthefollowingattributestopositionitbelowthebutton_toastview:

android:layout_below="@+id/button_toast"

7. Runtheapp.Theappworksthesamewayasbefore(sincewedidn'tchangeanyJavacode).However,thelayoutisdifferent,asshowninthefigurebelow.Changethedeviceoremulatororientationtolandscapetoseethatthenewlayoutworksforbothorientations.

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Tip:TolearnmoreabouthowtopositionviewsinaRelativeLayout,see"PositioningViews"inthe"RelativeLayout"topicoftheAPIGuide.

Solutioncode:AndroidStudioproject:HelloRelative

Task2:ChangethelayouttoConstraintLayoutConstraintLayoutisaviewgroupavailableintheConstraintLayoutlibrary,whichisincludedwithAndroidStudio2.2andhigher.Theconstraint-basedlayoutletsadeveloperbuildcomplexlayoutswithouthavingtonestviewgroups,whichcanimprovetheperformanceoftheapp.Itisbuiltintothelayouteditor,sothattheconstrainingtoolsareaccessiblefromtheDesigntabwithouthavingtoedittheXMLbyhand.

InthistaskyouwillcopyandrefactortheHelloToastapptocreatetheHelloConstraintapp.YouwillthenchangetherootLinearLayoutviewgroupinthemainlayouttobeConstraintLayout.Afterchangingtherootviewgroup,youwillrearrangetheviewsinthemainlayouttohaveconstraintsthatgoverntheirappearance.

2.1CopyandrefactortheHelloToastapp

1. CopytheHelloToastprojectfolder,renameittoHelloConstraint,andrefactorit.(SeetheAppendixforinstructionsoncopyingaproject.)

2. Afterrefactoring,changethestringname="app_name"valueinthestrings.xmlfile(withinapp>res>values)toHelloConstraint(withaspace)astheapp'sname.

2.2AddConstraintLayouttoyourproject

ChecktobesurethatConstraintLayoutisavailableinyourproject:

1. InAndroidStudio,chooseTools>Android>SDKManager.2. Intheleftpane,clickAndroidSDK.3. Intherightpane,clicktheSDKToolstabatthetopofthepane.4. ExpandSupportRepositoryandseeifConstraintLayoutforAndroidandSolverforConstraintLayoutarealready

checked.

If"Installed"appearsintheStatuscolumn,you'reallset.ClickCancel.If"Notinstalled"appears,or"Update"appears:

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i. ClickthecheckboxnexttoConstraintLayoutforAndroidandSolverforConstraintLayout.Adownloadiconshouldappearnexttoeachcheckbox.

ii. Clickoneofthefollowing:

ApplytostartinstallingthecomponentsandremaininSDKManagertomakeotherchanges.OKtoinstallthecomponents.

iii. Afterinstallingthecomponents(andmakingotherchangesifneeded),clickFinishtofinishusingtheSDKManager.

2.3ConvertalayouttoConstraintLayoutAndroidStudiohasabuilt-inconvertertohelpyouconvertalayouttoConstraintLayout.Followthesesteps:

1. Openthelayoutfile(activity_main.xml)inAndroidStudioandclicktheDesigntabatthebottomoftheeditorwindow.2. IntheComponentTreewindow,right-clickLinearLayoutandthenchooseConvertlayouttoConstraintLayoutfrom

thecontextmenu.3. Theconverterdisplaysanalertwithtwocheckboxesalreadychecked.Don'tuncheckthem—makesurebothoptions

remainchecked:

i. FlattenLayoutHierarchy:Thisoptionremovesallothernestedlayoutsinthehierarchy.Theresultisasingle,flatlayout,whichmaybemoreefficientforthesepurposes.

ii. Don'tflattenlayoutsreferencedfromotherfiles:Ifaparticularlayoutdefinesanandroid:idattributethatisreferencedinyourJavacode,youmaynotwanttoflattenthatlayoutbecauseyourcodemaynolongerwork.However,inHelloConstraint,youdon'thaveanandroid:idattributeforalayout,onlyforviews.

4. IntheAddProjectDependencyalert,clickOKtoaddtheconstraint-layoutlibrary.AndroidStudioautomaticallycopiestheappropriatedependencytoyourproject'sbuild.gradle(Module:app)fileandsyncsthechangeforyou.ThelayouteditorreappearswithConstraintLayoutastherootviewgroup.

Note:Ifthelayouteditorhasaproblemwiththechange,youseeaRenderingProblemswarning.ClickbuildinthemessageTip:Trytobuildtheproject.Thiswillre-syncyourproject'sbuild.gradle(Module:app)filewiththenewdependency.

5. Thelayouteditor'sComponentTreepanenowshowsConstraintLayoutastherootviewgroupforthelayoutwiththeotherviewsbeneathit,asshowninthefigurebelow.Clicktheshow_countviewintheComponentTreepane.Theshow_countviewisalsoselectedintheblueprint,anditspropertiesappearinthePropertiespaneontherightside.

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2.4Explorethelayouteditor

ThelayouteditoroffersmorefeaturesintheDesigntabwhenyouuseaConstraintLayout,includingmorevisuallayouttoolsandasecondrowoficonsformoretools.

Thevisuallayoutandblueprintofferhandlesfordefiningconstraints.Aconstraintisaconnectionoralignmenttoanotherview,totheparentlayout,ortoaninvisibleguideline.FollowthesestepstoexploretheconstraintsthatAndroidStudiocreatedwhenyouconvertedtheLinearLayouttoConstraintLayout:

1. Clicktheshow_countviewintheComponentTreepane.2. Hoverthecursorovertheshow_countviewinthelayout,asshowninthefigurebelow.

Eachconstraintappearsasalineextendingfromacircularhandle.Eachviewhasacircularconstrainthandleinthemiddleofeachside.AfterselectingaviewintheComponentTreepaneorclickingonitinthelayout,theviewalsoshowsresizinghandlesoneachcorner.

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Intheabovefigure:

1. Resizinghandle.2. Constraintlineandhandle.Inthefigure,theconstraintalignstheleftsideoftheshow_countviewtotheleftsideof

thebutton_toastbutton.3. Baselinehandle.Thebaselinehandlealignsthetextbaselineofaviewtothetextbaselineofanotherview.4. Constrainthandlewithoutaconstraintline.

Thelayouteditoralsooffersarowofbuttonsthatletyouconfiguretheappearanceofthelayout:

Inthefigureabove:

1. Design,Blueprint,andBoth:ClicktheDesignicon(firsticon)todisplayacolorpreviewofyourlayout.ClicktheBlueprinticon(middleicon)toshowonlyoutlinesforeachview.Youcanseebothviewssidebysidebyclickingthethirdicon.

2. Screenorientation:Clicktorotatethedevicebetweenlandscapeandportrait.3. Devicetypeandsize:Selectthedevicetype(phone/tablet,AndroidTV,orAndroidWear)andscreenconfiguration

(sizeanddensity).4. APIversion:SelecttheversionofAndroidonwhichtopreviewthelayout.5. Apptheme:SelectwhichUIthemetoapplytothepreview.6. Language:SelectthelanguagetoshowforyourUIstrings.Thislistdisplaysonlythelanguagesavailableinthestring

resources.7. LayoutVariants:Switchtooneofthealternativelayoutsforthisfile,orcreateanewone.

Tip:Tolearnmoreaboutusingthelayouteditor,seeBuildaUIwithLayoutEditor.TolearnmoreabouthowtobuildalayoutwithConstraintLayout,seeBuildaResponsiveUIwithConstraintLayout.

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2.5Clearconstraints

AndroidStudioautomaticallyinferstheconstraintsforlayoutelementswhenyouconvertalayouttouseConstraintLayout.However,theguessesmaynotbewhatyouwant.Followthesestepstocleartheconstraintsinordertofreelypositiontheelementsinthelayout:

1. Right-click(orControl-click)ConstraintLayoutintheComponentTreepane,andchooseClearAllConstraints.

Tip:Youcanalsodeleteasingleconstraintlinebyhoveringthecursorovertheconstrainthandleuntilaredcircleappears,andthenclickingthehandle.TheClearAllConstraintscommandisfasterforremovingallconstraints.

2. Withconstraintsremoved,youcannowmovetheviewsonthelayoutfreely.Dragthebutton_toastviewdowntoanypositionbelowthebutton_countview,sothattheyellowshow_countviewisatthetop,asshowninthefigurebelow.

2.6ResizeaviewThelayouteditoroffersresizinghandlesonallfourcornersofaviewtoresizetheviewquickly.Youcandragthehandlesoneachcorneroftheviewtoresizeit,butdoingsohard-codesthewidthandheightdimensions,whichyoushouldavoidformostviewsbecausehard-codedviewdimensionscannotadapttodifferentcontentandscreensizes.

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Instead,usethePropertiespaneontherightsideofthelayouteditortoselectasizingmodethatdoesn'tusehard-codeddimensions.ThePropertiespaneincludesasquaresizingpanelatthetop.Thesymbolsinsidethesquarerepresentthe

heightandwidthsettingsasfollows:

Intheabovefigure:

1. Horizontalviewsizecontrol.Thehorizontalsizecontrol,whichappearsintwosegmentsontheleftandrightsidesofthesquare,specifiesthelayout_width.Thestraightlinesindicatethatthedimensionisfixedandsetinthelayout_widthpropertybelowthesquare.

2. Verticalviewsizecontrol.Theverticalsizecontrol,whichappearsintwosegmentsonthetopandbottomsidesofthesquare,specifiesthelayout_heightproperty.Theanglesindicatethatthissizecontrolissettowrap_content,whichmeanstheviewwillexpandexactlyasneededtofititscontents.

Followthesestepstoresizetheshow_countview:

1. Clicktheshow_countviewintheComponentTreepane.2. ClickthehorizontalviewsizecontrolinthePropertiespane.Thestraightlineschangetospringcoils,asshowninthe

figurebelow,whichrepresents"anysize".Thelayout_widthpropertyissettozerobecausethereisnosetdimension,buttheviewcanexpandasmuchaspossibletomeetconstraintsandmarginsettings.

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Youwillusethissettingtoanchorthesizeoftheviewtoconstraints,butfirst,continuetoexperimentwithsettings.

3. Clickthehorizontalviewsizecontrolagain(eitherleftorrightside),justtoseewhatotherchoicesyouhave.Thespringcoilschangetoangles,asshowninthefigurebelow,indicatingthatthelayout_widthissettowrap_content.

4. Clickthehorizontalviewsizecontrolagain,andittogglesbacktothestraightlines,indicatingafixeddimension.Clickitagainsothatthelineschangetospringcoils,asshowninthefigurebelow,whichrepresents"anysize".

2.7AddconstraintstoviewsYouwilladdaconstrainttotheshow_countviewsothatitstretchestotherightedgeofthelayout,andanotherconstraintsothattheviewispositionedjustbelowthetopedgeofthelayout.Sincetheviewwassetto"anysize"inthepreviousstep,theviewwillexpandasneededtomatchtheconstraints.

Youwillalsomovethetwobuttonsintopositionontheleftsideoftheshow_countview,constrainthebutton_toastbuttontothetopandleftedgesofthelayout,andconstrainthebutton_countbuttonsothatitstextbaselinematchesthetextbaselineoftheshow_countview.

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1. Tocreatearight-sideconstraintfortheshow_countview,clicktheviewinthelayout,andthenhoverovertheviewtoseeitsconstrainthandles.Click-and-holdtheconstrainthandleontherightsideoftheview,anddragtheconstraintlinethatappearstotherightedgeofthelayout,asshowninthefigurebelow.

Asyoureleasefromtheclick-and-hold,theconstraintismade,andtheshow_countviewjumpstotherightedgeofthelayout.

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2. Click-and-holdtheconstrainthandleonthetopsideoftheview,anddragtheconstraintlinethatappearstothetopedgeofthelayoutundertheappbar,asshowninthefigurebelow.

Thisconstrainstheviewtothetopedge.Afterdraggingtheconstraint,theshow_countviewjumpstothetoprightedgeofthelayout,becauseitisanchoredtoboththetopandrightedges.

3. Clickthebutton_toastview,andusethePropertiespanelasshownpreviouslytoresizetheviewtowrap_contentforboththelayout_widthandlayout_height.Alsoresizethebutton_countviewtowrap_contentforboththelayout_widthandlayout_height.

Youusewrap_contentforthebuttonssothatifthebuttontextislocalizedintoadifferentlanguage,thebuttonwillappearwiderorthinnertoaccommodatethewordinthedifferentlanguage.

4. Dragthebutton_toastviewintopositionontheleftsideoftheshow_countviewasshowninthefigurebelow.Guidesappearsothatyoucansnaptheviewintopositionagainstthetopandleftmargins.

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5. Selectthebutton_toastviewinthelayout,clicktheconstrainthandlethatappearsonthetopoftheview,anddragittothetopedgeofthelayoutundertheappbarasshowninthefigurebelow.Thenclicktheconstrainthandlethatappearsontheleftsideoftheview,anddragittotheleftedgeofthelayout.

6. Selectthebutton_countview,clicktheconstrainthandlethatappearsontheleftsideoftheview,anddragittotheleft

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edgeofthelayout.7. Tocreateabaselineconstraintbetweenthebutton_countview'stextbaselineandtheshow_countview'stext

baseline,selectthebutton_countview,andthenhoverovertheview'sbaselinehandlefortwosecondsuntilthehandleblinkswhite.Thenclickanddragtheconstraintlinethatappearstothebaselineoftheshow_countview,asshowninthefigurebelow.

Younowhavealayoutinwhicheachviewissettonon-specificdimensionsandconstrainedtothelayout.Onebutton'stextisalignedtoaTextView'sbaseline,sothatifyoumovetheTextView,thebuttonmoveswithit.

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Tip:Ifaviewdoesn'thaveatleasttwoconstraints,itappearsatthetopofthelayout.

8. Althoughtheshow_countviewalreadyhastwoconstraints,youcanaddanotherconstrainttoit.Dragaconstraintlinefromtheconstrainthandleontheleftsideoftheviewtotherightsideofthebutton_countview,asshowninthe

figuresbelow.

9. Runtheapp.Thelayoutconformstoitsconstraints.

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Solutioncode:AndroidStudioproject:HelloConstraint

Task3:CreatelayoutvariantsYoucancreatevariantsofyourlayoutforlandscapeorientationandlargerdisplays.Youwillcreateanalternativeversionoftheprevioustask'slayouttooptimizeitforlandscapeorientation:

1. OpenyourlayoutfilefortheHelloConstraintapp,andbesureyou'reviewingtheDesigneditor(clicktheDesigntabatthebottomofthewindow).

2. ClicktheLayoutVariantsiconinthesecondrowoficons(refertothefigureinTask2Step4)andchooseCreateLandscapeVariation.The"land/activity_main.xml"tabappearsshowingthelayoutforthelandscape(horizontal)

orientation,asshowninthefigurebelow.

Youcanchangethelayoutforthelandscape(horizontal)versionwithoutchangingtheoriginalportrait(vertical)orientation,therebytakingadvantageofthewiderscreen.

3. InProject:AndroidviewintheleftmostpaneofAndroidStudio,lookinsidetheres>layoutdirectory,andyouwillseethatAndroidStudioautomaticallycreatedthevariantforyou,calledactivity_main.xml(land).

4. The"land/activity_main.xml"tabshouldstillbeopeninthelayouteditor;ifnot,double-clicktheactivity_main.xml(land)fileinthelayoutdirectory.

5. ClicktheTexttabtoviewthelayoutinXML.Findtheconstraintforthebutton_toastviewthatalignsitstopedgetotheparentview:

<Button

android:id="@+id/button_toast"

...

app:layout_constraintTop_toTopOf="parent"

...

6. Changethisconstraintsothatthebutton_toastview'sbottomedgeisalignedtothetopedgeofthebutton_countview.

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Hint:Iftheconstrainttoalignthetopofaviewtoanotherviewisapp:layout_constraintTop_toTopOf,whatdoyouthinktheconstraintistoalignthebottomofaviewtothetopofanotherview?Answer:

app:layout_constraintBottom_toTopOf="@id/button_count"

7. Runtheapp,andswitchtolandscapemodetoseethedifferentlayout.Thelayoutsshouldappearasshownbelow.

SolutioncodeAndroidStudioproject:HelloToast

AndroidStudioproject:HelloRelative

AndroidStudioproject:HelloConstraint

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterchapters.

Challenge:Addanotherlayoutvariantforalargedisplay.Thelayoutvariantshouldtakeadvantageofthelargerscreensizetoshowlargerelements.

Hint:ClicktheLayoutVariantsiconinthetoolbarandchooseCreatelayout-xlargeVariation.Resizeandpositiontheelementsinthelayout.

SummaryInthisexerciseyoulearnedhowto:

RearrangeviewsinaRelativeLayoutusingtheDesigntabofthelayouteditor.Viewthelayoutdesignanditsblueprint.Changeaview'sproperties(XMLattributes)inthelayouteditor.AlignaviewwiththeparentRelativeLayoutusing:

android:layout_alignParentToptoaligntheviewtothetopoftheparent.

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android:layout_alignParentLefttoaligntheviewtotheleftsideoftheparent.android:layout_alignParentStarttomakethestartedgeoftheviewmatchthestartedgeoftheparent.Thisattributeisusefulifyourappshouldworkondevicesinwhichthelanguageorlocalepreferencemaybedifferent.Thestartistheleftedgeofthescreenifthepreferenceisleft-to-right,oritistherightedgeofthescreenifthepreferenceisright-to-left.

Useandroid:layout_belowtopositionaviewunderneathanotherviewinaRelativeLayout.AddConstraintLayouttoyourproject.ConvertalayouttoConstraintLayoutbyright-clickingtherootviewgroupintheComponentTreepane,andthenclickingConvertlayouttoConstraintLayout.ClearallconstraintsinaConstraintLayoutbyright-clicking(orControl-clicking)ConstraintLayoutintheComponentTreepane,andchoosingClearAllConstraints.AddconstraintstoviewsintheConstraintLayoutlayout,andresizingviews.Changethepropertiesofviews,suchastextAppearanceandtextSize.Createvariantsofthelayoutforlandscapeorientationandforlargerscreensizes.

RelatedconceptsTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

Layouts,Views,andResources

LearnmoreDeveloperDocumentation:

ViewRelativeLayoutBuildaUIwithLayoutEditorBuildaResponsiveUIwithConstraintLayout

Other:

Codelabs:UsingConstraintLayouttodesignyourviews

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1.3:WorkingwithTextViewElementsContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1:AddseveraltextviewsTask2:AddactiveweblinksandaScrollViewTask3:ScrollmultipleelementsCodingchallengeSummaryRelatedconceptLearnmore

TheTextViewclassisasubclassoftheViewclassthatdisplaystextonthescreen.YoucancontrolhowthetextappearswithTextViewattributesintheXMLlayoutfile.ThispracticalshowshowtoworkwithmultipleTextViewelements,includingoneinwhichtheusercanscrollitscontentsvertically.

Ifyouhavemoreinformationthanfitsonthedevice'sdisplay,youcancreateascrollingviewsothattheusercanscrollverticallybyswipingupordown,orhorizontallybyswipingrightorleft.

Youwouldtypicallyuseascrollingviewfornewsstories,articles,oranylengthytextthatdoesn'tcompletelyfitonthedevicedisplay.Youcanalsouseascrollingviewtoenableuserstoentermultiplelinesoftext,ortocombineUIelements(suchasatextfieldandabutton)withinascrollingview.

TheScrollViewclassprovidesthelayoutforthescrollingview.ScrollViewisasubclassofFrameLayout,anddevelopersshouldplaceonlyoneviewasachildwithinit,wherethechildviewcontainstheentirecontentstoscroll.Thischildviewmayitselfbeaviewgroup(suchasalayoutmanagerlikeLinearLayout)withacomplexhierarchyofobjects.Notethatcomplexlayoutsmaysufferperformanceissueswithchildviewssuchasimages.AgoodchoiceforaviewwithinaScrollViewisaLinearLayoutthatisarrangedinaverticalorientation,presentingtop-levelitemsthattheusercanscrollthrough.

WithaScrollView,alloftheviewsareinmemoryandintheviewhierarchyeveniftheyaren'tdisplayedonscreen.ThismakesScrollViewidealforscrollingpagesoffree-formtextsmoothly,becausethetextisalreadyinmemory.However,ScrollViewcanuseupalotofmemory,whichcanaffecttheperformanceoftherestofyourapp.Todisplaylonglistsofitemsthatuserscanaddto,deletefrom,oredit,considerusingaRecyclerView,whichisdescribedinaseparatepractical.

WhatyoushouldalreadyKNOWFrompreviouspracticals,youshouldbeableto:

CreateaHelloWorldappwithAndroidStudio.Runanapponanemulatororadevice.ImplementaTextViewinalayoutforanapp.Createandusestringresources.Convertlayoutdimensionstoresources.

WhatyouwillLEARNYouwilllearnto:

UseXMLcodetoaddmultipleTextViewelements.

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UseXMLcodetodefineascrollingview.Displayfree-formtextwithsomeHTMLformattingtags.StyletheTextViewbackgroundcolorandtextcolor.Includeaweblinkinthetext.

WhatyouwillDOInthispractical,youwill:

CreatetheScrollingTextapp.AddtwoTextViewelementsforthearticleheadingandsubheading.UseTextAppearancestylesandcolorsforthearticleheadingandsubheading.UseHTMLtagsinthetextstringtocontrolformatting.UsethelineSpacingExtraattributetoaddlinespacingforreadability.AddaScrollViewtothelayouttoenablescrollingaTextViewelement.AddtheautoLinkattributetoenableURLsinthetexttobeactiveandclickable.

AppoverviewTheScrollingTextappdemonstratestheScrollViewUIcomponent.ScrollViewisaviewgroupthatinthisexamplecontainsaTextView.Itshowsalengthypageoftext—inthiscase,amusicalbumreview—thattheusercanscrollverticallytoreadbyswipingupanddown.Ascrollbarappearsintherightmargin.TheappshowshowyoucanusetextformattedwithminimalHTMLtagsforsettingtexttoboldoritalic,andwithnew-linecharacterstoseparateparagraphs.Youcanalsoincludeactiveweblinksinthetext.

Intheabovefigure,thefollowingappear:

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1. Anactiveweblinkembeddedinfree-formtext2. Thescrollbarthatappearswhenscrollingthetext

Task1:AddseveraltextviewsInthispractical,youwillcreateanAndroidprojectfortheScrollingTextapp,addTextViewstothelayoutforanarticletitleandsubtitle,andchangetheexisting"HelloWorld"TextViewelementtoshowalengthyarticle.Thefigurebelowisadiagramofthelayout.

YouwillmakeallthesechangesintheXMLcodeandinthestrings.xmlfile.YouwilledittheXMLcodeforthelayoutintheTextpane,whichyoushowbyclickingtheTexttab,ratherthanclickingtheDesigntabfortheDesignpane.SomechangestoUIelementsandattributesareeasiertomakedirectlyintheTextpaneusingXMLsourcecode.

1.1CreatetheprojectandTextViewelements1. InAndroidStudiocreateanewprojectwiththefollowingparameters:

Attribute Value

ApplicationName ScrollingText

CompanyName android.example.com(oryourowndomain)

PhoneandTabletMinimumSDK API15:Android4.0.3IceCreamSandwich

Template EmptyActivity

GenerateLayoutFilecheckbox Checked

2. Intheapp>res>layoutfolder,opentheactivity_main.xmlfile,andclicktheTexttabtoseetheXMLcodeifitisnotalreadyselected.

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Atthetop,orroot,oftheviewhierarchyisaviewgroupsuchasConstraintLayout.ChangethisviewgrouptoRelativeLayout.Thesecondlineofcodenowlookssomethinglikethis:

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

RelativeLayoutallowsyoutopositionitschildViewsrelativetoeachotherorrelativetotheparentRelativeLayoutitself.Thedefault"HelloWorld"TextViewelementthatiscreatedbytheEmptyLayouttemplateisachildViewwithintheRelativeLayoutviewgroup.FormoreinformationaboutusingaRelativeLayout,seetheRelativeLayoutAPIGuide.

3. AddaTextViewelementabovethe"HelloWorld"TextView.AddthefollowingattributestotheTextView:

TextView#1attribute Value

android:id "@+id/article_heading"

layout_width "match_parent"

layout_height "wrap_content"

android:background "@color/colorPrimary"

android:textColor "@android:color/white"

android:padding "10dp"

android:textAppearance "@android:style/TextAppearance.Large"

android:textStyle "bold"

android:text "ArticleTitle"

Tip:TheattributesforstylingthetextandbackgroundaresummarizedintheTextViewclassdocumentation.

4. Extractthestringresourcefortheandroid:textattribute'shard-codedstring"ArticleTitle"intheTextViewtocreateanentryforitinstrings.xml.

Placethecursoronthehard-codedstring,pressAlt-Enter(Option-EnterontheMac),andselectExtractstringresource.Thenedittheresourcenameforthestringvaluetoarticle_title.

Tip:StringresourcesaredescribedindetailintheStringResourcesdocumentation.

5. Extractthedimensionresourcefortheandroid:paddingattribute'shard-codedstring"10dp"intheTextViewtocreateanentryindimens.xml.

Placethecursoronthehard-codedstring,pressAlt-Enter(Option-EnterontheMac),andselectExtractdimensionresource.ThenedittheResourcenametopadding_regular.

6. AddanotherTextViewelementabovethe"HelloWorld"TextViewandbelowtheTextViewyoucreatedintheprevioussteps.AddthefollowingattributestotheTextView:

TextView#2Attribute Value

android:id "@+id/article_subheading"

layout_width "match_parent"

layout_height "wrap_content"

android:layout_below "@id/article_heading"

android:padding "@dimen/padding_regular"

android:textAppearance "@android:style/TextAppearance"

android:text "ArticleSubtitle"

Notethatsinceyouextractedthedimensionresourceforthe"10dp"stringtopadding_regularinthepreviouslycreatedTextView,youcanuse"@dimen/padding_regular"fortheandroid:paddingattributeinthisTextView.

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7. Extractthestringresourcefortheandroid:textattribute'shard-codedstring"ArticleSubtitle"intheTextViewtoarticle_subtitle.

8. Inthe"HelloWorld"TextViewelement,removethelayout_constraintattributes,iftheyarepresent.9. AddthefollowingTextViewattributestothe"HelloWorld"TextViewelement,andchangetheandroid:textattribute:

TextViewAttribute Value

android:id "@+id/article"

android:lineSpacingExtra "5sp"

android:layout_below "@id/article_subheading"

android:text Changeto"Articletext"

10. Extractthestringresourcefor"Articletext"toarticle_text,andextractthedimensionresourcefor"5sp"toline_spacing.

11. ReformatandalignthecodebychoosingCode>ReformatCode.Itisagoodpracticetoreformatandalignyourcodesothatitiseasierforyouandotherstounderstand.

1.2AddthetextofthearticleInarealappthataccessesmagazineornewspaperarticles,thearticlesthatappearwouldprobablycomefromanonlinesourcethroughacontentprovider,ormightbesavedinadvanceinadatabaseonthedevice.

Forthispractical,youwillcreatethearticleasasinglelongstringinthestrings.xmlresource.

1. Intheapp>res>valuesfolder,openstrings.xml.2. Enterthevaluesforthestringsarticle_titleandarticle_subtitlewithamade-uptitleandasubtitleforthearticle

youareadding.Thestringvaluesforeachshouldbesingle-linetextwithoutHTMLtagsormultiplelines.3. Enterorcopyandpastetextforthearticle_textstring.

Usethetextprovidedforthearticle_textstringinthestrings.xmlfileofthefinishedScrollingTextapp,oruseyourowngenerictext.Youcancopyandthenpastethesamesentenceoverandover,aslongastheresultisalongsectionoftextthatwillnotfitentirelyonthescreen.Keepinmindthefollowing(refertothefigurebelowforanexample):

i. Asyouenterorpastetextinthestrings.xmlfile,thetextlinesdon'twraparoundtothenextline—theyextendbeyondtherightmargin.Thisisthecorrectbehavior—eachnewlineoftextstartingattheleftmarginrepresentsanentireparagraph.

ii. Enter\ntorepresenttheendofaline,andanother\ntorepresentablankline.

Why?Youneedtoaddend-of-linecharacterstokeepparagraphsfromrunningintoeachother.

Tip:Ifyouwanttoseethetextwrappedinstrings.xml,youcanpressReturntoenterhardlineendings,orformatthetextfirstinatexteditorwithhardlineendings.

iii. Ifyouhaveanapostrophe(')inyourtext,youmustescapeitbyprecedingitwithabackslash(\').Ifyouhaveadouble-quoteinyourtext,youmustalsoescapeit(\").Youmustalsoescapeanyothernon-ASCIIcharacters.Seethe"FormattingandStyling"sectionofStringResourcesformoredetails.

iv. EntertheHTMLand</b>tagsaroundwordsthatshouldbeinbold.

v. EntertheHTMLand</i>tagsaroundwordsthatshouldbeinitalics.Note,however,thatifyouusecurledapostropheswithinanitalicphrase,youshouldreplacethemwithstraightapostrophes.

vi. Youcancombineboldanditalicsbycombiningthetags,asin...words...</i></b>.OtherHTMLtagsareignored.

vii. EncloseTheentiretextwithin<stringname="article_text"></string>inthestrings.xmlfile.

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viii. Includeaweblinktotest,suchaswww.google.com(theexamplebelowuseswww.rockument.com).Don'tuseanHTMLtag—anyHTMLtagsexcepttheboldanditalictagswillbeignoredandpresentedastext,whichisnotwhatyouwant.

4. Runtheapp.

Thearticleappears,andyoucanevenscrollit,butthescrollingisnotsmoothandthereisnoscrollbarbecauseyouhaven'tyetincludedaScrollView(whichyouwilldointhenexttask).Notealsothattappingaweblinkdoesnotcurrentlydoanything.Youwillalsofixthatinthenexttask.

SolutioncodeDependingonyourversionofAndroidStudio,theactivity_main.xmllayoutfilewilllooksomethinglikethefollowing:

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<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.scrollingtext.MainActivity">

<TextView

android:id="@+id/article_heading"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:background="@color/colorPrimary"

android:textColor="@android:color/holo_orange_light"

android:textColorHighlight="@color/colorAccent"

android:padding="10dp"

android:textAppearance="@android:style/TextAppearance.Large"

android:textStyle="bold"

android:text="@string/article_title"/>

<TextView

android:id="@+id/article_subheading"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_below="@id/article_heading"

android:padding="10dp"

android:textAppearance="@android:style/TextAppearance"

android:text="@string/article_subtitle"/>

<TextView

android:id="@+id/article"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_below="@id/article_subheading"

android:lineSpacingExtra="5sp"

android:text="@string/article_text"/>

</RelativeLayout>

Task2:AddactiveWeblinksandaScrollViewIntheprevioustaskyoucreatedtheScrollingTextappwithTextViewsforanarticletitle,subtitle,andlengthyarticletext.Youalsoincludedaweblink,butthelinkisnotyetactive.Youwilladdthecodetomakeitactive.

Also,theTextViewbyitselfcan'tenableuserstoscrollthearticletexttoseeallofit.YouwilladdanewviewgroupcalledScrollViewtotheXMLlayoutthatwillmaketheTextViewscrollable.

2.1AddtheautoLinkattributeforactiveweblinks

Addtheandroid:autoLink="web"attributetothearticleTextView.TheXMLcodeforthisTextViewshouldnowlooklikethis:

<TextView

android:id="@+id/article"

...

android:autoLink="web"

.../>

2.2AddaScrollViewtothelayout

Tomakeaview(suchasaTextView)scrollable,embedtheviewinsideaScrollView.

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1. AddaScrollViewbetweenthearticle_subheadingTextViewandthearticleTextView.Asyouenter<ScrollView,AndroidStudioautomaticallyadds</ScrollView>attheend,andpresentstheandroid:layout_widthandandroid:layout_heightattributeswithsuggestions.Choosewrap_contentfromthesuggestionsforbothattributes.Thecodeshouldnowlooklikethis:

<TextView

android:id="@+id/article_subheading"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_below="@id/article_heading"

android:padding="10dp"

android:textAppearance="@android:style/TextAppearance"

android:text="@string/article_subtitle"/>

<ScrollView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_below="@id/article_subheading"></ScrollView>

<TextView

android:id="@+id/article"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_below="@id/article_subheading"

android:lineSpacingExtra="5sp"

android:autoLink="web"

android:text="@string/article_text"/>

2. Movetheending</ScrollView>codeafterthearticleTextViewsothatthearticleTextViewattributesareinsidetheScrollViewXMLelement.

3. RemovethefollowingattributefromthearticleTextView,becausetheScrollViewitselfwillbeplacedbelowthearticle_subheadingelement,andthisattributeforTextViewwouldconflictwiththeScrollView:

android:layout_below="@id/article_subheading"

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Thelayoutshouldnowlooklikethis:

4. ChooseCode>ReformatCodetoreformattheXMLcodesothatthearticleTextViewnowappearsindentedinsidethe<Scrollviewcode.

5. Runtheapp.

Swipeupanddowntoscrollthearticle.Thescrollbarappearsintherightmarginasyouscroll.

Taptheweblinktogotothewebpage.Theandroid:autoLinkattributeturnsanyrecognizableURLintheTextView(suchaswww.rockument.com)intoaweblink.

6. Rotateyourdeviceoremulatorwhilerunningtheapp.Noticehowthescrollingviewwidenstousethefulldisplayandstillscrollsproperly.

7. Runtheapponatabletortabletemulator.Noticehowthescrollingviewwidenstousethefulldisplayandstillscrollsproperly.

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Intheabovefigure,thefollowingappear:

1. Anactiveweblinkembeddedinfree-formtext2. Thescrollbarthatappearswhenscrollingthetext

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DependingonyourversionofAndroidStudio,theactivity_main.xmllayoutfilewillnowlooksomethinglikethefollowing:

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<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.scrollingtext.MainActivity">

<TextView

android:id="@+id/article_heading"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:background="@color/colorPrimary"

android:textColor="@android:color/white"

android:paddingTop="10dp"

android:paddingBottom="10dp"

android:paddingLeft="10dp"

android:paddingRight="10dp"

android:textAppearance="@android:style/TextAppearance.Large"

android:textStyle="bold"

android:text="@string/article_title"/>

<TextView

android:id="@+id/article_subheading"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_below="@id/article_heading"

android:paddingTop="10dp"

android:paddingBottom="10dp"

android:paddingLeft="10dp"

android:paddingRight="10dp"

android:textAppearance="@android:style/TextAppearance"

android:text="@string/article_subtitle"/>

<ScrollView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_below="@id/article_subheading">

<TextView

android:id="@+id/article"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:lineSpacingExtra="5sp"

android:autoLink="web"

android:text="@string/article_text"/>

</ScrollView>

</RelativeLayout>

SolutioncodeAndroidStudioproject:ScrollingText

Task3:ScrollmultipleelementsAsnotedbefore,theScrollViewviewgroupcancontainonlyonechildview(suchasthearticleTextViewyoucreated);however,thatViewcanbeanotherviewgroupthatcontainsViews,suchasLinearLayout.YoucannestaviewgroupsuchasLinearLayoutwithintheScrollViewviewgroup,therebyscrollingeverythingthatisinsidetheLinearLayout.

Forexample,ifyouwantthesubheadingofthearticletoscrollalongwiththearticle,addaLinearLayoutwithintheScrollView,andmovethesubheading,alongwiththearticle,intotheLinearLayout.TheLinearLayoutviewgroupbecomesthesinglechildViewintheScrollViewasshowninthefigurebelow,andtheusercanscrolltheentireviewgroup:the

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subheadingandthearticle.

3.1AddaLinearLayouttotheScrollView

1. Onyourcomputer,makeacopyofAndroidStudio'sprojectfolderforScrollingText,andrenametheprojecttobeScrollingText2.Tocopyandrenameaproject,followthe"Copyandrenameaproject"instructionsintheAppendix.

2. OpenScrollingText2inAndroidStudio,andopentheactivity_main.xmlfiletochangetheXMLlayoutcode.3. AddaLinearLayoutabovethearticleTextViewintheScrollView.Asyouenter<LinearLayout,AndroidStudio

automaticallyadds</LinearLayout>totheend,andpresentstheandroid:layout_widthandandroid:layout_heightattributeswithsuggestions.Choosematch_parentandwrap_contentfromthesuggestionsforitswidthandheight,respectively.Thecodeshouldnowlooklikethis:

<LinearLayout

android:layout_width="match_parent"

android:layout_height="wrap_content"></LinearLayout>

Youusematch_parenttomatchthewidthoftheparentviewgroup,andwrap_contenttomaketheviewgrouponlybigenoughtoencloseitscontentsandpadding.

4. Movetheending</LinearLayout>codeafterthearticleTextViewbutbeforetheclosing</ScrollView>sothattheLinearLayoutincludesthearticleTextViewandiscompletelyinsidetheScrollView.

5. Addtheandroid:orientation="vertical"attributetotheLinearLayoutinordertosettheorientationoftheLinearLayouttovertical.TheLinearLayoutwithintheScrollViewshouldnowlooklikethis(chooseCode>ReformatCodetoindenttheviewgroupscorrectly):

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<ScrollView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_below="@id/article_subheading">

<LinearLayout

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:orientation="vertical">

<TextView

android:id="@+id/article"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:autoLink="web"

android:lineSpacingExtra="5sp"

android:text="@string/article_text"/>

</LinearLayout>

</ScrollView>

6. Movethearticle_subheadingTextViewtoapositioninsidetheLinearLayoutabovethearticleTextView.7. Removetheandroid:layout_below="@id/article_heading"attributefromthearticle_subheadingTextView.Sincethis

TextViewisnowwithintheLinearLayout,thisattributewouldconflictwiththeLinearLayoutattributes.8. ChangetheScrollViewlayoutattributefromandroid:layout_below="@id/article_subheading"to

android:layout_below="@id/article_heading".NowthatthesubheadingispartoftheLinearLayout,theScrollViewmustbeplacedbelowtheheading,notthesubheading.

9. Runtheapp.

Swipeupanddowntoscrollthearticle,andnoticethatthesubheadingnowscrollsalongwiththearticlewhiletheheadingstaysinplace.

SolutioncodeAndroidStudioproject:ScrollingText2

CodingchallengeNote:Allcodingchallengesareoptionalandarenotaprerequisiteforlaterlessons.

Challenge:AddanotherUIelement—aButton—totheLinearLayoutviewgroupthatiscontainedwithintheScrollView.MaketheButtonappearbelowthearticle.Theuserwouldhavetoscrolltotheendofthearticletoseethebutton.Usethetext"AddComment"fortheButton,foruserstoclicktoaddacommenttothearticle.Forthischallenge,thereisnoneedtocreateabutton-handlingmethodtoactuallyaddacomment;itissufficienttojustplacetheButtonelementintheproperplaceinthelayout.

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ChallengeSolutioncodeAndroidStudioproject:ScrollingText3

SummaryInthispractical,youlearnedaboutAndroidStudio'sviewelementsandhowtoscrollandnestcode.Youworkedto:

AddmultipleTextViewelementstotheXMLlayout.Displayfree-formtextinaTextViewwithHTMLformattingtagsforboldanditalics.Use\nasanend-of-linecharacterinfree-formtexttokeepaparagraphfromrunningintothenextparagraph.Usetheandroid:autoLink="web"attributetomakeweblinksinthetextclickable.

AddaScrollViewviewgrouptothelayouttodefineascrollingviewwithoneoftheTextViewelements.AddaLinearLayoutviewgroupwithinaScrollViewinordertoscrollseveralTextViewelementstogether.Extractstringvaluesintostringnamesinthestrings.xmlfileforeasierlocalizationofstringresources.

RelatedconceptsTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

TextandScrollingViews

LearnmoreDeveloperDocumentation:

TextViewScrollViewStringResourcesViewRelativeLayout

Other:

AndroidDevelopersBlog:LinkifyyourText!Codepath:WorkingwithaTextView

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1.4:LearningAboutAvailableResourcesContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.ExploretheofficialAndroiddocumentationTask2:UseprojecttemplatesTask3:LearnfromexamplecodeTask4:ManymoreresourcesSummaryRelatedconceptLearnmore

Inthispracticalyouwill:

ExploresomeofthemanyresourcesavailabletoAndroiddevelopersofalllevels.AddahomescreenicontoyourWordListapp;tappingtheiconwilllaunchtheapp.

WhatyoushouldalreadyKNOWFrompreviouspracticals,youshouldbeableto:

UnderstandthebasicworkflowofAndroidStudio.

WhatyouwillLEARNWheretofinddeveloperresources:

WithinAndroidStudio.IntheofficialAndroiddeveloperdocumentationontheweb.ElsewhereontheInternet.

WhatyouwillDOInthispracticalyouwill:

ExploreanduseAndroiddeveloperresources.Usedeveloperresourcestofigureouthowtoaddanicontothehomescreenofyourdevice.Whenthisiconisclicked,yourapplaunches.

AppOverviewYouwillusetheexistingHelloToastappandaddalaunchericontoit.

Task1.ExploretheofficialAndroiddeveloperdocumentationYoucanfindtheofficialAndroiddeveloperdocumentationat:

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http://developer.android.com/index.html

ThisdocumentationcontainsawealthofinformationthatiskeptcurrentbyGoogle.

1.1.ExploretheofficialAndroiddocumentation

1. Gotohttp://developer.android.com/index.html.2. Atthetopofthepage,lookfortheDesign,Develop,andDistributelinks.Followeachofthelinksandfamiliarize

yourselfwiththenavigationstructure.DesignisallaboutMaterialDesign,whichisaconceptualdesignphilosophythatoutlineshowappsshouldlookandworkonmobiledevices.Scrolltothebottomofthelandingpageforlinkstoresourcessuchasstickersheetsandcolorpalettes.DevelopiswhereyoucanfindAPIinformation,referencedocumentation,tutorials,toolguides,andcodesamples.Youcanusethesitenavigationorsearchtofindwhatyouneed.Distributeisabouteverythingthathappensafteryou'vewrittenyourapp:puttingitonthePlayStore,growingyouruserbase,andearningmoney.

3. Usesearchornavigatethedocumentationtocompletethefollowingtasks:AddalaunchericontotheWordListapp.SeetheAPIGuidetoLauncherIconstolearnmoreabouthowtodesigneffectivelaunchericons.Learnhowtomonitoryourapp'sresourceusageinAndroidStudio.

Task2.UseprojecttemplatesAndroidStudioprovidestemplatesforcommonandrecommendedappandactivitydesigns.Usingbuilt-intemplatessavestime,andhelpsyoufollowdesignbestpractices.

Eachtemplateincorporatesanskeletonactivityanduserinterface.You'vealreadyusedtheEmptyActivitytemplate.TheBasicActivitytemplatehasmorefeaturesandincorporatesrecommendedappfeatures,suchastheoptionsmenu.

2.1.ExploretheBasicActivityarchitectureTheBasicActivitytemplateisaversatiletemplateprovidedbyAndroidStudiotoassistyouinjump-startingyourappdevelopment.

1. InAndroidStudio,createanewprojectwiththeBasicActivitytemplate.2. Buildandruntheapp.

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3. Identifythelabelledpartsonthescreenshotandtablebelow.Findtheirequivalentsonyourdeviceoremulatorscreen.

ArchitectureoftheBasicActivitytemplate

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# UIDescription Codereference

1StatusbarThisbarisprovidedandcontrolledbytheAndroidsystem.

Notvisibleinthetemplatecode.It'spossibletoaccessitfromyouractivity.Forexample,youcanhidethestatusbar,ifnecessary.

2

AppBarLayout>ToolbarAppbar(alsocalledActionbar)providesvisualstructure,standardizedvisualelements,andnavigation.Forbackwardscompatibility,theAppBarLayoutinthetemplateembedsaToolbarwidgetwiththesamefunctionality.

ActionBarclass

Challenge:AppBarTutorial

activity_main.xmlLookforandroid.support.v7.widget.Toolbar

insideandroid.support.design.widget.AppBarLayout.

Changethetoolbartochangetheappearanceofitsparent,theappbar.

3ApplicationnameThisisderivedfromyourpackagename,butcanbeanythingyouchoose.

AndroidManifest.xmlandroid:label="@string/app_name"

4

OptionsmenuoverflowbuttonMenuitemsfortheactivity,aswellasglobaloptions,suchas"Search"and"Settings"forthesettingsmenu.Yourappmenuitemsgointothismenu.

MainActivity.javaonOptionsItemSelected()implementswhathappenswhenamenuitemisselected.

res>menu>menu_main.xml

Resourcethatspecifiesthemenuitemsfortheoptionsmenu.

5

CoordinatorLayoutCoordinatorLayoutisafeature-richlayoutthatprovidesmechanismsforviewstointeract.Yourapp'suserinterfacegoesinsidethisviewgroup.

activity_main.xmlNoticethattherearenoviewsspecifiedinthislayout;rather,itincludesanotherlayoutwith

<includelayout="@layout/content_main"/>

wheretheviewsarespecified.Thisseparatessystemviewsfromtheviewsuniquetoyourapp.

6TextViewIntheexample,usedtodisplay"HelloWorld".Replacethiswiththeviewsforyourapp.

content_main.xmlAllyourapp'sviewsaredefinedinthisfile.

7 FloatingActionbutton(FAB)activity_main.xmlMainActivity.java>onCreatehasastubthatsetsanonClicklistenerontheFAB.

4. AlsoinspectthecorrespondingJavacodeandXMLconfigurationfiles.

BeingfamiliarwiththeJavasourcecodeandXMLfileswillhelpyouextendandcustomizethistemplateforyourownneeds.

SeeAccessingResourcesfordetailsontheXMLsyntaxforaccessingresources.

5. Afteryouunderstandthetemplatecode,trythefollowing:Changethecoloroftheappbar(toolbar).Lookatthestylesassociatedwiththeappbar(toolbar).Changethenameofyourappthat'sdisplayedintheappbar(toolbar).

2.2.Explorehowtoaddanactivityusingtemplates

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Forthepracticalssofar,you'veusedtheEmptyActivityandBasicActivitytemplates.Inlaterlessons,thetemplatesusewillvary,dependingonthetask.

Theseactivitytemplatesarealsoavailablefrominsideyourproject,sothatyoucanaddmoreactivitiestoyourappaftertheinitialprojectsetup.(Youwilllearnmoreaboutthisthisinalaterchapter.)

1. Createanewprojectorchooseanexistingproject.2. Inyourprojectdirectory,intheAndroidview,right-clickthefolderwithyourjavafiles.3. ChooseNew>Activity>Gallery.4. Addoneofthoseactivities,forexample,theNavigationDrawerActivity.FindthelayoutfilesfortheNavigationDrawer

ActivityanddisplaytheminDesign.

Task3.LearnfromexamplecodeAndroidStudio,aswellastheAndroiddocumentationprovidemanycodesamplesthatyoucanstudy,copy,andincorporatewithyourprojects.

3.1.AndroidcodesamplesYoucanexplorehundredsofcodesamplesdirectlyfromAndroidStudio.

1. InAndroidStudio,chooseFile>New>ImportSample.2. Browsethesamples.3. LookattheDescriptionandPreviewtabstolearnmoreabouteachsample.4. ChooseasampleandclickNext.5. AcceptthedefaultsandclickFinish.

Note:Thesamplescontainedherearemeantasastartingpointforfurtherdevelopment.Weencourageyoutodesignandbuildyourownideasintothem.

3.2.UsetheSDKManagertoinstallofflinedocumentationInstallingAndroidStudioalsoinstallsessentialsoftheAndroidSDK(SoftwareDevelopmentKit).However,additionallibrariesanddocumentationareavailable,andyoucaninstallthemusingtheSDKManager.

1. ChooseTools>Android>SDKManager.ThisopenstheDefaultPreferencessettings.2. Intheleft-handnavigation,findandopenthesettingsforAndroidSDK.3. ClickSDKPlatformsinthesettingswindow.YoucaninstalladditionalversionsoftheAndroidsystemfromhere.4. ClickonSDKUpdateSites.AndroidStudiochecksthelistedandcheckedsitesregularlyforupdates.5. ClickontheSDKToolstab.HereyoucaninstalladditionalSDKToolsthatarenotinstalledbydefault,aswellasan

offlineversionoftheAndroiddeveloperdocumentation.Thisgivesyouaccesstodocumentationevenwhenyouarenotconnectedtotheinternet.

6. Check"DocumentationforAndroidSDK",clickApply,andfollowtheprompts.7. NavigatetotheAndroid/sdkdirectoryandopenthedocsfolder.8. Findindex.htmlandopenit.

Task4.ManymoreresourcesTheAndroidDeveloperYouTubechannelisagreatsourceoftutorialsandtips.TheAndroidteampostsnewsandandtipsontheOfficialAndroidBlog.StackOverflowisacommunityofmillionsofprogrammershelpingeachother.Ifyourunintoaproblem,chancesare,someoneelsehasalreadypostedanansweronthisforum.OnStackOverflow,youcanevenask,"HowdoIsetupanduseADBoverWiFi?",or"WhatarethemostcommonmemoryleaksinAndroiddevelopment?"Andlastbutnotleast,typeyourquestionsintoGooglesearch,andtheGooglesearchenginewillcollectrelevant

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resultsfromalloftheseresources.Forexample,"WhatisthemostpopularAndroidOSversioninIndia?"

4.1.SearchonStackOverflowusingtags

1. GotoStackOverflow2. Inthesearchbox,type[android].

The[]bracketsindicatethatyouwanttosearchforpoststhathavebeentaggedasbeingaboutAndroid.

3. Youcancombinetagsandsearchtermstomakeyoursearchmorespecific.Searchfor[android]and[layout][android]"helloworld"

4. ReadmoreaboutthemanywaysinwhichyoucansearchonStackoverflow.

SummaryOfficialAndroidDeveloperDocumentation-http://developer.android.comMaterialDesignisaconceptualdesignphilosophythatoutlineshowappsshouldlookandworkonmobiledevices.TheGooglePlaystoreisGoogle'sdigitaldistributionsystemforappsdevelopedwiththeAndroidSDK.AndroidStudioprovidestemplatesforcommonandrecommendedappandactivitydesigns.Thesetemplatesofferworkingcodeforcommonusecases.Whenyoucreateaproject,youcanchooseatemplateforyourfirstactivity.Whileyouarefurtherdevelopingyourapp,activitiesandotherappcomponentscanbecreatedfrombuilt-intemplates.AndroidStudiocontainsmanycodesamplesthatyoucanstudy,copy,andincorporatewithyourprojects.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

ResourcestoHelpYouLearn

LearnmoreDeveloperDocumentation:

OfficialAndroiddocumentationImageAssetStudioAndroidMonitorpageOfficialAndroidblogAndroidDevelopersblogGoogleI/OCodelabsStackOverflowAndroidvocabularyGoogleDeveloperTrainingwebsite

Code

SourcecodeforexercisesonGitHubAndroidcodesamplesfordevelopers

Videos

AndroidDeveloperYouTubechannelUdacityonlinecourses

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2.1:CreateandStartActivitiesContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.CreatetheTwoActivitiesprojectTask2.CreateandlaunchthesecondactivityTask3.SenddatafromthemainactivitytothesecondactivityTask4.ReturndatabacktothemainactivityCodingchallengeSummaryRelatedconceptLearnmore

Anactivityrepresentsasinglescreeninyourappwithwhichyourusercanperformasingle,focussedtasksuchasdialthephone,takeaphoto,sendanemail,orviewamap.Activitiesareusuallypresentedtotheuserasfull-screenwindows.

Anappusuallyconsistsofmultipleactivitiesthatarelooselyboundtoeachother.Typically,oneactivityinanapplicationisspecifiedasthe"main"activity,whichispresentedtotheuserwhentheappislaunched.Eachactivitycanthenstartotheractivitiesinordertoperformdifferentactions.

Eachtimeanewactivitystarts,thepreviousactivityisstopped,butthesystempreservestheactivityinastack(the"backstack").Whenanewactivitystarts,thatnewactivityispushedontothebackstackandtakesuserfocus.Thebackstackabidestothebasic"lastin,firstout"stackmechanism,so,whentheuserisdonewiththecurrentactivityandpressestheBackbutton,thatcurrentactivityispoppedfromthestack(anddestroyed)andthepreviousactivityresumes.

Androidactivitiesarestartedoractivatedwithanintent.Intentsareasynchronousmessagesthatyoucancanuseinyouractivitytorequestanactionfromanotheractivity(orotherappcomponent).Youuseintentstostartoneactivityfromanotherandtopassdatabetweenactivities.

Therearetwokindsofintents:explicitandimplicit.Anexplicitintentisoneinwhichyouknowthetargetofthatintent,thatis,youalreadyknowthefully-qualifiedclassnameofthatspecificactivity.Animplicitintentisoneinwhichyoudonothavethenameofthetargetcomponent,buthaveageneralactiontoperform.Inthispracticalyou'lllearnaboutexplicitintents.You'llfindoutaboutimplicitintentsinalaterpractical.

WhatyoushouldalreadyKNOWFromthepreviouspracticals,youshouldbeableto:

CreateandrunappsinAndroidStudio.CreateandeditUIelementswiththegraphicalLayoutEditor,ordirectlyinanXMLlayoutfile.AddonClickfunctionalitytoabutton.

WhatyouwillLEARNYouwilllearnto:

CreateanewactivityinAndroidstudio.Defineparentandchildactivitiesfor"Up"navigation.Startactivitieswithexplicitintents.Passdatabetweenactivitieswithintentextras.

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WhatyouwillDOInthispractical,youwill:

CreateanewAndroidappwithtwoactivities.Passsomedata(astring)fromthemainactivitytothesecondusinganintent,anddisplaythatdatainthesecondactivity.Sendaseconddifferentbitofdatabacktothemainactivity,alsousingintents.

AppOverviewInthischapteryouwillcreateandbuildanappcalledTwoActivitiesthat,unsurprisingly,containstwoactivities.Thisappwillbebuiltinthreestages.

Inthefirststage,createanappwhosemainactivitycontainsonlyonebutton(Send).Whentheuserclicksthisbutton,yourmainactivityusesanintenttostartthesecondactivity.

Inthesecondstage,you'lladdanEditTextviewtothemainactivity.TheuserentersamessageandclicksSend.Themainactivityusesanintenttobothstartthesecondactivity,andtosendtheuser'smessagetothethatactivity.Thesecondactivitydisplaysthemessageitreceived.

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InfinalstageoftheTwoActivitiesapp,addanEditTextviewandaReplybuttontothesecondactivity.TheusercannowtypeareplymessageandclickReply,andthereplyisdisplayedonthemainactivity.Atthispoint,useanintentheretopassthereplymessagebackfromthesecondactivitytothemainactivity.

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Task1.CreatetheTwoActivitiesprojectInthistaskyou'llsetuptheinitialprojectwithamainactivity,definethelayout,anddefineaskeletonmethodfortheonClickbuttonevent.

1.1CreatetheTwoActivitiesproject

1. StartAndroidStudioandcreateanewAndroidStudioproject.

Callyourapplication"TwoActivities"andchangethecompanydomainto"android.example.com."ChoosethesameMinimumSDKthatyouusedinthepreviousprojects.

2. ChooseEmptyActivityfortheprojecttemplate.ClickNext.3. Acceptthedefaultactivityname(MainActivity).MakesuretheGenerateLayoutfileboxischecked.ClickFinish.

1.2Definethelayoutforthemainactivity

1. Openres/layout/activity_main.xml.IntheLayoutEditor,clicktheTexttabatthebottomofthescreenandchangetherootviewgrouptoRelativeLayout,asyou'vedoneinpreviousexercises.

2. ClicktheDesigntabatthebottomofthescreenanddeletetheTextViewthatsays"HelloWorld."3. AddaButtontothelayoutinanyposition.4. SwitchtotheXMLEditor(clicktheTexttab)andmodifytheseattributesintheButton:

Attribute Value

android:id "@+id/button_main"

android:layout_width wrap_content

android:layout_height wrap_content

android:layout_alignParentRight "true"

android:layout_alignParentBottom "true"

android:layout_alignParentEnd "true"

android:text "Send"

android:onClick "launchSecondActivity"

Thismaygenerateanerrorthat"MethodlaunchSecondActivityismissinginMainActivity."Pleaseignorethiserrorfornow.Itwillbeaddresseditinthenexttask.

5. Placethecursorontheword"Send".6. PressAlt-Enter(Option-EnterontheMac)andselectExtractstringresources.7. SettheResourcenametobutton_mainandclickOK.

Thiscreatesastringresourceinthevalues/res/string.xmlfile,andthestringinyourcodeisreplacedwithareferencetothatstringresource.

8. ChooseCode>ReformatCodetoformattheXMLcode,ifnecessary.9. PreviewthelayoutofthemainactivityusingtheLayoutEditor.Thelayoutshouldlooklikethis:

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Solutioncode:DependingonyourversionofAndroidStudio,yourcodewilllooksomethinglikethefollowing.

<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.twoactivities.MainActivity">

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/button_main"

android:id="@+id/button_main"

android:layout_alignParentBottom="true"

android:layout_alignParentRight="true"

android:layout_alignParentEnd="true"

android:onClick="launchSecondActivity"/>

</RelativeLayout>

1.3Definethebuttonaction

Inthistask,youwillimplementtheonClickmethodyoudefinedinthelayout.

1. IntheXMLEditor,placethecursorontheword"launchSecondActivity".2. PressAlt-Enter(Option-EnterontheMac)andselectCreate'launchSecondActivity(View)'in'MainActivity.

TheMainActivity.javafilesopens,andAndroidStudiogeneratesaskeletonmethodfortheonClickhandler.

3. InsidelaunchSecondActivity,addalogstatementthatsays"ButtonClicked!"

Log.d(LOG_TAG,"Buttonclicked!");

LOG_TAGwillshowasred.Thedefinitionsforthatvariablewillbeaddedinalaterstep.

4. Placethecursorontheword"Log"andpressAlt-Enter(Option-EnterontheMac).AndroidStudioaddsanimportstatementforandroid.util.Log.

5. Atthetopoftheclass,addaconstantfortheLOG_TAGvariable:

privatestaticfinalStringLOG_TAG=

MainActivity.class.getSimpleName();

Thisconstantusesthenameoftheclassitselfasthetag.

6. Runyourapp.Whenyouclickthe"Send"buttonyouwillseethe"ButtonClicked!"messageintheAndroidMonitor(logcat).Ifthere'stoomuchoutputinthemonitor,typeMainActivityintothesearchboxandthelogwillonlyshowlinesthatmatchthattag.

Solutioncode:

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packagecom.example.android.twoactivities;

importandroid.support.v7.app.AppCompatActivity;

importandroid.os.Bundle;

importandroid.util.Log;

importandroid.view.View;

publicclassMainActivityextendsAppCompatActivity{

privatestaticfinalStringLOG_TAG=MainActivity.class.getSimpleName();

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

}

publicvoidlaunchSecondActivity(Viewview){

Log.d(LOG_TAG,"Buttonclicked!");

}

}

Task2.CreateandlaunchthesecondactivityEachnewactivityyouaddedtoyourprojecthasitsownlayoutandJavafiles,separatefromthoseofthemainactivity.Theyalsohavetheirown<activity>elementsintheAndroidmanifest.Aswiththemainactivity,newactivitiesyoucreateinAndroidStudioalsoextendfromtheAppCompatActivityclass.

Alltheactivitiesinyourappareonlylooselyconnectedwitheachother.However,youcandefineanactivityasaparentofanotheractivityintheAndroidManifest.xmlfile.Thisparent-childrelationshipenablesAndroidtoaddnavigationhintssuchasleft-facingarrowsinthetitlebarforeachactivity.

Activitiescommunicatewitheachother(bothinthesameappandacrossdifferentapps)withintents.Therearetwotypesofintents,explicitandimplicit.Anexplicitintentisoneinwhichthetargetofthatintentisknown,thatis,youalreadyknowthefully-qualifiedclassnameofthatspecificactivity.Animplicitintentisoneinwhichyoudonothavethenameofthetargetcomponent,buthaveageneralactiontoperform.You'lllearnaboutimplicitintentsinalaterpractical.

Inthistaskyou'lladdasecondactivitytoourapp,withitsownlayout.You'llmodifytheAndroidmanifesttodefinethemainactivityastheparentofthesecondactivity.Thenyou'llmodifytheonClickeventmethodinthemainactivitytoincludeanintentthatlaunchesthesecondactivitywhenyouclickthebutton.

2.1Createthesecondactivity1. ClicktheappfolderforyourprojectandchooseFile>New>Activity>EmptyActivity.2. Namethenewactivity"SecondActivity."MakesureGenerateLayoutFileischecked,andlayoutnamewillbefilledin

asactivity_second.3. ClickFinish.AndroidStudioaddsbothanewactivitylayout(activity_second)andanewJavafile(SecondActivity)to

yourprojectforthenewactivity.ItalsoupdatestheAndroidmanifesttoincludethenewactivity.

2.2ModifytheAndroidmanifest1. Openmanifests/AndroidManifest.xml.2. Findthe<activity>elementthatAndroidStudiocreatedforthesecondactivity.

<activityandroid:name=".SecondActivity"></activity>

3. Addtheseattributestothe<activity>element:

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Attribute Value

android:label "SecondActivity"

android:parentActivityName ".MainActivity"

Thelabelattributeaddsthetitleoftheactivitytotheactionbar.

TheparentActivityNameattributeindicatesthatthemainactivityistheparentofthesecondactivity.Thisparentactivityrelationshipisusedfor"upward"navigationwithinyourapp.Bydefiningthisattribute,theactionbarforthesecondactivitywillappearwithaleft-facingarrowtoenabletheusertonavigate"upward"tothemainactivity.

4. Placethecursoron"SecondActivity"andpressAlt-Enter(Option-EnterontheMac).5. ChooseExtractstringresource,nametheresource"activity2_name",andclickOK.AndroidStudioaddsastring

resourcefortheactivitylabel.6. Adda<meta-data>elementinsidethe<activity>elementforthesecondactivity.Usetheseattributes:

Attribute Value

android:name "android.support.PARENT_ACTIVITY"

android:value "com.example.android.twoactivities.MainActivity"

The<meta-data>elementprovidesadditionalarbitraryinformationabouttheactivityaskey-valuepairs.Inthiscasetheseattributesaccomplishthesamethingastheandroid:parentActivityNameattribute--theydefinearelationshipbetweentwoactivitiesforthepurposeofupwardnavigation.TheseattributesarerequiredforolderversionsofAndroid.android:parentActivityNameisonlyavailableforAPIlevels16andhigher.

Solutioncode:

<?xmlversion="1.0"encoding="utf-8"?>

<manifestxmlns:android="http://schemas.android.com/apk/res/android"

package="com.example.android.twoactivities">

<application

android:allowBackup="true"

android:icon="@mipmap/ic_launcher"

android:label="@string/app_name"

android:supportsRtl="true"

android:theme="@style/AppTheme">

<activityandroid:name=".MainActivity">

<intent-filter>

<actionandroid:name="android.intent.action.MAIN"/>

<categoryandroid:name="android.intent.category.LAUNCHER"/>

</intent-filter>

</activity>

<activityandroid:name=".SecondActivity"

android:label="@string/activity2_name"

android:parentActivityName=".MainActivity">

<meta-data

android:name="android.support.PARENT_ACTIVITY"

android:value="com.example.android.twoactivities.MainActivity"/>

</activity>

</application>

</manifest>

2.3Definethelayoutforthesecondactivity

1. Openres/layout/activity_second.xmlandchangetherootviewgrouptoRelativeLayout,asyou'vedoneinpreviousexercises.

2. AddaTextView("PlainTextview"intheLayoutEditor).GivetheTextViewtheseattributes:

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Attribute Value

android:id "@+id/text_header"

android:layout_width wrap_content

android:layout_height wrap_content

android:layout_marginBottom "@dimen/activity_vertical_margin"

android:text "MessageReceived"

android:textAppearance "?android:attr/textAppearanceMedium"

android:textStyle "bold"

ThevalueoftextAppearanceisaspecialAndroidthemeattributethatdefinesbasicfontstylesforsmall,medium,andlargefonts.You'lllearnmoreaboutthemesinalaterlesson.

3. Extractthe"MessageReceived"stringintoaresourcenamedtext_header.4. PreviewthelayoutintheLayoutEditor.Thelayoutshouldlooklikethis:

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Solutioncode:DependingonyourversionofAndroidStudio,yourcodewilllooksomethinglikethefollowing.

<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context=".SecondActivity">

<TextView

android:id="@+id/text_header"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginBottom="@dimen/activity_vertical_margin"

android:text="@string/text_header"

android:textAppearance="?android:attr/textAppearanceMedium"

android:textStyle="bold"/>

</RelativeLayout>

2.4Addanintenttothemainactivity

Inthistaskyou'lladdanexplicitintenttothemainactivity.ThisintentisusedtoactivatethesecondactivitywhentheSendbuttonisclicked.

1. OpentheJavafileforMainActivity(java/com.example.android.twoactivities/MainActivity).2. CreateanewintentinthelaunchSecondActivity()method.

TheIntentconstructortakestwoargumentsforanexplicitintent:anapplicationContextandthespecificcomponentthatwillreceivethatintent.Hereyoushouldusethisasthecontext,andSecondActivity.classasthespecificclass.

Intentintent=newIntent(this,SecondActivity.class);

3. PlacethecursoronIntentandpressAlt-Enter(Option-EnterontheMac)toaddanimportfortheIntentclass.4. CallthestartActivity()methodwiththenewintentastheargument.

startActivity(intent);

5. Runtheapp.

WhenyouclicktheSendbuttonthemainactivitysendstheintentandtheAndroidsystemlaunchesthesecondactivity.Thatsecondactivityappearsonthescreen.Toreturntothemainactivity,clicktheAndroidBackbuttonatthebottomleftofthescreen,oryoucanusetheleftarrowatthetopofthesecondactivitytoreturntothemainactivity.

CodingchallengeNote:Allcodingchallengesareoptional.Challenge:Whathappensifyouremovetheandroid:parentActivityNameandthe<meta-data>elementsfromthemanifest?Makethischangeandrunyourapp.

Task3.SenddatafromthemainactivitytothesecondactivityInthelasttask,youaddedanexplicitintenttothemainactivitythatactivatedthesecondactivity.Youcanalsouseintentstosenddatafromoneactivitytoanother.

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Inthistask,you'llmodifytheexplicitintentinthemainactivitytoincludeadditionaldata(inthiscase,auser-enteredstring)intheintentextras.You'llthenmodifythesecondactivitytogetthatdatabackoutoftheintentextrasanddisplayitonthescreen.

3.1AddanEditTexttothemainactivitylayout

1. Openres/layout/activity_main.xml.2. AddanEditTextview(PlainTextintheLayoutEditor.)GivetheEditTexttheseattributes:

Attribute Value

android:id "@+id/editText_main"

android:layout_width match_parent

android:layout_height wrap_content

android:layout_toLeftOf "@+id/button_main"

android:layout_toStartOf "@+id/button_main"

android:layout_alignParentBottom "true"

android:hint "EnterYourMessageHere"

3. Deletetheandroid:textattribute.4. Extractthe"EnterYourMessageHere"stringintoaresourcenamededitText_main.

Thenewlayoutforthemainactivitylookslikethis:

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Solutioncode:DependingonyourversionofAndroidStudio,yourcodewilllooksomethinglikethefollowing.

<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.twoactivities.MainActivity">

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/button_main"

android:id="@+id/button_main"

android:layout_alignParentBottom="true"

android:layout_alignParentRight="true"

android:layout_alignParentEnd="true"

android:onClick="launchSecondActivity"/>

<EditText

android:id="@+id/editText_main"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_alignParentBottom="true"

android:layout_toLeftOf="@+id/button_main"

android:layout_toStartOf="@+id/button_main"

android:hint="@string/editText_main"/>

</RelativeLayout>

3.2Addastringtothemainactivity'sintentextras

Yourintentobjectcanpassdatatothetargetactivityintwoways:inthedatafield,orintheintentextras.Theintent'sdataisaURIindicatingthespecificdatatobeactedon.IftheinformationyouwanttopasstoanactivitythroughanintentisnotaURI,oryouhavemorethanonepieceofinformationyouwanttosend,youcanputthatadditionalinformationintotheintentextrasinstead.

Theintentextrasarekey/valuepairsinaBundle.Abundleisacollectionofdata,storedaskey/valuepairs.Topassinformationfromoneactivitytoanother,youputkeysandvaluesintotheintentextrabundlefromthesendingactivity,andthengetthembackoutagaininthereceivingactivity.

1. Openjava/com.example.android.twoactivities/MainActivity.2. Addapublicconstantatthetopoftheclasstodefinethekeyfortheintentextra:

publicstaticfinalStringEXTRA_MESSAGE=

"com.example.android.twoactivities.extra.MESSAGE";

3. AddaprivatevariableatthetopoftheclasstoholdtheEditTextobject.ImporttheEditTextclass.

privateEditTextmMessageEditText;

4. IntheonCreate()method,usefindViewByIDtogetareferencetotheEditTextinstanceandassignittothatprivatevariable:

mMessageEditText=(EditText)findViewById(R.id.editText_main);

5. InthelaunchSecondActivity()method,justunderthenewintent,getthetextfromtheEditTextasastring:

Stringmessage=mMessageEditText.getText().toString();

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6. AddthatstringtotheintentasanextrawiththeEXTRA_MESSAGEconstantasthekeyandthestringasthevalue:

intent.putExtra(EXTRA_MESSAGE,message);

Solutioncode:

packagecom.example.android.twoactivities;

importandroid.content.Intent;

importandroid.support.v7.app.AppCompatActivity;

importandroid.os.Bundle;

importandroid.util.Log;

importandroid.view.View;

importandroid.widget.EditText;

publicclassMainActivityextendsAppCompatActivity{

privatestaticfinalStringLOG_TAG=MainActivity.class.getSimpleName();

publicstaticfinalStringEXTRA_MESSAGE=

"com.example.android.twoactivities.extra.MESSAGE";

privateEditTextmMessageEditText;

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

mMessageEditText=(EditText)findViewById(R.id.editText_main);

}

publicvoidlaunchSecondActivity(Viewview){

Log.d(LOG_TAG,"Buttonclicked!");

Intentintent=newIntent(this,SecondActivity.class);

Stringmessage=mMessageEditText.getText().toString();

intent.putExtra(EXTRA_MESSAGE,message);

startActivity(intent);

}

}

3.3AddaTextViewtothesecondactivityforthemessage

1. Openres/layout/activity_second.xml.2. AddasecondTextView.GivetheTextViewtheseattributes:

Attribute Value

android:id "@+id/text_message"

android:layout_width wrap_content

android:layout_height wrap_content

android:layout_below "@+id/text_header"

android:layout_marginLeft "@dimen/activity_horizontal_margin"

android:layout_marginStart "@dimen/activity_horizontal_margin"

android:textAppearance "?android:attr/textAppearanceMedium"

3. Deletetheandroid:textattribute(ifitexists).

Thenewlayoutforthesecondactivitylooksthesameasitdidintheprevioustask,becausethenewTextViewdoesnot(yet)containanytext,andthusdoesnotappearonthescreen.

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Solutioncode:DependingonyourversionofAndroidStudio,yourcodewilllooksomethinglikethefollowing.

<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.twoactivities.SecondActivity">

<TextView

android:id="@+id/text_header"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/text_header"

android:layout_marginBottom="@dimen/activity_vertical_margin"

android:textAppearance="?android:attr/textAppearanceMedium"

android:textStyle="bold"/>

<TextView

android:id="@+id/text_message"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_below="@+id/text_header"

android:layout_marginLeft="@dimen/activity_horizontal_margin"

android:layout_marginStart="@dimen/activity_horizontal_margin"

android:textAppearance="?android:attr/textAppearanceMedium"/>

</RelativeLayout>

3.4Modifythesecondactivitytogettheextrasanddisplaythemessage

1. Openjava/com.example.android.twoactivities/SecondActivity.2. IntheonCreate()method,gettheintentthatactivatedthisactivity:

Intentintent=getIntent();

3. GetthestringcontainingthemessagefromtheintentextrasusingtheMainActivity.EXTRA_MESSAGEstaticvariableasthekey:

Stringmessage=

intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

4. UsefindViewByIDtogetareferencetotheTextViewforthemessagefromthelayout(youmayneedtoimporttheTextViewclass):

TextViewtextView=(TextView)findViewById(R.id.text_message);

5. SetthetextofthatTextViewtothestringfromtheintentextra:

textView.setText(message);

6. Runtheapp.WhenyoutypeamessageinthemainactivityandclickSend,thesecondactivityislaunchedanddisplaysthatmessage.

Solutioncode:

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packagecom.example.android.twoactivities;

importandroid.content.Intent;

importandroid.support.v7.app.AppCompatActivity;

importandroid.os.Bundle;

importandroid.widget.TextView;

publicclassSecondActivityextendsAppCompatActivity{

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_second);

Intentintent=getIntent();

Stringmessage=

intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

TextViewtextView=(TextView)findViewById(R.id.text_message);

textView.setText(message);

}

}

Task4.ReturndatabacktothemainactivityNowthatyouhaveanappthatlaunchesanewactivityandsendsdatatoit,thefinalstepistoreturndatafromthesecondactivitybacktothemainactivity.You'llalsouseintentsandintentextrasforthistask.

4.1AddanEditTextandaButtontothesecondactivitylayout1. CopytheEditTextandButtonfromthemainactivitylayoutfileandpastethemintothesecondlayout.2. Intheactivity_second.xmlfile,modifytheattributevaluesforboththeButtonandEditTextviews.Usethesevalues:

Oldattribute(Button) Newattribute(Button)

android:id="@+id/button_main" android:id="@+id/button_second"

android:onClick="launchSecondActivity" android:onClick="returnReply"

android:text="@string/button_main" android:text="@string/button_second"

Oldattribute(EditText) Newattribute(EditText)

android:id="@+id/editText_main" android:id="@+id/editText_second"

android:layout_toLeftOf="@+id/button_main" android:layout_toLeftOf="@+id/button_second"

android:layout_toStartOf="@+id/button_main" android:layout_toStartOf="@+id/button_second"

android:hint="@string/editText_main" android:hint="@string/editText_second"

3. Openres/values/strings.xmlandaddstringresourcesforthebuttontextandthehintintheEditText:

<stringname="button_second">Reply</string>

<stringname="editText_second">EnterYourReplyHere</string>

4. IntheXMLlayouteditor,placethecursoron"returnReply",pressAlt-Enter(Option-EnterontheMac)andselectCreate'returnReply(View)'in'SecondActivity'.

TheSecondActivity.javafilesopen,andAndroidStudiogeneratesaskeletonmethodfortheonClickhandler.Youwillimplementthismethodinthenexttask.

Thenewlayoutforthesecondactivitylookslikethis:

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Solutioncode:DependingonyourversionofAndroidStudio,yourcodewilllooksomethinglikethefollowing.

<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.twoactivities.SecondActivity">

<TextView

android:id="@+id/text_header"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/text_header"

android:layout_marginBottom="@dimen/activity_vertical_margin"

android:textAppearance="?android:attr/textAppearanceMedium"

android:textStyle="bold"/>

<TextView

android:id="@+id/text_message"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_below="@+id/text_header"

android:layout_marginLeft="@dimen/activity_horizontal_margin"

android:layout_marginStart="@dimen/activity_horizontal_margin"

android:textAppearance="?android:attr/textAppearanceMedium"/>

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/button_second"

android:id="@+id/button_second"

android:layout_alignParentBottom="true"

android:layout_alignParentRight="true"

android:layout_alignParentEnd="true"

android:onClick="returnReply"/>

<EditText

android:id="@+id/editText_second"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_alignParentBottom="true"

android:layout_toLeftOf="@+id/button_second"

android:layout_toStartOf="@+id/button_second"

android:hint="@string/editText_second"/>

</RelativeLayout>

4.2Createaresponseintentinthesecondactivity

1. Openjava/com.example.android.twoactivities/SecondActivity.2. Atthetopoftheclass,addapublicconstanttodefinethekeyfortheintentextra:

publicstaticfinalStringEXTRA_REPLY=

"com.example.android.twoactivities.extra.REPLY";

3. AddaprivatevariableatthetopoftheclasstoholdtheEditTextobject.

privateEditTextmReply;

4. IntheonCreate()method,usefindViewByID()togetareferencetotheEditTextinstanceandassignittothatprivatevariable:

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mReply=(EditText)findViewById(R.id.editText_second);

5. InthereturnReply()method,getthetextoftheEditTextasastring:

Stringreply=mReply.getText().toString();

6. Createanewintentfortheresponse.Note:Donotreusetheintentobjectyoureceivedfromtheoriginalrequest.Createanewintentfortheresponse.

IntentreplyIntent=newIntent();

7. AddthereplystringfromtheEditTexttothenewintentasanintentextra.Sinceextrasarekey/valuepairs,herethekeyisEXTRA_REPLYandthethevalueisthereply:

replyIntent.putExtra(EXTRA_REPLY,reply);

8. SettheresulttoRESULT_OKtoindicatetheresponsewassuccessful.Resultcodes(includingRESULT_OKandRESULT_CANCELLED)aredefinedbytheActivityclass.

setResult(RESULT_OK,replyIntent);

9. Callfinish()toclosetheactivityandreturntothemainactivity.

finish();

Solutioncode:

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packagecom.example.android.twoactivities;

importandroid.content.Intent;

importandroid.support.v7.app.AppCompatActivity;

importandroid.os.Bundle;

importandroid.view.View;

importandroid.widget.EditText;

importandroid.widget.TextView;

publicclassSecondActivityextendsAppCompatActivity{

publicstaticfinalStringEXTRA_REPLY=

"com.example.android.twoactivities.extra.REPLY";

privateEditTextmReply;

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_second);

mReply=(EditText)findViewById(R.id.editText_second);

Intentintent=getIntent();

Stringmessage=

intent.getStringExtra(MainActivity.EXTRA_MESSAGE);

TextViewtextView=(TextView)findViewById(R.id.text_message);

textView.setText(message);

}

publicvoidreturnReply(Viewview){

Stringreply=mReply.getText().toString();

IntentreplyIntent=newIntent();

replyIntent.putExtra(EXTRA_REPLY,reply);

setResult(RESULT_OK,replyIntent);

finish();

}

}

4.3AddTextViewstothemainactivitylayouttodisplaythereplyThemainactivityneedsawaytodisplaythereplysentbackfromthesecondactivity.Inthistaskyou'lladdTextViewstothemainactivitylayouttodisplaythatreply.Tomakethiseasier,youwillcopytheTextViewsyouusedinthesecondactivity.

1. CopythetwoTextViewsforthemessagedisplayfromthesecondactivitylayoutfileandpastethemintothemainlayoutabovetheexistingEditTextandButtonviews.

2. ModifytheattributevaluesforbothofthesenewTextViews.Usethesevalues:

Oldattribute(headerTextView) Newattribute(headerTextView)

android:id="@+id/text_header" android:id="@+id/text_header_reply"

android:text="@string/text_header" android:text="@string/text_header_reply"

Oldattribute(messageTextView) Newattribute(messageTextView)

android:id="@+id/text_message" android:id="@+id/text_message_reply"

android:layout_below="@+id/text_header" android:layout_below="@+id/text_header_reply"

3. Addtheandroid:visibilityattributetoeachoftheTextViewstomaketheminitiallyinvisible.(Havingthemvisibleonthescreen,butwithoutanycontent,canbeconfusingtotheuser.)YouwillmaketheseTextViewsvisibleaftertheresponsedataispassedbackfromthesecondactivity.

android:visibility="invisible"

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4. Openres/values/strings.xmlandaddastringresourceforthereplyheader:

<stringname="text_header_reply">ReplyReceived</string>

Thelayoutforthemainactivitylooksthesameasitdidintheprevioustask--althoughyouhaveaddedtwonewTextViewstothelayout.However,sinceyousettheTextViewstoinvisible,theydonotappearonthescreen.

Solutioncode:DependingonyourversionofAndroidStudio,yourcodewilllooksomethinglikethefollowing.

<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.twoactivities.MainActivity">

<TextView

android:id="@+id/text_header_reply"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/text_header_reply"

android:visibility="invisible"

android:layout_marginBottom="@dimen/activity_vertical_margin"

android:textAppearance="?android:attr/textAppearanceMedium"

android:textStyle="bold"/>

<TextView

android:id="@+id/text_message_reply"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_below="@+id/text_header_reply"

android:visibility="invisible"

android:layout_marginLeft="@dimen/activity_horizontal_margin"

android:layout_marginStart="@dimen/activity_horizontal_margin"

android:textAppearance="?android:attr/textAppearanceMedium"/>

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/button_main"

android:id="@+id/button_main"

android:layout_alignParentBottom="true"

android:layout_alignParentRight="true"

android:layout_alignParentEnd="true"

android:onClick="launchSecondActivity"/>

<EditText

android:id="@+id/editText_main"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_alignParentBottom="true"

android:layout_toLeftOf="@+id/button_main"

android:layout_toStartOf="@+id/button_main"

android:hint="@string/editText_main"/>

</RelativeLayout>

4.4GetthereplyfromtheintentextraanddisplayitWhenyouuseanexplicitintenttostartanotheractivity,youmaynotexpecttogetanydataback--you'rejustactivatingthatactivity.Inthatcase,youusestartActivity()tostartthenewactivity,asyoudidearlierinthislesson.Ifyouwanttogetdatabackfromtheactivatedactivity,however,you'llneedtostartitwithstartActivityFromResult().

Inthistaskyou'llmodifytheapptostartthesecondactivityandexpectaresult,toextractthatreturndatafromtheintent,andtodisplaythatdataintheTextViewsyoucreatedinthelasttask.

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1. Openjava/com.example.android.twoactivities/MainActivity.2. Addapublicconstantatthetopoftheclasstodefinethekeyforaparticulartypeofresponseyou'reinterestedin:

publicstaticfinalintTEXT_REQUEST=1;

3. AddtwoprivatevariablestoholdthereplyheaderandreplyTextViews:

privateTextViewmReplyHeadTextView;

privateTextViewmReplyTextView;

4. IntheonCreate()method,usefindViewByIDtogetreferencesfromthelayouttothereplyheaderandreplyTextView.Assignthoseviewinstancestotheprivatevariables:

mReplyHeadTextView=(TextView)findViewById(R.id.text_header_reply);

mReplyTextView=(TextView)findViewById(R.id.text_message_reply);

5. InthelaunchSecondActivity()method,modifythecalltostartActivity()tobestartActivityForResult(),andincludetheTEXT_REQUESTkeyasanargument:

startActivityForResult(intent,TEXT_REQUEST);

6. CreatetheonActivityResult()callbackmethodwiththissignature:

publicvoidonActivityResult(intrequestCode,intresultCode,

Intentdata){}

7. InsideonActivityResult(),callsuper.onActivityResult():

super.onActivityResult(requestCode,resultCode,data);

8. AddcodetotestforbothTEXT_REQUEST(toprocesstherightintentresult,incasetherearemultipleones)andtheRESULT_CODE(tomakesuretherequestwassuccessful):

if(requestCode==TEXT_REQUEST){

if(resultCode==RESULT_OK){

}

}

9. Insidetheinnerifblock,gettheintentextrafromtheresponseintent(data).HerethekeyfortheextraistheEXTRA_REPLYconstantfromSecondActivity:

Stringreply=data.getStringExtra(SecondActivity.EXTRA_REPLY);

10. Setthevisibilityofthereplyheadertotrue:

mReplyHeadTextView.setVisibility(View.VISIBLE);

11. Setthereplytextviewtexttothereply,andsetitsvisibilitytotrue:

mReplyTextView.setText(reply);

mReplyTextView.setVisibility(View.VISIBLE);

12. Runtheapp.

Now,whenyousendamessagetothesecondactivityandgetareplyback,themainactivityupdatestodisplaythereply.

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Solutioncode:

packagecom.example.android.twoactivities;

importandroid.content.Intent;

importandroid.support.v7.app.AppCompatActivity;

importandroid.os.Bundle;

importandroid.util.Log;

importandroid.view.View;

importandroid.widget.EditText;

importandroid.widget.TextView;

publicclassMainActivityextendsAppCompatActivity{

privatestaticfinalStringLOG_TAG=MainActivity.class.getSimpleName();

publicstaticfinalStringEXTRA_MESSAGE=

"com.example.android.twoactivities.extra.MESSAGE";

publicstaticfinalintTEXT_REQUEST=1;

privateEditTextmMessageEditText;

privateTextViewmReplyHeadTextView;

privateTextViewmReplyTextView;

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

mMessageEditText=(EditText)findViewById(R.id.editText_main);

mReplyHeadTextView=(TextView)findViewById(R.id.text_header_reply);

mReplyTextView=(TextView)findViewById(R.id.text_message_reply);

}

publicvoidlaunchSecondActivity(Viewview){

Log.d(LOG_TAG,"Buttonclicked!");

Intentintent=newIntent(this,SecondActivity.class);

Stringmessage=mMessageEditText.getText().toString();

intent.putExtra(EXTRA_MESSAGE,message);

startActivityForResult(intent,TEXT_REQUEST);

}

publicvoidonActivityResult(intrequestCode,intresultCode,

Intentdata){

super.onActivityResult(requestCode,resultCode,data);

if(requestCode==TEXT_REQUEST){

if(resultCode==RESULT_OK){

Stringreply=

data.getStringExtra(SecondActivity.EXTRA_REPLY);

mReplyHeadTextView.setVisibility(View.VISIBLE);

mReplyTextView.setText(reply);

mReplyTextView.setVisibility(View.VISIBLE);

}

}

}

}

SolutioncodeAndroidStudioproject:TwoActivities

Codingchallenge

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Note:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:Createanappwiththreebuttonslabelled:TextOne,TextTwo,andTextThree.Whenanyofthosebuttonsareclicked,launchasecondactivity.ThatsecondactivityshouldcontainaScrollViewthatdisplaysoneofthreetextpassages(youcanincludeyourchoiceofpassages).Useintentstobothlaunchthesecondactivityandintentextrastoindicatewhichofthethreepassagestodisplay.

SummaryInthispractical,youhavelearnedthat:

AnActivityisanapplicationcomponentthatprovidesasinglescreenfocussedonasingleusertask.Eachactivityhasitsownuserinterfacelayoutfile.Youcanassignyouractivitiesaparent/childrelationshiptoenable"upward"navigationwithinyourapp.Toimplementanactivityinyourapp,dothefollowing:

CreateanactivityJavaclass.Implementauserinterfaceforthatactivity.Declarethatnewactivityintheappmanifest.Whenyoucreateanewprojectforyourapp,oraddanewactivitytoyourapp,inAndroidStudio(withFile>New>Activity),templatecodeforeachofthesetasksisprovidedforyou.Intentsallowyoutorequestanactionfromanothercomponentinyourapp,forexample,tostartoneactivityfromanother.Intentscanbeexplicitorimplicit.

Withexplicitintentsyouindicatethespecifictargetcomponenttoreceivethedata.Withimplicitintentsyouspecifythefunctionalityyouwantbutnotthetargetcomponent.Intentscanincludedataonwhichtoperformanaction(asaURI)oradditionalinformationasintentextras.Intentextrasarekey/valuepairsinabundlethataresentalongwiththeintent.

Viewscanbemadevisibleorinvisiblewiththeandroid:visibilityattribute

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

ActivitiesandIntents

LearnmoreAndroidApplicationFundamentalsStartingAnotherActivityActivity(APIGuide)Activity(APIReference)IntentsandIntentFilters(APIGuide)Intent(APIReference)

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2.2:ActivityLifecycleandInstanceStateContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.AddlifecyclecallbackstoTwoActivitiesTask2.SaveandrestoreactivitystateCodingchallengeSummaryRelatedconceptLearnmore

Inthispracticalyou'lllearnmoreabouttheactivitylifecycle.Theactivitylifecycleisthesetofstatesanactivitycanbeinduringitsentirelifetime,fromthetimeitisinitiallycreatedtowhenitisdestroyedandthesystemreclaimsthatactivity'sresources.Asausernavigatesbetweenactivitiesinyourapp(aswellasintoandoutofyourapp),thoseactivitieseachtransitionbetweendifferentstatesintheactivitylifecycle.

Eachstageinthelifecycleofanactivityhasacorrespondingcallbackmethod(onCreate(),onStart(),onPause(),andsoon).Whenanactivitychangesstate,theassociatedcallbackmethodisinvoked.You'vealreadyseenoneofthesemethods:onCreate().Byoverridinganyofthelifecyclecallbackmethodsinyouractivityclasses,youcanchangethedefaultbehaviorofhowyouractivitybehavesinresponsetodifferentuserorsystemactions.

Changestotheactivitystatecanalsooccurinresponsetodeviceconfigurationchangessuchasrotatingthedevicefromportraittolandscape.Theseconfigurationchangesresultintheactivitybeingdestroyedandentirelyrecreatedinitsdefaultstate,whichmaycausethelossofinformationtheuserhasenteredinthatactivity.It'simportanttodevelopyourapptopreventthistoavoiduserconfusion.Laterinthispracticalwe'llexperimentwithconfigurationchangesandlearnhowtopreservethestateofyouractivitiesinresponsetodeviceconfigurationchangesorotherActivitylifecycleevents.

Inthispracticalyou'lladdloggingstatementstotheTwoActivitiesappandobservethelifecyclechangesasyouusetheappinvariousways.Youwillthenbeginworkingwiththesechangesandexploringhowtohandleuserinputundertheseconditions..

WhatyoushouldalreadyKNOW

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Fromthepreviouspracticals,youshouldbeableto:

CreateandrunninganappprojectinAndroidStudio.AddlogstatementstoyourappandviewingthoselogsintheAndroidMonitor(logcat).Understandandworkwithactivitiesandintents,andbecomfortableinteractingwiththem.

WhatyouwillLEARNYouwilllearnto:

Understandtheactivitylifecycle,andwhenactivitiesarecreated,pause,stop,andaredestroyed.Understandthelifecyclecallbackmethodsassociatedwithactivitychanges.Understandtheeffectofactionssuchasconfigurationchangesthatcanresultinactivitylifecycleevents.Retainactivitystateacrosslifecycleevents.

WhatyouwillDOInthispractical,youwill:

ExtendtheTwoActivitiesappfromthepreviouspracticaltoimplementthevariousactivitylifecyclecallbackstoincludeloggingstatements.Observethestatechangesasyourapprunsandasyouinteractwiththeactivitiesinyourapp.Modifyyourapptoretaintheinstancestateofanactivitythatisunexpectedlyrecreatedinresponsetouserbehaviororconfigurationchangeonthedevice.

AppOverviewForthispracticalyou'lladdontotheTwoActivitiesapp.Theapplooksandbehavesroughlythesameasitdidinthelastsection:withtwoactivitiesandtwomessagesyoucansendbetweenthem.Thechangesyoumaketotheappinthispracticalwillnotaffectitsvisibleuserbehavior.

Task1.AddLifecycleCallbackstoTwoActivitiesInthistaskyouwillimplementalloftheactivitylifecyclecallbackmethodstoprintmessagestologcatwhenthosemethodsareinvoked.Theselogmessageswillallowyoutoseewhentheactivitylifecyclechangesstate,andhowthoselifecyclestatechangesaffectyourappasitruns.

1.1(Optional)CopytheTwoActivitiesProject

Forthetasksinthispractical,youwillmodifytheexistingTwoActivitiesprojectthatyoubuiltinthelastpractical.Ifyou'dprefertokeepthepreviousTwoActivitiesprojectintact,followthestepsintheAppendixtomakeacopyoftheproject.

1.2ImplementcallbacksintoMainActivity

1. Openjava/com.example.android.twoactivities/MainActivity.2. IntheonCreate()method,addthefollowinglogstatements:

Log.d(LOG_TAG,"-------");

Log.d(LOG_TAG,"onCreate");

3. AddanewmethodfortheonStart()callback,withastatementtothelogforthatevent:

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@Override

publicvoidonStart(){

super.onStart();

Log.d(LOG_TAG,"onStart");

}

TIP:SelectCode>OverrideMethodsinAndroidStudio.Adialogappearswithallofthepossiblemethodsyoucanoverrideinyourclass.Choosingoneormorecallbackmethodsfromthelistinsertsacompletetemplateforthosemethods,includingtherequiredcalltothesuperclass.

4. UsetheonStart()methodasatemplatetoimplementtheotherlifecyclecallbacks:

onPause()onRestart()onResume()onStop()onDestroy()

Allthecallbackmethodshavethesamesignatures(exceptforthename).IfyoucopyandpasteonStart()tocreatetheseothercallbackmethods,don'tforgettoupdatethecontentstocalltherightmethodinthesuperclass,andtologthecorrectmethod.

5. Buildandrunyourapp.

SolutionCode(nottheentireclass):

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@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

Log.d(LOG_TAG,"-------");

Log.d(LOG_TAG,"onCreate");

mMessageEditText=(EditText)findViewById(R.id.editText_main);

mReplyHeadTextView=(TextView)findViewById(R.id.text_header_reply);

mReplyTextView=(TextView)findViewById(R.id.text_message_reply);

}

@Override

publicvoidonStart(){

super.onStart();

Log.d(LOG_TAG,"onStart");

}

@Override

publicvoidonRestart(){

super.onRestart();

Log.d(LOG_TAG,"onRestart");

}

@Override

publicvoidonResume(){

super.onResume();

Log.d(LOG_TAG,"onResume");

}

@Override

publicvoidonPause(){

super.onPause();

Log.d(LOG_TAG,"onPause");

}

@Override

publicvoidonStop(){

super.onStop();

Log.d(LOG_TAG,"onStop");

}

@Override

publicvoidonDestroy(){

super.onDestroy();

Log.d(LOG_TAG,"onDestroy");

}

1.3ImplementlifecyclecallbacksinSecondActivityNowthatyou'veimplementedthelifecyclecallbackmethodsforMainActivity,dothesameforSecondActivity.

1. Openjava/com.example.android.twoactivities/SecondActivity.2. Atthetopoftheclass,addaconstantfortheLOG_TAGvariable:

privatestaticfinalStringLOG_TAG=

SecondActivity.class.getSimpleName();

3. Addthelifecyclecallbacksandlogstatementstothesecondactivity.(YoucanalsojustcopyandpastethecallbackmethodsfromMainActivity)

4. AddalogstatementtothereturnReply()method,justbeforethefinish()method:

Log.d(LOG_TAG,"EndSecondActivity");

SolutionCode(nottheentireclass):

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privatestaticfinalStringLOG_TAG=SecondActivity.class.getSimpleName();

publicvoidreturnReply(Viewview){

Stringreply=mReply.getText().toString();

IntentreplyIntent=newIntent();

replyIntent.putExtra(EXTRA_REPLY,reply);

setResult(RESULT_OK,replyIntent);

Log.d(LOG_TAG,"EndSecondActivity");

finish();

}

@Override

protectedvoidonStart(){

super.onStart();

Log.d(LOG_TAG,"onStart");

}

@Override

publicvoidonRestart(){

super.onRestart();

Log.d(LOG_TAG,"onRestart");

}

@Override

publicvoidonResume(){

super.onResume();

Log.d(LOG_TAG,"onResume");

}

@Override

publicvoidonPause(){

super.onPause();

Log.d(LOG_TAG,"onPause");

}

@Override

publicvoidonStop(){

super.onStop();

Log.d(LOG_TAG,"onStop");

}

@Override

publicvoidonDestroy(){

super.onDestroy();

Log.d(LOG_TAG,"onDestroy");

}

1.4Observethelogastheappruns1. Runyourapp.2. ClickAndroidMonitoratthebottomofAndroidStudiotoopentheAndroidMonitor.3. Selectthelogcattab.4. Type"Activity"intheAndroidMonitorsearchbox.

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TheAndroidlogcatcanbeverylongandcluttered.BecausetheLOG_TAGvariableineachclasscontainseitherthewordsMainActivityorSecondActivity,thiskeywordletsyoufilterthelogforonlythethingsyou'reinterestedin.

5. Experimentusingyourappandnotethatthelifecycleeventsoccurinresponsetodifferentactions.Inparticular,trythesethings:

Usetheappnormally(sendamessage,replywithanothermessage.)Usethebackbuttontogobackfromthesecondactivitytothemainactivity.Usetheleftarrowintheactionbartogobackfromthesecondactivitytothemainactivity.Rotatethedeviceonboththemainandsecondactivityatdifferenttimesinyourappandobservewhathappensinthelogandonthescreen.TIP:Ifyou'rerunningyourappinanemulator,youcansimulaterotationwithCtrl-F11orCtrl-Fn-F11.Presstheoverviewbutton(thesquarebuttontotherightofHome)andclosetheapp(taptheX).Returntothehomescreenandrestartyourapp.

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:WatchforonDestroy()inparticular.WhyisonDestroy()calledsometimes(afterclickingthebackbutton,orondevicerotation)andnotothers(manuallystoppingandrestartingtheapp)?

Task2.SaveandrestoretheactivityinstancestateDependingonsystemresourcesanduserbehavior,theactivitiesinyourappmaybedestroyedandreconstructedfarmorefrequentlythanyoumightthink.Youmayhavenoticedthissetofactivitiesinthelastsectionwhenyourotatedthedeviceoremulator.Rotatingthedeviceisoneexampleofadeviceconfigurationchange.Althoughrotationisthemostcommonone,allconfigurationchangesresultinthecurrentactivitybeingdestroyedandrecreatedasifitwerenew.Ifyoudon'taccountforthisbehaviorinyourcode,whenaconfigurationchangeoccurs,youractivity'slayoutmayreverttoitsdefaultappearanceandinitialvalues,andyourusermaylosetheirplace,theirdata,orthestateoftheirprogressinyourapp.

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Thestateofeachactivityisstoredasasetofkey/valuepairsinaBundleobjectcalledtheactivityinstancestate.Thesystemsavesdefaultstateinformationtoinstancestatebundlejustbeforetheactivityisstopped,andpassesthatbundletothenewactivityinstancetorestore.

Tokeepfromlosingdatainyouractivitieswhentheyareunexpectedlydestroyedandrecreated,youneedtoimplementtheonSaveInstanceState()method.Thesystemcallsthismethodonyouractivity(betweenonPause()andonStop())whenthereisapossibilitytheactivitymaybedestroyedandrecreated.

Thedatayousaveintheinstancestateisspecifictoonlythisinstanceofthisspecificactivityduringthecurrentappsession.Whenyoustopandrestartanewappsession,theactivityinstancestateislostandyouractivitieswillreverttotheirdefaultappearance.Ifyouneedtosaveuserdatabetweenappsessions,usesharedpreferencesoradatabase.You'lllearnaboutbothoftheseinalaterpractical.

2.1SavetheactivityinstancestatewithonSaveInstanceState()Youmayhavenoticedthatrotatingthedevicedoesnotaffectthestateofthesecondactivityatall.Thisisbecausethesecondactivity'slayoutandstatearegeneratedfromthelayoutandtheintentthatactivatedit.Eveniftheactivityisrecreated,theintentisstillthereandthedatainthatintentisstillusedeachtimethesecondactivity'sonCreate()iscalled.

Inaddition,youmaynoticethatinbothactivities,anytextyoutypedintomessageorreplyEditTextsisretainedevenwhenthedeviceisrotated.Thisisbecausethestateinformationofsomeoftheviewsinyourlayoutareautomaticallysavedacrossconfigurationchanges,andthecurrentvalueofanEditTextisoneofthosecases.

Theonlyactivitystatesyou'reinterestedinaretheTextViewsforthereplyheaderandthereplytextinthemainactivity.BothTextViewsareinvisiblebydefault;theyonlyappearonceyousendamessagebacktothemainactivityfromthesecondactivity.

Inthistaskyou'lladdcodetopreservetheinstancestateofthesetwoTextViewsusingonSaveInstanceState().

1. Openjava/com.example.android.twoactivities/MainActivity.2. AddthisskeletonimplementationofonSaveInstanceState()totheactivity,oruseCode>OverrideMethodstoinsert

askeletonoverride.

@Override

publicvoidonSaveInstanceState(BundleoutState){

super.onSaveInstanceState(outState);

}

3. Checktoseeiftheheaderiscurrentlyvisible,andifsoputthatvisibilitystateintothestatebundlewiththeputBoolean()methodandthekey"reply_visible".

if(mReplyHeadTextView.getVisibility()==View.VISIBLE){

outState.putBoolean("reply_visible",true);

}

Rememberthatthereplyheaderandtextaremarkedinvisibleuntilthereisareplyfromthesecondactivity.Iftheheaderisvisible,thenthereisreplydatathatneedstobesaved.We'reonlyinterestedinthatvisibilitystate--theactualtextoftheheaderdoesn'tneedtobesaved,becausethattextneverchanges.

4. Insidethatsamecheck,addthereplytextintothebundle.

outState.putString("reply_text",mReplyTextView.getText().toString());

Iftheheaderisvisibleyoucanassumethatthereplymessageitselfisalsovisible.Youdon'tneedtotestfororsavethecurrentvisibilitystateofthereplymessage.Onlytheactualtextofthemessagegoesintothestatebundlewiththekey"reply_text".

Weonlysavethestateofthoseviewsthatmightchangeaftertheactivityiscreated.

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Theotherviewsinyourapp(theEditText,theButton)canberecreatedfromthedefaultlayoutatanytime.

Note:Thesystemwillsavethestateofsomeviews,suchasthecontentsoftheEditText.

SolutionCode(nottheentireclass):

@Override

publicvoidonSaveInstanceState(BundleoutState){

super.onSaveInstanceState(outState);

//Iftheheadingisvisible,wehaveamessagethatneedstobesaved.

//Otherwisewe'restillusingdefaultlayout.

if(mReplyHeadTextView.getVisibility()==View.VISIBLE){

outState.putBoolean("reply_visible",true);

outState.putString("reply_text",mReplyTextView.getText().toString());

}

}

2.2RestoretheactivityinstancestateinonCreate()Onceyou'vesavedtheactivityinstancestate,youalsoneedtorestoreitwhentheactivityisrecreated.YoucandothiseitherinonCreate(),orbyimplementingtheonRestoreInstanceState()callback,whichiscalledafteronStart()aftertheactivityiscreated.

MostofthetimethebetterplacetorestoretheactivitystateisinonCreate(),toensurethatyouruserinterfaceincludingthestateisavailableassoonaspossible.ItissometimesconvenienttodoitinonRestoreInstanceState()afteralloftheinitializationhasbeendone,ortoallowsubclassestodecidewhethertouseyourdefaultimplementation.

1. IntheonCreate()method,addatesttomakesurethebundleisnotnull.

if(savedInstanceState!=null){

}

Whenyouractivityiscreated,thesystempassesthestatebundletoonCreate()asitsonlyargument.ThefirsttimeonCreate()iscalledandyourappstarts,thebundleisnull-there'snoexistingstatethefirsttimeyourappstarts.SubsequentcallstoonCreate()haveabundlepopulatedwithanythedatayoustoredinonSaveInstanceState().

2. Insidethatcheck,getthecurrentvisibility(trueorfalse)outofthebundlewiththekey"reply_visible"

if(savedInstanceState!=null){

booleanisVisible=

savedInstanceState.getBoolean("reply_visible");

}

3. AddatestbelowthatpreviouslinefortheisVisiblevariable.

if(isVisible){

}

Ifthere'sareply_visiblekeyinthestatebundle(andisVisibleisthustrue),wewillneedtorestorethestate.

4. InsidetheisVisibletest,maketheheadervisible.

mReplyHeadTextView.setVisibility(View.VISIBLE);

5. Getthetextreplymessagefromthebundlewiththekey"reply_text",andsetthereplyTextViewtoshowthatstring.

mReplyTextView.setText(savedInstanceState.getString("reply_text"));

6. MakethereplyTextViewvisibleaswell:

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mReplyTextView.setVisibility(View.VISIBLE);

7. Runtheapp.Tryrotatingthedeviceortheemulatortoensurethatthereplymessage(ifthereisone)remainsonthescreenaftertheactivityisrecreated.

SolutionCode(nottheentireclass):

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

Log.d(LOG_TAG,"-------");

Log.d(LOG_TAG,"onCreate");

//Initializealltheviewvariables.

mMessageEditText=(EditText)findViewById(R.id.editText_main);

mReplyHeadTextView=(TextView)findViewById(R.id.text_header_reply);

mReplyTextView=(TextView)findViewById(R.id.text_message_reply);

//Restorethesavedstate.SeeonSaveInstanceState()forwhatgetssaved.

if(savedInstanceState!=null){

booleanisVisible=savedInstanceState.getBoolean("reply_visible");

//Showboththeheaderandthemessageviews.IfisVisibleis

//falseormissingfromthebundle,usethedefaultlayout.

if(isVisible){

mReplyHeadTextView.setVisibility(View.VISIBLE);

mReplyTextView.setText(savedInstanceState.getString("reply_text"));

mReplyTextView.setVisibility(View.VISIBLE);

}

}

}

SolutioncodeAndroidStudioProject:TwoActivitiesLifecycle

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:Createasimpleshoppinglistbuilderappwithtwoactivities.Themainactivitycontainsthelistitself,whichismadeupoften(empty)textviews.Abuttononthemainactivitylabelled"AddItem"launchesasecondactivitythatcontainsalistofcommonshoppingitems(Cheese,Rice,Apples,andsoon).UseButtonstodisplaytheitems.Choosinganitemreturnsyoutothemainactivity,andupdatesanemptyTextViewtoincludethechosenitem.

Useintentstopassinformationbetweenthetwoactivities.Makesurethatthecurrentstateoftheshoppinglistissavedwhenyourotatethedevice.

SummaryTheActivitylifecycleisasetofstatesanactivitymigratesthrough,beginningwhenitisfirstcreatedandendingwhentheAndroidsystemreclaimsthatactivity'sresources.Astheusernavigatesbetweenactivitiesandinsideandoutsideofyourapp,eachactivitymovesbetweenstatesintheactivitylifecycle.EachstateintheactivitylifecyclehasacorrespondingcallbackmethodyoucanoverrideinyourActivityclass.Thoselifecyclemethodsare:

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onCreate()onStart()onPause()onRestart()onResume()onStop()onDestroy()

Overridingalifecyclecallbackmethodallowsyoutoaddbehaviorthatoccurswhenyouractivitytransitionsintothatstate.YoucanaddskeletonoverridemethodstoyourclassesinAndroidStudiowithCode>Override.Deviceconfigurationchangessuchasrotationresultsintheactivitybeingdestroyedandrecreatedasifitwerenew.Aportionoftheactivitystateispreservedonaconfigurationchange,includingthecurrentvaluesofofEditTexts.Forallotherdata,youmustexplicitlysavethatdatayourself.SaveactivityinstancestateintheonSaveInstanceState()method.Instancestatedataisstoredassimplekey/valuepairsinaBundle.UsetheBundlemethodstoputdataintoandgetdatabackoutofthebundle.RestoretheinstancestateinonCreate(),whichisthepreferredway,oronRestoreInstanceState().

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

ActivityLifecycleandSavingState

LearnmoreActivity(APIGuide)Activity(APIReference)ManagingtheActivityLifecycleRecreatinganActivityHandlingRuntimeChanges

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2.3:StartActivitieswithImplicitIntentsContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.CreatenewprojectandlayoutTask2.ImplementopenwebsiteTask3.ImplementopenlocationTask4.ImplementsharethistextTask5.ReceiveimplicitintentsCodingchallengeSummaryRelatedconceptLearnmore

Inaprevioussectionyoulearnedaboutexplicitintents--activatingaspecificactivityinyourapporadifferentappbysendinganintentwiththefully-qualifiedclassnameofthatactivity.Inthissectionyou'lllearnmoreaboutimplicitintents,andhowyoucanusethemtoactivateactivitiesaswell.

Implicitintentsallowyoutoactivateanactivityifyouknowtheaction,butnotthespecificapporactivitythatwillhandlethataction.Forexample,ifyouwantyourapptotakeaphoto,orsendemail,ordisplayalocationonamap,youtypicallydonotcarewhichspecificapporactivityactuallyperformstheseactions.

Conversely,youractivitiescandeclareoneormoreintentfiltersintheAndroidmanifestthatadvertisethatactivity'sabilitytoacceptimplicitintentsandtodefinetheparticulartypeofintentsitwillaccept.

Tomatchyourrequestwithaspecificappinstalledonthedevice,theAndroidsystemmatchesyourimplicitintentwithanactivitywhoseintentfiltersindicatethattheycanperformthataction.Iftherearemultipleappsinstalledthatmatch,theuserispresentedwithanappchooserthatletsthemselectwhichapptheywanttousetohandlethatintent.

Inthispracticalyou'llbuildanappthatsendsthreeimplicitintents:toopenaURLinawebbrowser,toopenalocationonamap,andtoshareabitoftext.Sharing--sendingapieceofinformationtootherpeoplethroughemailorsocialmedia--isacommonandpopularfeatureinmanyapps.Forthesharingactionwe'llusetheShareCompat.IntentBuilderclass,whichmakesiteasytobuildintentsforsharingdata.

Finally,we'llcreateasimpleintentreceiverappthatacceptsimplicitintentsforaspecificaction.

WhatyoushouldalreadyKNOWFromthepreviouspracticals,youshouldbeableto:

Createanduseactivities.Createandsendintentsbetweenactivities.

WhatyouwillLEARNYouwilllearnto:

Createimplicitintents,andusetheiractionsandcategories.UsetheShareCompat.IntentBuilderhelperclasstoeasilycreateimplicitintentsforsharingdata.AdvertisethatyourappcanacceptimplicitintentsbydeclaringintentfiltersintheAndriodmanifest

Introduction

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WhatyouwillDOInthispracticalyouwill:

Createanewapptosendimplicitintents.Implementtwoimplicitintentsthatopenawebpageandopenalocationonamap.Implementanactiontoshareasnippetoftext.Createanewappthatcanacceptimplicitintentsforopeningawebpage.

AppoverviewInthissectionyou'llcreateanewappwithoneactivityandthreeoptionsforactions:openawebsite,openalocationonamap,andshareasnippetoftext.Allofthetextfieldsareeditable(EditText),butcontaindefaultvalues.

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129

Task1.CreatenewprojectandlayoutForthisexercise,you'llcreateanewprojectandappcalledImplicitIntentswithanewlayout.

1.1Createtheproject

1. StartAndroidStudioandcreateanewAndroidStudioproject.Callyourapplication"ImplicitIntents."2. ChooseEmptyActivityfortheprojecttemplate.ClickNext.3. Acceptthedefaultactivityname(MainActivity).MakesuretheGenerateLayoutfileboxischecked.ClickFinish.

1.2Createthelayout

Inthistask,createthelayoutfortheapp.UseaLinearLayout,threeButtons,andthreeEditTexts,likethis:

1. Editres/values/strings.xmltoincludethesestringresources:

<stringname="edittext_uri">http://developer.android.com</string>

<stringname="button_uri">OpenWebsite</string>

<stringname="edittext_loc">GoldenGateBridge</string>

<stringname="button_loc">OpenLocation</string>

<stringname="edittext_share">\'Twasbrilligandtheslithytoves</string>

<stringname="button_share">ShareThisText</string>

2. ChangethelayouttoLinearLayout.Addtheandroid:orientationattributeandgiveitthevalue"vertical."

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<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.implicitintents.MainActivity"

android:orientation="vertical">

3. Removethe"HelloWorld"TextView.4. AddanEditTextandaButtontothelayoutfortheOpenWebsitefunction.Usetheseattributevalues:

Attribute(EditText) Value(EditText)

android:id "@+id/website_edittext"

android:layout_width "match_parent"

android:layout_height "wrap_content"

android:text "@string/edittext_uri"

Attribute(Button) Value(Button)

android:id "@+id/open_website_button"

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:layout_marginBottom "24dp"

android:text "@string/button_uri"

android:onClick "openWebsite"

5. AddasecondEditTextandaButtonfortheOpenWebsitefunction.6. Usethesameattributesasthoseinthepreviousstep,butmodifytheseattributesasnotedbelow:

Attribute(EditText) Value(EditText)

android:id "@+id/location_edittext"

android:text "@string/edittext_loc"

Attribute(Button) Value(Button)

android:id "@+id/open_location_button"

android:text "@string/button_loc"

android:onClick "openLocation"

7. AddathirdEditTextandaButtonfortheShareThisfunction.Makethesechanges:

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Attribute(EditText) Value(EditText)

android:id "@+id/share_edittext"

android:text "@string/edittext_share"

Attribute(Button) Value(Button)

android:id "@+id/share_text_button"

android:text "@string/button_share"

android:onClick "shareText"

Solutioncode:

DependingonyourversionofAndroidStudio,yourcodewilllooksomethinglikethefollowing.

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<?xmlversion="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.implicitintents.MainActivity"

android:orientation="vertical">

<EditText

android:id="@+id/website_edittext"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:text="@string/edittext_uri"/>

<Button

android:id="@+id/open_website_button"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginBottom="24dp"

android:onClick="openWebsite"

android:text="@string/button_uri"/>

<EditText

android:id="@+id/location_edittext"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:text="@string/edittext_loc"/>

<Button

android:id="@+id/open_location_button"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginBottom="24dp"

android:onClick="openLocation"

android:text="@string/button_loc"/>

<EditText

android:id="@+id/share_edittext"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:text="@string/edittext_share"/>

<Button

android:id="@+id/share_text_button"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_marginBottom="24dp"

android:onClick="shareText"

android:text="@string/button_share"/>

</LinearLayout>

Task2.Implement"openwebsite"Inthistaskyou'llimplementtheon-clickhandlermethodforthefirstbuttoninthelayout("OpenWebsite.")ThisactionusesanimplicitintenttosendthegivenURItoanactivitythatcanhandlethatImplicitIntent(suchasawebbrowser).

2.1DefinetheopenWebsitemethod1. OpenMainActivity.java.2. AddaprivatevariableatthetopoftheclasstoholdtheEditTextobjectforthewebsiteURI.

privateEditTextmWebsiteEditText;

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3. IntheonCreate()method,usefindViewById()togetareferencetotheEditTextinstanceandassignittothatprivatevariable:

mWebsiteEditText=(EditText)findViewById(R.id.website_edittext);

4. CreateanewmethodcalledopenWebsite(),withthissignature:

publicvoidopenWebsite(Viewview){}

5. GetthestringvalueoftheEditText:

Stringurl=mWebsiteEditText.getText().toString();

6. EncodeandparsethatstringintoaUriobject:

Uriwebpage=Uri.parse(url);

7. CreateanewIntentwithIntent.ACTION_VIEWastheactionandtheURIasthedata:

Intentintent=newIntent(Intent.ACTION_VIEW,webpage);

Thisintentconstructorisdifferentfromtheoneyouusedtocreateanexplicitintent.Inyourpreviousconstructor,youspecifiedthecurrentcontextandaspecificcomponent(activityclass)tosendtheintent.Inthisconstructoryouspecifyanactionandthedataforthataction.ActionsaredefinedbytheIntentclassandcanincludeACTION_VIEW(toviewthegivendata),ACTION_EDIT(toeditthegivendata),orACTION_DIAL(todialaphonenumber).InthiscasetheactionisACTION_VIEWbecausewewanttoopenandviewthewebpagespecifiedbytheURIinthewebpagevariable.

8. UsetheresolveActivity()andtheAndroidpackagemanagertofindanactivitythatcanhandleyourimplicitintent.Checktomakesurethethatrequestresolvedsuccessfully.

if(intent.resolveActivity(getPackageManager())!=null){

}

Thisrequestthatmatchesyourintentactionanddatawiththeintentfiltersforinstalledapplicationsonthedevicetomakesurethereisatleastoneactivitythatcanhandleyourrequests.

9. Insidetheif-statement,callstartActivity()tosendtheintent.

startActivity(intent);

10. Addanelseblocktoprintalogmessageiftheintentcouldnotberesolved.

}else{

Log.d("ImplicitIntents","Can'thandlethis!");

}

Solutioncode(nottheentireclass):

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publicvoidopenWebsite(Viewview){

//GettheURLtext.

Stringurl=mWebsiteEditText.getText().toString();

//ParsetheURIandcreatetheintent.

Uriwebpage=Uri.parse(url);

Intentintent=newIntent(Intent.ACTION_VIEW,webpage);

//Findanactivitytohandtheintentandstartthatactivity.

if(intent.resolveActivity(getPackageManager())!=null){

startActivity(intent);

}else{

Log.d("ImplicitIntents","Can'thandlethisintent!");

}

}

Task3.Implement"openlocation"Inthistaskyou'llimplementtheon-clickhandlermethodforthesecondbuttonintheUI("OpenLocation.")ThismethodisalmostidenticaltotheopenWebsite()method.ThedifferenceistheuseofageoURItoindicateamaplocation.YoucanuseageoURIwithlatitudeandlongitude,oruseaquerystringforagenerallocation.Inthisexamplewe'veusedthelatter.

3.1DefinetheopenLocationmethod1. OpenMainActivity.java(java/com.example.android.implicitintents/MainActivity).2. AddaprivatevariableatthetopoftheclasstoholdtheEditTextobjectforthelocationURI.

privateEditTextmLocationEditText;

3. IntheonCreate()method,usefindViewByID()togetareferencetotheEditTextinstanceandassignittothatprivatevariable:

mLocationEditText=(EditText)findViewById(R.id.location_edittext);

4. CreateanewmethodcalledopenLocationtouseastheonClickmethodfortheOpenLocationbutton.UsethesamemethodsignatureasopenWebsite().

5. GetthestringvalueofthemLocationEditTextEditText.

Stringloc=mLocationEditText.getText().toString();

6. ParsethatstringintoaUriobjectwithageosearchquery:

UriaddressUri=Uri.parse("geo:0,0?q="+loc);

7. CreateanewIntentwithIntent.ACTION_VIEWastheactionandlocasthedata.

Intentintent=newIntent(Intent.ACTION_VIEW,addressUri);

8. Resolvetheintentandchecktomakesuretheintentresolvedsuccessfully.Ifso,startActivity(),otherwiseloganerrormessage.

if(intent.resolveActivity(getPackageManager())!=null){

startActivity(intent);

}else{

Log.d("ImplicitIntents","Can'thandlethisintent!");

}

Solutioncode(nottheentireclass):

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135

publicvoidopenLocation(Viewview){

//Getthestringindicatingalocation.Inputisnotvalidated;itis

//passedtothelocationhandlerintact.

Stringloc=mLocationEditText.getText().toString();

//Parsethelocationandcreatetheintent.

UriaddressUri=Uri.parse("geo:0,0?q="+loc);

Intentintent=newIntent(Intent.ACTION_VIEW,addressUri);

//Findanactivitytohandletheintent,andstartthatactivity.

if(intent.resolveActivity(getPackageManager())!=null){

startActivity(intent);

}else{

Log.d("ImplicitIntents","Can'thandlethisintent!");

}

}

Task4.ImplementsharethistextSharingactionsareaneasywayforuserstoshareitemsinyourappwithsocialnetworksandotherapps.Althoughyoucouldbuildashareactioninyourownappusingimplicitintents,AndroidprovidestheShareCompat.IntentBuilderhelperclasstomakeimplementingsharingeasy.YoucanuseShareCompat.IntentBuildertobuildanintentandlaunchachoosertolettheuserchoosethedestinationappforsharing.

Inthisfinaltaskwe'llimplementsharingabitoftextinatexteditwiththeShareCompat.IntentBuilderclass.

4.1ImplementtheshareTextmethod

1. OpenMainActivity.java.2. AddaprivatevariableatthetopoftheclasstoholdtheEditTextobjectforthewebsiteURI.

privateEditTextmShareTextEditText;

3. IntheonCreate()method,usefindViewById()togetareferencetotheEditTextinstanceandassignittothatprivatevariable:

mShareTextEditText=(EditText)findViewById(R.id.share_edittext);

4. CreateanewmethodcalledshareThis()touseastheonClickmethodfortheShareThisTextbutton.UsethesamemethodsignatureasopenWebsite().

5. GetthestringvalueofthemShareTextEditTextEditText.

Stringtxt=mShareTextEditText.getText().toString();

6. Definethemimetypeofthetexttoshare:

StringmimeType="text/plain";

7. CallShareCompat.IntentBuilderwiththesemethods:

ShareCompat.IntentBuilder

.from(this)

.setType(mimeType)

.setChooserTitle("Sharethistextwith:")

.setText(txt)

.startChooser();

ThiscalltoShareCompat.IntentBuilderusesthesemethods:

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136

</tr></table>Thisformat,withallthebuilder'ssettermethodsstrungtogetherinonestatement,isaneasyshorthandwaytocreateandlaunchtheintent.Youcanaddanyoftheadditionalmethodstothislist.

Method Description

from() Theactivitythatlaunchesthisshareintent(this).

setType() TheMIMEtypeoftheitemtobeshared.

setChooserTitle() Thetitlethatappearsonthesystemappchooser.

setText() Theactualtexttobeshared

startChooser() Showthesystemappchooserandsendtheintent.

Solutioncode(nottheentireclass):

publicvoidshareText(Viewview){

Stringtxt=mShareTextEditText.getText().toString();

StringmimeType="text/plain";

ShareCompat.IntentBuilder

.from(this)

.setType(mimeType)

.setChooserTitle("Sharethistextwith:")

.setText(txt)

.startChooser();

}

Task5.ReceiveimplicitintentsSofar,you'vecreatedappsthatusebothexplicitandimplicitintentsinordertolaunchsomeotherapp'sactivity.Inthistaskwe'lllookattheproblemfromtheotherwayaround:allowinganactivityinyourapptorespondtoimplicitintentssentfromsomeotherapp.

Activitiesinyourappcanalwaysbeactivatedfrominsideoroutsideyourappwithexplicitintents.Toallowanactivitytoreceiveimplicitintents,youdefineanintentfilterinyourmanifesttoindicatewhichimplicitintentsyouractivityisinterestedinhandling.

Tomatchyourrequestwithaspecificappinstalledonthedevice,theAndroidsystemmatchesyourimplicitintentwithanactivitywhoseintentfiltersindicatethattheycanperformthataction.Iftherearemultipleappsinstalledthatmatch,theuserispresentedwithanappchooserthatletsthemselectwhichapptheywanttousetohandlethatintent.

Whenanapponthedevicesendsanimplicitintent,theAndroidsystemmatchesthatintent'sactionanddatawithavailableactivitiesthatincludetherightintentfilters.Ifyouractivity'sintentfiltersmatchtheintent,youractivitycaneitherhandletheintentitself(ifitistheonlymatchingactivity),or(iftherearemultiplematches)anappchooserappearstoallowtheusertopickwhichappthey'dprefertoexecutethataction.

Inthistaskyou'llcreateaverysimpleappthatreceivesimplicitintentstoopentheURIforawebpage.Whenactivatedbyanimplicitintent,thatappdisplaystherequestedURIasastringinaTextView.

5.1Createtheprojectandlayout

1. StartAndroidStudioandcreateanewAndroidStudioproject.2. Callyourapplication"ImplicitIntentsReceiver."3. ChooseEmptyActivityfortheprojecttemplate.4. Acceptthedefaultactivityname(MainActivity).ClickNext.5. MakesuretheGenerateLayoutfileboxischecked.ClickFinish.6. Openres/layout/activity_main.xml.7. Changetheexisting("HelloWorld")TextViewtheseattributes:

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137

Attribute Value

android:id "@+id/text_uri_message"

android:layout_width wrap_content

android:layout_height wrap_content

android:textSize "18sp"

android:textStyle "bold"

8. Deletetheandroid:textattribute.There'snotextinthisTextViewbydefault,butyou'lladdtheURIfromtheintentinonCreate().

5.2ModifytheAndroidmanifesttoaddanintentfilter

1. Openmanifests/AndroidManifest.xml.2. Notethatthemainactivityalreadyhasthisintentfilter:

<intent-filter>

<actionandroid:name="android.intent.action.MAIN"/>

<categoryandroid:name="android.intent.category.LAUNCHER"/>

</intent-filter>

Thisintentfilter,whichispartofthedefaultprojectmanifest,indicatesthatthisactivityisthemainentrypointforyourapp(ithasanintentactionof"android.intent.action.MAIN"),andthatthisactivityshouldappearasatop-leveliteminthelauncher(itscategoryis"android.intent.category.LAUNCHER")

3. Addasecond&lt;intent-filter&gt;taginside&lt;activity&gt;,andincludetheseelements:

<actionandroid:name="android.intent.action.VIEW"/>

<categoryandroid:name="android.intent.category.DEFAULT"/>

<categoryandroid:name="android.intent.category.BROWSABLE"/>

<dataandroid:scheme="http"android:host="developer.android.com"/>

Theselinesdefineanintentfilterfortheactivity,thatis,thekindofintentsthattheactivitycanhandle.Thisintentfilterdeclarestheseelements:

Filtertype Value Matches

action "android.intent.action.VIEW" Allintentswithviewactions.

category "android.intent.category.DEFAULT" Allimplicitintents.Thiscategorymustbeincludedforyouractivitytoreceiveanyimplicitintents.

category "android.intent.category.BROWSABLE" Requestsforbrowsablelinksfromwebpages,email,orothersources.

data android:scheme="http"android:host="developer.android.com"

URIsthatcontainaschemeofhttpANDahostnameofdeveloper.android.com.

NotethatthedatafilterhasarestrictiononboththekindoflinksitwillacceptandthehostnameforthoseURIs.Ifyou'dpreferyourreceivertobeabletoacceptanylinks,youcanleavethe&lt;data&gt;elementoutaltogether.

Solutioncode

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138

<?xmlversion="1.0"encoding="utf-8"?>

<manifestxmlns:android="http://schemas.android.com/apk/res/android"

package="com.example.android.implicitintentsreceiver">

<application

android:allowBackup="true"

android:icon="@mipmap/ic_launcher"

android:label="@string/app_name"

android:supportsRtl="true"

android:theme="@style/AppTheme">

<activityandroid:name=".MainActivity">

<intent-filter>

<actionandroid:name="android.intent.action.MAIN"/>

<categoryandroid:name="android.intent.category.LAUNCHER"/>

</intent-filter>

<intent-filter>

<actionandroid:name="android.intent.action.VIEW"/>

<categoryandroid:name="android.intent.category.DEFAULT"/>

<categoryandroid:name="android.intent.category.BROWSABLE"/>

<dataandroid:scheme="http"

android:host="developer.android.com"/>

</intent-filter>

</activity>

</application>

</manifest>

5.3ProcesstheintentIntheonCreate()methodforyouractivity,youprocesstheincomingintentforanydataorextrasitincludes.Inthiscase,theincomingimplicitintenthastheURIstoredintheIntentdata.

1. OpenMainActivity.java.2. IntheonCreate()method,gettheincomingintentthatwasusedtoactivatetheactivity:

Intentintent=getIntent();

3. Gettheintentdata.IntentdataisalwaysaURIobject:

Uriuri=intent.getData();

4. Checktomakesuretheurivariableisnotnull.Ifthatcheckpasses,createastringfromthatURIobject:

if(uri!=null){

Stringuri_string="URI:"+uri.toString();

}

5. Insidethatsameifblock,getthetextviewforthemessage:

TextViewtextView=(TextView)findViewById(R.id.text_uri_message);

6. Alsoinsidetheif-block,setthetextofthatTextViewtotheURI:

textView.setText(uri_string);

7. Runthereceiverapp.

Runningtheapponitsownshowsablankactivitywithnotext.Thisisbecausetheactivitywasactivatedfromthesystemlauncher,andnotwithanintentfromanotherapp.

8. RuntheImplicitIntentsapp,andclickOpenWebsitewiththedefaultURI.

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AnappchooserappearsaskingifyouwanttousethedefaultbrowserortheImplicitIntentsReceiverapp.Choose"JustOnce"forthereceiverapp.TheImplicitIntentsReceiverapplaunchesandthemessageshowstheURIfromtheoriginalrequest.

9. TapthebackbuttonandenteradifferentURI.ClickOpenWebsite.

ThereceiverapphasaveryrestrictiveintentfilterthatmatchesonlyexactURIprotocol(http)andhost(developer.android.com).AnyotherURIopensinthedefaultwebbrowser.

SolutioncodeAndroidStudioproject:ImplicitIntents

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:Inthelastsection'schallengeyoucreatedashoppinglistappbuilderwithtwoactivities:onetodisplaythelist,andonetopickanitem.AddanEditTextandaButtontotheshoppinglistactivitytolocateaparticularstoreonamap.

SummaryImplicitintentsallowyoutoactivateanactivityifyouknowtheaction,butnotthespecificapporactivitythatwillhandlethataction.ActivitiesthatcanreceiveimplicitintentsmustdefineintentfiltersintheirAndroidmanifestthatmatchoneormoreintentactionsandcategories.TheAndroidsystemmatchesthecontentofanimplicitintentandtheintentfiltersofallavailableactivitiestodeterminewhichactivitytoactivate.Ifthereismorethanoneavailableactivity,thesystemprovidesachoosersotheusercanpickone.TheShareCompat.IntentBuilderclassmakesiteasytobuildimplicitintentsforsharingdatatosocialmediaoremail.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

ActivitiesandImplicitIntents

LearnmoreActivity(APIGuide)Activity(APIReference)IntentsandIntentFilters(APIGuide)Intent(APIReference)UriGoogleMapsIntentsShareCompat.IntentBuilder(APIReference)

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3.1P:UsingtheDebuggerContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.CreatetheSimpleCalcProjectandAppTask2.RunSimpleCalcintheDebuggerTask3.ExploreDebuggerFeaturesCodingchallengeSummaryRelatedconceptLearnmore

InpreviouspracticalsyouusedtheLogclasstoprintinformationtothesystemlog(logcat)whenyourappruns.Addingloggingstatementstoyourappisonewaytofinderrorsandimproveyourapp'soperation.AnotherwayistousethedebuggerbuiltintoAndroidStudio.

Inthispracticalyou'lllearnhowtodebugyourappinanemulatorandonthedevice,setandviewbreakpoints,stepthroughyourcode,andexaminevariables.

WhatyoushouldalreadyKNOWFromthepreviouspracticalsyoushouldbeableto:

CreateanAndroidStudioproject,andworkwithEditTextandButtonviews.BuildandrunyourappinAndroidStudio,onbothanemulatorandonadevice.Readandanalyzeastacktrace,includinglaston,firstoff.Addlogstatementsandviewthesystemlog(logcat)inAndroidMonitor.

WhatyouwillLEARNYouwilllearnto:

Runyourappindebugmodeinanemulatororonadevice.Stepthroughtheexecutionofyourapp.Setandorganizebreakpoints.Examineandmodifyvariablesinthedebugger.

WhatyouwillDOInthispractical,youwill:

BuildtheSimpleCalcapp.SetandviewbreakpointsinthecodeforSimpleCalc.Stepthroughyourcodeasitruns.Examinevariablesandevaluateexpressions.Identifyandfixproblemsinthesampleapp.

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AppOverviewTheSimpleCalcapphastwoedittextsandfourbuttons.Whenyouentertwonumbersandclickabutton,theappperformsthecalculationforthatbuttonanddisplaystheresult.

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Task1.CreatetheSimpleCalcProjectandAppForthispracticalyouwon'tbuildtheSimpleCalcappyourself.ThecompleteprojectisavailableatSimpleCalc.InthistaskyouwillopentheSimpleCalcprojectintoAndroidStudioandexploresomeoftheapp'skeyfeatures.

1.1DownloadandOpentheSimpleCalcProject

1. DownloadandunziptheSimpleCalcprojectfolder.2. StartAndroidStudioandselectFile>Open.3. NavigatetothefolderforSimpleCalc,selectthatfolderfile,andclickOK.

TheSimpleCalcprojectbuilds.Opentheprojectviewifitisnotalreadyopen.

Warning:Thisappcontainserrorsthatyouwillfindandfix.Ifyouruntheapponadeviceoremulatoryoumightrunintounexpectedbehaviorwhichmayincludecrashesintheapp.

1.2ExploretheLayout1. Openres/layout/activity_main.xml.2. PreviewthelayoutintheLayoutEditor.3. Examinethelayoutcodeanddesignandnotethefollowing:

ThelayoutcontainstwoEditTextsfortheinput,fourButtonviewsforthecalculations,andoneTextViewstodisplaytheresult.Eachcalculationbuttonhasit'sownonClickhandler(onAdd,OnSub,andsoon.)TheTextViewfortheresultdoesnothaveanytextinitbydefault.ThetwoEditTextviewshavethepropertyandroid:inputTypeandthevalue"numberDecimal".ThispropertyindicatesthattheEditTextonlyacceptsnumbersasinput.Thekeyboardthatappearsonscreenwillonlycontainnumbers.YouwilllearnmoreaboutinputtypesforEditTextsinalaterpractical.

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1.3Exploretheappcode

1. Expandtheapp/javafolderintheAndroidprojectview.InadditiontotheMainActivityclass,thisprojectalsoincludesautilityCalculatorclass.

2. OpenCalculator(java/com.example.android.simplecalc/Calculator.java).Examinethecode.Uponexamination,youcanmakethefollowingobservations:

TheoperationsthecalculatorcanperformaredefinedbytheOperatorenum.Alloftheoperationmethodsarepublic.

3. OpenMainActivity(java/com.example.android.simplecalc/MainActivity).Examinethecode.Whatobservationscanyoumakeaboutthecodeandactivity?Thinkaboutyouranswerandconfirmthefollowing:

AlloftheonClickhandlerscalltheprivatecompute()method,withtheoperationnameasoneofthevaluesfromtheCalculator.Operatorenumeration.Thecompute()methodcallstheprivatemethodgetOperand()(whichinturncallsgetOperandText())toretrievethenumbervaluesfromtheEditTexts.Thecompute()methodthenusesaswitchontheoperandnametocalltheappropriatemethodintheCalculatorclass.ThecalculationmethodsintheCalculatorclassperformtheactualarithmeticandreturnavalue.Thelastpartofthecompute()methodupdatestheTextViewwiththeresultofthecalculation.

4. Runtheapp.Trythesethings:Enterbothintegerandfloating-pointvaluesforthecalculation.Enterfloating-pointvalueswithlargedecimalfractions(forexample,1.6753456)Divideanumberbyzero.LeaveoneorbothoftheEditTextviewsempty,andtryanycalculation.

5. ExaminethestacktraceinAndroidStudiowhentheappreportsanerror.

Ifthestacktraceisnotvisible,clicktheAndroidMonitorbuttonatthebottomoftheAndroidStudio,andthenclicklogcat.

IfoneorbothoftheEditTextviewsinSimpleCalcisempty,theappreports"Error"andthesystemlogdisplaysthestateoftheexecutionstackatthetimetheappproducedtheerror.Thestacktraceusuallyprovidesimportantinformationaboutwhyanerroroccurred.

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CodingChallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.Challenge:Examinethestacktraceandtrytofigureoutwhatcausedtheerror(butdon'tfixityet.)

Task2.RunSimpleCalcintheDebuggerInthistaskyou'llgetanintroductiontothedebuggerinAndroidStudio,andlearnhowtorunyourappindebugmode.

2.1StartandRunyourappindebugmode

1. InAndroidStudio,selectRun>DebugapporclicktheDebugicon inthetoolbar.

Ifyourappisalreadyrunning,youwillbeaskedifyouwanttorestartyourappindebugmode.ClickRestartapp.

AndroidStudiobuildsandrunsyourappontheemulatororonthedevice.Debuggingisthesameineithercase.WhileAndroidStudioisinitializingthedebugger,youmayseeamessagethatsays"Waitingfordebugger"onthedevicebeforeyoucanuseyourapp.

IftheDebugviewdoesnotautomaticallyappearinAndroidStudio,clicktheDebugtabatthebottomofthescreen,andthentheDebuggertab.

2. OpentheMainActivity.javafileandclickinthefourthlineofthecompute()method(thelinejustafterthetrystatement).3. Clickintheleftgutteroftheeditorwindowatthatline,nexttothelinenumbers.Areddotappearsatthatline,

indicatingabreakpoint.

YoucanalsouseRun>ToggleLineBreakpointorControl-F8(Command-F8onOSX)tosetorclearabreakpointataline.

4. IntheSimpleCalcapponadevice,enternumbersintheEditTextviewsandclickoneofthecalculatebuttons.

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Theexecutionofyourappstopswhenitreachesthebreakpointyouset,andthedebuggershowsthecurrentstateofyourappatthatbreakpoint.

5. ExaminethetheDebugwindow.Itincludestheseparts:6. Framespanel:showsthecurrentexecutionstackframesforagiventhread.Theexecutionstackshowseachclass

andmethodthathavebeencalledinyourappandintheAndroidruntime,withthemostrecentmethodatthetop.Threadsappearinadropdownmenu.Yourappiscurrentlyrunninginthemainthread,andthattheappisexecutingthecompute()methodinMainActivity.

7. Variablespanel:displaysthevariablesinthecurrentscopeandtheirvalues.Atthisstageofyourapp'sexecution,theavailablevariablesare:this(fortheactivity),operator(theoperatornamefromCalculator.Operatorthatthemethodwascalledfrom),aswellastheglobalvariablesfortheEditTextsandtheTextView.Eachvariableinthispanelhasadisclosuretriangletoallowyoutoviewthepropertiesoftheobjectscontainedinthosevariables.Tryexpandingavariabletoexploreitsproperties.

8.Watchespanel:displaysthevaluesforanyvariablewatchesyouhaveset.Watchesallowyoutokeeptrackofaspecificvariableinyourprogram,andseehowthatvariablechangesasyourprogramruns.

9. Resumeyourapp'sexecutionwithRun>ResumeProgramorclicktheResume iconontheleftsideofthedebuggerwindow.

TheSimpleCalcappcontinuesrunning,andyoucaninteractwiththeappuntilthenexttimecodeexecutionarrivesatthebreakpoint.

2.2DebugarunningappIfyourappisalreadyrunningonadeviceoremulator,andyoudecideyouwanttodebugthatapp,youcanswitchanalreadyrunningapptodebugmode.

1. RuntheSimpleCalcappnormally,withtheRun icon.

2. SelectRun>AttachdebuggertoAndroidprocessorclicktheAttach iconinthetoolbar.

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3. Selectyourapp'sprocessfromthedialogthatappears.ClickOK.

TheDebugwindowappears,andyoucannowdebugyourappasifyouhadstarteditindebugmode.

Note:IftheDebugwindowdoesnotautomaticallyappear,clicktheDebugtabatthebottomofthescreen,andthentheDebuggertab.

Task3.ExploreDebuggerFeaturesInthistaskwe'llexplorethevariousfeaturesintheAndroidStudiodebugger,includingexecutingyourapplinebyline,workingwithbreakpoints,andexaminingvariables.

3.1Stepthroughyourapp'sexecutionAfterabreakpoint,youcanusethedebuggertoexecuteeachlineofcodeinyourapponeatatime,andexaminethestateofvariablesastheappruns.

1. DebugyourappinAndroidStudio,withthebreakpointyousetinthelasttask.2. Intheapp,enternumbersinbothEditTextviewsandclicktheAddbutton.

Yourapp'sexecutionstopsatthebreakpointthatyousetearlier,andthedebuggershowsthecurrentstateoftheapp.Thecurrentlineishighlightedinyourcode.

3. ClicktheStepOver buttonatthetopofthedebuggerwindow.

Thedebuggerexecutesthecurrentlineinthecompute()method(wherethebreakpointis,theassignmentforoperandOne),andthehighlightmovestothenextlineinthecode(theassignmentforoperandTwo).TheVariablespanelupdatestoreflectthenewexecutionstate,andthecurrentvaluesofvariablesalsoappearsaftereachlineofyoursourcecodeinitalics.

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YoucanalsouseRun>StepOver,orF8,tostepoveryourcode.

4. Atthenextline(theassignmentforoperandTwo),clicktheStepInto icon.

StepIntojumpsintotheexecutionofamethodcallinthecurrentline(versusjustexecutingthatmethodandremainingonthesameline).Inthiscase,becausethatassignmentincludesacalltogetOperand(),thedebuggerscrollstheMainActivitycodetothatmethoddefinition.

Whenyoustepintoamethod,theFramespanelupdatestoindicatethenewframeinthecallstack(here,getOperand()),andtheVariablespanelshowstheavailablevariablesinthenewmethodscope.YoucanclickanyofthelinesintheFramespaneltoseethepointinthepreviousstackframewherethemethodwasinvoked.

YoucanalsouseRun>StepInto,orF7,tostepintoamethod.

5. ClickStepOver toruneachofthelinesingetOperand().Notethatwhenthemethodcompletesthedebuggerreturnsyoutothepointwhereyoufirststeppedintothemethod,andallthepanelsupdatewiththenewinformation.

6. UseStepOvertwicetomovetheexecutionpointtothefirstlineinsidethecasestatementforADD.

7. ClickStepInto .

ThedebuggerexecutestheappropriatemethoddefinedintheCalculatorclass,openstheCalculator.javafile,andscrollstotheexecutionpointinthatclass.Again,thevariouspanelsupdatetoreflectthenewstate.

8. UsetheStepOut icontoexecutetheremainderofthatcalculationmethodandpopbackouttothecompute()methodinMainActivity.Youcanthencontinuedebuggingthecompute()methodfromwhereyouleftoff.

YoucanalsouseRun>StepOutorShift-F8tostepoutofamethodexecution.

3.2WorkwithBreakpoints

Usebreakpointstoindicatewhereinyourcodeyouwanttointerruptyourapp'sexecutiontodebugthatportionofthatapp.

1. Findthebreakpointyousetinthelasttaskatthestartofthecompute()methodinMainActivity.

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2. Addabreakpointtothestartoftheswitchstatement.3. Right-clickonthatnewbreakpointandenterthefollowingtestintheConditionfield:

(operandOne==42)||(operandTwo==42)

4. ClickDone.

Thissecondbreakpointisaconditionalbreakpoint.Theexecutionofyourappwillonlystopatthisbreakpointifthetestintheconditionistrue.Inthiscase,theexpressionisonlytrueifoneortheotheroperandsyouenteredis42.YoucanenteranyJavaexpressionasaconditionaslongasitreturnsaboolean.

5. Runyourappindebugmode(Run>Debug),orclickResume ifitisalreadyrunning.Intheapp,entertwonumbersotherthan42andclicktheAddbutton.Executionhaltsatthefirstbreakpointinthecompute()method.

6. ClickResumetocontinuedebuggingtheapp.Observethatexecutiondidnotstopatyoursecondbreakpoint,becausetheconditionwasnotmet.

7. RightclickthefirstbreakpointanduncheckEnabled.ClickDone.Observethatthebreakpointiconnowhasagreendotwitharedborder.

Disablingabreakpointenablesyoutotemporarily"mute"thatbreakpointwithoutactuallyremovingitfromyourcode.Ifyouremoveabreakpointaltogetheryoualsoloseanyconditionsyoucreatedforthatbreakpoint,sodisablingitisoftenabetterchoice.

YoucanalsomuteallbreakpointsinyourappatoncewiththeMuteBreakpoints icon.

8. Intheapp,enter42inthefirstEditTextandclickanybutton.Observethattheconditionalbreakpointattheswitchstatementhaltsexecution(theconditionwasmet.)

9. ClicktheViewBreakpoints iconontheleftedgeofthedebuggerwindow.TheBreakpointswindowappears.

TheBreakpointswindowenablesyoutoviewallthebreakpointsinyourapp,enableordisableindividualbreakpoints,andaddadditionalfeaturesofbreakpointsincludingconditions,dependenciesonotherbreakpoints,andlogging.

10. ClickDonetoclosethebreakpointswindow.

3.3Examineandmodifyvariables

TheAndroidStudiodebuggerletsyouexaminethestateofthevariablesinyourappasthatappruns.

1. RuntheSimpleCalcappindebugmodeifitisnotalreadyrunning.2. Intheapp,entertwonumbers,oneofthem42,andclicktheAddbutton.

Thefirstbreakpointincompute()isstillmuted.Executionstopsatthesecondbreakpoint(attheswitchstatement),andthedebuggerappears.

3. ObserveintheVariablespanelthattheoperandOneandoperandTwovariableshavethevaluesyouenteredintotheapp.

4. ObservethatthethisvariableisaMainActivityobject.Clickthedisclosurearrowtoviewthemembervariablesofthatobject.

5. Right-clicktheoperandOnevariableintheVariablespanel,andselectSetValue.YoucanalsouseF2.6. ChangethevalueofoperandOneto10andpressReturn.7. ModifythevalueofoperandTwoto10inthesamewayandpressReturn.8. ClicktheResumeicontocontinuerunningyourapp.Observethattheresultintheappisnow20,basedonthe

variablevaluesyouchangedinthedebugger.9. Intheapp,clicktheAddbutton.Executionhaltsatthebreakpoint.

10. ClicktheEvaluateExpression icon,orselectRun>EvaluateExpression.TheEvaluateCodeFragmentwindowappears.Youcanalsoright-clickonanyvariableandchooseEvaluateExpression.

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UseEvaluateExpressiontoexplorethestateofvariablesandobjectsinyourapp,includingcallingmethodsonthoseobjects.Youcanenteranycodeintothiswindow.

11. TypemOperandOneEditText.getHint()intotheExpressionwindowandclickEvaluate.12. TheEvaluateExpressionwindowupdateswiththeresultofthatexpression.ThehintforthisEditTextisthestring

"TypeOperand1",aswasoriginallydefinedintheXMLforthatEditText.

Theresultyougetfromevaluatinganexpressionisbasedontheapp'scurrentstate.Dependingonthevaluesofthevariablesinyourappatthetimeyouevaluateexpressions,youmaygetdifferentresults.

NotealsothatifyouuseEvaluateExpressiontochangethevaluesofvariablesorobjectproperties,youchangetherunningstateoftheapp.

13. ClickClosetohidetheEvaluateExpressionwindow.

CodingchallengeNote:Allcodingchallengesareoptionalandnotprerequisitesforlaterlessons.

Challenge:InTask1.3,youtriedrunningtheSimpleCalcappwithnovaluesineitheroftheEditTextviews,resultinginanerrormessage.Usethedebuggertostepthroughtheexecutionofthecodeanddeterminepreciselywhythiserroroccurs.Fixthebugthatcausesthiserror.

SummaryViewlogginginformationinAndroidStudiowiththelogcattaboftheAndroidMonitorpane.RunyourappindebugmodebyclickingthedebugiconorchoosingRun>Debugapp.Abreakpointisaplaceinyourcodewhereyouwanttopausenormalexecutionofyourapptoperformotheractions.SetorclearadebuggingbreakpointbyclickingintheleftgutteroftheeditorwindowimmediatelynexttothetargetlineTheDebugwindowinAndroidStudioshows(stack)Frames,VariablesinthatframeandWatches(activetrackingofavariablewhiletheprogramruns).

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

DebuggingYourApp

LearnmoreDebugYourApp(AndroidStudioUserGuide)DebuggingandTestinginAndroidStudio(video)

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3.2:TestingAppsWithUnitTestsContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.ExploreandrunSimpleCalcinAndroidStudioTask2.AddmoreunitteststoCalculatorTestCodingchallengesSummaryRelatedConceptLearnMore

Testingyourcodecanhelpyoucatchbugsearlyonindevelopment—whentheyaretheleastexpensivetoaddress—andimprovetherobustnessofyourcodeasyourappgetslargerandmorecomplex.Withtestsinyourcode,youcanexercisesmallportionsofyourappinisolation,andinanautomatableandrepeatablemanner.

AndroidStudioandtheAndroidTestingSupportLibrarysupportseveraldifferentkindsoftestsandtestingframeworks.Inthispracticalyou'llexploreAndroidStudio'sbuilt-infunctionalityfortesting,andlearnhowtowriteandrunlocalunittests.

LocalunittestsareteststhatarecompiledandrunentirelyonyourlocalmachinewiththeJavaVirtualMachine(JVM).Uselocalunitteststotestthepartsofyourapp(suchastheinternallogic)thatdonotneedaccesstotheAndroidframeworkoranAndroiddeviceoremulator,orthoseforwhichyoucancreatefake("mock"orstub)objectsthatpretendtobehaveliketheframeworkequivalents.UnittestsarewrittenwithJUnit,acommonunittestingframeworkforJava.

WhatyoushouldalreadyKNOWFromthepreviouspracticalsyoushouldbefamiliarwith:

HowtocreateprojectsinAndroidStudio.ThemajorcomponentsofyourAndroidStudioproject(manifest,resources,Javafiles,gradlefiles).Howtobuildandrunapps.

WhatyouwillLEARNHoworganizingandrunningtestsworksinAndroidStudioWhataunittestis,andhowtowriteunittestsforyourcode.HowtocreateandrunlocalunittestsinAndroidStudio.

WhatyouwillDORuntheinitialtestsintheSimpleCalcapp.AddmoreteststotheSimpleCalcapp.Runthoseunitteststheseetheresults.

AppOverviewThispracticalusesthesameSimpleCalcappfromthelastpractical.Youcanmodifythatappinplace,orcopyyourprojectintoanewapp.

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Task1.ExploreandrunSimpleCalcinAndroidStudioYoubothwriteandrunyourtests(bothunittestsandinstrumentedtests)insideAndroidStudio,alongsidethecodeforyourapp.EverynewAndroidprojectincludesbasicsampleclassesfortestingthatyoucanextendorreplaceforyourownuses.

Inthistaskwe'llreturntotheSimpleCalcapp,whichincludesabasicunittestingclass.

1.1ExploresourcesetsandSimpleCalcSourcesetsareacollectionofrelatedcodeinyourprojectthatarefordifferentbuildtargetsorother"flavors"ofyourapp.WhenAndroidStudiocreatesyourproject,itcreatesthreesourcesets:

Themainsourceset,foryourapp'scodeandresources.Thetestsourceset,foryourapp'slocalunittests.TheandroidTestsourceset,forAndroidinstrumentedtests.

Inthistaskyou'llexplorehowsourcesetsaredisplayedinAndroidStudio,examinethegradleconfigurationfortesting,andruntheunittestsfortheSimpleCalcapp.You'llusetheandroidTestsourcesetinmoredetailinalaterpractical.

1. OpentheSimpleCalcprojectinAndroidStudioifyouhavenotalreadydoneso.Ifyoudon'thaveSimpleCalcyoucanfinditatthisdownloadlink.

2. OpentheProjectview,andexpandtheappandjavafolders.

ThejavafolderintheAndroidviewlistsallthesourcesetsintheappbypackagename(com.android.example.simplecalc),withtestandandroidTestshowninparenthesesafterthepackagename.IntheSimpleCalcapp,onlythemainandtestsourcesetsareused.

3. Expandthecom.android.example.simplecalc(test)folder.

Thisfolderiswhereyouputyourapp'slocalunittests.AndroidStudiocreatesasampletestclassforyouinthisfolderfornewprojects,butforSimpleCalcthetestclassiscalledCalculatorTest.

4. OpenCalculatorTest.java.5. Examinethecodeandnotethefollowing:

Theonlyimportsarefromtheorg.junit,org.hamcrest,andandroid.testpackages.TherearenodependenciesontheAndroidframeworkclasseshere.The@RunWith(JUnit4.class)annotationindicatestherunnerthatwillbeusedtorunthetestsinthisclass.Atestrunnerisalibraryorsetoftoolsthatenablestestingtooccurandtheresultstobeprintedtoalog.Fortestswithmorecomplicatedsetuporinfrastructurerequirements(suchasEspresso)you'llusedifferenttestrunners.Forthis

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examplewe'reusingthebasicJUnit4testrunner.The@SmallTestannotationindicatesthatallthetestsinthisclassareunitteststhathavenodependencies,andruninmilliseconds.The@SmallTest,@MediumTest,and@LargeTestannotationsareconventionsthatmakeiteasiertobundlegroupsoftestsintosuitesofsimilarfunctionality.ThesetUp()methodisusedtosetuptheenvironmentbeforetesting,andincludesthe@Beforeannotation.InthiscasethesetupcreatesanewinstanceoftheCalculatorclassandassignsittothemCalculatormembervariable.TheaddTwoNumbers()methodisanactualtest,andisannotatedwith@Test.Onlymethodsinatestclassthathavean@Testannotationareconsideredteststothetestrunner.Notethatbyconventiontestmethodsdonotincludetheword"test."ThefirstlineofaddTwoNumbers()callstheadd()methodfromtheCalculatorclass.Youcanonlytestmethodsthatarepublicorpackage-protected.InthiscasetheCalculatorisapublicclasswithpublicmethods,soalliswell.Thesecondlineistheassertionforthetest.Assertionsareexpressionsthatmustevaluateandresultintrueforthetesttopass.Inthiscasetheassertionisthattheresultyougotfromtheaddmethod(1+1)matchesthegivennumber2.You'lllearnmoreabouthowtocreateassertionslaterinthispractical.

1.2RuntestsinAndroidStudio

Inthistaskyou'llruntheunittestsinthetestfolderandviewtheoutputforbothsuccessfulandfailedtests.

1. Intheprojectview,right-clicktheCalculatorTestclassandselectRun'CalculatorTest'.

Theprojectbuilds,ifnecessary,andthetestingviewappearsatthebottomofthescreen.Atthetopofthescreen,thedropdown(foravailableexecutionconfigurations)alsochangestoCalculatorTest.

AllthetestsintheCalculatorTestclassrun,andifthosetestsaresuccessful,theprogressbaratthetopoftheviewturnsgreen.(Inthiscase,thereiscurrentlyonlytheonetest.)Astatusmessageinthefooteralsoreports"TestsPassed."

2. IntheCalculatorTestclass,changetheassertioninaddTwoNumbers()to:

assertThat(resultAdd,is(equalTo(3d)));

3. Intherunconfigurationsdropdownatthetopofthescreen,selectCalculatorTest(ifitisnotalreadyselected)and

clickRun .

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Thetestrunsagainasbefore,butthistimetheassertionfails(3isnotequalto1+1.)Theprogressbarintherunviewturnsred,andthetestinglogindicateswherethetest(assertion)failedandwhy.

4. ChangetheassertioninaddTwoNumbers()backtothecorrecttestandrunyourtestsagaintoensuretheypass.5. Intherunconfigurationsdropdown,selectapptorunyourappnormally.

Task2.AddmoreunitteststoCalculatorTestWithunittesting,youtakeasmallbitofcodeinyourappsuchasamethodoraclass,andisolateitfromtherestofyourapp,sothatthetestsyouwritemakessurethatonesmallbitofthecodeworksinthewayyou'dexpect.Typicallyunittestscallamethodwithavarietyofdifferentinputs,andverifiesthattheparticularmethoddoeswhatyouexpectandreturnswhatyouexpectittoreturn.

Inthistaskyou'lllearnmoreabouthowtoconstructunittests.You'llwriteadditionalunittestsforthemethodsintheCalculatorutilitymethodsintheSimpleCalcapp,andrunthoseteststomakesuretheyproducetheoutputyouexpect.

Note:Unittesting,test-drivendevelopmentandtheJUnit4APIarealllargeandcomplextopicsandoutsidethescopeofthiscourse.SeetheResourcesforlinkstomoreinformation.

2.1Addmoretestsfortheadd()method

Althoughitisimpossibletotesteverypossiblevaluethattheadd()methodmayeversee,it'sagoodideatotestforinputthatmightbeunusual.Forexample,considerwhathappensiftheadd()methodgetsarguments:

Withnegativeoperands.Withfloating-pointnumbers.Withexceptionallylargenumbers.Withoperandsofdifferenttypes(afloatandadouble,forexample)Withanoperandthatiszero.Withanoperandthatisinfinity.

Inthistaskwe'lladdmoreunittestsfortheadd()methodtotestdifferentkindsofinputs.

1. AddanewmethodtoCalculatorTestcalledaddTwoNumbersNegative().Usethisskeleton:

@Test

publicvoidaddTwoNumbersNegative(){

}

ThistestmethodhasasimilarstructuretoaddTwoNumbers:itisapublicmethod,withnoparameters,thatreturnsvoid.Itisannotatedwiththe@Testannotation,whichindicatesitisasingleunittest.

WhynotjustaddmoreassertionstoaddTwoNumbers?Groupingmorethanoneassertionintoasinglemethodcanmakeyourtestshardertodebugifonlyoneassertionfails,andobscurestheteststhatdosucceed.Thegeneralruleforunittestsistoprovideatestmethodforeveryindividualassertion.

2. RunalltestsinCalculatorTests,asbefore.

InthetestwindowbothaddTwoNumbersandaddTwoNumbersNegativearelistedasavailable(andpassing)testsintheleftpanel.TheaddTwoNumbersNegativeteststillpasseseventhoughitdoesn'tcontainanycode--atestthatdoesnothingisstillconsideredasuccessfultest.

3. Addalinetoinvoketheadd()methodintheCalculatorclasswithanegativeoperand.

doubleresultAdd=mCalculator.add(-1d,2d);

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The"d"notationaftereachoperandindicatesthatthesearenumbersoftypedouble.Sincetheadd()methodisdefinedwithdoubleparameters,floatsorintswillalsowork.Indicatingthetypeexplicitlyenablesyoutotestothertypesseparately,ifyouneedto.

4. AddanassertionwithassertThat().

assertThat(resultAdd,is(equalTo(1d)));

TheassertThat()methodisaJUnit4assertionthatclaimstheexpressioninthefirstargumentisequaltotheoneinthesecondargument.OlderversionsofJUnitusedmorespecificassertionmethods(assertEquals(),assertNull(),assertTrue()),butassertThat()isamoreflexible,moredebuggableandofteneasiertoreadformat.

TheassertThat()methodisusedwithmatchers.Matchersarethechainedmethodcallsinthesecondoperandofthisassertion(is(equalto()).Theavailablematchersyoucanusetobuildanassertionaredefinedbythehamcrestframework(Hamcrestisananagramformatchers.)Hamcrestprovidesmanybasicmatchersformostbasicassertions.Youcanalsodefineyourowncustommatchersformorecomplexassertions.

Inthiscasetheassertionisthattheresultoftheadd()operation(-1+2)isequalto1.

5. AddanewunittesttoCalculatorTestforfloating-pointnumbers:

@Test

publicvoidaddTwoNumbersFloats(){

doubleresultAdd=mCalculator.add(1.111f,1.111d);

assertThat(resultAdd,is(equalTo(2.222d)));

}

Again,averysimilartesttotheprevioustestmethod,butwithoneargumenttoadd()thatisexplicitlytypefloatratherthandouble.Theadd()methodisdefinedwithparametersoftypedouble,soyoucancallitwithafloattype,andthatnumberispromotedtoadouble.

6. RunalltestsinCalculatorTests,asbefore.

7. ClickRun torunallthetestsagain.

Thistimethetestfailed,andtheprogressbarisred.Thisistheimportantpartoftheerrormessage:

java.lang.AssertionError:

Expected:is<2.222>

but:was<2.2219999418258665>

Arithmeticwithfloating-pointnumbersisinexact,andthepromotionresultedinasideeffectofadditionalprecision.Theassertioninthetestistechnicallyfalse:theexpectedvalueisnotequaltotheactualvalue.

Thequestionhereis:whenyouhaveaprecisionproblemwithpromotingfloatargumentsisthataproblemwithyourcode,oraproblemwithyourtest?Inthisparticularcasebothinputargumentstotheadd()methodfromtheCalculatorappwillalwaysbetypedouble,sothisisanarbitraryandunrealistictest.However,ifyourappwaswrittensuchthattheinputtotheadd()methodcouldbeeitherdoubleorfloatandyouonlycareaboutsomeprecision,youneedtoprovidesomewiggleroomtothetestsothat"closeenough"countsasasuccess.

8. ChangetheassertThat()methodtousethecloseTo()matcher:

assertThat(resultAdd,is(closeTo(2.222,0.01)));

Forthistest,ratherthattestingforexactequalityyoucantestforequalitywithinaspecificdelta.InthiscasethecloseTo()matchermethodtakestwoarguments:theexpectedvalueandtheamountofdelta.Herethatdeltaisjusttwodecimalpointsofprecision.

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2.2Addunittestsfortheothercalculationmethods

UsewhatyoulearnedintheprevioustasktofillouttheunittestsfortheCalculatorclass.

1. AddaunittestcalledsubTwoNumbers()thatteststhesub()method.2. AddaunittestcalledsubWorksWithNegativeResults()thatteststhesub()methodwherethegivencalculationresults

inanegativenumber.3. AddaunittestcalledmulTwoNumbers()thatteststhemul()method.4. AddaunittestcalledmulTwoNumbersZero()thatteststhemulmethodwithatleastoneargumentaszero.5. AddaunittestcalleddivTwoNumbers()thatteststhediv()methodwithtwonon-zeroarguments.

Challenge:AddaunittestcalleddivByZero()thatteststhediv()methodwithasecondargumentof0.Hint:Trythisintheappfirsttoseewhattheresultis.

SolutionCode:

@Test

publicvoidaddTwoNumbers(){

doubleresultAdd=mCalculator.add(1d,1d);

assertThat(resultAdd,is(equalTo(2d)));

}

@Test

publicvoidaddTwoNumbersNegative(){

doubleresultAdd=mCalculator.add(-1d,2d);

assertThat(resultAdd,is(equalTo(1d)));

}

@Test

publicvoidaddTwoNumbersFloats(){

doubleresultAdd=mCalculator.add(1.111f,1.111d);

assertThat(resultAdd,is(closeTo(2.222,0.01)));

}

@Test

publicvoidsubTwoNumbers(){

doubleresultSub=mCalculator.sub(1d,1d);

assertThat(resultSub,is(equalTo(0d)));

}

@Test

publicvoidsubWorksWithNegativeResult(){

doubleresultSub=mCalculator.sub(1d,17d);

assertThat(resultSub,is(equalTo(-16d)));

}

@Test

publicvoidmulTwoNumbers(){

doubleresultMul=mCalculator.mul(32d,2d);

assertThat(resultMul,is(equalTo(64d)));

}

@Test

publicvoiddivTwoNumbers(){

doubleresultDiv=mCalculator.div(32d,2d);

assertThat(resultDiv,is(equalTo(16d)));

}

@Test

publicvoiddivTwoNumbersZero(){

doubleresultDiv=mCalculator.div(32d,0);

assertThat(resultDiv,is(equalTo(Double.POSITIVE_INFINITY)));

}

SolutioncodeAndroidStudioproject:SimpleCalcTest

Codingchallenges

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Note:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge1:Dividingbyzeroisalwaysworthtestingfor,becauseitaspecialcaseinarithmetic.IfyoutrytodividebyzerointhecurrentversionoftheSimpleCalcapp,itbehavesthewayJavadefined:Dividinganumberbyreturnsthe"Infinity"constant(Double.POSITIVE_INFINITY).Dividing0by0returnsthenotanumberconstant(Double.NaN).AlthoughthesevaluesarecorrectforJava,they'renotnecessarilyusefulvaluesfortheuserintheappitself.Howmightyouchangetheapptomoregracefullyhandledividebyzero?Toaccomplishthischallenge,startwiththetestfirst--considerwhattherightbehavioris,andthenwritethetestsasifthatbehavioralreadyexisted.Thenchangeoraddtothecodesothatitmakesthetestscomeupgreen.

Challenge2:Sometimesit'sdifficulttoisolateaunitofcodefromallofitsexternaldependencies.Ratherthanartificiallyorganizeyourcodeincomplicatedwaysjustsoitcanbemoreeasilytested,youcanuseamockframeworktocreatefake("mock")objectsthatpretendtobedependencies.ResearchtheMockitoframework,andlearnhowtosetitupinAndroidStudio.WriteatestclassforthecalcButton()methodinSimpleCalc,anduseMockitototosimulatetheAndroidcontextinwhichyourtestswillrun.

SummaryAndroidStudiohasbuilt-infeaturesforrunninglocalunittests.

LocalunittestsusetheJVMofyourlocalmachineanddonotusetheAndroidframework.UnittestsarewrittenwithJUnit,acommonunittestingframeworkforJava.The"test"folder(AndroidStudio'sProjectView)iswhereJUnittestsarelocated.Localunittestsonlyneedthepackages:org.junit,org.hamcrestandandroid.testThe@RunWith(JUnit4.class)annotationtellsthetestrunnertoruntestsinthisclass.@SmallTest,@MediumTest,and@LargeTestannotationsareconventionsthatmakeiteasiertobundlesimilargroupsoftestsThe@SmallTestannotationindicatesallthetestsinaclassareunitteststhathavenodependenciesandruninmilliseconds.

InstrumentedtestsareteststhatrunonanAndroiddeviceoremulator.InstrumentedtestshaveaccesstotheAndroidframework.

Atestrunnerisalibraryorsetoftoolsthatenablestestingtooccurandtheresultstobeprintedtothelog.

RelatedConceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

TestingYourApp

LearnMoreBestPracticesforTestingGettingStartedwithTestingBuildingLocalUnitTestsJUnit4HomePageJUnit4APIReferenceMockitoHomePageAndroidTestingSupport-TestingPatterns(video)AndroidTestingCodelabAndroidToolsProtip:TestSizeAnnotationsTheBenefitsofUsingassertThatoverotherAssertMethodsinUnitTests

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Introduction

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3.3:UsingTheAndroidSupportLibrariesContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.SetupyourprojecttousesupportlibrariesTask2.ImplementbuttonbehaviorCodingchallengeSummaryRelatedconceptLearnmore

TheAndroidSDKincludesseverallibrariescollectivelycalledtheAndroidsupportlibrary.TheselibrariesprovideanumberoffeaturesthatarenotbuiltintotheAndroidframework,including:

Backward-compatibleversionsofframeworkcomponents:thesupportlibraryallowsappsrunningonolderversionsoftheAndroidplatformtosupportfeaturesmadeavailableonnewerversions.AdditionallayoutanduserinterfaceelementsSupportfordifferentdeviceformfactors,suchasTVorwearablesComponentstosupportmaterialdesignelementsVariousotherfeaturessuchaspalettesupport,annotations,percentage-basedlayoutdimensions,andpreferences.

WhatyoushouldalreadyKNOWFromthepreviouspracticalsyoushouldbefamiliarwith:

HowtocreateprojectsinAndroidStudio.ThemajorcomponentsofyourAndroidStudioproject(manifest,resources,Javafiles,gradlebuildfiles).

WhatyouwillLEARNHowtoverifythatthetheAndroidsupportlibrariesareavailableinAndroidStudio.Howtoindicatesupportlibraryclassesinyourapp.HowtotellthedifferencebetweenthevaluesforcompileSdkVersion,targetSdkVersion,andminSdkVersion.HowtorecognizedeprecatedorunavailableAPIsinyourcode.WheretofindmoreinformationontheAndroidsupportlibraries.

WhatyouwillDOInthispractical,youwill:

Createanewappwithonetextviewandonebutton.VerifythattheAndroidSupportLibraryisavailableonyoursystem.Explorethebuild.gradleforyourapp.ManageclassormethodcallsthatareunavailablefortheversionofAndroidyourappsupports.Useacompatibilityclassfromthesupportlibrarytoprovidebackward-compatibilityforyourapp.

Appoverview

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Inthispracticalyou'llcreateanappcalledHelloCompatwithonetextviewthatdisplays"HelloWorld"onthescreen,andonebutton,thatchangesthecolorofthetext.Thereare20possiblecolors,definedasresourcesinthecolor.xmlfile,andeachbuttonclickrandomlypicksoneofthosecolors.

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Themethodstogetacolorvaluefromtheapp'sresourceshavechangedwithdifferentversionsfortheAndroidframework.ThisexampleusestheContextCompatclass,partoftheAndroidsupportlibrary,whichallowsyoutouseamethodthatworksforallversions.

Task1.SetupyourprojecttousesupportlibrariesForthistaskyou'llsetupanewprojectfortheHelloCompatappandimplementthelayoutandbasicbehavior.

1.1VerifythattheAndroidSupportLibraryisavailable

TheAndroidsupportlibrariesaredownloadedaspartoftheAndroidSDK,andavailableintheAndroidSDKmanager.InAndroidStudio,you'llusetheAndroidSupportRepository—thelocalrepositoryforthesupportlibraries—togetaccesstothelibraryfromwithinyourgradlebuildfiles.Inthistaskyou'llverifythattheAndroidSupportRepositoryisdownloadedandavailableforyourprojects.

1. InAndroidStudio,selectTools>Android>SDKManager,orclicktheSDKManager icon.

TheSDKManagerpreferencepaneappears.

2. ClicktheSDKToolstabandexpandSupportRepository.3. LookforAndroidSupportRepositoryinthelist.4. IfInstalledappearsintheStatuscolumn,you'reallset.ClickCancel.5. IfNotinstalledorUpdateAvailableappears,clickthecheckboxnexttoAndroidSupportRepository.Adownloadicon

shouldappearnexttothecheckbox.ClickOK.6. ClickOKagain,andthenFinishwhenthesupportrepositoryhasbeeninstalled.

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1.2Setuptheprojectandexaminebuild.gradle

1. CreateanewprojectcalledHelloCompat,andchoosetheEmptyActivitytemplate.

OntheTargetAndroidDevicespage,notethatAPI15:Android4.0.3(IceCreamSandwich)isselectedfortheminimumSDK.Asyou'velearnedinpreviouslessons,thisistheoldestversionoftheAndroidplatformyourappwillsupport.

2. InAndroidStudio,makesuretheProjectpaneisopenandtheAndroidtabisselected.3. ExpandGradleScripts,ifnecessary,andopenthebuild.gradle(Module:app)file.

Notethatbuild.gradlefortheoverallproject(build.gradle(Project:app_name))isadifferentfilefromthebuild.gradlefortheappmodule.

4. LocatethecompileSdkVersionlinenearthetopofthefile.Forexample:

compileSdkVersion24

ThecompileversionistheAndroidframeworkversionyourappiscompiledwithinAndroidStudio.FornewprojectsthecompileversionisthemostrecentsetofframeworkAPIsyouhaveinstalled.ThisvalueaffectsonlyAndroidStudioitselfandthewarningsorerrorsyougetinAndroidStudioifyouuseolderornewerAPIs.

5. LocatetheminSdkVersionlineinthedefaultConfigsectionafewlinesdown.

minSdkVersion15

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TheminimumversionistheoldestAndroidAPIversionyourapprunsunder.It'sthesamenumberyouchoseinStep1whenyoucreatedyourproject.TheGooglePlaystoreusesthisnumbertomakesureyourappcanrunonagivenuser'sdevice.AndroidStudioalsousesthisnumbertowarnyouaboutusingdeprecatedAPIs.

6. LocatethetargetSdkVersionlineinthedefaultConfigsection.Forexample:

targetSdkVersion24

ThetargetversionindicatestheAPIversionyourappisdesignedandtestedfor.IftheAPIoftheAndroidplatformishigherthanthisnumber(thatis,yourappisrunningonanewerdevice),theplatformmayenablecompatibilitybehaviorstomakesureyourappcontinuestoworkthewayitwasdesignedto.Forexample,Android6.0(API23)providesanewruntimepermissionsmodel.IfyourapptargetsalowerAPIlevel,theplatformfallsbacktotheolderinstall-timepermissionsmodel.

AlthoughthetargetSDKcanbethesamenumberasthecompileSDK,itisoftenalowernumberthatindicatesthemostrecentversionoftheAPIforwhichyouhavetestedyourapp.

7. Locatethedependenciessectionofbuild.gradle,neartheendofthefile.Forexample:

dependencies{

compilefileTree(dir:'libs',include:['*.jar'])

androidTestCompile(

'com.android.support.test.espresso:espresso-core:2.2.2',{

excludegroup:'com.android.support',

module:'support-annotations'

})

compile'com.android.support:appcompat-v7:24.2.1'

testCompile'junit:junit:4.12'

}

ThedependenciessectionforanewprojectincludesseveraldependenciestoenabletestingwithEspresso,JUnit,aswellasthev7appcompatsupportlibrary.Notethattheversionnumbersfortheselibrariesinyourprojectmaybedifferentthanthoseshownhere.

Thev7appcompatsupportlibraryprovidesbackward-compatibilityforolderversionsofAndroidallthewaybacktoAPI9.Itincludesthev4compatlibraryaswell,soyoudon'tneedtoaddbothasadependency.

8. Updatetheversionnumbers,ifnecessary.

Ifthecurrentversionnumberforalibraryislowerthanthecurrentlyavailablelibraryversionnumber,AndroidStudiowillhighlightthelineandwarnyouthatanewversionisavailable.("anewerversionofcom.android.support:appcompat-v7isavailable").Edittheversionnumbertotheupdatedversion.

Tip:YoucanalsoclickanywhereinthehighlightlineandtypeAlt-Enter(Option-EnterontheMac).Select"ChangetoXX.X.X"fromthemenu,whereXX.X.Xisthemostup-to-dateversionavailable.

9. UpdatethecompileSdkVersionnumber,ifnecessary.

Themajorversionnumberofthesupportlibrary(thefirstnumber)mustmatchyourcompileSdkVersion.WhenyouupdatethesupportlibraryversionyoumayalsoneedtoupdatecompileSdkVersiontomatch.

10. ClickSyncNowtosyncyourupdatedgradlefileswiththeproject,ifprompted.11. InstallmissingSDKplatformfiles,ifnecessary.

IfyouupdatecompileSdkVersionyoumayneedtoinstalltheSDKplatformcomponentstomatch.ClickInstallmissingplatform(s)andsyncprojecttostartthisprocess.

1.3Addthelayoutandcolors

Inthistask,modifythelayoutfortheapp.

1. Openres/layout/activity_main.xml.IntheLayoutEditor,clicktheTexttabatthebottomofthescreenandchange

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166

therootviewgrouptoRelativeLayout,asyou'vedoneinpreviousexercises.2. IftheTextViewelementincludesanylayout-contraintattributes,removethem.3. ModifytheTextViewelementtohavetheseattributes:

Attribute Value

android:id "@+id/hello_textview"

android:layout_width "match_parent"

android:layout_height "wrap_content"

android:padding "@dimen/activity_horizontal_margin"

android:gravity "center"

android:textSize "100sp"

android:textStyle "bold"

android:text "HelloWorld!"

4. Extractthestringfor"HelloWorld"intoastringresource.5. AddaButtonviewundertheTextView,andaddtheseattributes:

Attribute Value

android:id "@+id/color_button"

android:layout_width "match_parent"

android:layout_height "wrap_content"

android:layout_alignParentBottom "true"

android:paddingTop "@dimen/activity_vertical_margin"

android:text "ChangeColor"

android:onClick "changeColor"

6. Extractthestringfor"ChangeColor"intoastringresource.7. Openres/values/colors.xml.8. Addthesecolorresourcestothefile:

<colorname="red">#F44336</color>

<colorname="pink">#E91E63</color>

<colorname="purple">#9C27B0</color>

<colorname="deep_purple">#673AB7</color>

<colorname="indigo">#3F51B5</color>

<colorname="blue">#2196F3</color>

<colorname="light_blue">#03A9F4</color>

<colorname="cyan">#00BCD4</color>

<colorname="teal">#009688</color>

<colorname="green">#4CAF50</color>

<colorname="light_green">#8BC34A</color>

<colorname="lime">#CDDC39</color>

<colorname="yellow">#FFEB3B</color>

<colorname="amber">#FFC107</color>

<colorname="orange">#FF9800</color>

<colorname="deep_orange">#FF5722</color>

<colorname="brown">#795548</color>

<colorname="grey">#9E9E9E</color>

<colorname="blue_grey">#607D8B</color>

<colorname="black">#000000</color>

ThesecolorvaluesandnamescomefromtherecommendedcolorpalettesforAndroidappsdefinedatMaterialDesign-Style-Color.ThecodesindicatecolorRGBvaluesinhexadecimal.

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Solutioncode(activity_main.xml)DependingonyourversionofAndroidStudio,yourcodewilllooksomethinglikethefollowing.

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:id="@+id/activity_main"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.hellocompat.MainActivity">

<TextView

android:id="@+id/hello_textview"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:gravity="center"

android:padding="@dimen/activity_horizontal_margin"

android:text="@string/hello_text_string"

android:textSize="100sp"

android:textStyle="bold"/>

<Button

android:id="@+id/color_button"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_alignParentBottom="true"

android:onClick="changeColor"

android:paddingTop="@dimen/activity_vertical_margin"

android:text="@string/button_label"/>

</RelativeLayout>

1.4AddbehaviortoMainActivity

Inthistaskyou'llfinishsettinguptheprojectbyaddingprivatevariablesandimplementingonCreate()andonSaveInstanceState().

1. OpenMainActivity.java.2. AddaprivatevariableatthetopoftheclasstoholdtheTextViewobjectfortheHelloWorldtextview.

privateTextViewmHelloTextView;

3. Addthefollowingcolorarrayjustaftertheprivatevariable:

privateString[]mColorArray={"red","pink","purple","deep_purple",

"indigo","blue","light_blue","cyan","teal","green",

"light_green","lime","yellow","amber","orange","deep_orange",

"brown","grey","blue_grey","black"

};

Eachofthesecolornamescorrespondtothenamesofthecolorresourcesfromcolor.xml.

4. IntheonCreate()method,usefindViewById()togetareferencetotheTextViewinstanceandassignittothatprivatevariable:

mHelloTextView=(TextView)findViewById(R.id.hello_textview);

5. AlsoinonCreate(),restorethesavedinstancestate,ifany:

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//restoresavedinstancestate(thetextcolor)

if(savedInstanceState!=null){

mHelloTextView.setTextColor(savedInstanceState.getInt("color"));

}

6. AddtheonSaveInstanceState()methodtoMainActivitytosavethetextcolor:

@Override

publicvoidonSaveInstanceState(BundleoutState){

super.onSaveInstanceState(outState);

//savethecurrenttextcolor

outState.putInt("color",mHelloTextView.getCurrentTextColor());

}

Solutioncode(notthewholeclass)

//TextviewforHelloWorld.

privateTextViewmHelloTextView;

//arrayofcolornames,thesematchthecolorresourcesincolor.xml

privateString[]mColorArray={"red","pink","purple","deep_purple",

"indigo","blue","light_blue","cyan","teal","green",

"light_green","lime","yellow","amber","orange","deep_orange",

"brown","grey","blue_grey","black"

};

...

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

//Initializethemaintextview

mHelloTextView=(TextView)findViewById(R.id.hello_textview);

//restoresavedinstancestate(thetextcolor)

if(savedInstanceState!=null){

mHelloTextView.setTextColor(savedInstanceState.getInt("color"));

}

}

...

@Override

publicvoidonSaveInstanceState(BundleoutState){

super.onSaveInstanceState(outState);

//savethecurrenttextcolor

outState.putInt("color",mHelloTextView.getCurrentTextColor());

}

Task2.ImplementbuttonbehaviorTheChangeColorbuttonintheHelloCompatapppicksoneofthe20colorsfromthecolor.xmlresourcefileatrandomandsetsthecolorofthetexttothatcolor.Inthistaskyou'llimplementtheonClick()behaviorforthishandler.

2.1AddthechangeButton()onClickhandler

1. Openres/layout/activity_main.xml,ifitisnotalreadyopen.2. Clickanywhereintheandroid:onClickattribute,insidetheButtonelement.3. PressAlt-Enter(Option-EnterontheMac),andselectCreateonClickeventhandler.4. ChooseMainActivityandclickOK.

ThiscreatesaplaceholdermethodstubforthechangeColor()methodinMainActivity.java.

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2.2Implementthebuttonaction

1. OpenMainActivity.java,ifitisnotalreadyopen.2. InthechangeColor()method,createarandomnumberobject.

Randomrandom=newRandom();

UsetheRandomclass(aJavaclass)togeneratesimplerandomnumbers.

3. UsetherandominstancetopickarandomcolorfromthemColorArrayarray:

StringcolorName=mColorArray[random.nextInt(20)];

ThenextInt()methodwiththeargument20getsanotherrandomintegerbetween0and19.Usethatintegerastheindexofthearraytogetacolorname.

4. Gettheresourceidentifier(aninteger)forthecolornameoutoftheresources:

intcolorResourceName=getResources().getIdentifier(colorName,

"color",getApplicationContext().getPackageName());

Whenyourappiscompiled,theAndroidsystemconvertsthedefinitionsinyourXMLfilesintoresourceswithinternalintegerIDs.ThereareseparateIDsforboththenamesandthevalues.ThislinematchesthecolorstringsfromthecolorNamearraywiththecorrespondingcolornameIDsintheXMLresourcefile.ThegetResources()methodgetsalltheresourcesforyourapp.ThegetIdentifier()methodlooksupthecolorname(thestring)inthecolorresources("color")forthecurrentpackagename.

5. GettheintegerIDfortheactualcolorfromtheresourcesandassignittoacolorResvariable:

intcolorRes=getResources().getColor(colorResourceName);

ThegetResources()methodgetsthesetofresourcesforyourapp,andthegetColor()methodretrievesaspecificcolorfromthoseresourcesbytheIDofthecolorname.

NotethatthegetColor()methodappearswithastrikethroughintheAndroidStudioeditor.IfyouhoveryourmouseovergetColor(),theerror"getColor(int)isdeprecated"appears.InAPI23,thegetColor()methodwasmodifiedtoincludeasecondargumentfortheapp'stheme.SinceyourapphasacompileSdkVersionof24(orhigher),AndroidStudioprovidesthiswarningthatyou'reusinganolder,deprecatedmethod.

YoucanstillcompileyourappanditwouldstillrunonbothnewandoldAndroiddevices--thedeprecationwarningisawarning,notanerror.Butit'sbestnottoignorewarningswheretheyexist,asdeprecatedmethodscanresultinunexpectedbehavior.

6. ChangethecolorResassignmentlinetoincludethesecondargumenttogetColor():

intcolorRes=

getResources().getColor(colorResourceName,this.getTheme());

YoucanusethegetTheme()methodtogetthethemeforthecurrentapplicationcontext.Onlynowwiththischangeyou'llnotethatgetColor()hasaredunderlinedhighlight.IfyouhoverovergetColor()AndroidStudioreports:"CallrequiresAPI23(currentminis15)".SinceyourminSdkVersionis15,you'llgetthismessageifyoutrytouseanyAPIsthatwereintroducedafterAPI15.Youcanstillcompileyourapp,butbecausethisnewversionofgetColor()withtwoargumentsisnotavailableondevicespriortoAPI23,yourappwillcrashwhentheusertapstheChangebutton.

AtthisstageyoucouldcheckfortheplatformversionandusetherightversionofgetColor()dependingonwheretheappisrunning.(youwillstillgetawarningforbothcallsinAndroidStudio).ThebetterwaytosupportbotholderandnewerAndroidAPIswithoutwarningsistouseoneofthecompatibilityclassesinthesupportlibrary.

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7. ChangethecolorResassignmentlinetousetheContextCompatclass:

intcolorRes=ContextCompat.getColor(this,colorResourceName);

ContextCompatprovidesmanycompatibilitymethodstoaddressAPIdifferencesintheapplicationcontextandappresources.ThegetColor()methodinContextCompattakestwoarguments:thecurrentcontext(here,theactivityinstance,this),andthenameofthecolor.

TheimplementationofthismethodinthesupportlibraryhidestheimplementationdifferencesindifferentversionsoftheAPI.YoucancallthismethodregardlessofyourcompileSDKorminimumSDKversionswithnowarnings,errors,orcrashes.

8. SetthecoloroftheHelloWorldtextviewtothecolorresourceID:

mHelloTextView.setTextColor(colorRes);

9. Compileandruntheapponadeviceoremulator.

TheChangeColorbuttonshouldnowchangethecolorofthetextinHelloWorld.

Solutioncode(changeColor()methodonly)

publicvoidchangeColor(Viewview){

//getarandomcolornamefromthecolorarray(20colors)

Randomrandom=newRandom();

StringcolorName=mColorArray[random.nextInt(20)];

//getthecoloridentifierthatmatchesthecolorname

intcolorResourceName=getResources().getIdentifier(colorName,"color",

getApplicationContext().getPackageName());

//getthecolorIDfromtheresources

intcolorRes=ContextCompat.getColor(this,colorResourceName);

//Setthetextcolor

mHelloTextView.setTextColor(colorRes);

}

SolutioncodeAndroidStudioproject:HelloCompat

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.Challenge:InsteadofusingContextCompatfortogetthecolorresource,useatestofthevaluesintheBuildclasstoperformadifferentoperationiftheappisrunningonadevicethatsupportslessthanAPI23.

SummaryInthispractical,youlearnedthat:

AndroidusesthreedirectivestoindicatehowyourappshouldbehavefordifferentAPIversions:minSdkVersion:theminimumAPIversionyourappsupports.compileSdkVersion:theAPIversionyourappshouldbecompiledwith.targetSdkVersion:theAPIversionyourappwasdesignedfor.

TheAndroidSupportLibrarycanbeinstalledintheSDKmanager

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Youcanaddlibrarydependenciesforsupportlibrariesinthegradle.buildfileTheContextCompatclassprovidesmethodsforcompatibilitywithcontextandresource-relatedmethodsforbotholdandnewAPIlevels.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

TheAndroidSupportLibrary

LearnmoreAndroidSupportLibrary(introduction)SupportLibrarySetupSupportLibraryFeaturesSupportingDifferentPlatformVersionsPickingyourcompileSdkVersion,minSdkVersion,andtargetSdkVersionAllthethingsCompatAPIReference(allpackagesthatstartwithandroid.support)

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4.1:UsingKeyboards,InputControls,Alerts,andPickersContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1:ExperimentwithtextentrykeyboardattributesTask2:ChangethekeyboardtypeTask3:AddaspinnerinputcontrolforselectingaphonelabelTask4:UseadialogforanalertrequiringadecisionTask5:UseapickerforuserinputTask6:UseimageviewsasbuttonsTask7:UseradiobuttonsCodingchallengeSummaryRelatedconceptLearnmore

Youcancustomizeinputmethodstomakeenteringdataeasierforusers.

Inthispractical,you'lllearnto:

Usedifferenton-screenkeyboardsandcontrolsforuserinput.Showanalertmessagethatuserscaninteractwith.Provideinterfaceelementsforselectingatimeanddate.Useimagesasbuttonstolaunchanactivity.Addradiobuttonsfortheusertoselectoneitemfromasetofitems.

WhatyoushouldalreadyKNOWForthispracticalyoushouldbeableto:

CreateanAndroidStudioprojectfromatemplateandgeneratingthemainlayout.Runappsontheemulatororaconnecteddevice.Makeacopyofanappproject,andrenamingtheapp.CreateandeditingUIelementsusingtheLayoutEditorandXMLcode.AccessUIelementsfromyourcodeusingfindViewById().ConvertthetextinaviewtoastringusinggetText().toString().Handleabuttonclick.Displayatoastmessage.Startanactivitywithanotherappusinganimplicitintent.Useanadaptertoconnectyourdatatoaview,suchastheRecyclerViewinapreviouslesson.

WhatyouwillLEARNInthispractical,youwilllearnto:

Changetheinputmethodstoenablespellingsuggestions,auto-capitalization,andpasswordobfuscation.Changethegenericon-screenkeyboardtoaphonekeypadorotherspecializedkeyboards.Addaspinnerinputcontroltoshowadropdownmenuwithvalues,fromwhichtheusercanselectone.AddanalertwithOKandCancelforauserdecision.

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Usedateandtimepickersandrecordingtheselections.Useimagesasbuttonstolaunchanactivity.Addradiobuttonsfortheusertoselectoneitemfromasetofitems.

WhatyouwillDOCreatenewAndroidStudioprojectstoshowkeyboards,aspinner,analert,andtimeanddatepickers.Providespellingsuggestionswhenauserenterstext,andautomaticallycapitalizenewsentences,byexperimentingwiththeinputmethod.Experimentwiththeinputtypeattributetochangetheon-screenkeyboardtoaspecialkeyboardforenteringemailaddresses,andthentoanumerickeypadtoforcenumericentry.Addaspinnerinputcontrolforthephonenumberfieldforselectingonevaluefromasetofvalues.Createanewprojectwithanalertdialogtonotifytheusertomakeadecision,suchasOKorCancel.Addthedatepickerandtimepickertothenewproject,anduselistenerstorecordtheuser'sselection.Createanewprojecttouseimagesasbuttons.Createasecondactivityandaddradiobuttonsforselectinganoption.SetonClickhandlersfortheimagesusedasbuttonstolaunchasecondactivity.

AppoverviewInthispractical,you'llcreateandbuildanewappcalledKeyboardSamplesforexperimentingwiththeandroid:inputTypeattributefortheEditTextUIelement.Youwillchangethekeyboardsothatitsuggestsspellingcorrectionsandcapitalizeseachnewsentence,asshownontheleftsideofthefigurebelow.Tokeeptheappsimple,you'lldisplaytheenteredtextinatoastmessage,shownontherightsideofthefigurebelow.

Youwillalsochangethekeyboardtoonethatoffersthe"@"symbolinaprominentlocationforenteringemailaddresses,andtoaphonekeypadforenteringphonenumbers,asshownontheleftsideandinthecenterofthefigurebelow.Asachallenge,youwillimplementalistenerfortheactionkeyinthekeyboardinordertosendanimplicitintenttoanotherapptodialthephonenumber.

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YouwillthencopytheapptocreatePhoneNumberSpinnerthatoffersaspinnerinputcontrolforselectingthelabel(Home,Work,Other,Custom)forthephonenumber,asshownontherightsideofthefigurebelow.

Thefigureaboveshowsthefollowing:

1. Theemailkeyboardwiththe"@"symbolinaneasy-to-findlocation2. Thephonekeypad3. Thespinner

You'llalsocreateAlertSampletoexperimentwithanalertdialog,shownontheleftsideofthefigurebelow,andDateTimePickerstoexperimentwithadatepickerandatimepicker,showninthecenterandontherightsideofthefigurebelow,andusethetimeanddateselectionsinyourapp.

ThelasttasksinvolvecreatinganappfromtheBasicActivitytemplatethatletsausertapimagebuttonstolaunchanactivity,asshownontheleftsideofthefigurebelow,andchooseasingledeliveryoptionfromradio-buttonchoicesforafoodorder,asshownontherightsideofthefigurebelow.

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Task1.ExperimentwithtextentrykeyboardattributesTouchinganEditTexteditabletextfieldplacesthecursorinthetextfieldandautomaticallydisplaystheon-screenkeyboard.Youwillchangeattributesofthetextentryfieldsothatthekeyboardsuggestsspellingcorrectionswhileyoutype,andautomaticallystartseachnewsentencewithcapitalletters.Forexample:

android:inputType="textCapSentences":Setsthekeyboardtocapitallettersatthebeginningofsentences.android:inputType="textAutoCorrect":Setsthekeyboardtoshowautomaticspellingcorrectionsasyouentercharacters.android:inputType="textMultiLine":EnablestheReturnkeyonthekeyboardtoendlinesandcreatenewblanklineswithoutclosingthekeyboard.android:inputType="textPassword":Setsthecharacterstheuserentersintodotstoconcealtheenteredpassword.

1.1CreatethemainlayoutandtheshowTextmethod

YouwilladdaButton,andchangetheTextViewelementtoanEditTextelementsothattheusercanentertext.Theapp'slayoutwilllooklikethefollowingfigure.

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1. CreateanewprojectcalledKeyboardSamples,andchoosetheEmptyActivitytemplate.2. Opentheactivity_main.xmllayoutfile.IntheLayoutEditor,clicktheTexttabatthebottomofthescreenandchange

therootviewgrouptoRelativeLayout,asyou'vedoneinpreviousexercises.3. AddaButtonabovetheexistingTextViewelementwiththefollowingattributes:

Buttonattribute Newvalue

android:id "@+id/button_main"

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:layout_alignParentBottom "true"

android:layout_alignParentRight "true"

android:onClick "showText"

android:text "Show"

4. Extractthestringresourcefortheandroid:textattributevaluetocreateandentryforitinstrings.xml:Placethecursoron"Show",pressAlt-Enter(Option-EnterontheMac),andselectExtractstringresources.ThenchangetheResourcenameforthestringvaluetoshow.

Youextractstringresourcesbecauseitmakestheappprojectmoreflexibleforchangingstrings.Thestringresourceassignmentsarestoredinthestrings.xmlfile(underapp>res>values).Youcaneditthisfiletochangethestringassignmentssothattheappcanbelocalizedwithadifferentlanguage.Forexample,the"Show"valuefortheresourcenamedshowcouldbechangedto"Montrer"fortheFrenchversionoftheapp.

5. ChangetheexistingTextViewelementasfollows:i. Deletetheandroid:textattributethatspecified"HelloWorld!".ii. IftheTextViewelementincludesanylayout-constraintattributes,removethem.iii. ChangetheTextViewtagtoanEditTexttag,andmakesuretheendingtagis/>.iv. Addorchangethefollowingattributes:

EditTextattribute TextViewoldvalue EditTextnewvalue

android:id "@+id/editText_main"

android:layout_width "wrap_content" "match_parent"

android:layout_height "wrap_content" "wrap_content"

android:layout_alignParentBottom "true"

android:layout_toLeftOf "@id/button_main"

android:hint "Enteramessage"

Youlearnedabouttheandroid:layout_toLeftOfandandroid:layout_alignParentBottomattributesinapreviouslesson.Theselayout-relatedattributesworkwiththeRelativeLayoutviewgrouptopositionchildviewsrelativetoeachotherortotheparent.Theandroid:hintattributesetsthetexttoappearinthefieldthatprovidesahintfortheusertoprovideinput,suchas"Enteramessage"

6. Extractthestringresourcefortheandroid:hintattributevalue"Enteramessage"totheresourcenameenter.DependingonyourversionofAndroidStudio,youractivity_main.xmllayoutfilewilllooksomethinglikethefollowing:

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<RelativeLayout

xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.keyboardsamples.MainActivity">

<Button

android:id="@+id/button_main"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentBottom="true"

android:layout_alignParentRight="true"

android:onClick="showText"

android:text="@string/show"/>

<EditText

android:id="@+id/editText_main"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_alignParentBottom="true"

android:layout_toLeftOf="@id/button_main"

android:hint="@string/enter"/>

</RelativeLayout>

7. OpenMainActivity.javaandenterthefollowingshowTextmethod,whichretrievestheinformationenteredintotheEditTextelementandshowsitinatoastmessage:

publicvoidshowText(Viewview){

EditTexteditText=(EditText)findViewById(R.id.editText_main);

if(editText!=null){

StringshowString=editText.getText().toString();

Toast.makeText(this,showString,Toast.LENGTH_SHORT).show();

}

}

8. Openstrings.xml(inapp>res>values),andedittheapp_namevalueto"KeyboardSamples"(besuretoincludeaspacebetween"Keyboard"and"Samples").

9. Runtheappandexaminehowthekeyboardworks.

TappingtheShowbuttonshowsthetoastmessageofthetextentry.

Toclosetheon-screenkeyboard,tapthedown-pointingarrowinthebottomrowoficons.

Inthestandardkeyboardlayout,acheckmarkiconinagreencircle,shownbelow,appearsinthelowerrightcornerofthe

keypad.ThisisknownastheReturn(orEnter)key,anditisusedtoenteranewline:

WiththedefaultattributesfortheEditTextelement,tappingtheReturnkeyaddsanotherlineoftext.Inthenextsection,youwillchangethekeyboardsothatitcapitalizessentencesasyoutype.Asaresultofsettingtheandroid:inputTypeattribute,thedefaultattributefortheReturnkeychangestoshiftfocusawayfromtheEditTextelementandclosethekeyboard.

1.2Setthekeyboardtocapitalizesentences

1. Addtheandroid:inputTypeattributetotheEditTextelementusingthetextCapSentencesvaluetosetthekeyboardtocapitallettersatthebeginningofasentence,sothatuserscanautomaticallystartasentencewithacapitalletter:

android:inputType="textCapSentences"

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2. Runyourapp.

Capitalletterswillnowappearonthekeyboardatthebeginningofsentences.WhenyoutaptheReturnkeyonthekeyboard,thekeyboardclosesandyourtextentryisfinished.Youcanstilltapthetextentryfieldtoaddmoretextoreditthetext.TapShowtoshowthetextinatoastmessage.

Fordetailsabouttheandroid:inputTypeattribute,seeSpecifyingtheInputMethodType.

1.3Setthekeyboardtohideapasswordwhenenteringit1. ChangetheEditTextelementtousethetextPasswordvaluefortheandroid:inputTypeattribute.

android:inputType="textPassword"

2. Changetheandroid:hintto"Enteryourpassword".3. Runtheapp.

Thecharacterstheuserentersturnintodotstoconcealtheenteredpassword.Forhelp,seeTextFields.

Solutioncode:

AndroidProject:KeyboardSamples

Task2.ChangethekeyboardtypeEverytextfieldexpectsacertaintypeoftextinput,suchasanemailaddress,phonenumber,password,orjustplaintext.It'simportanttospecifytheinputtypeforeachtextfieldinyourappsothatthesystemdisplaystheappropriatesoftinputmethod,suchas:

Thestandardon-screenkeyboardforplaintextThekeyboardforanemailaddresswhichincludesthe"@"symbolinaprominentlocationThephonekeypadforaphonenumber

2.1UseanemailkeyboardModifythemainactivity'sEditTextelementtoshowanemailkeyboardratherthanastandardkeyboard:

1. IntheEditTextelementintheactivity_main.xmllayoutfile,changetheandroid:inputTypeattributetothefollowing:

android:inputType="textEmailAddress"

2. Changetheandroid:hintattributeto"Enteranemailaddress".3. Extractthestringresourcefortheandroid:hintvaluetoenter_email.4. Runtheapp.Tappingthefieldbringsuptheon-screenemailkeyboardwiththe"@"symbollocatednexttothespace

key.

2.2Useaphonekeypad

Modifythemainactivity'sEditTextelementtoshowaphonekeypadratherthanastandardkeyboard:

1. IntheEditTextelementintheactivity_main.xmllayoutfile,changetheandroid:inputTypeattributetothefollowing:

android:inputType="phone"

2. Changetheandroid:hintattributeto"Enteraphonenumber".3. Extractthestringresourcefortheandroid:hintvaluetoenter_phone.4. Runtheapp.

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Tappingthefieldnowbringsuptheon-screenphonekeypadinplaceofthestandardkeyboard.

Note:Whenrunningtheappontheemulator,thefieldwillstillaccepttextratherthannumbersifyoutypeonthecomputer'skeyboard.However,whenrunonthedevice,thefieldonlyacceptsthenumbersofthekeypad.

Task3.AddaspinnerinputcontrolforselectingaphonelabelInputcontrolsaretheinteractivecomponentsinyourapp'suserinterface.AndroidprovidesawidevarietyofcontrolsyoucanuseinyourUI,suchasbuttons,seekbars,checkboxes,zoombuttons,togglebuttons,spinners,andmanymore.(Formoreinformationaboutinputcontrols,seeInputControls.)

Aspinnerprovidesaquickwaytoselectonevaluefromaset.Touchingthespinnerdisplaysadrop-downlistwithallavailablevalues,fromwhichtheusercanselectone.Ifyouareprovidingonlytwoorthreechoices,youmightwanttouseradiobuttonsforthechoicesifyouhaveroominyourlayoutforthem;however,withmorethanthreechoices,aspinnerworksverywell,scrollsasneededtodisplayitems,andtakesuplittleroominyourlayout.

Formoreinformationaboutspinners,seeSpinners.

Toprovideawaytoselectalabelforaphonenumber(suchasHome,Work,Mobile,andOther),youcanaddaspinnertothelayouttoappearrightnexttothephonenumberfield.

3.1CopytheKeyboardSamplesprojectandmodifythelayoutUsethefollowingfigureasasaguideforthemainactivity'slayout:

Intheabovefigure:

1. ThefirstLinearLayoutwithanEditTextview,aspinnericon,andtheShowbutton.2. ThesecondLinearLayoutwithtwoTextViews.

Followthesesteps:

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1. CopytheKeyboardSamplesprojectfolder,renameittoPhoneNumberSpinner,andrefactorittopopulatethenewnamethroughouttheappproject.(SeetheAppendixforinstructionsoncopyingaproject.)

2. Afterrefactoring,changethe<stringname="app_name">valueinthestrings.xmlfile(withinapp>res>values)toPhoneNumberSpinner(withspaces)astheapp'sname.

3. Opentheactivity_main.xmllayoutfile.4. EnclosetheexistingEditTextandButtonelementsfromthepreviouslessonwithinaLinearLayoutwithahorizontal

orientation,placingtheEditTextelementabovetheButton:

<LinearLayout

android:layout_width="match_parent"

android:layout_height="match_parent"

android:layout_marginTop="@dimen/activity_vertical_margin"

android:orientation="horizontal">

<EditText

…

<Button

…

</LinearLayout>

5. MakethefollowingchangestotheEditTextandButtonelements:i. RemovethefollowingattributesfromtheEditTextelement:

android:layout_toLeftOf

android:layout_alignParentBottom

ii. RemovethefollowingattributesfromtheButtonelement:android:layout_alignParentRight

android:layout_alignParentBottom

iii. ChangethreeotherattributesoftheEditTextelementasfollows:

EditTextattribute Value

android:layout_width "wrap_content"

android:inputType "phone"

android:hint "Enterphonenumber"

6. AddaSpinnerelementbetweentheEditTextelementandtheButtonelement:

<Spinner

android:id="@+id/label_spinner"

android:layout_width="wrap_content"

android:layout_height="wrap_content">

</Spinner>

TheSpinnerelementprovidesthedrop-downlist.Inthenexttaskyouwilladdcodethatwillfillthespinnerlistwithvalues.ThelayoutcodefortheEditText,Spinner,andButtonelementswithintheLinearLayoutshouldnowlooklikethis:

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<LinearLayout

android:layout_width="match_parent"

android:layout_height="match_parent"

android:layout_marginTop="@dimen/activity_vertical_margin"

android:orientation="horizontal">

<EditText

android:id="@+id/editText_main"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:inputType="phone"

android:hint="Enterphonenumber"/>

<Spinner

android:id="@+id/label_spinner"

android:layout_width="wrap_content"

android:layout_height="wrap_content">

</Spinner>

<Button

android:id="@+id/button_main"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:onClick="showText"

android:text="Show"/>

</LinearLayout>

7. AddanotherLinearLayoutbelowtheLinearLayoutyoujustcreated,withahorizontalorientationtoenclosetwoTextViewelementsside-by-side—atextdescription,andatextfieldtoshowthephonenumberandthephonelabel—andaligntheLinearLayouttotheparent'sbottom(refertothefigureabove):

<LinearLayout

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:orientation="horizontal"

android:layout_alignParentBottom="true">

<TextView

…

<TextView

…

</LinearLayout>

8. AddthefollowingTextViewelementswithintheLinearLayout:

TextViewattribute Value

android:id "@+id/title_phonelabel"

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:text "PhoneNumber:"

TextViewattribute Value

android:id "@+id/text_phonelabel"

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:text "Nothingentered."

9. CheckyourlayoutbyclickingthePreviewtabontherightsideofthelayoutwindow.

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Youshouldnowhaveascreen(refertothefigureabove)withthephoneentryfieldatthetopontheleft,askeletalspinnernexttothefield,andtheShowbuttonontheright.Atthebottomshouldappearthetext"PhoneNumber:"followedby"Nothingentered."

10. Extractyourstringsintostringresources:Placethecursoronthehard-codedstring,pressAlt-Enter(Option-EnterontheMac),andselectExtractstringresources.ThenedittheResourcenameforthestringvalue.Extractasfollows:

Element String Stringresource

EditText "Enterphonenumber" "@string/hint_phonenumber"

Button "Show" "@string/show_button"

TextView "PhoneNumber:" "@string/phonenumber_label"

TextView "Nothingentered." "@string/nothing_entered"

3.2Addcodetoactivatethespinneranditslistener

Thechoicesforthisphonelabelspinnerarewell-definedstaticstrings("Home","Work",etc),soyoucanuseatextarraydefinedinstrings.xmltoholdthevaluesforit.

Toactivatethespinneranditslistener,implementtheAdapterView.OnItemSelectedListenerinterface,whichrequiresalsoaddingtheonItemSelected()andonNothingSelected()callbackmethods.

1. Openstrings.xmltodefinetheselectablevalues(Home,Work,Mobile,andOther)forthespinnerasthestringarraylabels_array:

<string-arrayname="labels_array">

<item>Home</item>

<item>Work</item>

<item>Mobile</item>

<item>Other</item>

</string-array>

2. Todefinetheselectioncallbackforthespinner,changeyourMainActivityclasstoimplementthe

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AdapterView.OnItemSelectedListenerinterfaceasshown:

publicclassMainActivityextendsAppCompatActivityimplements

AdapterView.OnItemSelectedListener{

AsyoutypeAdapterView.intheabovestatement,AndroidStudioautomaticallyimportstheAdapterViewwidget.ThereasonwhyyouneedtheAdapterViewisbecauseyouneedanadapter—specificallyanArrayAdapter—toassignthearraytothespinner.Anadapterconnectsyourdata—inthiscase,thearrayofspinneritems—tothespinnerview.Youwilllearnmoreaboutthispatternofusinganadaptertoconnectdatainanotherlesson.Thislineshouldappearinyourblockofimportstatements:

importandroid.widget.AdapterView;

AftertypingOnItemSelectedListenerintheabovestatement,waitafewsecondsforaredlightbulbtoappearintheleftmargin.

3. ClickthebulbandchooseImplementmethods.TheonItemSelected()andonNothingSelected()methods,whicharerequiredforOnItemSelectedListener,shouldalreadybehighlighted,andthe"Insert@Override"optionshouldbechecked.ClickOK.

ThisstepautomaticallyaddsemptyonItemSelected()andonNothingSelected()callbackmethodstothebottomoftheMainActivityclass.BothmethodsusetheparameterAdapterView<?>.The<?>isaJavatypewildcard,enablingthemethodtobeflexibleenoughtoacceptanytypeofAdapterViewasanargument.

4. InstantiateaspinnerobjectintheonCreate()methodusingtheSpinnerelementinthelayout(label_spinner),andsetitslistener(spinner.setOnItemSelectedListener)intheonCreate()method.AddthecodetotheonCreate()method:

@Override

protectedvoidonCreate(BundlesavedInstanceState){

...

//Createthespinner.

Spinnerspinner=(Spinner)findViewById(R.id.label_spinner);

if(spinner!=null){

spinner.setOnItemSelectedListener(this);

}

...

5. ContinuingtoedittheonCreate()method,addastatementthatcreatestheArrayAdapterwiththestringarray(labels_array)usingtheAndroid-suppliedsimplespinnerlayoutforeachitem(layout.simple_spinner_item):

...

//CreateArrayAdapterusingthestringarrayanddefaultspinnerlayout.

ArrayAdapter<CharSequence>adapter=ArrayAdapter.createFromResource(this,

R.array.labels_array,android.R.layout.simple_spinner_item);

...

Thesimple_spinner_itemlayoutusedinthisstep,andthesimple_spinner_dropdown_itemlayoutusedinthenextstep,arethedefaultpre-definedlayoutsprovidedbyAndroidintheR.layoutclass.Youshouldusetheselayoutsunlessyouwanttodefineyourownlayoutsfortheitemsinthespinnerandthespinner'sappearance.

6. Specifythelayoutforthespinner'schoicestobesimple_spinner_dropdown_item,andthenapplytheadaptertothespinner:

...

//Specifythelayouttousewhenthelistofchoicesappears.

adapter.setDropDownViewResource

(android.R.layout.simple_spinner_dropdown_item);

//Applytheadaptertothespinner.

if(spinner!=null){

spinner.setAdapter(adapter);

}

...

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3.3Addcodetorespondtotheuser'sselections

Whentheuserselectsaniteminthespinner,theSpinnerobjectreceivesanon-item-selectedevent.Tohandlethisevent,youalreadyimplementedtheAdapterView.OnItemSelectedListenerinterfaceinthepreviousstep,addingemptyonItemSelected()andonNothingSelected()callbackmethods.

InthisstepyouwillfirstdeclaremSpinnerLabelasthestringtoholdtheselecteditem.YouwillthenfillinthecodefortheonItemSelected()methodtoretrievetheselectediteminthespinner,usinggetItemAtPosition(),andassigntheitemtomSpinnerLabel:

1. DeclarethemSpinnerLabelstringatthebeginningoftheMainActivityclassdefinition:

publicclassMainActivityextendsAppCompatActivityimplements

AdapterView.OnItemSelectedListener{

privateStringmSpinnerLabel="";

...

}

2. AddcodetotheemptyonItemSelected()callbackmethod,asshownbelow,toretrievetheuser'sselecteditemusinggetItemAtPosition,andassignittomSpinnerLabel.YoucanalsoaddacalltotheshowText()methodyoualreadyaddedtothepreviousversionoftheapp:

publicvoidonItemSelected(AdapterView<?>adapterView,Viewview,int

i,longl){

mSpinnerLabel=adapterView.getItemAtPosition(i).toString();

showText(view);

}

Tip:ByaddingtheshowText()methodtotheaboveonItemSelected()method,youhaveenabledthespinnerselectionlistenertodisplaythespinnerchoicealongwiththephonenumber,sothatyounolongerneedtheShowbuttonthatcalledtheshowText()method.

3. AddcodetotheemptyonNothingSelected()callbackmethod,asshownbelow,todisplayalogcatmessageifnothingisselected:

publicvoidonNothingSelected(AdapterView<?>adapterView){

Log.d(TAG,"onNothingSelected:");

}

TheTAGintheabovestatementisinredbecauseithasn'tbeendefined.

4. Extractthestringresourcefor"onNothingSelected:"tonothing_selected.

5. ClickTAG,clicktheredlightbulb,andchooseCreateconstantfield'TAG'fromthepop-upmenu.AndroidStudioaddsthefollowingundertheMainActivityclassdeclaration:

privatestaticfinalStringTAG=;

1. AddMainActivity.class.getSimpleName()tousethesimplenameoftheclassforTAG:

privatestaticfinalStringTAG=MainActivity.class.getSimpleName();

1. ChangetheStringshowStringstatementintheshowTextmethodtoshowboththeenteredstringandtheselectedspinneritem(mSpinnerLabel):

StringshowString=(editText.getText().toString()+"-"+mSpinnerLabel);

1. Runtheapp.

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Thespinnerappearsnexttothephoneentryfieldandshowsthefirstchoice(Home).Tappingthespinnerrevealsallthechoices,asshownontheleftsideofthefigurebelow.Afterenteringaphonenumberandchoosingaspinneritem,amessageappearsatthebottomofthescreenwiththephonenumberandtheselectedspinneritem,asshownontherightsideofthefigurebelow.(YoucanalsotaptheShowbuttontoshowboththephonenumberandthespinneritem,butsincethisisredundant,youcannowremovetheShowbutton.)

Solutioncode:

AndroidStudioproject:PhoneNumberSpinner

Task4.UseadialogforanalertrequiringadecisionYoucanprovideadialogforanalerttorequireuserstomakeadecision.Adialogisawindowthatappearsontopofthedisplayorfillsthedisplay,interruptingtheflowofactivity.

Forexample,analertdialogmightrequiretheusertoclickContinueafterreadingit,orgivetheuserachoicetoagreewithanactionbyclickingapositivebutton(suchasOKorAccept),ortodisagreebyclickinganegativebutton(suchasCancel).InAndroid,youusetheAlertDialogsubclassoftheDialogclasstoshowastandarddialogforanalert.

Tip:Usedialogssparinglyastheyinterrupttheuser'sworkflow.ReadtheDialogsdesignguideforbestdesignpractices,andDialogsintheAndroiddeveloperdocumentationforcodeexamples.

Inthispractical,youwilluseabuttontotriggerastandardalertdialog.Inarealworldapp,youmighttriggeranalertdialogbasedonsomecondition,orbasedontheusertappingsomething.

AndroidStudioproject:AlertSample

4.1Createanewprojectwithalayouttoshowanalertdialog

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Inthisexercise,you'llbuildanalertwithOKandCancelbuttons,whichwillbetriggeredbytheuserclickingabutton.

1. CreateanewprojectcalledAlertSamplebasedontheEmptyActivitytemplate.2. Opentheactivity_main.xmllayoutfile.IntheLayoutEditor,clicktheTexttabatthebottomofthescreenandchange

therootviewgrouptoRelativeLayout,asyou'vedoneinpreviousexercises.3. IftheTextViewelementincludesanylayout-constraintattributes,removethem.4. MakethefollowingchangestotheTextView:

TextViewattribute Value

android:id "@+id/top_message"

android:text "Taptotestthealert:"

5. Extracttheandroid:textstringaboveintotheresourcetap_testtomakeiteasiertotranslate.6. AddaButtonwiththefollowingattributes:

Buttonattribute Value

android:id "@+button1"

android:layout_width wrap_content

android:layout_height wrap_content

android:layout_below "@id/top_message"

android:layout_marginTop "36dp"

android:text "Alert"

android:onClick "onClickShowAlert"

7. Extracttheandroid:textstringaboveintotheresourcealert_buttontomakeiteasiertotranslate.8. Extractthedimensionvalueforandroid:layout_marginTopthesameway:Placethecursoron"36dp",pressAlt-Enter

(Option-EnterontheMac),andselectExtractdimensionresource.ThenedittheResourcenameforthevaluetobutton_top_margin.

Thedimensionresourceassignmentsarestoredinthedimens.xmlfile(underapp>res>values>dimens).Youcaneditthisfiletochangetheassignmentssothattheappcanbechangedfordifferentdisplaysizes.

4.2AddanalertdialogtothemainactivityThebuilderdesignpatternmakesiteasytocreateanobjectfromaclassthathasalotofrequiredandoptionalattributesandwouldthereforerequirealotofparameterstobuild.Withoutthispattern,youwouldhavetocreateconstructorsforcombinationsofrequiredandoptionalattributes;withthispattern,thecodeiseasiertoreadandmaintain.Formoreinformationaboutthebuilderdesignpattern,seeBuilderpattern.

Thebuilderclassisusuallyastaticmemberclassoftheclassitbuilds.YouuseAlertDialog.Buildertobuildastandardalertdialog,usingsetTitletosetitstitle,setMessagetosetitsmessage,andsetPositiveButtonandsetNegativeButtontosetitsbuttons.

Tomakethealert,youneedtomakeanobjectofAlertDialog.Builder.YouwilladdtheonClickShowAlert()method,whichmakesthisobjectasitsfirstorderofbusiness.

Note:Tokeepthisexamplesimpletounderstand,thealertdialogiscreatedintheonClickShowAlert()method.ThisoccursonlyiftheonClickShowAlert()methodiscalled,whichiswhathappenswhentheuserclicksthebutton.Thismeanstheappbuildsanewdialogonlywhenthebuttonisclicked,whichisusefulifthedialogisseenonlyrarely(whentheusertakesacertainpaththroughtheapp).However,ifthedialogappearsoften,youmaywanttobuildthedialogonceintheonCreate()method,andtheninvokethedialogintheonClickShowAlert()method.1. AddtheonClickShowAlert()methodtoMainActivity.javaasfollows:

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188

publicvoidonClickShowAlert(Viewview){

AlertDialog.BuildermyAlertBuilder=new

AlertDialog.Builder(MainActivity.this);

Note:IfAlertDialog.Builderisnotrecognizedasyouenterit,clicktheredlightbulbicon,andchoosethesupportlibraryversion(android.support.v7.app.AlertDialog)forimportingintoyouractivity.

2. SetthetitleandthemessageforthealertdialoginsideonClickShowAlert()afterthecodeinthepreviousstep:

...

//Setthedialogtitle.

myAlertBuilder.setTitle("Alert");

//Setthedialogmessage.

myAlertBuilder.setMessage("ClickOKtocontinue,orCanceltostop:");

...

3. Extractthetitleandmessageintostringresources.Thepreviouslinesofcodeshouldnowbe:

...

//Setthedialogtitle.

myAlertBuilder.setTitle(R.string.alert_title);

//Setthedialogmessage.

myAlertBuilder.setMessage(R.string.alert_message);

...

4. AddtheOKbuttontothealertwithsetPositiveButton()andusingonClickListener():

...

//Addthebuttons.

myAlertBuilder.setPositiveButton("OK",newDialogInterface.OnClickListener(){

publicvoidonClick(DialogInterfacedialog,intwhich){

//UserclickedOKbutton.

Toast.makeText(getApplicationContext(),"PressedOK",

Toast.LENGTH_SHORT).show();

}

});

...

Yousetthepositive(OK)andnegative(Cancel)buttonsusingthesetPositiveButton()andsetNegativeButton()methods.AftertheusertapstheOKbuttoninthealert,youcangrabtheuser'sselectionanduseitinyourcode.Inthisexample,youdisplayatoastmessageiftheOKbuttonisclicked.

5. Extractthestringresourcefor"OK"andfor"PressedOK".Thestatementshouldnowbe:

...

//Addthebuttons.

myAlertBuilder.setPositiveButton(R.string.ok,new

DialogInterface.OnClickListener(){

publicvoidonClick(DialogInterfacedialog,intwhich){

//UserclickedOKbutton.

Toast.makeText(getApplicationContext(),R.string.pressed_ok,

Toast.LENGTH_SHORT).show();

}

});

...

6. AddtheCancelbuttontothealertwithsetNegativeButton()andonClickListener(),displayatoastmessageifthebuttonisclicked,andthencancelthedialog:

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...

myAlertBuilder.setNegativeButton("Cancel",new

DialogInterface.OnClickListener(){

publicvoidonClick(DialogInterfacedialog,intwhich){

//Usercancelledthedialog.

Toast.makeText(getApplicationContext(),"PressedCancel",

Toast.LENGTH_SHORT).show();

}

});

...

7. Extractthestringresourcefor"Cancel"and"PressedCancel".Thestatementshouldnowbe:

...

myAlertBuilder.setNegativeButton(R.string.cancel,new

DialogInterface.OnClickListener(){

publicvoidonClick(DialogInterfacedialog,intwhich){

//Usercancelledthedialog.

Toast.makeText(getApplicationContext(),R.string.pressed_cancel,

Toast.LENGTH_SHORT).show();

}

});

...

8. Addshow(),whichcreatesandthendisplaysthealertdialog,totheendofonClickShowAlert():

...

//CreateandshowtheAlertDialog.

myAlertBuilder.show();

}

Tip:TolearnmoreaboutonClickListenerandotherlisteners,seeUserInterface:InputEvents.

9. Runtheapp.

YoushouldbeabletotaptheAlertbutton,shownontheleftsideofthefigurebelow,toseethealertdialog,showninthecenterofthefigurebelow.ThedialogshowsOKandCancelbuttons,andatoastmessageappearsshowingwhichoneyoupressed,asshownontherightsideofthefigurebelow.

Solutioncode:

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190

AndroidStudioproject:AlertSample

Task5.UseapickerforuserinputAndroidprovidesready-to-usedialogs,calledpickers,forpickingatimeoradate.Youcanusethemtoensurethatyouruserspickavalidtimeordatethatisformattedcorrectlyandadjustedtotheuser'slocaltimeanddate.Eachpickerprovidescontrolsforselectingeachpartofthetime(hour,minute,AM/PM)ordate(month,day,year).YoucanreadallaboutsettinguppickersinPickers.

Inthistaskyou'llcreateanewproject,andaddthedatepickerandtimepicker.Youwillalsolearnhowtousefragments.Afragmentisabehaviororaportionofuserinterfacewithinanactivity.It'slikeamini-activitywithinthemainactivity,withitsownownlifecycle,andit'susedforbuildingapicker.Alltheworkisdoneforyou.Tolearnaboutfragments,seeFragmentsintheAPIGuide.

Onebenefitofusingfragmentsforthepickersisthatyoucanisolatethecodesectionsformanagingthedateandthetimeforvariouslocalesthatdisplaydateandtimeindifferentways.ThebestpracticetoshowapickeristouseaninstanceofDialogFragment,whichisasubclassofFragment.ADialogFragmentdisplaysadialogwindowfloatingontopofitsactivity'swindow.Inthisexercise,you'lladdafragmentforeachpickerdialoganduseDialogFragmenttomanagethedialoglifecycle.

Tip:Anotherbenefitofusingfragmentsforthepickersisthatyoucanimplementdifferentlayoutconfigurations,suchasabasicdialogonhandset-sizeddisplaysoranembeddedpartofalayoutonlargedisplays.

5.1Createthemainactivitylayout

Tostartthistask,createthemainactivitylayouttoprovidebuttonstoaccessthetimeanddatepickers.RefertotheXMLlayoutcodebelow:

1. StartanewprojectcalledDateTimePickersusingtheEmptyActivitytemplate.2. Openactivity_main.xmltoeditthelayoutcode.3. ChangethelayouttoLinearLayoutandaddandroid:orientation="vertical"toorientthelayoutvertically.Don'tworry

abouttheappearanceofthelayoutyet.ThegoalistousealayoutthatembedsaRelativeLayoutwithinthe

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LinearLayout:4. ChangethefirstTextViewelement'stextto"Choosethedateandtime:"andextractthetexttothestringresource

choose_datetime.

TextViewattribute Oldvalue Newvalue

android:text "HelloWorld" "@string/choose_datetime"

5. Addtheandroid:textSizeattributeandenteratextsizeof20sp.Extracttheandroid:textSizedimensiontotext_size.

TextViewattribute Oldvalue Newvalue

android:textSize "@dimen/text_size"

6. AddaRelativeLayoutchildinsidetheLinearLayouttocontaintheButtonelements,andacceptthe"matchparent"defaultwidthandheight.

7. AddthefirstButtonelementwithintheRelativeLayoutwiththefollowingattributes:

FirstButtonattribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:id "@+id/button_date"

android:layout_marginTop "12dp"

android:text "Date"

android:onClick "showDatePickerDialog"

Don'tworrythattheshowDatePickerDialogreferenceisinred.Themethodhasn'tbeendefinedyet—youdefineitlater.8. Extractthestring"Date"intothestringresourcedate_button.9. Extractthedimension"12dp"forandroid:layout_marginToptobutton_top_margin.10. AddthesecondButtonelementinsidetheRelativeLayoutchildwiththefollowingattributes:

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SecondButtonattribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:id "@+id/button_time"

android:layout_marginTop "@dimen/button_top_margin"

android:layout_alignBottom "@id/button_date"

android:layout_toRightOf "@id/button_date"

android:text "Time"

android:onClick "showTimePickerDialog"

TheshowTimePickerDialogreferenceisinred.Themethodhasn'tbeendefinedyet—youdefineitlater.11. Extractthestring"Time"intothestringresourcetime_button.12. Ifyouhaven'talreadydoneso,clickthePreviewtabtoshowapreviewofthelayout.Itshouldlooklikethecodeand

figurebelow.

Solutioncodeforthemainlayout:

DependingonyourversionofAndroidStudio,yourcodewilllooksomethinglikethefollowing.

<?xmlversion="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:orientation="vertical"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.DateTimePickers.MainActivity">

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:textSize="@dimen/text_size"

android:text="@string/choose_datetime"/>

<RelativeLayout

android:layout_width="match_parent"

android:layout_height="match_parent">

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:id="@+id/button_date"

android:layout_marginTop="@dimen/button_top_margin"

android:text="@string/date_button"

android:onClick="showDatePickerDialog"/>

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:id="@+id/button_time"

android:layout_marginTop="@dimen/button_top_margin"

android:layout_alignBottom="@id/button_date"

android:layout_toRightOf="@id/button_date"

android:text="@string/time_button"

android:onClick="showTimePickerDialog"/>

</RelativeLayout>

</LinearLayout>

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5.2Createanewfragmentforthedatepicker

Inthisexercise,you'lladdafragmentforthedatepicker.Afragmentislikeamini-activitywithinthemainactivity,withitsownownlifecycle.

1. Expandapp>java>com.example.android.DateTimePickersandselectMainActivity.2. ChooseFile>New>Fragment>Fragment(Blank),andnamethefragmentDatePickerFragment.Uncheckallthree

checkboxoptionssothatyoudonotcreatealayoutXML,donotincludefragmentfactorymethods,anddonotincludeinterfacecallbacks.Youdon'tneedtocreatealayoutforastandardpicker.ClickFinishtocreatethefragment.

3. OpenDatePickerFragmentandedittheDatePickerFragmentclassdefinitiontoextendDialogFragmentandimplementDatePickerDialog.OnDateSetListenertocreateastandarddatepickerwithalistener.SeePickerformoreinformationaboutextendingDialogFragmentforadatepicker:

publicclassDatePickerFragmentextendsDialogFragment

implementsDatePickerDialog.OnDateSetListener{

AsyoutypeDialogFragmentandDatePickerDialog.OnDateSetListener,AndroidStudioautomaticallyaddsthefollowingintheimportblockatthetop:

importandroid.app.DatePickerDialog;

importandroid.support.v4.app.DialogFragment;

Inaddition,aredbulbiconappearsintheleftmarginafterafewseconds.4. ClicktheredbulbiconandchooseImplementmethodsfromthepop-upmenu.AdialogappearswithonDateSet()

alreadyselectedandthe"Insert@Override"optionchecked.ClickOKtocreatetheemptyonDateSet()method.Thismethodwillbecalledwhentheusersetsthedate.AfteraddingtheemptyonDateSet()method,AndroidStudioautomaticallyaddsthefollowingintheimportblockatthetop:

importandroid.widget.DatePicker;

TheonDateSet()method'sparametersshouldbeintyear,intmonth,andintdayOfMonth.ChangethedayOfMonthparametertodayforbrevity:

publicvoidonDateSet(DatePickerview,intyear,intmonth,intday)

5. RemovetheemptypublicconstructorforDatePickerFragment.6. ReplaceonCreateView()withonCreateDialog()thatreturnsDialog,andannotateonCreateDialog()with@NonNull

toindicatethatthereturnvalueDialogcan'tbenull—anyattempttorefertothereturnvalueDialogmustbenull-checked.

@NonNull

@Override

publicDialogonCreateDialog(BundlesavedInstanceState){

...

}

7. AddthefollowingcodetoonCreateDialog()toinitializetheyear,month,anddayfromCalendar,andreturnthedialogandthesevaluestothemainactivity.AsyouenterCalendar,specifytheimporttobejava.util.Calendar.

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@NonNull

@Override

publicDialogonCreateDialog(BundlesavedInstanceState){

//Usethecurrentdateasthedefaultdateinthepicker.

finalCalendarc=Calendar.getInstance();

intyear=c.get(Calendar.YEAR);

intmonth=c.get(Calendar.MONTH);

intday=c.get(Calendar.DAY_OF_MONTH);

//CreateanewinstanceofDatePickerDialogandreturnit.

returnnewDatePickerDialog(getActivity(),this,year,month,day);

}

SolutioncodeforDatePickerFragment:

publicclassDatePickerFragmentextendsDialogFragment

implementsDatePickerDialog.OnDateSetListener{

@NonNull

@Override

publicDialogonCreateDialog(BundlesavedInstanceState){

//Usethecurrentdateasthedefaultdateinthepicker.

finalCalendarc=Calendar.getInstance();

intyear=c.get(Calendar.YEAR);

intmonth=c.get(Calendar.MONTH);

intday=c.get(Calendar.DAY_OF_MONTH);

//CreateanewinstanceofDatePickerDialogandreturnit.

returnnewDatePickerDialog(getActivity(),this,year,month,day);

}

publicvoidonDateSet(DatePickerview,intyear,intmonth,intday){

//Dosomethingwiththedatechosenbytheuser.

}

}

5.3Createanewfragmentforthetimepicker

AddafragmenttotheDateTimePickersprojectforthetimepicker:

1. SelectMainActivityagain.2. ChooseFile>New>Fragment>Fragment(Blank),andnamethefragmentTimePickerFragment.Uncheckallthree

optionssoyoudonotcreatealayoutXML,donotincludefragmentfactorymethods,anddonotincludeinterfacecallbacks.ClickFinishtocreatethefragment.

3. OpenTimePickerFragmentandfollowthesameproceduresaswithDatePickerFragment,implementingtheonTimeSet()blankmethod,replacingonCreateView()withonCreateDialog(),andremovingtheemptypublicconstructorforTimePickerFragment.TimePickerFragmentperformsthesametasksastheDatePickerFragment,butwithtimevalues:

ItextendsDialogFragmentandimplementsTimePickerDialog.OnTimeSetListenertocreateastandardtimepickerwithalistener.SeePickerformoreinformationaboutextendingDialogFragmentforatimepicker.ItusestheonCreateDialog()methodtoinitializethehourandminutefromCalendar,andreturnsthedialogandthesevaluestothemainactivityusingthe24-hourdateformat.AsyouenterCalendar,specifytheimporttobejava.util.Calendar.ItalsodefinestheemptyonTimeSet()methodforyoutoaddcodetousethehourOfDayandminutetheuserselects.Thismethodwillbecalledwhentheusersetsthetime:

publicvoidonTimeSet(TimePickerview,

inthourOfDay,intminute){

//Dosomethingwiththetimechosenbytheuser.

}

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Note:Asyoumakethechanges,AndroidStudioautomaticallyaddsthefollowingintheimportblockatthetop:

importandroid.support.v4.app.DialogFragment;

importandroid.app.TimePickerDialog;

importandroid.widget.TimePicker;

importjava.util.Calendar;

SolutioncodeforTimePickerFragment:

publicclassTimePickerFragmentextendsDialogFragment

implementsTimePickerDialog.OnTimeSetListener{

@NonNull

@Override

publicDialogonCreateDialog(BundlesavedInstanceState){

//Usethecurrenttimeasthedefaultvaluesforthepicker.

finalCalendarc=Calendar.getInstance();

inthour=c.get(Calendar.HOUR_OF_DAY);

intminute=c.get(Calendar.MINUTE);

//CreateanewinstanceofTimePickerDialogandreturnit.

returnnewTimePickerDialog(getActivity(),this,hour,minute,

DateFormat.is24HourFormat(getActivity()));

}

publicvoidonTimeSet(TimePickerview,inthourOfDay,intminute){

//Dosomethingwiththetimechosenbytheuser.

}

}

5.4Modifythemainactivity

Whilemuchofthecodeinthemainactivitystaysthesame,youneedtoaddmethodsthatcreateinstancesofFragmentManagertomanageeachfragmentandshoweachpicker.

1. Createstringresourcesinstrings.xml:

<stringname="date_picker">datePicker</string>

<stringname="time_picker">timePicker</string>

2. OpenMainActivity.3. AddtheshowDatePickerDialog()andshowTimePickerDialog()methods,referringtothecodebelow.Itcreatesan

instanceofFragmentManagertomanagethefragmentautomatically,andtoshowthepicker.Formoreinformationaboutfragments,seeFragments.

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publicclassMainActivityextendsAppCompatActivity{

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

}

publicvoidshowDatePickerDialog(Viewv){

DialogFragmentnewFragment=newDatePickerFragment();

newFragment.show(getSupportFragmentManager(),

getString(R.string.date_picker));

}

publicvoidshowTimePickerDialog(Viewview){

DialogFragmentnewFragment=newTimePickerFragment();

newFragment.show(getSupportFragmentManager(),

getString(R.string.time_picker));

}

}

4. Runtheapp.Youshouldseethedateandtimepickersaftertappingthebuttons.

5.5Usethechosendateandtime

Inthisexerciseyou'llpassthedateandtimebacktoMainActivity,andconvertthedateandtimetostringsthatyoucanshowinatoastmessage.

1. OpenMainActivityandaddtheprocessDatePickerResult()methodsignaturethattakestheyear,month,anddayasarguments:

publicvoidprocessDatePickerResult(intyear,intmonth,intday){

}

2. AddthefollowingcodetotheprocessDatePickerResult()methodtoconvertthemonth,day,andyeartoseparatestrings:

Stringmonth_string=Integer.toString(month+1);

Stringday_string=Integer.toString(day);

Stringyear_string=Integer.toString(year);

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Tip:Themonthintegerreturnedbythedatepickerstartscountingat0forJanuary,soyouneedtoadd1toittostartshowmonthsstartingat1.

3. AddthefollowingaftertheabovecodetoconcatenatethethreestringsandincludeslashmarksfortheU.S.dateformat:

StringdateMessage=(month_string+"/"+

day_string+"/"+year_string);

4. Addthefollowingaftertheabovestatementtodisplayatoastmessage:

Toast.makeText(this,"Date:"+dateMessage,

Toast.LENGTH_SHORT).show();

5. Extractthehard-codedstring"Date:"intoastringresourcenameddate.Thisautomaticallyreplacesthehard-codedstringwithgetString(R.string.date).ThecodefortheprocessDatePickerResult()methodshouldnowlooklikethis:

publicvoidprocessDatePickerResult(intyear,intmonth,intday){

Stringmonth_string=Integer.toString(month+1);

Stringday_string=Integer.toString(day);

Stringyear_string=Integer.toString(year);

//AssigntheconcatenatedstringstodateMessage.

StringdateMessage=(month_string+"/"+

day_string+"/"+year_string);

Toast.makeText(this,getString(R.string.date)+dateMessage,

Toast.LENGTH_SHORT).show();

}

6. OpenDatePickerFragment,andaddthefollowingtotheonDateSet()methodtoinvoketheprocessDatePickerResult()methodinMainActivityandpassittheyear,month,andday:

publicvoidonDateSet(DatePickerview,intyear,intmonth,intday){

//SettheactivitytotheMainActivity.

MainActivityactivity=(MainActivity)getActivity();

//InvokeMainActivity'sprocessDatePickerResult()method.

activity.processDatePickerResult(year,month,day);

}

YouusegetActivity()which,whenusedinafragment,returnstheactivitythefragmentiscurrentlyassociatedwith.Youneedthisbecauseyoucan'tcallamethodinMainActivitywithoutthecontextofMainActivity(youwouldhavetouseanintentinstead,asyoulearnedinapreviouslesson).Theactivityinheritsthecontext,soyoucanuseitasthecontextforcallingthemethod(asinactivity.processDatePickerResult).

7. TheTimePickerFragmentusesthesamelogic.OpenMainActivityandaddtheprocessTimePickerResult()methodsignaturethattakesthehourOfDayandminuteasarguments:

publicvoidprocessTimePickerResult(inthourOfDay,intminute){

}

8. AddthefollowingcodetotheprocessTimePickerResult()methodtoconvertthehourOfDayandminutetoseparatestrings:

Stringhour_string=Integer.toString(hourOfDay);

Stringminute_string=Integer.toString(minute);

9. Addthefollowingaftertheabovecodetoconcatenatethestringsandincludeacolonforthetimeformat:

StringtimeMessage=(hour_string+":"+minute_string);

10. Addthefollowingaftertheabovestatementtodisplayatoastmessage:

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Toast.makeText(this,"Time:"+timeMessage,

Toast.LENGTH_SHORT).show();

11. Extractthehard-codedstring"Time:"intoastringresourcenamedtime.Thisautomaticallyreplacesthehard-codedstringwithgetString(R.string.time).ThecodefortheprocessDatePickerResult()methodshouldnowlooklikethis:

publicvoidprocessTimePickerResult(inthourOfDay,intminute){

//Converttimeelementsintostrings.

Stringhour_string=Integer.toString(hourOfDay);

Stringminute_string=Integer.toString(minute);

//AssigntheconcatenatedstringstotimeMessage.

StringtimeMessage=(hour_string+":"+minute_string);

Toast.makeText(this,getString(R.string.time)+timeMessage,

Toast.LENGTH_SHORT).show();

}

12. OpenTimePickerFragmentandaddthefollowingtotheonTimeSet()methodtoinvoketheprocessTimePickerResult()methodinMainActivityandpassitthehourOfDayandminute:

publicvoidonTimeSet(TimePickerview,inthourOfDay,intminute){

//SettheactivitytotheMainActivity.

MainActivityactivity=(MainActivity)getActivity();

//InvokeMainActivity'sprocessTimePickerResult()method.

activity.processTimePickerResult(hourOfDay,minute);

}

13. Youcannowruntheapp.Afterselectingthedateortime,thedateortimeappearsinatoastmessageatthebottom,

asshowninthefigurebelow.

Solutioncode:

AndroidStudioproject:DateTimePickers

Task6:UseimageviewsasbuttonsYoucanmakeaviewclickable,asabutton,byaddingtheandroid:onClickattributeintheXMLlayout.Forexample,youcanmakeanimageactlikeabuttonbyaddingandroid:onClicktotheImageView.

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Tip:Ifyouareusingmultipleimagesasclickableimages,arrangetheminaviewgroupsothattheyaregroupedtogether.

Inthistaskyou'llcreateaprototypeofanappfororderingdessertsfromacafé.AfterstartinganewprojectbasedontheBasicActivitytemplate,you'llmodifythe"HelloWorld"TextViewwithappropriatetext,andaddimagestouseforthe"Addtoorder"buttons.

6.1Startthenewproject

1. StartanewAndroidStudioprojectwiththeappnameDroidCafe.ChoosetheBasicActivitytemplate,acceptthedefaultsettings,andclickFinish.Theprojectopenswithtwolayoutsintheres>layoutfolder:activity_main.xml,andcontent_main.xml.

2. Openthecontent_main.xmllayoutfile.IntheLayoutEditor,clicktheTexttabatthebottomofthescreenandchangetherootviewgrouptoRelativeLayout,asyou'vedoneinpreviousexercises.

3. Opencontent_main.xml.IftheTextViewelementincludesanylayout-constraintattributes,removethem.Extractthe"HelloWorld"stringintheTextViewtousetheintro_textresourcename.

4. Openstrings.xmlandredefinetheintro_textresourcetousemoredescriptivetext,suchas"DroidDesserts":

<stringid="intro_text">DroidDesserts</string>

5. ChangetheTextViewinthelayouttousealargertextsizeof24spandpaddingof10dp,andaddtheandroid:idattributewiththeidsettotextintro.

6. Extractthedimensionresourcefortheandroid:paddingattributetotheresourcenamepadding_regular,andtheandroid:textSizeattributetotheresourcenametext_heading.Youwillusetheseresourcenamesinsubsequentsteps.

7. AddanotherTextViewunderthetextintroTextViewwiththefollowingattributes:

TextViewattribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:padding "@dimen/padding_regular"

android:id "@+id/choose_dessert"

android:layout_below "@id/textintro"

android:text "Chooseadessert."

8. Extractthestringresourcefortheandroid:textattributetotheresourcenamechoose_a_dessert.

6.2Addtheimages

1. Theimagesnameddonut_circle.jpg,froyo_circle.jpg,andicecream_circle.jpgareprovidedwiththestarterappsinthe4_1_P_starter_images.zipfile,whichyoucanunziponyourcomputer.Tocopytheimagestoyourproject,followthesesteps:i. Closeyourproject.ii. Copytheimagefilesintoyourproject'sdrawablefolder.Findthedrawablefolderinaprojectbyusingthispath:

project_name>app>src>main>res>drawableiii. Reopenyourproject.

2. Opencontent_main.xmlfileagainandaddanImageViewforthedonutimagetothelayoutunderthechoose_dessertview,usingthefollowingattributes:

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ImageViewattributefordonut Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:padding "@dimen/padding_regular"

android:id "@+id/donut"

android:layout_below "@id/choose_dessert"

android:contentDescription "Donutsareglazedandsprinkledwithcandy."

android:src "@drawable/donut_circle"

3. Extracttheandroid:contentDescriptionattributevaluetothestringresourcedonuts.Youwillusethisstringresourceinthenextstep.

4. AddaTextViewthatwillappearnexttothedonutimageasadescription,withthefollowingattributes:

TextViewattribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:padding "35dp"

android:layout_below "@+id/choose_dessert"

android:layout_toRightOf "@id/donut"

android:text "@string/donuts"

5. Extractthedimensionresourcefortheandroid:paddingattributetotheresourcenamepadding_wide.Youwillusethisresourcenameinsubsequentsteps.

6. AddasecondImageViewtothelayoutfortheicecreamsandwich,usingthefollowingattributes:

ImageViewattributeforice_cream Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:padding "@dimen/padding_regular"

android:id "@+id/ice_cream"

android:layout_below "@id/donut"

android:contentDescription "Icecreamsandwicheshavechocolatewafersandvanillafilling."

android:src "@drawable/icecream_circle"

7. Extracttheandroid:contentDescriptionattributevaluetothestringresourceice_cream_sandwiches.8. AddaTextViewthatwillappearnexttotheicecreamsandwichasadescription,withthefollowingattributes:

TextViewattribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:padding "@dimen/padding_wide"

android:layout_below "@+id/donut"

android:layout_toRightOf "@id/ice_cream"

android:text "@string/ice_cream_sandwiches"

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9. AddathirdImageViewtothelayoutforthefroyo,usingthefollowingattributes:

ImageViewattributeforice_cream Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:padding "@dimen/padding_regular"

android:id "@+id/froyo"

android:layout_below "@id/ice_cream"

android:contentDescription "FroYoispremiumself-servefrozenyogurt."

android:src "@drawable/froyo_circle"

10. Extracttheandroid:contentDescriptionattributevaluetothestringresourcefroyo.11. AddaTextViewthatwillappearnexttothefroyoasadescription,withthefollowingattributes:

TextViewattribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:padding "@dimen/padding_wide"

android:layout_below "@+id/ice_cream"

android:layout_toRightOf "@id/froyo"

android:text "@string/froyo"

6.3AddonClickmethodsfortheimageviews

Youcanaddtheandroid:onClickattributetoanyViewtomakeitclickableasabutton.Inthisstepyouwilladdandroid:onClicktotheimagesinthecontent_main.xmllayout.Youneedtoalsoaddamethodfortheandroid:onClickattributetocall.Themethod,forthistask,displaysatoastmessageshowingwhichimagewastapped.(Inalatertask,youwillmodifythemethodtolaunchanotheractivitycalledOrderActivity.)

1. Addthefollowingstringresourcestothestrings.xmlfileforthestringstobeshowninthetoastmessage:

<stringname="donut_order_message">Youorderedadonut.</string>

<stringname="ice_cream_order_message">Youorderedanicecreamsandwich.</string>

<stringname="froyo_order_message">YouorderedaFroYo.</string>

2. AddthefollowingdisplayToast()methodfordisplayingatoastmessage:

publicvoiddisplayToast(Stringmessage){

Toast.makeText(getApplicationContext(),message,

Toast.LENGTH_SHORT).show();

}

3. AddthefollowingshowFoodOrder()methodtotheendofMainActivity(beforetheclosingbracket).Forthistask,usethedisplayToast()methodtodisplayatoastmessage:

/**

*Displaysatoastmessageforthefoodorder

*andstartstheOrderActivityactivity.

*@parammessageMessagetodisplay.

*/

publicvoidshowFoodOrder(Stringmessage){

displayToast(message);

}

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Tip:ThefirstfourlinesareacommentintheJavadocformat,whichmakesthecodeeasiertounderstandandalsohelpsgeneratedocumentationforyourcodeifyouuseJavadoc.Itisabestpracticetoaddsuchacommenttoeverynewmethodyoucreate.Formoreinformationabouthowtowritecomments,seeHowtoWriteDocCommentsfortheJavadocTool.

AlthoughyoucouldhaveaddedthismethodinanypositionwithinMainActivity,itisbestpracticetoputyourownmethodsbelowthemethodsalreadyprovidedinMainActivitybythetemplate.

1. AddthefollowingmethodstotheendofMainActivity(youcanaddthembeforeshowFoodOrder()):

/**

*Showsamessagethatthedonutimagewasclicked.

*/

publicvoidshowDonutOrder(Viewview){

showFoodOrder(getString(R.string.donut_order_message));

}

/**

*Showsamessagethattheicecreamsandwichimagewasclicked.

*/

publicvoidshowIceCreamOrder(Viewview){

showFoodOrder(getString(R.string.ice_cream_order_message));

}

/**

*Showsamessagethatthefroyoimagewasclicked.

*/

publicvoidshowFroyoOrder(Viewview){

showFoodOrder(getString(R.string.froyo_order_message));

}

2. Addtheandroid:onClickattributetothethreeImageViewsincontent_main.xml:

<ImageView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:padding="10dp"

android:id="@+id/donut"

android:layout_below="@id/choose_dessert"

android:contentDescription="@string/donut"

android:src="@drawable/donut_circle"

android:onClick="showDonutOrder"/>

...

<ImageView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:padding="10dp"

android:id="@+id/ice_cream"

android:layout_below="@id/donut"

android:contentDescription="@string/ice_cream_sandwich"

android:src="@drawable/icecream_circle"

android:onClick="showIceCreamOrder"/>

...

<ImageView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:padding="10dp"

android:id="@+id/froyo"

android:layout_below="@id/ice_cream"

android:contentDescription="@string/froyo"

android:src="@drawable/froyo_circle"

android:onClick="showFroyoOrder"/>

3. Runtheapp.

Clickingthedonut,icecreamsandwich,orfroyoimagedisplaysatoastmessageabouttheorder,asshowninthefigurebelow.

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Task7:UseradiobuttonsRadiobuttonsareinputcontrolsthatareusefulforselectingonlyoneoptionfromasetofoptions.Youshoulduseradiobuttonsifyouwanttheusertoseeallavailableoptionsside-by-side.Ifit'snotnecessarytoshowalloptionsside-by-side,youmaywanttouseaspinnerinstead.

Laterinthispracticalyouwilladdanotheractivityandscreenlayoutforsettingthedeliveryoptionsforafoodorder,anduseradiobuttonsforthedeliverychoices.

Foranoverviewandmoresamplecodeforradiobuttons,seeRadioButtons.

7.1AddanotheractivityAsyoulearnedinapreviouslesson,anactivityrepresentsasinglescreeninyourappinwhichyourusercanperformasingle,focusedtask.Youalreadyhaveoneactivity,MainActivity.java.Youwillnowaddanotheractivityforsettingthedeliveryoptionsforanorder,anduseanexplicitintenttolaunchthesecondactivity.

1. Right-clickthecom.example.android.droidcafefolderintheleftcolumnandchooseNew>Activity>EmptyActivity.EdittheActivityNametobeOrderActivity,andtheLayoutNametobeactivity_order.Leavetheotheroptionsalone,andclickFinish.

TheOrderActivityclassshouldnowbelistedunderMainActivityinthejavafolder,andactivity_order.xmlshouldnowbelistedinthelayoutfolder.TheEmptyActivitytemplateaddedthesefiles.

2. Opentheactivity_order.xmllayoutfile.IntheLayoutEditor,clicktheTexttabatthebottomofthescreenandchangetherootviewgrouptoRelativeLayout,asyou'vedoneinpreviousexercises.

3. OpenMainActivity.ChangetheshowFoodOrder()methodtomakeanexplicitintenttostartOrderActivity:

publicvoidshowFoodOrder(Stringmessage){

displayToast(message);

Intentintent=newIntent(this,OrderActivity.class);

startActivity(intent);

}

4. Runtheapp.Clickinganimagebuttonnowlaunchesthesecondactivity,whichisablankscreen.(Thetoastmessageappearsbrieflyontheblankscreen.)

7.2Addthelayoutforradiobuttons

Tocreateeachradiobuttonoption,youwillcreateRadioButtonelementsintheactivity_order.xmllayoutfile,whichislinkedtoOrderActivity.Aftereditingthelayoutfile,thelayoutfortheradiobuttonsinOrderActivitywilllooksomethinglikethe

figurebelow,dependingonyourversionofAndroidStudio.

Sinceradiobuttonselectionsaremutuallyexclusive,youwillgroupthemtogetherinsideaRadioGroup.Bygroupingthemtogether,theAndroidsystemensuresthatonlyoneradiobuttoncanbeselectedatatime.

Note:TheorderinwhichyoulisttheRadioButtonelementsdeterminestheorderthattheyappearonthescreen.1. Openactivity_order.xml_acandaddaTextViewelementwiththeidsettoorder_intro_text:

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TextViewattribute Value

android:id "@+id/order_intro_text"

android:layout_width "match_parent"

android:layout_height "wrap_content"

android:layout_marginTop "24dp"

android:layout_marginBottom "6dp"

android:textSize "18sp"

android:text "Chooseadeliverymethod:"

2. Extractthestringresourcefor"Chooseadeliverymethod:"tobechoose_delivery_method.3. Extractthedimensionresourcesforthemarginvalues:4. "24dp"totext_margin_top5. "6dp"totext_margin_bottom6. "18sp"tointro_text_size7. AddaRadioGrouptothelayoutunderneaththeTextViewyoujustadded:

<RadioGroup

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:orientation="vertical"

android:layout_below="@id/order_intro_text">

</RadioGroup>

8. AddthefollowingthreeRadioButtonelementswithintheRadioGroup,usingthefollowingattributes.The"onRadioButtonClicked"entryfortheonClickattributewillbehighlighteduntilyouaddthatmethodinthenexttask.

RadioButton#1attribute Value

android:id "@+id/sameday"

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:text "Samedaymessengerservice"

android:onClick "onRadioButtonClicked"

RadioButton#2attribute Value

android:id "@+id/nextday"

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:text "Nextdaygrounddelivery"

android:onClick "onRadioButtonClicked"

RadioButton#3attribute Value

android:id "@+id/pickup"

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:text "Pickup"

android:onClick "onRadioButtonClicked"

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9. Extractthethreestringresourcesfortheandroid:textattributestothefollowingnames,sothatthestringscanbeeasilytranslated:

same_day_messenger_service

next_day_ground_delivery

pick_up

7.3Addtheradiobuttonclickhandler

Theandroid:onClickattributeforeachradiobuttonelementspecifiestheonRadioButtonClicked()methodtohandletheclickevent.Therefore,youneedtoaddanewonRadioButtonClicked()methodintheOrderActivityclass.

Ordinarilyyourappwoulddisplaysomemessageregardingwhichtypeofdeliverywaschosen.YouwillaccomplishthiswithatoastmessagebycreatingamethodcalleddisplayToast()inOrderActivity.

IntheonRadioButtonClicked()methodyouwilluseaswitchcaseblocktocheckifaradiobuttonhasbeenclicked.Attheendoftheswitchcaseblock,youwilladdadefaultstatementthatdisplaysalogmessageifnoneoftheradiobuttonswerechecked.

1. Openstrings.xmlandcreatethefollowingstringresources:i. Aresourcenamedchosenforthestring"Chosen:"(includethespaceafterthecolonandthequotationmarks).ii. Aresourcenamednothing_clickedforthestring"onRadioButtonClicked:Nothingclicked."

2. OpenOrderActivityandaddthefollowingstatementtodefineTAG_ACTIVITYforthelogmessage:

privatestaticfinalStringTAG_ACTIVITY=

OrderActivity.class.getSimpleName();

3. AddthefollowingdisplayToastmethodtoOrderActivity:

publicvoiddisplayToast(Stringmessage){

Toast.makeText(getApplicationContext(),message,

Toast.LENGTH_SHORT).show();

}

4. AddthefollowingonRadioButtonClicked()method,whichcheckstoseeifaradiobuttonhasbeenchecked,andusesaswitchcaseblocktodeterminewhichradiobuttonitemwasselected,inordertosettheappropriatemessageforthatitemtousewithdisplayToast():

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publicvoidonRadioButtonClicked(Viewview){

//Isthebuttonnowchecked?

booleanchecked=((RadioButton)view).isChecked();

//Checkwhichradiobuttonwasclicked

switch(view.getId()){

caseR.id.sameday:

if(checked)

//Samedayservice

displayToast(getString(R.string.chosen)+

getString(R.string.same_day_messenger_service));

break;

caseR.id.nextday:

if(checked)

//Nextdaydelivery

displayToast(getString(R.string.chosen)+

getString(R.string.next_day_ground_delivery));

break;

caseR.id.pickup:

if(checked)

//Pickup

displayToast(getString(R.string.chosen)+

getString(R.string.pick_up));

break;

default:

Log.d(TAG_ACTIVITY,getString(R.string.nothing_clicked));

break;

}

}

5. Runtheapp.TapanimagetoseetheOrderActivityactivity,whichshowsthedeliverychoices.Tapadeliverychoice,andyouwillseeatoastmessageatthebottomofthescreenwiththechoice,asshowninthefigurebelow.

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Introduction

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SolutioncodeAndroidStudioproject:DroidCafePart1

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:YoucanalsoperformanactiondirectlyfromthekeyboardandreplacetheReturn(Enter)keywitha"send"key,

suchasfordialingaphonenumber:

Forthischallenge,usetheandroid:imeOptionsattributefortheEditTextcomponentwiththeactionSendvalue:

android:imeOptions="actionSend"

IntheonCreate()methodforthismainactivity,youcanusesetOnEditorActionListener()tosetthelistenerfortheEditTextviewtodetectifthekeyispressed:

EditTexteditText=(EditText)findViewById(R.id.editText_main);

if(editText!=null)

editText.setOnEditorActionListener(newTextView.OnEditorActionListener(){

...

});

Forhelpsettingthelistener,see"SpecifyingtheInputAction"inHandlingKeyboardInputand"SpecifyingKeyboardActions"inTextFields.

ThenextstepistooverrideonEditorAction()andusetheIME_ACTION_SENDconstantintheEditorInfoclasstorespondtothepressedkey.Intheexamplebelow,thekeyisusedtocallthedialNumber()methodtodialthephonenumber:

@Override

publicbooleanonEditorAction(TextViewtextView,intactionId,KeyEventkeyEvent){

booleanmHandled=false;

if(actionId==EditorInfo.IME_ACTION_SEND){

dialNumber();

mHandled=true;

}

returnmHandled;

}

Tofinishthechallenge,createthedialNumber()method,whichusesanimplicitintentwithACTION_DIALtopassthephonenumbertoanotherappthatcandialthenumber.Itshouldlooklikethis:

privatevoiddialNumber(){

EditTexteditText=(EditText)findViewById(R.id.editText_main);

StringmPhoneNum=null;

if(editText!=null)mPhoneNum="tel:"+editText.getText().toString();

Log.d(TAG,"dialNumber:"+mPhoneNum);

Intentintent=newIntent(Intent.ACTION_DIAL);

intent.setData(Uri.parse(mPhoneNum));

if(intent.resolveActivity(getPackageManager())!=null){

startActivity(intent);

}else{

Log.d("ImplicitIntents","Can'thandlethis!");

}

}

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SummaryInthispractical,youlearnedhowto:

SetupXMLlayoutattributestocontrolthekeyboardforanEditTextelement:UsethetextAutoCorrectvaluefortheandroid:inputTypeattributetochangethekeyboardsothatitsuggestsspellingcorrections.UsethetextCapSentencesvaluefortheandroid:inputTypeattributetostarteachnewsentencewithacapitalletter.UsethetextPasswordvaluefortheandroid:inputTypeattributetohideapasswordwhenenteringit.UsethetextEmailAddressvaluefortheandroid:inputTypeattributetoshowanemailkeyboardratherthanastandardkeyboard.Usethephonevaluefortheandroid:inputTypeattributetoshowaphonekeypadratherthanastandardkeyboard.Challenge:Usetheandroid:imeOptionsattributewiththeactionSendvaluetoperformanactiondirectlyfromthekeyboardandreplacetheReturnkeywithanactionkey,suchasanimplicitintenttoanotherapptodialaphonenumber.

UseaSpinnerinputcontroltoprovideadrop-downmenu,andwritecodetocontrolit:UseanArrayAdaptertoassignanarrayoftextvaluesasthespinnermenuitems.ImplementtheAdapterView.OnItemSelectedListenerinterface,whichrequiresalsoaddingtheonItemSelected()andonNothingSelected()callbackmethodstoactivatethespinneranditslistener.UsetheonItemSelected()callbackmethodtoretrievetheselectediteminthespinnermenuusinggetItemAtPosition.

UseAlertDialog.Builder,asubclassofAlertDialog,tobuildastandardalertdialog,usingsetTitletosetitstitle,setMessagetosetitsmessage,andsetPositiveButtonandsetNegativeButtontosetitsbuttons.Usethestandarddateandtimepickers:

Addafragmentforadatepicker,andextendtheDialogFragmentclasstoimplementDatePickerDialog.OnDateSetListenerforastandarddatepickerwithalistener.Addafragmentforatimepicker,andextendtheDialogFragmentclasstoimplementTimePickerDialog.OnTimeSetListenerforastandardtimepickerwithalistener.ImplementtheonDateSet(),onTimeSet(),andonCreateDialog()methods.UsetheonFinishDateDialog()andonFinishTimeDialog()methodstoretrievetheselecteddateandtime.

Useimagesinaproject:Copyanimageintotheproject,anddefineanImageViewelementtouseit.Addtheandroid:onClickattributetomaketheImageViewelementsclickablelikebuttons.YoucanmakeanyViewclickablewiththeandroid:onClickattribute.

Useradiobuttons:Createasecondactivity.AddRadioButtonelementswithinaRadioGroupinthesecondactivity.Createradiobuttonhandlers.Launchthesecondactivityfromanimageclick.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

UserInputControls

LearnmoreAndroidAPIGuide,"Develop"section:

SpecifyingtheInputMethodType

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211

TextFieldsInputControlsSpinnersDialogsFragmentsInputEventsPickersDateFormatImageViewRadioButtons(UserInterfacesection)

MaterialDesignSpecification:Dialogsdesignguide

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4.2:UsinganOptionsMenuContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1:AdditemstotheoptionsmenuTask2:AddiconsformenuitemsCodingchallenge#1Task3:HandletheselectedmenuitemCodingchallenge#2SummaryRelatedconceptLearnmore

Theappbar(alsocalledtheactionbar)isadedicatedspaceatthetopofeachactivityscreen.Whenyoucreateanactivityfromatemplate(suchasBasicActivityTemplate),anappbarisautomaticallyincludedfortheactivityinaCoordinatorLayoutrootviewgroupatthetopoftheviewhierarchy.

Theoptionsmenuintheappbarprovidesnavigationtootheractivitiesintheapp,ortheprimaryoptionsthataffectusingtheappitself—butnotonesthatperformanactiononanelementonthescreen.Forexample,youroptionsmenumightprovidetheuserchoicesfornavigatingtootheractivities,suchasplacinganorder,orforactionsthathaveaglobalimpactontheapp,suchaschangingsettingsorprofileinformation.

Inthispracticalyou'lllearnaboutsettinguptheappbarandoptionsmenuinyourapp(showninthefigurebelow).

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Intheabovefigure:

1. Appbar.Theappbarincludestheapptitle,theoptionsmenu,andtheoverflowbutton.2. Optionsmenuactionicons.Thefirsttwooptionsmenuitemsappearasiconsintheappbar.3. Overflowbutton.Theoverflowbutton(threeverticaldots)opensamenuthatshowsmoreoptionsmenuitems.4. Optionsoverflowmenu.Afterclickingtheoverflowbutton,moreoptionsmenuitemsappearintheoverflowmenu.

Optionsmenuitemsappearintheoptionsoverflowmenu(seefigureabove).However,youcanplacesomeitemsasicons—asmanyascanfit—intheappbar.UsingtheappbarfortheoptionsmenumakesyourappconsistentwithotherAndroidapps,allowinguserstoquicklyunderstandhowtooperateyourappandhaveagreatexperience.

Tip:Toprovideafamiliarandconsistentuserexperience,youshouldusetheMenuAPIstopresentuseractionsandotheroptionsinyouractivities.SeeMenusfordetails.

WhatyoushouldalreadyKNOWFromthepreviouschapters,youshouldbefamiliarwithhowtodothefollowing:

CreatingandrunningappsinAndroidStudio.CreatingandeditingUIelementsusingtheLayoutEditor,enteringXMLcodedirectly,andaccessingelementsfromyourJavacode.AddingonClickfunctionalitytoabutton.

WhatyouwillLEARNAddingmenuitemstotheoptionsmenu.Addingiconsforitemsintheoptionsmenu.Settingmenuitemstoshowintheactionbar.Addingtheeventhandlersformenuitemclicks.

WhatyouwillDOContinueaddingfeaturestotheDroidCafeprojectfromthepreviouspractical.Addmenuitemstotheoptionsmenu.Addiconsformenuitemstoappearintheactionbar.Connectmenuitemclickstoeventhandlersthatprocesstheclickevents.

AppoverviewInthepreviouspracticalyoucreatedanappcalledDroidCafe,showninthefigurebelow,usingtheBasicActivitytemplate.Thistemplatealsoprovidesaskeletaloptionsmenuintheappbaratthetopofthescreen.Youwilllearnhowto:

Setuptheappbar.Modifytheoptionsmenu.Addiconsforsomeofthemenuitems.Showtheiconforthemenuitemintheappbarratherthantheoverflowmenu.Showtheitemintheoverflowmenu,dependingonthescreensizeandorientation.

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Forthisexerciseyouareusingthev7appcompatsupportlibrary'sToolbarasanappbar.Thereareotherwaystoimplementanappbar.Forexample,somethemessetupanActionBarasanappbarbydefault.ButusingtheappcompatToolbarmakesiteasytosetupanappbarthatworksonthewidestrangeofdevices,andalsogivesyouroomtocustomizeyourappbarlateronasyourappdevelops.

Toreadmoreaboutdesignconsiderationsforusingtheappbar,seeAppBarintheMaterialDesignspecification.

Tostarttheprojectfromwhereyouleftoffinthepreviouspractical,download:

AndroidStudioproject:DroidCafePart1

Task1.AdditemstotheoptionsmenuYouwillopentheDroidCafeprojectfromthepreviouspractical,andaddmenuitemstotheoptionsmenuintheappbaratthetopofthescreen.

1.1Examinetheappbarcode1. OpentheDroidCafeprojectfromthepreviouspractical.Theprojectincludesthefollowinglayoutfilesintheres>

layoutfolder:

i. activity_main.xml:ThemainlayoutforMainActivity,thefirstscreentheusersees.

ii. content_main.xml:ThelayoutforthecontentoftheMainActivityscreen,which(asyouwillseeshortly)isincludedwithinactivity_main.xml.

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215

iii. activity_order.xml:ThelayoutforOrderActivity,whichyouaddedinthepreviouspractical.

2. Opencontent_main.xml.Inthepreviouspractical,youaddedTextViewsandImageViewstotherootviewgroup(whichyouchangedtoRelativeLayout).

ThelayoutbehaviorfortheRelativeLayoutissetto@string/appbar_scrolling_view_behavior,whichcontrolsthescrollingbehaviorofthescreeninrelationtotheappbaratthetop.Right-click(Control-click)thisstringresourceandchooseGoTo>Declarationtoseethestringresource'sactualvalue,whichisdefinedinafilecalled"values.xml".ThisfileisgeneratedbyAndroidStudio,notvisibleintheProject:Androidviewandshouldnotbeedited.Theactualvalueof@string/appbar_scrolling_view_behaviorinvalues.xmlis"android.support.design.widget.AppBarLayout$ScrollingViewBehavior".

Formoreaboutscrollingbehavior,seetheAndroidDesignSupportLibraryblogentryintheAndroidDevelopersBlog.Fordesignpracticesinvolvingscrollingmenus,seeScrollingTechniquesintheMaterialDesignspecification.

3. Openactivity_main.xmltoseethemainlayout,whichusesaCoordinatorLayoutlayoutwithanembeddedAppBarLayoutlayout.TheCoordinatorLayoutandtheAppBarLayouttagsrequirefullyqualifiednamesthatspecifyandroid.support.design,whichistheAndroidDesignSupportLibrary.

AppBarLayoutisaverticalLinearLayoutwhichusestheToolbarclassinthesupportlibrary,insteadofthenativeActionBar,toimplementanappbar.Theappbarisasectionatthetopofthedisplaythatcandisplaytheactivitytitle,navigation,andotherinteractiveitems.ThenativeActionBarbehavesdifferentlydependingontheversionofAndroidrunningonthedevice.Forthisreason,ifyouareaddinganoptionsmenu,youshouldusethev7appcompatsupportlibrary'sToolbarasanappbar.UsingtheToolbarmakesiteasytosetupanappbarthatworksonthewidestrangeofdevices,andalsogivesyouroomtocustomizeyourappbarlateronasyourappdevelops.Toolbarincludesthemostrecentfeatures,andworksforanydevicethatcanusethesupportlibrary.

TheToolbarwithinthislayouthastheidtoolbar,andisalsospecified,liketheAppBarLayout,withafullyqualifiedname(android.support.v7.widget):

<android.support.design.widget.AppBarLayout

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:theme="@style/AppTheme.AppBarOverlay">

<android.support.v7.widget.Toolbar

android:id="@+id/toolbar"

android:layout_width="match_parent"

android:layout_height="?attr/actionBarSize"

android:background="?attr/colorPrimary"

app:popupTheme="@style/AppTheme.PopupOverlay"/>

</android.support.design.widget.AppBarLayout>

FormoredetailsabouttheAppBarLayoutclass,seeAppBarLayoutintheAndroidDeveloperReference.Formoredetailsabouttoolbars,seeToolbarintheAndroidDeveloperReference.

Tip:Theactivity_main.xmllayoutalsousesanincludelayoutstatementtoincludetheentirelayoutdefinedincontent_main.xml.Thisseparationoflayoutdefinitionsmakesiteasiertochangethelayout'scontentapartfromthelayout'stoolbardefinitionandcoordinatorlayout.Thisisabestpracticeforseparatingyourcontent(whichmayneedtobetranslated)fromtheformatofyourlayout.

4. Runtheapp.Noticethebaratthetopofthescreenshowingthenameoftheapp(DroidCafe).Italsoshowstheactionoverflowbutton(threeverticaldots)ontherightside.Taptheoverflowbuttontoseetheoptionsmenu,whichatthispointhasonlyonemenuoption,Settings.

5. ExaminetheAndroidManifest.xmlfile.The.MainActivityactivityissettousetheNoActionBartheme:

android:theme="@style/AppTheme.NoActionBar"

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TheNoActionBarthemeisdefinedinthestyles.xmlfile(expandapp>res>values>styles.xmltoseeit).Stylesarecoveredinanotherlesson,butyoucanseethattheNoActionBarthemesetsthewindowActionBarattributetofalse(nowindowactionbar),andthewindowNoTitleattributetotrue(notitle).

Thereasonthesevaluesaresetisbecauseyouaredefiningtheappbarinyourlayout(activity_main.xml)withAppBarLayout,ratherthanusinganActionBar.UsingoneoftheNoActionBarthemespreventstheappfromusingthenativeActionBarclasstoprovidetheappbar.ThenativeActionBarclassbehavesdifferentlydependingonwhatversionoftheAndroidsystemadeviceisusing.Bycontrast,themostrecentfeaturesareaddedtothesupportlibrary'sversionofToolbarandavailableonanydevicethatcanusethesupportlibrary.Forthisreason,youshouldusethesupportlibrary'sToolbarclasstoimplementyouractivities'appbarsinsteadofActionBar.Usingthesupportlibrary'sToolbarensuresthatyourapphasconsistentbehavioracrossthewidestrangeofdevices.

6. LookatMainActivity,whichextendsAppCompatActivityandstartswiththeonCreate()method:

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

Toolbartoolbar=(Toolbar)findViewById(R.id.toolbar);

setSupportActionBar(toolbar);

...

Aftersettingthecontentviewtotheactivity_main.xmllayout,theonCreate()methodsetstoolbartobetheToolbardefinedintheactivity_main.xmllayout.Itthencallstheactivity'ssetSupportActionBar()method,andpassestoolbartoit,settingthetoolbardefinedinactivity_main.xmlastheappbarfortheactivity.

Forbestpracticesaboutaddingtheappbartoyourapp,seeAddingtheAppBarinBestPracticesforUserInterface.

1.2Addmoremenuitemstotheoptionsmenu

YouwilladdthefollowingmenuitemstotheoptionsmenuoftheDroidCafeapp:

Order:GototheOrderActivityscreentoseethefoodorder.Status:Checkthestatusofafoodorder.Favorites:Showfavoritefoods.Contact:Contactingtherestaurant.Sinceyoudon'tneedtheexistingSettingsitem,youwillchangeSettingstoContact.

AndroidprovidesastandardXMLformattodefinemenuitems.Insteadofbuildingamenuinyouractivity'scode,youcandefineamenuandallofitsmenuitemsinanXMLmenuresource.Youcantheninflatethemenuresource(loaditasaMenuobject)inyouractivityorfragment:

1. Takealookatmenu_main.xml(expandres>menuintheProjectview).Itdefinesmenuitemswiththe<item></item>tagwithinthe<menu></menu>block.Theonlymenuitemprovidedfromthetemplateisaction_settings(theSettingschoice),whichisdefinedas:

<item

android:id="@+id/action_settings"

android:orderInCategory="100"

android:title="@string/action_settings"

app:showAsAction="never"/>

InAndroidStudio,theandroid:titleattributeshowsthestringvalue"Settings"eventhoughthestringisdefinedasaresource.AndroidStudiodisplaysthevaluesothatyoucanseeat-a-glancewhatthevalueiswithouthavingtoopenthestrings.xmlresourcefile.Ifyouclickonthisstring,itchangestoshowthestringresource"@string/action_settings".

2. Changethefollowingattributesoftheaction_settingsitemtomakeittheaction_contactitem(don'tchangetheexistingandroid:orderInCategoryattribute):

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Attribute Value

android:id "@+id/action_contact"

android:title "Contact"

app:showAsAction "never"

3. Extractthehard-codedstring"Contact"intothestringresourceaction_contact.4. Addanewmenuitemusingthe<item></item>tagwithinthe<menu></menu>block,andgivetheitemthefollowing

attributes:

Attribute Value

android:id "@+id/action_order"

android:orderInCategory "10"

android:title "Order"

app:showAsAction "never"

Theandroid:orderInCategoryattributespecifiestheorderinwhichthemenuitemsappearinthemenu,withthelowestnumberappearinghigherinthemenu.TheContactitemissetto100,whichisabignumberinordertospecifythatitshowsupatthebottomratherthanthetop.YousettheOrderitemto10,whichputsitaboveContact,andleavesplentyofroominthemenuformoreitems.

5. Extractthehard-codedstring"Order"intothestringresourceaction_order.6. Addtwomoremenuitemsthesamewaywiththefollowingattributes:

Statusitemattribute Value

android:id "@+id/action_status"

android:orderInCategory "20"

android:title "Status"

app:showAsAction "never"

Favoritesitemattribute Value

android:id "@+id/action_favorites"

android:orderInCategory "40"

android:title "Favorites"

app:showAsAction "never"

7. Extract"Status"intotheresourceaction_status,and"Favorites"intotheresourceaction_favorites.8. Youwilldisplayatoastmessagewithanactionmessagedependingonwhichmenuitemtheuserselects.Addthe

followingstringnamesandvaluesinstrings.xmlforthesemessages:

<stringname="action_order_message">YouselectedOrder.</string>

<stringname="action_status_message">YouselectedStatus.</string>

<stringname="action_favorites_message">YouselectedFavorites.</string>

<stringname="action_contact_message">YouselectedContact.</string>

9. OpenMainActivity,andchangetheifstatementintheonOptionsItemSelected()methodreplacingtheidaction_settingswiththenewidaction_order:

if(id==R.id.action_order)

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Runtheapp,andtaptheactionoverflowicon,shownontheleftsideofthefigurebelow,toseetheoptionsmenu,shownontherightsideofthefigurebelow.Youwillsoonaddcallbackstorespondtoitemsselectedfromthismenu.

Intheabovefigure:

1. Taptheoverflowiconintheappbartoseetheoptionsmenu.2. Theoptionsmenudropsdownfromtheappbar.

Noticetheorderofitemsintheoptionsmenu.Youusedtheandroid:orderInCategoryattributetospecifythepriorityofthemenuitemsinthemenu:TheOrderitemis10,followedbyStatus(20)andFavorites(40),andContactislast(100).Thefollowingtableshowsthepriorityofitemsinthemenu:

Menuitem orderInCategoryattribute

Order 10

Status 20

Favorites 40

Contact 100

Task2.AddiconsformenuitemsWheneverpossible,youwanttoshowthemostfrequentlyusedactionsusingiconsintheappbarsotheusercanclickthemwithouthavingtofirstclicktheoverflowicon.Inthistask,you'lladdiconsforsomeofthemenuitems,andshowsomeofmenuitemsintheappbaratthetopofthescreenasicons.

Inthisexample,let'sassumetheOrderandStatusactionsareconsideredthemostfrequentlyused.Favoritesisoccasionallyused,andContactistheleastfrequentlyused.Youcanseticonsfortheseactions,andspecifythefollowing:

OrderandStatusshouldalwaysbeshownintheappbar.Favoritesshouldbeshownintheappbarifitwillfit;ifnot,itshouldappearintheoverflowmenu.Contactshouldnotappearintheappbar;itshouldonlyappearintheoverflowmenu.

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2.1Addiconsformenuitems

Tospecifyiconsforactions,youneedtofirstaddtheiconsasimageassetstothedrawablefolder.

1. ExpandresintheProjectview,andright-click(orControl-click)drawable.2. ChooseNew>ImageAsset.TheConfigureImageAssetdialogappears.3. ChooseActionBarandTabItemsinthedrop-downmenu.4. Changeic_action_nametoic_order_white(fortheOrderaction).TheConfigureImageAssetscreenshouldlookas

follows(seeCreateAppIconswithImageAssetStudioforacompletedescription.)

5. Clicktheclipartimage(theAndroidlogonextto"Clipart:")toselectaclipartimageastheicon.Apageoficonsappears.ClicktheiconyouwanttousefortheOrderaction(forexample,theshoppingcarticonmaybeappropriate).

6. ChooseHOLO_DARKfromtheThemedrop-downmenu.Thissetstheicontobewhiteagainstadark-colored(orblack)background.ClickNext.

7. ClickFinishintheConfirmIconPathdialog.8. RepeattheabovestepsfortheStatusandFavoritesicons,namingthemic_status_whiteandic_favorites_white

respectively.Youmaywanttousethecircled-iiconforStatus(typicallyusedforInfo),andthehearticonforFavorites.

2.2ShowthemenuitemsasiconsintheappbarToshowmenuitemsasiconsintheappbar,usetheapp:showAsActionattributeinmenu_main.xml.Thefollowingvaluesfortheattributespecifywhetherornottheactionshouldappearintheappbarasanicon:

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"always":Alwaysappearsintheappbar.(Ifthereisn'tenoughroomitmayoverlapwithothermenuicons.)"ifRoom":Appearsintheappbarifthereisroom."never":Neverappearsintheappbar;it'stextappearsintheoverflowmenu.

Followthesestepstoshowsomeofthemenuitemsasicons:

1. Openmenu_main.xmlagain,andaddthefollowingattributestotheOrder,Status,andFavoritesitemssothatthefirsttwo(OrderandStatus)alwaysappear,andtheFavoritesitemappearsonlyifthereisroomforit:

Orderitemattribute Oldvalue Newvalue

android:icon "@drawable/ic_order_white"

app:showAsAction "never" "always"

Statusitemattribute Oldvalue Newvalue

android:icon "@drawable/ic_status_white"

app:showAsAction "never" "always"

Favoritesitemattribute Oldvalue Newvalue

android:icon "@drawable/ic_favorites_white"

app:showAsAction "never" "ifRoom"

2. Runtheapp.Youshouldnowseeatleasttwoiconsintheappbar:theiconforOrderandtheiconforStatusasshowninthefigurebelowIfyourdeviceortheemulatorisdisplayinginverticalorientation,theFavoritesandContactoptionsappearintheoverflowmenu.

3. Rotateyourdevicetothehorizontalorientation,orifyou'rerunningintheemulator,clicktheRotateLeftorRotateRighticonstorotatethedisplayintothehorizontalorientation.YoushouldthenseeallthreeiconsintheappbarforOrder,Status,andFavorites.

Tip:Howmanyactionbuttonswillfitintheappbar?Itdependsontheorientationandthesizeofthedevicescreen.Fewerbuttonsappearinaverticalorientation,asshownontheleftsideofthefigurebelow,comparedtoahorizontalorientationasshownontherightsideofthefigurebelow.Actionbuttonsmaynotoccupymorethanhalfofthemainappbar'swidth.

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Codingchallenge#1Note:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge1:Whenyouclickthefloatingactionbuttonwiththeemailiconthatappearsatthebottomofthescreen,thecodeinMainActivitydisplaysadrawerthatopensandcloses,calledasnackbar.Asnackbarprovidesfeedbackaboutanoperation—itshowsabriefmessageatthebottomofthescreenonasmartphone,orinthelowerleftcorneronlargerdevices.Formoreinformation,seeSnackbar.

Lookathowotherappsimplementthefloatingactionbutton.Forexample,theGmailappprovidesafloatingactionbuttontocreateanewemailmessage,andtheContactsappprovidesonetocreateanewcontact.Formoreinformationaboutfloatingactionbuttons,seeFloatingActionButton.

Nowthatyouknowhowtoaddiconsformenuitems,usethesametechniquetoaddanothericon,andassignthaticontothefloatingactionbutton,replacingtheemailicon.Forexample,youmightwantthefloatingactionbuttontostartachatsession;inwhichcaseyoumightwanttouseaniconshowingahuman.

Hint:Thefloatingactionbuttonisdefinedinactivity_main.xml.

Whileaddingtheicon,alsochangethetextthatappearsinthesnackbaraftertappingthefloatingactionbutton.YouwillfindthistextintheSnackbar.makestatementinthemainactivity.Extractthestringresourceforthistexttobesnackbar_text.

Task3.HandletheselectedmenuitemInthistask,you'lladdamethodtodisplayamessageaboutwhichmenuitemistapped,andusetheonOptionsItemSelected()methodtodeterminewhichmenuitemwastapped.

3.1Createamethodtodisplaythemenuchoice

1. OpenMainActivity.2. Ifyouhaven'talreadyaddedthefollowingmethod(inthepreviouslesson)fordisplayingatoastmessage,additnow:

publicvoiddisplayToast(Stringmessage){

Toast.makeText(getApplicationContext(),message,

Toast.LENGTH_SHORT).show();

}

ThedisplayToast()methodgetsthemessagefromtheappropriatestring(suchasaction_contact_message).

3.2UsetheonOptionsItemSelectedeventhandlerTheonOptionsItemSelected()methodhandlesselectionsfromtheoptionsmenu.Youwilladdaswitchcaseblocktodeterminewhichmenuitemwasselected,andwhatmessagetocreateforeachselecteditem.(Ratherthancreatingamessageforeachitem,youcouldimplementaneventhandlerforeachitemthatperformsanaction,suchasstartinganotheractivity,asshownlaterinthislesson.)

1. FindtheonOptionsItemSelected()method.Theifstatementinthemethod,providedbythetemplate,determinesifacertainmenuitemwasclicked,usingthemenuitem'sid(action_orderinthebelowexample):

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@Override

publicbooleanonOptionsItemSelected(MenuItemitem){

intid=item.getItemId();

if(id==R.id.action_order){

returntrue;

}

returnsuper.onOptionsItemSelected(item);

}

2. Replacetheifstatementandtheassignmenttoidwiththefollowingswitchcaseblockthatsetstheappropriatemessagebasedonthemenuitem'sid:

@Override

publicbooleanonOptionsItemSelected(MenuItemitem){

switch(item.getItemId()){

caseR.id.action_order:

displayToast(getString(R.string.action_order_message));

returntrue;

caseR.id.action_status:

displayToast(getString(R.string.action_status_message));

returntrue;

caseR.id.action_favorites:

displayToast(getString(R.string.action_favorites_message));

returntrue;

caseR.id.action_contact:

displayToast(getString(R.string.action_contact_message));

returntrue;

default:

//Donothing

}

returnsuper.onOptionsItemSelected(item);

}

3. Runtheapp.Youshouldnowseeadifferenttoastmessageonthescreen,asshownontherightsideofthefigurebelow,basedonwhichmenuitemyouchoose.

Intheabovefigure:

1. SelectingtheContactitemintheoptionsmenu.2. Thetoastmessagethatappears.

Solutioncode(includescodingchallenge#1)

Introduction

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AndroidStudioproject:DroidCafePart2

Codingchallenge#2Note:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge2:Inthepreviouschallenge,youchangedtheiconforthefloatingactionbuttonthatappearsatthebottomoftheMainActivityscreeninyourapp.

Forthischallenge:

1. Changetheiconforthefloatingactionbuttonagain,butthistimetoanappropriateiconforamap,suchastheworldicon.

2. InMainActivity,replacetheactiontodisplayasnackbarwithanimplicitintenttolaunchtheMapsappwhenthefloatingactionbuttonistapped.

3. Addthefollowingspecificcoordinates(forGoogleheadquarters)andthezoomlevel(12)toastringresourcecalledgoogle_mtv_coord_zoom12:

<stringname="google_mtv_coord_zoom12">geo:37.422114,-122.086744?z=12</string>

4. AddthefollowingmethodtostarttheMapsapp,whichpassestheabovestringasdatausinganimplicitintent:

publicvoiddisplayMap(){

Intentintent=newIntent();

intent.setAction(Intent.ACTION_VIEW);

//UsingthecoordinatesforGoogleheadquarters.

Stringdata=getString(R.string.google_mtv_coord_zoom12);

intent.setData(Uri.parse(data));

if(intent.resolveActivity(getPackageManager())!=null){

startActivity(intent);

}

}

Forexamplesofimplicitintents,includingopeningtheMapsapp,seeCommonImplicitIntentsongithub.

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AftertappingthefloatingactionbuttontogototheMapsapp,asshowninthefigurebelow,theusercantaptheBackbuttonbelowthescreentoreturntoyourapp.

Solutioncode(includescodingchallenge#2)AndroidStudioProject:DroidCafePart3

YouwillfinishtheDroidCafeappinthenextlesson.

SummaryInthispractical,youlearnedhowtodothefollowing:

Setupanoptionsmenuintheappbar:UsingtheBasicActivitytemplatetoautomaticallysetuptheoptionsmenuandafloatingactionbutton.Using@string/appbar_scrolling_view_behaviortoprovidethestandardscrollingbehavioroftheappbar'soptionsmenu.UsingaCoordinatorLayoutviewgroupwiththeAppBarLayoutclasstocreateanoptionsmenuintheappbar.UsinganincludelayoutstatementinanXMLlayoutfiletoincludeanentirelayoutdefinedinanotherXMLfile.UsingtheNoActionBarthemetopreventtheappfromusingthenativeActionBarclassattributesfortheappbar,inordertosetthewindowActionBarattributetofalse(nowindowactionbar),andthewindowNoTitleattributetotrue(notitle).Usinganactivity'sonCreate()methodtocalltheactivity'ssetSupportActionBar()methodtosetthetoolbardefinedinthelayoutastheappbarfortheactivity.DefiningamenuandallitsitemsinanXMLmenuresource,andtheninflatingthemenuresourceinanactivityor

Introduction

225

fragmenttoloaditasaMenuobject.Usingtheandroid:orderInCategoryattributetospecifytheorderinwhichthemenuitemsappearinthemenu,withthelowestnumberappearinghigherinthemenu.Usingtheapp:showAsActionattributetoshowmenuitemsasiconsintheappbar.Addingeventhandlersforoptionsmenuitems,andusingtheonOptionsItemSelected()methodtoretrievetheselectionfromtheoptionsmenu.

Useiconsinaproject:Addingiconstoaprojectandusingthemtoshowmenuitemsintheappbar.Challenge:Changingtheiconforafloatingactionbutton,andchangingtheSnackbar.makecode.

Challenge:MakinganimplicitintenttolaunchtheMapsappwithspecificcoordinates.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

Menus

LearnmoreAndroidDeveloperReference:

AppBarLayoutToolbarMenus

AndroidDevelopersBlog:AndroidDesignSupportLibraryMaterialDesignSpec:

AppBarScrollingTechniques

BestPracticesforUserInterface:AddingtheAppBarGithub:CommonImplicitIntentsImagesandicons:

ImageAssetStudioCompareIconsforDrawablesIconsandotherdownloadableresources

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4.3:UsingtheAppBarandTabsforNavigationContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1:AddanUpbuttonforancestralnavigationTask2:UsetabnavigationwithswipeviewsCodingchallengesSummaryRelatedconceptLearnmore

Intheearlystagesofdevelopinganapp,youshoulddeterminethepathsusersshouldtakethroughyourappinordertodosomething,suchasplacinganorderorbrowsingthroughcontent.Eachpathenablesuserstonavigateacross,into,andbackoutfromthedifferenttasksandpiecesofcontentwithintheapp.

Inthispractical,you'lllearnhowtoaddanUpbutton(aleft-facingarrow)totheappbarofyourapp,asshownbelow,tonavigatefromachildscreenuptotheparentscreen.

TheUpbuttonisalwaysusedtonavigatetotheparentscreeninthehierarchy.ItdiffersfromtheBackbutton(thetriangleatthebottomofthescreen),whichprovidesnavigationtowhateverscreentheuserviewedpreviously.

Thispracticalalsointroducestabnavigation,inwhichtabsappearacrossthetopofascreen,providingnavigationtootherscreens.Tabnavigationisaverypopularsolutionforlateralnavigationfromonechildscreentoanotherchildscreenthatisasibling,asshowninthediagrambelow.TabsprovidenavigationtoandfromthesiblingscreensTopStories,TechNews,andCookingwithouthavingtonavigateuptotheparent.Tabscanalsoprovidenavigationtoandfromstories,whicharesiblingscreensundertheTopStoriesparent.

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Tabsaremostappropriateforfourorfewersiblingscreens.Theusercantapatabtoseeadifferentscreen,orswipeleftorrighttoseeadifferentscreen.

Intheabovefigure:

1. Lateralnavigationfromonecategoryscreentoanother2. Lateralnavigationfromonestoryscreentoanother

WhatyoushouldalreadyKNOWFromthepreviouschapters,youshouldbeableto:

CreateandrunappsinAndroidStudio.CreateandeditUIelementsusingtheLayoutEditor,enteringXMLcodedirectly,andaccessingelementsfromyourJavacode.Addmenuitemsandiconstotheoptionsmenuintheappbar.

WhatyouwillLEARNInthispractical,youwilllearnto:

AddtheUpbuttontotheappbar.Setupanappwithtabnavigationandswipeviews.

WhatyouwillDOContinueaddingfeaturestotheDroidCafeprojectfromthepreviouspractical.ProvidetheUpbuttonintheappbartonavigatetothepreviousscreenwithinanactivity.Createanewappwithtabsfornavigatingactivityscreensthatcanalsobeswiped.

Appoverview

Introduction

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InthepreviouspracticalyoucreatedanappcalledDroidCafeinthreeparts,usingtheBasicActivitytemplate.Thistemplatealsoprovidesanappbaratthetopofthescreen.YouwilllearnhowtoaddanUpbutton(aleft-facingarrow)totheappbarforupnavigationfromthesecondactivity(OrderActivity)tothemainactivity(MainActivity).ThiswillcompletetheDroidCafeapp.

Tostarttheprojectfromwhereyouleftoffinthepreviouspractical,downloadtheAndroidStudioprojectDroidCafePart3.

Thesecondappyouwillcreatefortabnavigationwillshowthreetabsbelowtheappbartonavigatetosiblingscreens.Astheusertapsatab,thescreenshowsacontentscreendependingonwhichtabistapped.Theusercanalsoswipeleftandrighttovisitthecontentscreens.SwipingviewsishandledautomaticallybytheViewPagerclass.

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Task1.AddanUpbuttonforancestralnavigationYourappshouldmakeiteasyforuserstofindtheirwaybacktotheapp'smainscreen,whichistheparentactivity.OnewaytodothisistoprovideanUpbuttonontheappbarforallactivitiesthatarechildrenoftheparentactivity.

TheUpbuttonprovidesancestral"up"navigation,enablingtheusertogoupfromachildpagetotheparentpage.TheUpbuttonistheleft-facingarrowontheleftsideoftheappbar,asshownontheleftsideofthefigurebelow.

WhentheusertouchestheUpbutton,theappnavigatestotheparentactivity.ThediagramontherightsideofthefigurebelowshowshowtheUpbuttonisusedtonavigatewithinanappbasedonthehierarchicalrelationshipsbetweenscreens.

Intheabovefigure:

1. Navigatingfromthefirst-levelsiblingstotheparent.2. Navigatingfromsecond-levelsiblingstothefirst-levelchildscreenactingasaparentscreen

Tip:TheBackbutton(thetriangleatthebottomofthescreen)differsfromtheUpbutton.TheBackbuttonprovidesnavigationtowhateverscreenyouviewedpreviously.Ifyouhaveseveralchildscreensthattheusercannavigatethroughusingalateralnavigationpattern(asdescribedinthenextsection),theBackbuttonwouldsendtheuserbacktothepreviouschildscreen,nottotheparentscreen.UseanUpbuttonifyouwanttoprovideancestralnavigationfromachildscreenbacktotheparentscreen.FormoreinformationaboutUpnavigation,seeProvidingUpNavigation.

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Asyoulearnedpreviously,whenaddingactivitiestoanapp,youcanaddUp-buttonnavigationtoachildactivitysuchasOrderActivitybydeclaringtheactivity'sparenttobeMainActivityintheAndroidManifest.xmlfile.Youcanalsosettheandroid:labelattributeforatitlefortheactivityscreen,suchas"OrderActivity":

1. Ifyoudon'talreadyhavetheDroidCafeappopenfromthepreviouspractical,downloadtheAndroidStudioprojectDroidCafePart3andrenametheprojecttoDroidCafe.

2. OpentheDroidCafeproject.3. OpenAndroidManifest.xml.4. ChangetheactivityelementforOrderActivitytothefollowing:

<activityandroid:name=".OrderActivity"

android:label="OrderActivity"

android:parentActivityName="com.example.android.

droidcafe.MainActivity">

<meta-data

android:name="android.support.PARENT_ACTIVITY"

android:value=".MainActivity"/>

</activity>

5. Extracttheandroid:labelvalue"OrderActivity"toastringresourcenamedtitle_activity_order.6. Runtheapp.

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TheOrderActivityscreennowincludestheUpbutton(highlightedinthefigurebelow)intheappbartonavigatebacktothe

parentactivity.

Solutioncode:

AndroidStudioproject:DroidCafe

Task2.UsetabnavigationwithswipeviewsWithlateralnavigation,youenabletheusertogofromonesiblingtoanother(atthesamelevelinamultitierhierarchy).Forexample,ifyourappprovidesseveralcategoriesofstories(suchasTopStories,TechNews,andCooking,asshowninthefigurebelow),youwouldwanttoprovideyouruserstheabilitytonavigatefromonecategorytothenext,withouthavingto

Introduction

232

navigatebackuptotheparentscreen.AnotherexampleoflateralnavigationistheabilitytoswipeleftorrightinaGmailconversationtoviewanewerorolderoneinthesameInbox.

Intheabovefigure:

1. Lateralnavigationfromonecategoryscreentoanother2. Lateralnavigationfromonestoryscreentoanother

Youcanimplementlateralnavigationwithtabsthatrepresenteachscreen.Tabsappearacrossthetopofascreen,asshownontheleftsideofthefigureabove,inordertoprovidenavigationtootherscreens.Tabnavigationisaverypopularsolutionforlateralnavigationfromonechildscreentoanotherchildscreenthatisasibling—inthesamepositioninthehierarchyandsharingthesameparentscreen.Tabnavigationisoftencombinedwiththeabilitytoswipechildscreensleft-to-rightandright-to-left.

TheprimaryclassusedfordisplayingtabsisTabLayoutintheAndroidDesignSupportLibrary.Itprovidesahorizontallayouttodisplaytabs.Youcanshowthetabsbelowtheappbar,andusethePagerAdapterclasstopopulatescreens"pages"insideofaViewPager.ViewPagerisalayoutmanagerthatletstheuserflipleftandrightthroughscreens.Thisisacommonpatternforpresentingdifferentscreensofcontentwithinanactivity—useanadaptertofillthecontentscreentoshowintheactivity,andalayoutmanagerthatchangesthecontentscreensdependingonwhichtabisselected.

YousupplyanimplementationofaPagerAdaptertogeneratethescreensthattheviewshows.ViewPagerismostoftenusedinconjunctionwithFragment.Byusingfragments,youhaveaconvenientwaytomanagethelifecycleofeachscreen"page".

TouseclassesintheAndroidSupportLibrary,addcom.android.support:design:xx.xx.x(inwhichxx.xx.xisthenewestversion)tothebuild.gradle(Module:app)file.

ThefollowingarestandardadaptersforusingfragmentswiththeViewPager:

FragmentPagerAdapter:Designedfornavigatingbetweensiblingscreens(pages)representingafixed,smallnumberofscreens.FragmentStatePagerAdapter:Designedforpagingacrossacollectionofscreens(pages)forwhichthenumberofscreensisundetermined.Itdestroysfragmentsastheusernavigatestootherscreens,minimizingmemoryusage.TheappforthispracticalchallengeusesFragmentStatePagerAdapter.

2.1Createthelayoutfortabnavigation

1. CreateanewprojectusingtheEmptyActivitytemplate.NametheappTabExperiment.

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2. Editthebuild.gradle(Module:app)file,andaddthefollowinglines(iftheyarenotalreadyadded)tothedependenciessection:

compile'com.android.support:design:25.0.1'

compile'com.android.support:support-v4:25.0.1'

IfAndroidStudiosuggestsaversionwithahighernumber,edittheabovelinestoupdatetheversion.Also,ifAndroidStudiosuggestsanewerversionofcompileSdkVersion,buildToolsVersion,and/ortargetSdkVersion,editthemtoupdatetheversion.

3. InordertouseaToolbarratherthananactionbarandapptitle,addthefollowingstatementstotheres>values>styles.xmlfiletohidetheactionbarandthetitle:

<stylename="AppTheme"parent="Theme.AppCompat.Light.DarkActionBar">

...

<itemname="windowActionBar">false</item>

<itemname="windowNoTitle">true</item>

</style>

4. Opentheactivity_main.xmllayoutfile.IntheLayoutEditor,clicktheTexttabatthebottomofthescreenandchangetherootviewgrouptoRelativeLayout,asyou'vedoneinpreviousexercises.

5. Intheactivity_main.xmllayout,removetheTextViewsuppliedbythetemplate,andaddaToolbar,aTabLayout,andaViewPagerwithintherootlayout.

Asyoutypetheapp:popupThemeattributeforToolbarasshownbelow,appwillbeinredifyoudidn'taddthefollowingstatementtoRelativeLayout:

<RelativeLayoutxmlns:app="http://schemas.android.com/apk/res-auto"

YoucanclickonappandpressOption-Return,andAndroidStudioautomaticallyaddsthestatement.

DependingonyourversionofAndroidStudio,yourlayoutcodewilllooksomethinglikethefollowing:

Solutioncode:

Introduction

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<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

xmlns:app="http://schemas.android.com/apk/res-auto"

android:id="@+id/activity_main"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.tabexperiment.MainActivity">

<android.support.v7.widget.Toolbar

android:id="@+id/toolbar"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_alignParentTop="true"

android:background="?attr/colorPrimary"

android:minHeight="?attr/actionBarSize"

android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"

app:popupTheme="@style/ThemeOverlay.AppCompat.Light"/>

<android.support.design.widget.TabLayout

android:id="@+id/tab_layout"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:layout_below="@id/toolbar"

android:background="?attr/colorPrimary"

android:minHeight="?attr/actionBarSize"

android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"/>

<android.support.v4.view.ViewPager

android:id="@+id/pager"

android:layout_width="match_parent"

android:layout_height="fill_parent"

android:layout_below="@id/tab_layout"/>

</RelativeLayout>

2.2Createalayoutandclassforeachfragment1. Addafragmentrepresentingeachtabbedscreen:TabFragment1,TabFragment2,andTabFragment3.Toaddeach

fragment:

i. Clickcom.example.android.tabexperimentintheprojectview.

ii. ChooseFile>New>Fragment>Fragment(Blank).

iii. NamethefragmentTabFragment1.

iv. Checkthe"CreatelayoutXML?"option,andchangetheFragmentLayoutNamefortheXMLfiletotab_fragment1.

v. Uncheckthe"Includefragmentfactorymethods?"andthe"includeinterfacecallbacks?"options.Youdon'tneedthesemethods.

vi. ClickFinish.

vii. Repeattheabovesteps,usingTabFragment2andTabFragment3forStepC,andtab_fragment2andtab_fragment3forStepD.

Eachfragment(TabFragment1,TabFragment2,andTabFragment3)iscreatedwithitsclassdefinitionsettoextendFragment.Also,eachfragmentinflatesthelayoutassociatedwiththescreen(tab_fragment1,tab_fragment2,andtab_fragment3),usingthefamiliarresource-inflatedesignpatternyoulearnedinapreviouschapterwiththeoptionsmenu.

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235

Forexample,TabFragment1lookslikethis:

publicclassTabFragment1extendsFragment{

@Override

publicViewonCreateView(LayoutInflaterinflater,

ViewGroupcontainer,BundlesavedInstanceState){

returninflater.inflate(R.layout.tab_fragment1,container,false);

}

}

AndroidStudioautomaticallyincludesthefollowingimportstatements:

importandroid.os.Bundle;

importandroid.support.v4.app.Fragment;

importandroid.view.LayoutInflater;

importandroid.view.View;

importandroid.view.ViewGroup;

2. EditeachfragmentlayoutXMLfile(tab_fragment1,tab_fragment2,andtab_fragment3):

i. ChangetheRootTagtoRelativeLayout.

ii. AddaTextViewwithtextsuchas"Thesearethetopstories".

iii. Setthetextappearancewithandroid:textAppearance="?android:attr/textAppearanceLarge".

iv. RepeattheabovestepsforeachfragmentlayoutXMLfile,enteringdifferenttextfortheTextViewinstepB.

3. ExamineeachfragmentlayoutXMLfile.Forexample,tab_fragment1shouldlooklikethis:

<?xmlversion="1.0"encoding="utf-8"?>

<RelativeLayoutxmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:layout_height="match_parent">

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="Thesearethetopstories:"

android:textAppearance="?android:attr/textAppearanceLarge"/>

</RelativeLayout>

4. InthefragmentlayoutXMLfiletab_fragment1,extractthestringfor"Thesearethetopstories:"intothestringresourcetab_1.Dothesameforthestringsintab_fragment2,andtab_fragment3.

2.3AddaPagerAdapter

Theadapter-layoutmanagerpatternletsyouprovidedifferentscreensofcontentwithinanactivity—useanadaptertofillthecontentscreentoshowintheactivity,andalayoutmanagerthatchangesthecontentscreensdependingonwhichtabisselected.

1. AddanewPagerAdapterclasstotheappthatextendsFragmentStatePagerAdapteranddefinesthenumberoftabs(mNumOfTabs):

publicclassPagerAdapterextendsFragmentStatePagerAdapter{

intmNumOfTabs;

publicPagerAdapter(FragmentManagerfm,intNumOfTabs){

super(fm);

this.mNumOfTabs=NumOfTabs;

}

}

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Whileenteringtheabovecode,AndroidStudioautomaticallyimports:

importandroid.support.v4.app.Fragment;

importandroid.support.v4.app.FragmentManager;

importandroid.support.v4.app.FragmentStatePagerAdapter;

IfFragmentManagerintheabovecodeisinred,aredlightbulbiconshouldappearwhenyouclickonit.ClickthelightbulbiconandchooseImportclass.Importchoicesappear.Selectthefollowingimportchoice:

FragmentManager(android.support.v4)

Choosingtheaboveimportsthefollowing:

importandroid.support.v4.app.FragmentManager;

Also,AndroidStudiounderlinestheclassdefinitionforPagerAdapterand,ifyouclickonPagerAdapter,displaysaredbulbicon.ClicktheiconandchooseImplementMethods,andthenclickOKtoimplementthealreadyselectedgetItem()andgetCount()methods.

2. ChangethenewlyaddedgetItem()methodtothefollowing,whichusesaswitchcaseblocktoreturnthefragmenttoshowbasedonwhichtabisclicked

@Override

publicFragmentgetItem(intposition){

switch(position){

case0:

returnnewTabFragment1();

case1:

returnnewTabFragment2();

case2:

returnnewTabFragment3();

default:

returnnull;

}

}

3. ChangethenewlyaddedgetCount()methodtothefollowingtoreturnthenumberoftabs:

@Override

publicintgetCount(){

returnmNumOfTabs;

}

2.4InflatetheToolbarandTabLayout

Sinceyouareusingtabsthatfitunderneaththeappbar,youhavesetuptheappbarandToolbarintheactivity_main.xmllayoutinthefirststepofthistask.NowyouneedtoinflatetheToolbar(usingthesamemethoddescribedinapreviouschapterabouttheoptionsmenu),andcreateaninstanceofTabLayouttopositionthetabs.

1. InflatetheToolbarintheonCreate()methodinMainActivity.java:

@Override

protectedvoidonCreate(BundlesavedInstanceState){

...

Toolbartoolbar=(Toolbar)findViewById(R.id.toolbar);

setSupportActionBar(toolbar);

//Createaninstanceofthetablayoutfromtheview.

...

}

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Intheabovecode,Toolbarisinred,andaredlightbulbiconshouldappear.ClicktheiconandchooseImportclass.Importchoicesappear.SelectToolbar(android.support.v7.widget.Toolbar),andthefollowingimportstatementappearsinyourcode:

importandroid.support.v7.widget.Toolbar;

2. Openstrings.xml,andcreatethefollowingstringresources:

<stringname="tab_label1">TopStories</string>

<stringname="tab_label2">TechNews</string>

<stringname="tab_label3">Cooking</string>

3. AttheendoftheonCreate()method,createaninstanceofthetablayoutfromthetab_layoutelementinthelayout,andsetthetextforeachtabusingaddTab():

...

//Createaninstanceofthetablayoutfromtheview.

TabLayouttabLayout=(TabLayout)findViewById(R.id.tab_layout);

//Setthetextforeachtab.

tabLayout.addTab(tabLayout.newTab().setText(R.string.tab_label1));

tabLayout.addTab(tabLayout.newTab().setText(R.string.tab_label2));

tabLayout.addTab(tabLayout.newTab().setText(R.string.tab_label3));

//Setthetabstofilltheentirelayout.

tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

//UsePagerAdaptertomanagepageviewsinfragments.

...

2.5UsePagerAdaptertomanagescreenviews

1. BelowthecodeyouaddedtotheonCreate()methodintheprevioustask,addthefollowingcodetousePagerAdaptertomanagescreen(page)viewsinthefragments:

...

//UsingPagerAdaptertomanagepageviewsinfragments.

//Eachpageisrepresentedbyitsownfragment.

//Thisisanotherexampleoftheadapterpattern.

finalViewPagerviewPager=(ViewPager)findViewById(R.id.pager);

finalPagerAdapteradapter=newPagerAdapter

(getSupportFragmentManager(),tabLayout.getTabCount());

viewPager.setAdapter(adapter);

//Settingalistenerforclicks.

...

2. AttheendoftheonCreate()method,setalistener(TabLayoutOnPageChangeListener)todetectifatabisclicked,andcreatetheonTabSelected()methodtosettheViewPagertotheappropriatetabbedscreen.Thecodeshouldlookasfollows:

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...

//Settingalistenerforclicks.

viewPager.addOnPageChangeListener(new

TabLayout.TabLayoutOnPageChangeListener(tabLayout));

tabLayout.addOnTabSelectedListener(newTabLayout.OnTabSelectedListener(){

@Override

publicvoidonTabSelected(TabLayout.Tabtab){

viewPager.setCurrentItem(tab.getPosition());

}

@Override

publicvoidonTabUnselected(TabLayout.Tabtab){

}

@Override

publicvoidonTabReselected(TabLayout.Tabtab){

}

});

}

3. Runtheapp.Tapeachtabtoseeeach"page"(screen).Youshouldalsobeabletoswipeleftandrighttovisitthedifferent"pages".

e

SolutioncodeAndroidStudioProject:TabExperiment(includingcodingchallenge1)

AndroidStudioProject:NavDrawerExperiment(codingchallenge2)

CodingchallengesNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge1:Whenyoucreatedthelayoutfortabnavigationinthefirststepofthepreviouslesson,youestablishedaToolbarfortheappbarintheactivity_main.xmllayoutfile.Addanoptionsmenutotheappbarasachallenge.

Tostart,youwillwanttocreatethemenu_main.xmlfile,andaddmenuitemsfortheoptionsmenu.Youmustaddatleastonemenuitem,suchasSettings.

YoucaninflatetheoptionsmenuintheToolbarbyaddingtheonCreateOptionsMenu()method,asyoudidinapreviouslessononusingtheoptionsmenu.

FinallyyoucandetectwhichoptionsmenuitemischeckedbyusingtheonOptionsItemSelected()method.

Challenge2:Createanewappwithanavigationdrawer.Whentheusertapsanavigationdrawerchoice,closethedraweranddisplayatoastmessageshowingwhichchoicewasselected.

Anavigationdrawerisapanelthatusuallydisplaysnavigationoptionsontheleftedgeofthescreen,asshownontherightsideofthefigurebelow.Itishiddenmostofthetime,butisrevealedwhentheuserswipesafingerfromtheleftedgeofthescreenortouchesthenavigationiconintheappbar,asshownontheleftsideofthefigurebelow.

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Intheabovefigure:

1. Navigationiconintheappbar2. Navigationdrawer3. Navigationdrawermenuitem

Tomakeanavigationdrawerinyourapp,youneedtodothefollowing:

1. Createthefollowinglayouts:Anavigationdrawerastheactivitylayout'srootview.Anavigationviewforthedraweritself.Anappbarlayoutthatwillincludeanavigationiconbutton.Acontentlayoutfortheactivitythatdisplaysthenavigationdrawer.Alayoutforthenavigationdrawerheader.

2. Populatethenavigationdrawermenuwithitemtitlesandicons.3. Setupthenavigationdraweranditemlistenersintheactivitycode.4. Handlethenavigationmenuitemselections.

Tocreateanavigationdrawerlayout,usetheDrawerLayoutAPIsavailableintheSupportLibrary.Fordesignspecifications,followthedesignprinciplesfornavigationdrawersintheNavigationDrawerdesignguide.

Toaddanavigationdrawer,useaDrawerLayoutastherootviewofyouractivity'slayout.InsidetheDrawerLayout,addoneviewthatcontainsthemaincontentforthescreen(yourprimarylayoutwhenthedrawerishidden)andanotherview,typicallyaNavigationView,thatcontainsthecontentsofthenavigationdrawer.

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Tip:Tomakeyourlayoutssimplertounderstand,usetheincludetagtoincludeanXMLlayoutwithinanotherXMLlayout.Thefigurebelowisavisualrepresentationoftheactivity_main.xmllayoutanditsincludedXMLlayouts:

Intheabovefigure:

1. DrawerLayoutistherootviewoftheactivity'slayout.2. Theincludedapp_bar_mainusesaCoordinatorLayoutasitsroot,anddefinestheappbarlayoutwithaToolbarwhich

willincludethenavigationicontoopenthedrawer.3. TheNavigationViewdefinesthenavigationdrawerlayoutanditsheader,andaddsmenuitemstoit.

SummaryAddUp-buttonnavigationtoachildactivitybydeclaringtheactivity'sparentintheAndroidManifest.xmlfile.Setuptabnavigation:

Tabsareagoodsolutionfor"lateralnavigation"betweensiblingviews.TheprimaryclassusedfortabsisTabLayoutinthedesignsupportlibrary.Youshouldusetheadapterpatternwhenpopulatingtabs(pages)withdata.AViewPagerisalayoutmanagerthatallowstheusertoflipleftandrightthroughpagesofdata.ViewPagerismostoftenusedinconjunctionwithfragments.TherearetwostandardadaptersforusingViewPager:FragmentPagerAdapterandFragmentStatePagerAdapter.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

ScreenNavigation

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LearnmoreAndroiddeveloperdocumentation:

ProvidingUpNavigationTabLayoutCreatingSwipeViewswithTabsNavigationDrawerDrawerLayoutSupportLibrary

AndroidDevelopersBlog:AndroidDesignSupportLibraryOther

AndroidHive:AndroidMaterialDesignworkingwithTabsTruiton:AndroidTabsExample–WithFragmentsandViewPager

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4.4:CreateaRecyclerViewContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppOverviewTask1.CreateandconfigureaWordListprojectTask2:CreateadatasetTask3:CreateaRecyclerViewTask4:AddonClicktolistitemsTask5:AddaFABtoinsertitemsCodingchallengeSummaryRelatedconceptLearnmore

Displayingandmanipulatingascrollablelistofsimilardataitems,asyoudidinthescrollingviewpractical,isacommonfeatureofapps.Forexample,contacts,playlists,photos,dictionaries,shoppinglists,anindexofdocuments,oralistingofsavedgamesareallexamplesofscrollablelists.

Earlierinthisclass,youusedScrollViewtoperformscrollingofotherViews.ScrollViewiseasytouse,butitisnotrecommendedforproductionuse,especiallyforlonglistsofscrollableitems.

RecyclerViewisasubclassofViewGroupandisamoreresource-efficientwaytodisplayscrollablelists.Insteadofcreatingaviewforeachitem,whetherornotit'svisible,RecyclerViewcreatesalimitednumberoflistitemsandreusesthemforvisiblecontent.

InthisseriesofpracticalsyouwilluseaRecyclerViewto:

Displayascrollablelistofitems.Addaclickhandlertoeachitem.Additemstothelistusingafloatingactionbutton(FAB),thepinkbuttoninthescreenshotbelow.Afloatingactionbuttonscanbeusedforcommonactions,orapromotedaction,thatis,anactionthatyouwanttheusertotake.

WhatyoushouldalreadyKNOWForthispracticalyoushouldbefamiliarwithhowto:

CreateaHelloWorldappwithAndroidStudio.Implementdifferentlayoutsforapps.Createandusingstringresources.AddanonClickhandlertoaview.

WhatyouwillLEARNInthispractical,youwilllearnto:

UsetheRecyclerViewclasstodisplayitemsinascrollablelist.DynamicallyadditemstotheRecyclerViewastheybecomevisiblethroughscrolling.Performanactionwhentheusertapsaspecificitem.Showafloatingactionbuttonandperformanactionwhentheusertapsit.

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WhatyouwillDOCreateanewapplicationthatusesaRecyclerViewtodisplayalistofitemsasascrollablelistandassociateclickbehaviorwiththelistitems.UseafloatingactionbuttontolettheuseradditemstotheRecyclerView.

AppOverviewThe"RecyclerView"appwilldisplayalonglistofwords.

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Tappinganitemmarksitclicked.Tappingthefloatingactionbuttonaddsanitem.Thereisnouserinputofwordsforthisapp.

Task1.CreateandconfigureanewprojectInthistask,youwillcreateandconfigureanewprojectfortheRecyclerViewsampleapp.

1.1.Createtheproject

1. StartAndroidStudioandcreateanewprojectwiththefollowingparameters:

Attribute Value

ApplicationName RecyclerView

CompanyName com.example.androidoryourowndomain

PhoneandTabletMinimumSDK API15:Android4.0.3IceCreamSandwich

Template EmptyActivity

GenerateLayoutfilebox Checked

2. Runyourapponanemulatororhardwaredevice.Youshouldseethe"RecyclerView"titleand"HelloWorld"inablankview.

1.2.AddsupportlibrariestothebuildfileInordertousetheRecyclerViewandthefloatingactionbutton(FAB),youneedtoaddtherespectiveAndroidSupportLibrariestoyourbuild.

Why:AndroidSupportlibrariesprovidebackward-compatibleversionsofAndroidframeworkAPIs,additionalUIcomponentsandasetofusefulutilities.TheRecyclerViewclassislocatedintheAndroidSupportpackage;twodependenciesmustbeincludedintheGradlebuildprocesstouseit.

Followthesestepsandrefertothescreenshot:

1. InAndroidStudio,inyournewproject,makesureyouareintheProjectpane(1)andintheAndroidview(2).2. Inthehierarchyoffiles,findtheGradleScriptsfolder(3).3. ExpandGradleScripts,ifnecessary,andopenthebuild.gradle(Module:app)file(4).

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4. Towardstheendofthebuild.gradle(Module:app)file,findthedependenciessection.5. Addthesetwodependenciesasthelasttwolinesinsidethedependenciessection:

compile'com.android.support:recyclerview-v7:23.1.1'

compile'com.android.support:design:23.1.1'

Thereisprobablyanexistinglinelikethisone,butthenumbermaybedifferent:compile'com.android.support:appcompat-v7:23.1.1'

Addyourlinesbelowthatline.Matchtheversionnumberofyourlinestotheversionnumberofthatexistingline.MakesuretheversionnumbersofallthelibrariesarethesameandmatchupwiththecompiledSdkVersionatthetopofthefile.Ifthesedon'tmatch,youwillgetabuildtimeerror.

6. Ifprompted,syncyourappnow.7. Runyourapp.Youshouldseethesame"RecyclerView"appdisplaying"HelloWorld".Ifyougetgradleerrors,sync

yourproject.Youdonotneedtoinstalladditionalplugins.

Solution:

Thisisanexampleofthedependenciessectionofthebuild.gradlefile.Yourfilemaybeslightlydifferentandyourentriesmayhaveadifferentversionnumber.

dependencies{

compilefileTree(dir:'libs',include:['*.jar'])

testCompile'junit:junit:4.12'

compile'com.android.support:appcompat-v7:23.1.1'

compile'com.android.support:recyclerview-v7:23.1.1'

compile'com.android.support:design:23.1.1'

}

Task2.Createadataset

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Beforeyoucandisplayanything,youneeddatatodisplay.Inamoresophisticatedapp,yourdatacouldcomefrominternalstorage(afile,SQLitedatabase,savedpreferences),fromanotherapp(Contacts,Photos),orfromtheinternet(cloudstorage,GoogleSheets,oranydatasourcewithanAPI).Forthisexercise,youwillsimulatedatabycreatingitinthemainactivitiesonCreate()method.

Why:Storingandretrievingdataisatopicofitsowncoveredinthedatastoragechapter.Youwillhaveanopportunitytoextendyourapptouserealdatainthatlaterlesson.

2.1.Addcodetocreatedata

Inthistaskyouwilldynamicallycreatealinkedlistoftwentywordstringsthatendinincreasingnumbers,suchthat["Word1","Word2","Word3",….].

YoumustuseaLinkedListforthispractical.Refertothesolutioncode,ifyouneedhelp.

1. OpentheMainActivity.javafile.2. AddaprivatemembervariableforthemWordListlinkedlist.3. AddanintegercountermCountvariabletotracktheword'snumber.4. AddcodethatpopulatesmWordListwithwords.Concatenatethestring"Word"withthevalueofmCount,then

increasethecount.5. Sinceyoucannotdisplaythewordsyetfortesting,addalogstatementthatverifiesthatwordsarecorrectlyaddedto

thelinkedlist.6. Runyourapptomakesuretherearenoerrors.

TheappUIhasnotchanged,butyoushouldseealistoflogmessagesinlogcat,suchas:android.example.com.wordlistD/WordList:Word1

Solution:

Classvariables:

privatefinalLinkedList<String>mWordList=newLinkedList<>();

privateintmCount=0;

IntheonCreatemethodofMainActivity:

for(inti=0;i<20;i++){

mWordList.addLast("Word"+mCount++);

Log.d("WordList",mWordList.getLast());

}

Task3.CreateaRecyclerViewInthispractical,youwilldisplaydatainaRecyclerView.SincethereareseveralpartstocreatingaworkingRecyclerView,makesureyouimmediatelyfixanyerrorsthatyouseeinAndroidStudio.

TodisplayyourdatainaRecyclerView,youneedthefollowingparts:

Data.YouwillusethemWordList.ARecyclerView.Thescrollinglistthatcontainsthelistitems.Layoutforoneitemofdata.Alllistitemslookthesame.Alayoutmanager.Thelayoutmanagerhandlestheorganization(layout)ofuserinterfacecomponentsinaview.YouhavealreadyusedtheLinearLayoutinapreviouspracticalwheretheAndroidsystemhandlesthelayoutforyou.RecyclerViewrequiresanexplicitlayoutmanagertomanagethearrangementoflistitemscontainedwithinit.Thislayoutcouldbevertical,horizontal,oragrid.YouwilluseaverticallinearlayoutmanagerprovidedbyAndroid.Anadapter.TheadapterconnectsyourdatatotheRecyclerView.Itpreparesthedatainaviewholder.Youwillcreateanadapterthatinsertsintoandupdatesyourgeneratedwordsinyourviews.

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Aviewholder.Insideyouradapter,youwillcreateaViewHolderclassthatcontainstheviewinformationfordisplayingoneitemfromtheitem'slayout.

Thediagrambelowshowstherelationshipbetweenthedata,theadapter,theviewholder,andthelayoutmanager.

Implementationstepsoverview

Toimplementthesepieces,youwillneedto:

1. CreatetheXMLlayoutforthe"RecyclerView"app(activity_main.xml).2. CreatetheXMLlayoutusedtolayoutonelistitem,whichisWordListItem(wordlist_item.xml).3. Createanadapter(WordListAdapter)withaviewholder(WordViewHolder).Implementthemethodthattakesthedata,

placesitinaviewholder,andlet'sthelayoutmanagerknowtodisplayit.4. IntheonCreatemethodofMainActivity,createaRecyclerViewandinitializeitwiththeadapterandastandardlayout

manager.Let'sdotheseoneatatime.

3.1.Createthemainlayoutinactivity_main.xmlInthepreviousapps,youusedLinearLayouttoarrangeyourviews.InordertoaccommodatetheRecyclerViewandthefloatingactionbuttonthatyouwilladdlater,youneedtouseadifferentviewgroupcalledacoordinatorlayout.CoordinatorLayoutismoreflexiblethanLinearLayoutwhenarrangingviews.Forexample,viewslikethefloatingactionbuttoncanoverlayotherviews.

Inmain_activity.xml,replacethecodecreatedbytheEmptyActivitywithcodeforaCoordinatorLayout,andthenaddaRecyclerView:

1. Openbuild.gradle(Module:app)andverifythattherecyclerviewdependencyexists.

compile'com.android.support:recyclerview-v7:24.1.1'

2. Openactivity_main.xml.3. Selectallthecodeinactivity_main.xmlandreplaceitwiththiscode:

<?xmlversion="1.0"encoding="utf-8"?>

<android.support.design.widget.CoordinatorLayout

xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical">

</android.support.design.widget.CoordinatorLayout>

4. Inspectthecodeandnotethefollowing:ThepropertiesspecifiedforthisviewgrouparethesameasforLinearLayout,becausesomebasicproperties,suchaslayout_widthandlayout_height,arerequiredforallviewsandviewgroups.BecauseCoordinatorLayoutisinthesupportlibrary,youhavetospecifythefullpathtothesupportlibrary.YouwillhavetodothesamefortheRecyclerView.

5. AddtheRecyclerViewcodeinsidetheCoordinatorLayout:

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Youneedtospecifythefullpath,becauseRecyclerViewispartofthesupportlibrary.

<android.support.v7.widget.RecyclerView>

</android.support.v7.widget.RecyclerView>

6. GiveyourRecyclerViewthefollowingproperties:

Attribute Value

android:id "@+id/recyclerview"

android:layout_width match_parent

android:layout_height match_parent

7. Runyourapp,andmakesuretherearenoerrorsdisplayedinlogcat.Youwillonlyseeablankscreen,becauseyouhaven'tputanyitemsintotheRecyclerViewyet.

Solution:

<?xmlversion="1.0"encoding="utf-8"?>

<android.support.design.widget.CoordinatorLayout

xmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical">

<android.support.v7.widget.RecyclerView

android:id="@+id/recyclerview"

android:layout_width="match_parent"

android:layout_height="match_parent">

</android.support.v7.widget.RecyclerView>

</android.support.design.widget.CoordinatorLayout>

3.2.Createthelayoutforonelistitem

Theadapterneedsthelayoutforoneiteminthelist.Alltheitemsusethesamelayout.Youneedtospecifythatlistitemlayoutinaseparatelayoutresourcefile,becauseitisusedbytheadapter,separatelyfromtheRecyclerView.

CreateasimpleworditemlayoutusingaverticalLinearLayoutwithaTextView:

1. Right-clicktheapp/res/layoutfolderandchooseNew>Layoutresourcefile.2. Namethefilewordlist_itemandclickOK.3. InTextmode,changetheLinearLayoutthatwascreatedwiththefiletomatchwiththefollowingattributes.Extract

resourcesasyougo.

Attribute Value

android:layout_width "match_parent"

android:layout_height "wrap_content"

android:orientation "vertical"

android:padding "6dp"

4. AddaTextViewforthewordtotheLinearLayout:

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Attribute Value

android:id "@+id/word"

android:layout_width "match_parent"

android:layout_height "wrap_content"

android:textSize "24sp"

android:textStyle "bold"

3.3CreateastylefromtheTextViewattributes

Youcanusestylestoallowelementstosharegroupsofdisplayattributes.AneasywaytocreateastyleistoextractthestyleofaUIelementthatyoualreadycreated.Extractthestyleinformationforthewordtextview:

1. Whileyouhavewordlist_item.xmlopen,hoverthemouseovertheTextViewsectionyoujustcreatedandRight-click>Refactor>Extract>Style.

2. IntheExtractAndroidStyledialog,Nameyourstyleword_title.Leaveallboxeschecked.ChecktheLaunch'UseStyleWherePossible'box.ClickOK.

3. Whenprompted,applythestyletotheWholeProject.4. Findandexaminetheword_titlestyleinvalues/styles.xml.5. Gobacktowordlist_item.xml.Thetextviewnowreferencesthestyleinsteadofusingindividualstylingproperties.6. Runyourapp.Sinceyouhaveremovedthedefault"HelloWorld"textview,youshouldseethe"RecyclerView"titleand

ablankview.

Solution:

<?xmlversion="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:layout_height="wrap_content"

android:orientation="vertical"

android:padding="6dp">

<TextView

android:id="@+id/word"

style="@style/word_title"/>

</LinearLayout>

3.4.CreateanadapterwithaviewholderAndroidusesadapters(fromtheAdapterclass)toconnectdatawiththeirviews.Therearemanydifferentkindsofadaptersavailable.Youcanalsowriteyourowncustomadapters.Inthistaskyouwillcreateanadapterthatassociatesyourlistofwordswithwordlistitemviews.

Toconnectdatawithviews,theadapterneedstoknowabouttheviewsintowhichitwillplacethedata.Therefore,theadaptercontainsaviewholder(fromtheViewHolderclass)thatdescribesanitemviewanditspositionwithintheRecyclerView.

InthistaskyouwillbuildanadapterwithaviewholderthatbridgesthegapbetweenthedatainyourwordlistandtheRecyclerViewthatdisplaysit.

1. Right-clickjava/com.android.example.recyclerviewandselectNew>JavaClass.2. NametheclassWordListAdapter.3. GiveWordListAdapterthefollowingsignature:

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publicclassWordListAdapterextends

RecyclerView.Adapter<WordListAdapter.WordViewHolder>{}

WordListAdapterextendsagenericadapterforRecyclerViewtouseaviewholderthatisspecificforyourappanddefinedinsideWordListAdapter.WordViewHoldershowsanerror,becauseyouhavenotdefinedityet.

4. Clickontheclassdeclaration(WordListAdapter)andthenclickontheredlightbulbontheleftsideofthepane.ChooseImplementmethods.Thisbringsupadialogboxthatasksyoutochoosewhichmethodstoimplement.SelectallthreemethodsandclickOK.Thiscreatesemptyplaceholdersforallthemethodsthatyoumustimplement.NotehowonCreateViewHolderandonBindViewHolderbothreferencetheWordViewHolder,whichhasn'tbeenimplementedyet.

3.5Createtheviewholder

1. InsidetheWordListAdapterclass,addanewWordViewHolderinnerclasswiththissignature:

classWordViewHolderextendsRecyclerView.ViewHolder{}

2. Youwillseeanerroraboutamissingdefaultconstructor.Youcanseedetailsabouttheerrorsbyhoveringyourmousecursoroverthered-underlinedsourcecodeoroveranyredhorizontallineontherightmarginoftheopen-filespane.

3. AddvariablestotheWordViewHolderinnerclassforthetextviewandtheadapter:

publicfinalTextViewwordItemView;

finalWordListAdaptermAdapter;

4. IntheinnerclassWordViewHolder,addaconstructorthatinitializestheviewholder'stextviewfromtheXMLresourcesandsetsitsadapter:

publicWordViewHolder(ViewitemView,WordListAdapteradapter){

super(itemView);

wordItemView=(TextView)itemView.findViewById(R.id.word);

this.mAdapter=adapter;

}

5. Runyourapptomakesureyouhavenoerrors.Yourwillstillseeonlyablankview.TakenoteoftheE/RecyclerView:Noadapterattached;skippinglayoutwarninginlogcat.

3.6Storingyourdataintheadapter

1. Toholdyourdataintheadapter,createaprivatelinkedlistofstringsinWordListAdapterandcallitmWordList.

privatefinalLinkedList<String>mWordList;

2. YoucannowfillinthegetItemCount()methodtoreturnthesizeofmWordList.

@Override

publicintgetItemCount(){

returnmWordList.size();

}

Next,WordListAdapterneedsaconstructorthatinitializesthewordlistfromthedata.Tocreateaviewforalistitem,theWordListAdapterneedstoinflatetheXMLforalistitem.Youusealayoutinflaterforthatjob.ALayoutInflatorreadsalayoutXMLdescriptionandconvertsitintothecorrespondingviews.

3. CreateamembervariablefortheinflaterinWordListAdapter.

privateLayoutInflatermInflater;

4. ImplementtheconstructorforWordListAdapter.Theconstructorneedstohavehaveacontextparameter,andalinkedlistofwordswiththeapp'sdata.ThemethodneedstoinstantiatealayoutinflaterformInflaterandsetmWordListto

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thepassedindata.

publicWordListAdapter(Contextcontext,LinkedList<String>wordList){

mInflater=LayoutInflater.from(context);

this.mWordList=wordList;

}

5. FillouttheonCreateViewHolder()methodwiththecodebelow.TheonCreateViewHoldermethodissimilartotheonCreatemethod.Itinflatestheitemlayout,andreturnsaviewholderwiththelayoutandtheadapter.

@Override

publicWordViewHolderonCreateViewHolder(ViewGroupparent,intviewType){

ViewmItemView=mInflater.inflate(R.layout.wordlist_item,parent,false);

returnnewWordViewHolder(mItemView,this);

}

6. FillouttheonBindViewHoldermethodwiththecodebelow.TheonBindViewHoldermethodconnectsyourdatatotheviewholder.

@Override

publicvoidonBindViewHolder(WordViewHolderholder,intposition){

StringmCurrent=mWordList.get(position);

holder.wordItemView.setText(mCurrent);

}

7. Runyourapptomakesuretherearenoerrors.Youwillstillseethe"E/RecyclerView:Noadapterattached;skippinglayout"warning.Youwillfixthatinthenexttask.

3.7.CreatetheRecyclerViewintheMainActivityNowthatyouhaveanadapterwithaviewholder,youcanfinallycreateaRecyclerViewandconnectallthepiecestodisplayyourdata.

1. OpenMainActivity.java2. AddmembervariablestoMainActivityfortheRecyclerViewandtheadapter.

privateRecyclerViewmRecyclerView;

privateWordListAdaptermAdapter;

3. IntheonCreatemethodofMainActivity,addthefollowingcodethatcreatestheRecyclerViewandconnectsitwithanadapterandthedata.Readthecodecomments!NotethatyoumustinsertthiscodeafterthemWordListinitialization.

//GetahandletotheRecyclerView.

mRecyclerView=(RecyclerView)findViewById(R.id.recyclerview);

//Createanadapterandsupplythedatatobedisplayed.

mAdapter=newWordListAdapter(this,mWordList);

//ConnecttheadapterwiththeRecyclerView.

mRecyclerView.setAdapter(mAdapter);

//GivetheRecyclerViewadefaultlayoutmanager.

mRecyclerView.setLayoutManager(newLinearLayoutManager(this));

4. Runyourapp.Youshouldseeyourlistofwordsdisplayed,andyoucanscrollthelist.

Task4.MakethelistinteractiveLookingatlistsofitemsisinteresting,butit'salotmorefunandusefulifyourusercaninteractwiththem.

ToseehowtheRecyclerViewcanrespondtouserinput,youwillprogrammaticallyattachaclickhandlertoeachitem.Whentheitemistapped,theclickhandlerisexecuted,andthatitem'stextwillchange.

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4.1.Makeitemsrespondtoclicks

1. OpentheWordListAdapter.javafile.2. ChangetheWordViewHolderclasssignaturetoimplementView.onClickListener.

classWordViewHolderextendsRecyclerView.ViewHolderimplementsView.OnClickListener

3. Clickontheclassheaderandontheredlightbulbtoimplementstubsfortherequiredmethods,whichinthiscaseisjusttheonClick()method.

4. AddthefollowingcodetothebodyoftheonClick()method.

//Getthepositionoftheitemthatwasclicked.

intmPosition=getLayoutPosition();

//UsethattoaccesstheaffectediteminmWordList.

Stringelement=mWordList.get(mPosition);

//ChangethewordinthemWordList.

mWordList.set(mPosition,"Clicked!"+element);

//Notifytheadapter,thatthedatahaschangedsoitcan

//updatetheRecyclerViewtodisplaythedata.

mAdapter.notifyDataSetChanged();

5. ConnecttheonClickListenerwiththeview.AddthiscodetotheWordViewHolderconstructor(belowthe"this.mAdapter=adapter"line):

itemView.setOnClickListener(this);

6. Runyourapp.Clickonitemstoseetheirtextchange.

Solutioncode:WordListAdapter.javaandMainActivity.java

Task5.AddaFABtoinsertitemsTherearemultiplewaysinwhichyoucanaddadditionalbehaviorstothelistandlistitems.Onewayistouseafloatingactionbutton(FAB).Forexample,inGmail,theFABisusedtocomposeanewemail.InthistaskyouwillimplementaFABtoaddanitemtothewordlist.

Why?Youhavealreadyseenthatyoucanchangethecontentoflistitems.ThelistofitemsthataRecyclerViewdisplayscanbemodifieddynamically--it'snotjustastaticlistofitems.

Forthispractical,youwillgenerateanewwordtoinsertintothelist.Foramoreusefulapplication,youwouldgetdatafromyourusers.

5.1.AddaFloatingActionButton(FAB)

TheFABisastandardcontrolfromtheMaterialDesignSpecificationandispartoftheAndroidDesignSupportLibrary.YouwilllearnmoreinthechapteraboutMaterialDesign.TheseUIcontrolshavepredefinedproperties.TocreateaFABforyourapp,addthefollowingcodeinsidethecoordinatorlayoutofactivity_main.xml.

<android.support.design.widget.FloatingActionButton

android:id="@+id/fab"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_gravity="bottom|end"

android:layout_margin="16dp"

android:clickable="true"

android:src="@drawable/ic_add_24dp"/>

Notethefollowing:

<code>@+id/fab</code>ItiscustomarytogivetheFABthe"fab"id.

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android:layout_gravity="bottom|end".TheFABiscommonlyplacedatthebottomandattheendofthereading/writingflow.android:src="@drawable/ic_add_black_24dp".IsmarkedredbyAndroidStudiobecausetheresourceismissing.

AndroidprovidesaniconlibraryforstandardAndroidicons.ic_add_black_24dpisoneofthestandardicons.Youhavetoaddittoyourdrawableresourcestouseit.

1. Right-clickyourdrawablefolder.2. SelectNew>VectorAsset3. MakesuretheAssetTypeisMaterialIcon.4. ClicktheiconbuttonnexttoIcon.5. IntheContentsectionfindthe+sign.Theresourcenameisic_add_black_24dp.6. LeaveeverythingelseuncheckedandclickNext.7. ClickFinish.8. Runyourapp.

Note:Becausethisisavectordrawing,itisstoredasanXMLfile.Vectordrawingsareautomaticallyscaled,soyoudonotneedtokeeparoundabitmapforeachscreenresolution.Learnmore:AndroidVectorAssetStudio.

5.2.AddbehaviortotheFABInthistaskyou'lladdtotheFABanonClicklistenerthatdoesthefollowing:

Addsawordtotheendofthelistofwords.Notifiestheadapterthatthedatahaschanged.Scrollstotheinserteditem.InMainActivity.java,attheendoftheonCreate()method,addthefollowingcode:

//Addafloatingactionclickhandlerforcreatingnewentries.

FloatingActionButtonfab=(FloatingActionButton)findViewById(R.id.fab);

fab.setOnClickListener(newView.OnClickListener(){

@Override

publicvoidonClick(Viewview){

intwordListSize=mWordList.size();

//AddanewwordtotheendofthewordList.

mWordList.addLast("+Word"+wordListSize);

//Notifytheadapter,thatthedatahaschangedsoitcan

//updatetheRecyclerViewtodisplaythedata.

mRecyclerView.getAdapter().notifyItemInserted(wordListSize);

//Scrolltothebottom.

mRecyclerView.smoothScrollToPosition(wordListSize);

}

});

Runyourapp.Totestyourappdothefollowing:1. Scrollthelistofwords.2. Clickonitems.3. AdditemsbyclickingontheFAB.4. Whathappensifyourotatethescreen?Youwilllearninalaterlessonhowtopreservethestateofanappwhen

thescreenisrotated.

SolutioncodeAndroidStudioproject:RecyclerView

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

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Challenge:Creatingaclicklistenerforeachiteminthelistiseasy,butitcanhurttheperformanceofyourappifyouhavealotofdata.Researchhowyoucouldimplementthismoreefficiently.Thisisanadvancedchallenge.Startbythinkingaboutitconceptually,andthensearchforanimplementationexample.

SummaryRecyclerViewisaresource-efficientwaytodisplayascrollablelistofitems.TouseRecyclerView,youassociatethedatatotheAdapter/ViewHolderthatyoucreateandtothelayoutmanagerofyourchoice.ClicklistenerscanbecreatedtodetectmouseclicksinaRecyclerView.Androidsupportlibrariescontainbackward-compatibleversionsoftheAndroidframework.Androidsupportlibrariescontainarangeofusefulutilitiesforyourapps.Builddependenciesareaddedtothebuild.gradle(Moduleapp)file.Layoutscanbespecifiedasaresourcefile.ALayoutInflaterreadsalayoutresourcefileandcreatestheViewobjectsfromthatfile.AFloatingActionButton(FAB)candynamicallymodifytheitemsinaRecyclerView.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

RecyclerView

LearnmoreCoordinatorLayoutRecyclerViewAndroidSupportLibrary.CreatingListsandCardsRecyclerViewAnimationsandBehindtheScenes(AndroidDevSummit2015)

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5.1:Drawables,Styles,andThemesContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1:CreatetheScorekeeperProjectTask2:CreateaDrawableresourceTask3:ApplystylestoyourviewsTask4:UpdatethethemefromthemenubarCodingchallengeSummaryRelatedconceptsLearnmore

Inthischapter,youwilllearnhowtoreduceyourcode,increaseitsreadabilityandeaseofmaintenancebyapplyingcommonstylestoyourviews,usedrawableresources,andapplythemestoyourapplication.

WhatyoushouldalreadyKNOWFromthepreviouschaptersyoushouldbefamiliarwithbasicconceptsoftheActivitylifecycle,andhowto:

CreateandrunappsinAndroidStudio.CreateandeditUIelementsusingtheLayoutEditor,XML,andcode.AddonClickfunctionalitytoabutton.Updateviewsatruntime.AddmenuitemswithonClickfunctionality.PassdatabetweenactivitiesusingIntents.

WhatyouwillLEARNInthispractical,youwilllearnto:

Defineastyle.Applyastyletoaview.ApplyathemetoanactivityorapplicationbothinXMLandprogrammatically.Usedrawableresources.

WhatyouwillDOCreateanewAndroidappandaddbuttonsandTextViewviewstothelayout.CreatedrawableresourcesinXMLandusethemasbackgroundsforyourbuttons.ApplystylestotheUIelementsoftheapplication.Addamenuitemthatchangesthethemeoftheapplicationtoalowcontrast"nightmode."

AppOverview

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The"Scorekeeper"applicationconsistsoftwosetsofbuttonsandtwotextviewsusedtokeeptrackofthescoreforanypoint-basedgamewithtwoplayers.

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Task1:CreateTheScorekeeperAppInthissection,youwillcreateyourAndroidStudioproject,modifythelayout,andaddonClickfunctionalitytoitsbuttons.

1.1Createthe"Scorekeeper"Project

1. StartAndroidStudioandcreateanewAndroidStudioProject.Nameyourproject"Scorekeeper".AcceptthedefaultsfortheCompanyDomainandProjectlocation.

2. AcceptthedefaultMinimumSDK.3. ChoosetheEmptyActivitytemplate.4. Acceptthedefaultnamefortheactivity,makesureGenerateLayoutFileischeckedandclickFinish.

1.2Createthelayoutforthemainactivity

Definetherootview:

1. Openthelayoutfileforthemainactivity.2. DeletetheTextViewthatsays"HelloWorld."3. ChangetherootviewtoaLinearLayoutandaddthefollowingattributes(withoutremovingtheexistingattributes):

Attribute Value

android:orientation "vertical"

Definethescorecontainers:

1. InsidetheLinearLayout,addtwoRelativeLayoutviewgroups(onetocontainthescoreforeachteam)withthefollowingattributes:

Attribute Value

android:layout_width "match_parent"

android:layout_height "0dp"

android:layout_weight "1"

Youmaybesurprisedtoseethatthelayout_heightattributeissetto0dpintheseviews.Thisisbecauseweareusingthe"layout_weight"attributetodeterminehowmuchspacetheseviewstakeupintheparentlayout.SeetheLinearLayoutDocumentationformoreinformation.

AddviewstoyourUI

1. AddtwoImageButtonviews(oneforincreasingthescoreandonefordecreasingthescore)andaTextViewfordisplayingthescoreinbetweenthebuttonstoeachRelativeLayout.

2. Addandroid:idattributestothescoreTextViewsandalloftheImageButtons.3. AddonemoreTextViewtoeachRelativeLayoutabovethescoretorepresenttheTeamNames.

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Addvectorassets

1. SelectFile>New>VectorAssettoopentheVectorAssetStudio.2. Clickontheicontochangeittoalistofmaterialiconfiles.SelecttheContentcategory.3. ChoosetheplusiconandclickOK.4. Renametheresourcefile"ic_plus"andchecktheOverridecheckboxnexttosizeoptions.5. Changethesizeoftheiconto40dpx40dp.6. ClickNextandthenFinish.7. Repeatthisprocesstoadda"minus"iconandnamethefile"ic_minus".

Addattributestoyourviews

1. Changethescoretextviewstoread"0"andtheteamtextviewstoread"Team1"and"Team2".2. Addthefollowingattributestoyourleftimagebuttons:

android:src="@drawable/ic_minus"

android:contentDescription="MinusButton"

3. Addthefollowingattributestoyourrightimagebuttons:

android:src="@drawable/ic_plus"

android:contentDescription="PlusButton"

4. Extractallofyourstringresources.ThisprocessremovesallofyourstringsfromtheJavacodeandputstheminthestring.xmlfile.Thisallowsforyourapptobeeasilylocalizedintodifferentlanguages.Tolearnhowtoextractstringresources,seetheExtractingResourcessectionintheAppendix.

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SolutionCode:

Note:Yourcodemaybealittledifferentastherearemultiplewaystoachievethesamelayout.

<?xmlversion="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

tools:context="com.example.android.scorekeeper.MainActivity">

<RelativeLayout

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1">

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentTop="true"

android:layout_centerHorizontal="true"

android:text="@string/team_1"/>

<ImageButton

android:id="@+id/decreaseTeam1"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentLeft="true"

android:layout_alignParentStart="true"

android:layout_centerVertical="true"

android:contentDescription="@string/minus_button"

android:src="@drawable/ic_minus"/>

<TextView

android:id="@+id/score_1"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_centerHorizontal="true"

android:layout_centerVertical="true"

android:text="@string/initial_count"/>

<ImageButton

android:id="@+id/increaseTeam1"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentEnd="true"

android:layout_alignParentRight="true"

android:layout_centerVertical="true"

android:contentDescription="@string/plus_button"

android:src="@drawable/ic_plus"/>

</RelativeLayout>

<RelativeLayout

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1">

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentTop="true"

android:layout_centerHorizontal="true"

android:text="@string/team_2"/>

<ImageButton

android:id="@+id/decreaseTeam2"

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android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentLeft="true"

android:layout_alignParentStart="true"

android:layout_centerVertical="true"

android:contentDescription="@string/minus_button"

android:src="@drawable/ic_minus"/>

<TextView

android:id="@+id/score_2"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_centerHorizontal="true"

android:layout_centerVertical="true"

android:text="@string/initial_count"/>

<ImageButton

android:id="@+id/increaseTeam2"

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:layout_alignParentEnd="true"

android:layout_alignParentRight="true"

android:layout_centerVertical="true"

android:contentDescription="@string/plus_button"

android:src="@drawable/ic_plus"/>

</RelativeLayout>

</LinearLayout>

1.3InitializeyourTextViewsandscorecountvariablesInordertokeeptrackofthescores,youwillneedtwothings:

Integervariablessoyoucankeeptrackofthescores.AreferencetoyourscoreTextViewsinMainActivitysoyoucanupdatethescores.IntheonCreate()methodofMainActivity,findyourscoreTextViewsbyidandassignthemtomembervariables.Createtwointegermembervariables,representingthescoreofeachteam,andinitializethemto0.

1.4ImplementtheonClickfunctionalityforyourbuttons

1. InyourMainActivityimplementtwoonClickmethods:increaseScore()anddecreaseScore().

Note:onClickmethodsallhavethesamesignature-theyreturnvoidandtakeaViewasanargument.2. TheleftbuttonsshoulddecrementthescoreTextView,whiletherightonesshouldincrementit.

SolutionCode:

Note:Youmustalsoaddtheandroid:onClickattributetoeverybuttonintheactivity_main.xmlfile.Youcanidentifywhichbuttonwasclickedbycallingview.getId()intheonClickmethods.

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/**

*MethodthathandlestheonClickofboththedecrementbuttons

*@paramviewThebuttonviewthatwasclicked

*/

publicvoiddecreaseScore(Viewview){

//GettheIDofthebuttonthatwasclicked

intviewID=view.getId();

switch(viewID){

//IfitwasonTeam1

caseR.id.decreaseTeam1:

//DecrementthescoreandupdatetheTextView

mScore1--;

mScoreText1.setText(String.valueOf(mScore1));

break;

//IfitwasTeam2

caseR.id.decreaseTeam2:

//DecrementthescoreandupdatetheTextView

mScore2--;

mScoreText2.setText(String.valueOf(mScore2));

}

}

/**

*MethodthathandlestheonClickofboththeincrementbuttons

*@paramviewThebuttonviewthatwasclicked

*/

publicvoidincreaseScore(Viewview){

//GettheIDofthebuttonthatwasclicked

intviewID=view.getId();

switch(viewID){

//IfitwasonTeam1

caseR.id.increaseTeam1:

//IncrementthescoreandupdatetheTextView

mScore1++;

mScoreText1.setText(String.valueOf(mScore1));

break;

//IfitwasTeam2

caseR.id.increaseTeam2:

//IncrementthescoreandupdatetheTextView

mScore2++;

mScoreText2.setText(String.valueOf(mScore2));

}

}

Task2:CreateaDrawableresourceYounowhaveafunctioningscorekeeperapplication!However,thelayoutisdullanddoesnotcommunicatethefunctionofthebuttons.Inordertomakeitmoreclear,thestandardgreybackgroundofthebuttonscanbechanged.

InAndroid,graphicsareoftenhandledbyaresourcecalledaDrawable.InthefollowingexerciseyouwilllearnhowtocreateacertaintypeofdrawablecalledaShapeDrawable,andapplyittoyourbuttonsasabackground.

FormoreinformationonDrawables,seeDrawableResourceDocumentation.

2.1CreateaShapeDrawable

AShapeDrawableisaprimitivegeometricshapedefinedinanxmlfilebyanumberofattributesincludingcolor,shape,paddingandmore.Itdefinesavectorgraphic,whichcanscaleupanddownwithoutlosinganydefinition.

1. Rightclickonthedrawablefolderinyourresourcesdirectory.2. ChooseNew>Drawableresourcefile.3. Namethefile"button_background"andclickOK.4. Removeallofthecodeexcept:

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<?xmlversion="1.0"encoding="utf-8"?>

5. Addthefollowingcodewhichcreatesanovalshapewithanoutline:

<shape

xmlns:android="http://schemas.android.com/apk/res/android"

android:shape="oval">

<stroke

android:width="2dp"

android:color="@color/colorPrimary"/>

</shape>

2.2Applytheshapedrawableasabackground1. Openthelayoutfileforyourmainactivity.2. Forallofthebuttons,addthedrawableasthebackground:android:background="@drawable/button_background".Note

thatthebackgroundautomaticallyscalestofitthesizeoftheview.3. Thesizeofthebuttonsneedstobesuchthatitrendersproperlyonalldevices.Changethe"layout_height"and

"layout_width"attributesforeachbuttonto70dp,whichisagoodsizeonmostdevices.Itisnotbestpracticetousehard-codeddimensions,butusingweightswithnestedlinearlayoutstoachievethedesiredsizeistoomuchdetailforthispractical.

android:layout_width="70dp"

android:layout_height="70dp"

4. Extractthedimensionresourcesoyoucanaccessitinonelocation.Forinformationonhowtodothis,seetheAppendix.

5. Runyourapp.

Task3:StyleyourviewsAsyoucontinuetoaddviewsandattributestoyourlayout,yourcodewillstarttobecomelargeandrepetitive,especiallywhenyouapplythesameattributestomanysimilarelements.Astylecanspecifycommonpropertiessuchaspadding,fontcolor,fontsize,andbackgroundcolor.Attributesthatarelayout-orientedsuchasheight,widthandrelativelocationshouldremaininthelayoutresourcefile.

Inthefollowingexercise,youwilllearnhowtocreatestylesandapplythemtomultipleviewsandlayouts,allowingcommonattributestobeupdatedsimultaneouslyfromonelocation.

Note:Stylesaremeantforattributesthatmodifythelookoftheview.Layoutparameterssuchasheight,weightandrelativelocationshouldstayinthelayoutfile.

3.1Createbuttonstyles

InAndroid,stylescaninheritpropertiesfromotherstyles.Youcandeclareaparentforyourstyleusinganoptional"parent"parameterandhasthefollowingproperties:

Anystyleattributesdefinedbytheparentstyleareautomaticallyincludedinthechildstyle.Astyleattributedefinedinboththeparentandchildstyleusesthechildstyle'sdefinition(thechildoverridestheparent).Achildstylecanincludeadditionalattributesthattheparentdoesnotdefine.

Forexample,allfourbuttonsinthisexampleshareacommonbackgrounddrawablebutwithdifferenticonsforplusandminus.Furthermore,thetwoincrementbuttonssharethesameicon,asdothetwodecrementbuttons.Youcanthereforecreate3styles:

1. Ascorebuttonstyleforallofthebuttons,whichincludesthedefaultpropertiesofanImageButtonviewandalsothe

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drawablebackground.2. Aminusbuttonstyleforthedecrementbuttons,whichinheritstheattributesofthepreviousstyleandalsoincludesthe

minusicon.3. Aplusbuttonstyleforthedecrementbuttons,againinheritingfromthescorebuttonstyleandalsoincludestheplus

icon.

Thesestylesarerepresentedinthefigurebelow.

Dothefollowing:

1. Inyourresourcesdirectory,locateandopenthe"values/styles.xml"file.Thisiswhereallofyourstylecodewillbelocated.The"AppTheme"styleisalwaysautomaticallyadded,andyoucanseethatitextendsfrom"Theme.AppCompat.Light.DarkActionBar".

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<stylename="AppTheme"parent="Theme.AppCompat.Light.DarkActionBar">

Notethe"parent"attribute,whichishowyouspecifyyourparentstyleusingXML.Thenameattribute,inthiscase"AppTheme",definesthenameofthestyle.Theparentattribute,inthiscase"Theme.AppCompat.Light.DarkActionBar",declarestheparentstyleattributeswhich"AppTheme"inherits.InthiscaseitistheAndroiddefaulttheme,withalightbackgroundandadarkactionbar.Athemeisastylethatisappliedtoanentireactivityorapplication,insteadofasingleview.Thisallowsforaconsistentstylethroughoutanentireactivityorapplication(suchasaconsistentlookandfeelfortheAppBarineverypartofyourapplication).

2. Inbetweenthe<resources>tags,addanewstylewiththefollowingattributestocreateacommonstyleforallbuttons:

Settheparentstyleto"Widget.AppCompat.Button"toretainthedefaultattributesofabutton.Addanattributethatchangesthebackgroundofthedrawabletotheoneyoucreatedintheprevioustask.

<stylename="ScoreButtons"parent="Widget.AppCompat.Button">

<itemname="android:background">@drawable/button_background</item>

</style>

3. Createthestylefortheplusbuttonsbyextendingthe"ScoreButtons"style:

<stylename="PlusButtons"parent="ScoreButtons">

<itemname="android:src">@drawable/ic_plus</item>

<itemname="android:contentDescription">@string/plus_button</item>

</style>

Note:ThecontentDescriptionattributeisforvisuallyimpairedusers.ItactsasalabelthatcertainaccessibilitydevicesusetoreadoutloudtoprovidesomecontextaboutthemeaningoftheUIelement.

4. Createthestylefortheminusbuttons:

<stylename="MinusButtons"parent="ScoreButtons">

<itemname="android:src">@drawable/ic_minus</item>

<itemname="android:contentDescription">@string/minus_button</item>

</style>

5. Inthelayoutfileforthemainactivity,removealloftheattributesthatyoudefinedinthestylesforeachbuttonandreplacethemwiththeappropriatestyle:

style="@style/MinusButtons"

style="@style/PlusButtons"

Note:Thestyleattributedoesnotusethe"android:"namespace,becauseitispartofthedefaultXMLattributes.

3.2CreateTextViewstyles

Theteamnameandscoredisplaytextviewscanalsobestyledsincetheyhavecommoncolorsandfonts.Dothefollowing:

1. AddthefollowingattributetoallTextViews:

android:textAppearance="@style/TextAppearance.AppCompat.Headline"

2. Right-clickanywhereinthefirstscoreTextViewattributesandchooseRefactor>Extract>Style…3. Namethestyle"ScoreText"andcheckthetextAppearancebox(theattributeyoujustadded)aswellastheLaunch

'UseStylesWherePossible'refactoringafterthestyleisextracted(usingthecheckboxes).Thiswillscanthelayoutfileforviewswiththesameattributesandapplythestyleforyou.Donotextracttheattributesthatarerelatedtothelayout.

4. ChooseOK.5. Makesurethescopeissettotheactivity_main.xmllayoutfileandclickOK.

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6. ApaneatthebottomofAndroidStudiowillopenifthesamestyleisfoundinotherviews.SelectDoRefactortoapplythenewstyletotheviewswiththesameattributes.

7. Runyourapp.Thereshouldbenochangeexceptthatallofyourstylingcodeisnowinyourresourcesfileandyourlayoutfileisshorter.

SolutionCode:

styles.xml

<resources>

<!--Baseapplicationtheme.-->

<stylename="AppTheme"parent="Theme.AppCompat.Light.DarkActionBar">

<!--Customizeyourthemehere.-->

<itemname="colorPrimary">@color/colorPrimary</item>

<itemname="colorPrimaryDark">@color/colorPrimaryDark</item>

<itemname="colorAccent">@color/colorAccent</item>

</style>

<stylename="ScoreButtons"parent="AppTheme">

<itemname="android:background">@drawable/button_background</item>

</style>

<stylename="PlusButtons"parent="ScoreButtons">

<itemname="android:src">@drawable/ic_plus</item>

<itemname="android:contentDescription">@string/plus_button</item>

</style>

<stylename="MinusButtons"parent="ScoreButtons">

<itemname="android:src">@drawable/ic_minus</item>

<itemname="android:contentDescription">@string/minus_button</item>

</style>

<stylename="ScoreText">

<itemname="android:textAppearance">@style/TextAppearance.AppCompat.Headline</item>

</style>

</resources>

activity_main.xml

<?xmlversion="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

xmlns:tools="http://schemas.android.com/tools"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:orientation="vertical"

android:paddingBottom="@dimen/activity_vertical_margin"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

android:weightSum="2"

tools:context="com.example.android.scorekeeper.MainActivity">

<RelativeLayout

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1">

<TextView

android:layout_height="wrap_content"

android:layout_width="wrap_content"

android:layout_alignParentTop="true"

android:layout_centerHorizontal="true"

android:text="@string/team_1"

style="@style/ScoreText"/>

<ImageButton

android:id="@+id/decreaseTeam1"

android:layout_height="@dimen/button_size"

android:layout_width="@dimen/button_size"

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android:layout_alignParentLeft="true"

android:layout_alignParentStart="true"

android:layout_centerVertical="true"

android:onClick="decreaseScore"

style="@style/MinusButtons"/>

<TextView

android:layout_height="wrap_content"

android:layout_width="wrap_content"

android:layout_centerVertical="true"

android:layout_centerHorizontal="true"

android:id="@+id/score_1"

android:text="@string/initial_count"

style="@style/ScoreText"/>

<ImageButton

android:id="@+id/increaseTeam1"

android:layout_height="@dimen/button_size"

android:layout_width="@dimen/button_size"

android:layout_alignParentRight="true"

android:layout_alignParentEnd="true"

android:layout_centerVertical="true"

android:onClick="increaseScore"

style="@style/PlusButtons"/>

</RelativeLayout>

<RelativeLayout

android:layout_width="match_parent"

android:layout_height="0dp"

android:layout_weight="1">

<TextView

android:layout_height="wrap_content"

android:layout_width="wrap_content"

android:layout_alignParentTop="true"

android:layout_centerHorizontal="true"

android:text="@string/team_2"

style="@style/ScoreText"/>

<ImageButton

android:id="@+id/decreaseTeam2"

android:layout_height="@dimen/button_size"

android:layout_width="@dimen/button_size"

android:layout_alignParentLeft="true"

android:layout_alignParentStart="true"

android:layout_centerVertical="true"

android:onClick="decreaseScore"

style="@style/MinusButtons"/>

<TextView

android:layout_height="wrap_content"

android:layout_width="wrap_content"

android:layout_centerVertical="true"

android:layout_centerHorizontal="true"

android:id="@+id/score_2"

android:text="@string/initial_count"

style="@style/ScoreText"/>

<ImageButton

android:id="@+id/increaseTeam2"

android:layout_height="@dimen/button_size"

android:layout_width="@dimen/button_size"

android:layout_alignParentRight="true"

android:layout_alignParentEnd="true"

android:layout_centerVertical="true"

android:onClick="increaseScore"

style="@style/PlusButtons"/>

</RelativeLayout>

</LinearLayout>

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3.3Updatingthestyles

Thepowerofusingstylesbecomesapparentwhenyouwanttomakechangestoseveralelementsofthesamestyle.Youcanmakethetextbigger,bolderandbrighter,andchangetheiconstothecolorofthebuttonbackgrounds.

Makethefollowingchangesinyourstyles.xmlfile:

1. Addormodifyeachofthefollowingattributesinthespecifiedstyleblock:

Attribute StyleBlock

@color/colorPrimary ScoreButtons

@style/TextAppearance.AppCompat.Display3 ScoreText

Note:ThecolorPrimaryvalueisautomaticallygeneratedbyAndroidStudiowhenyoucreatetheprojectandcanbefoundinthevalues/colors.xmlfile.TheTextAppearance.AppCompat.Display3attributeisapredefinedtextstylesuppliedbyAndroid.

2. Createanewstylecalled"TeamText"withthefollowingattribute:

<itemname="android:textAppearance">@style/TextAppearance.AppCompat.Display1</item>

3. ChangethestyleattributeoftheteamnameTextViewstothenewlycreatedTeamTextstyleinactivity_main.xml.4. Runyourapp.Withonlytheseadjustmentstothestyle.xmlfile,alloftheviewsupdatedtoreflectthechanges.

Task4:ThemesandFinalTouchesYou'veseenthatviewswithsimilarcharacteristicscanbestyledtogetherinthe"styles.xml"file.Butwhatifyouwanttodefinestylesforanentireactivity,orevenapplication?It'spossibletoaccomplishthisbyusing"Themes".TosetathemeforanActivityorsetofActivities,youneedtomodifytheAndroidManifest.xmlfile.

Inthistask,youwilladdthe"nightmode"themetoyourapp,whichwillallowtheuserstousealowcontrastversionofyourappthatiseasierontheeyesatnighttime,aswellasmakeafewpolishingtouchestotheUserInterface.

4.1Explorethemes1. IntheAndroidmanifestfile,findthe<application>tagandchangetheandroid:themeattributeto:

android:theme="@style/Theme.AppCompat.Light.NoActionBar"

Thisisapredefinedthemethatremovestheactionbarfromyouractivity.

2. Runyourapp.Thetoolbardisappears!

3. ChangethethemeoftheapplicationbacktoAppTheme,whichisachildoftheTheme.Appcompat.Light.DarkActionBarthemeascanbeseeninstyles.xml.

Toapplyathemetoanactivityinsteadoftheentireapplication,placethethemeattributeintheactivitytaginsteadoftheapplicationtag.FormoreinformationonThemesandStyles,seetheStyleandThemeGuide.

4.2AddthemebuttontothemenuOneuseforsettingathemeforyourapplicationistoprovideanalternatevisualexperienceforbrowsingatnight.Insuchconditions,itisoftenbettertohavealowcontrast,darklayout.TheAndroidframeworkprovidesathemethatisdesignedexactlyforthis:TheDayNighttheme.Thisthemehasseveralbuiltinoptionsthatallowyoutocontrolthecolorsinyourappprogrammatically:eitherbysettingittochangeautomaticallybytime,orbyusercommand.Inthisexerciseyouwilladdamenubuttonthatwilltoggletheapplicationbetweentheregularthemeanda"night-mode"theme.

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1. Rightclickonthe"res"directoryandchooseNew>Androidresourcefile.2. Namethefile"main_menu",changetheResourceTypetoMenu,andclickOK.3. Addamenuitemwiththefollowingattributes:

<item

android:id="@+id/night_mode"

android:title="@string/night_mode"/>

4. Navigateto"strings.xml"andcreatetwostringresources:

<stringname="night_mode">NightMode</string>

<stringname="day_mode">DayMode</string>

5. PressCtrl-OtoopentheOverrideMethodmenuinyourmainactivityJavafile,andselecttheonCreateOptionsMenumethodlocatedunderthe"android.app.Activity"category.ClickOK.

6. InflatethemenuyoujustcreatedwithintheonCreateOptionsMenu()method:

getMenuInflater().inflate(R.menu.main_menu,menu);

4.3Changethethemefromthemenu

TheDayNightthemeusestheAppCompatDelegateclasstosetthenightmodeoptionsinyouractivity.Tolearnmoreaboutthistheme,visitthisblogpost.

1. Inyourstyles.xmlfile,modifytheparentofAppThemeto"Theme.AppCompat.DayNight.DarkActionBar.2. OverridetheonOptionsItemSelected()methodinMainActivity,andcheckwhichmenuitemwasclicked:

@Override

publicbooleanonOptionsItemSelected(MenuItemitem){

//Checkifthecorrectitemwasclicked

if(item.getItemId()==R.id.night_mode){}

}

3. Inresponsetoaclickonthemenubutton,youcanverifythecurrentnightmodesettingbycallingAppCompatDelegate.getDefaultNightMode().

4. Ifthenightmodeisenabled,changeittothedisabledstate:

//Getthenightmodestateoftheapp

intnightMode=AppCompatDelegate.getDefaultNightMode();

//Setthethememodefortherestartedactivity

if(nightMode==AppCompatDelegate.MODE_NIGHT_YES){

AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_NO);

}

5. Otherwise,enableit:

else{

AppCompatDelegate.setDefaultNightMode(AppCompatDelegate.MODE_NIGHT_YES);

}

6. Thethemecanonlychangewhiletheactivityisbeingcreated,socallrecreate()forthethemechangetotakeeffect.7. YouronOptionsItemSelected()methodshouldreturntrue,sincetheitemclickwashandled.8. Runyourapp.The"NightMode"menuitemshouldnowtogglethethemeofyouractivity.Youmaynoticethatthelabel

foryourmenuitemalwaysreads"NightMode",whichmaybeconfusingtoyouruseriftheappisalreadyinthedarktheme.

9. AddthefollowingcodeintheonCreateOptionsMenumethod:

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@Override

publicbooleanonCreateOptionsMenu(Menumenu){

//InflatethemenufromXML

getMenuInflater().inflate(R.menu.main_menu,menu);

//Changethelabelofthemenubasedonthestateoftheapp

intnightMode=AppCompatDelegate.getDefaultNightMode();

if(nightMode==AppCompatDelegate.MODE_NIGHT_YES){

menu.findItem(R.id.night_mode).setTitle(R.string.day_mode);

}else{

menu.findItem(R.id.night_mode).setTitle(R.string.night_mode);

}

returntrue;

}

10. Runyourapp.Themenubuttonlabelnowchangeswiththetheme.

4.4SaveInstanceState

Youlearnedinpreviouslessonsthatyoumustbepreparedforyouractivitytobedestroyedandrecreatedatunexpectedtimes,forexamplewhenyourscreenisrotated.Inthisapplication,theTextViewscontainingthescoresareresettotheinitialvalueof0whenthedeviceisrotated.Tofixthis,Dothefollowing:

1. OverridetheonSaveInstanceState()methodinMainActivitytopreservethevaluesofthetwoscoreTextViews:

@Override

protectedvoidonSaveInstanceState(BundleoutState){

//Savethescores

outState.putInt(STATE_SCORE_1,mScore1);

outState.putInt(STATE_SCORE_2,mScore2);

super.onSaveInstanceState(outState);

}

2. IntheonCreate()methodofMainActivity.java,checkifthereisasavedInstanceState.Ifthereis,restorethescorestothetextviews:

if(savedInstanceState!=null){

mScore1=savedInstanceState.getInt(STATE_SCORE_1);

mScore2=savedInstanceState.getInt(STATE_SCORE_2);

//Setthescoretextviews

mScoreText1.setText(String.valueOf(mScore1));

mScoreText2.setText(String.valueOf(mScore2));

}

That'sit!Congratulations,younowhaveastyledScorekeeperApplication.

SolutioncodeAndroidStudioproject:Scorekeeper

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:Rightnow,yourbuttonsdonotbehaveintuitivelybecausetheydonotchangetheirappearancewhentheyarepressed.AndroidhasanothertypeofdrawablecalledStateListDrawablewhichallowsforadifferentgraphictobeuseddependingonthestateoftheobject.

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Forthischallengeproblem,createadrawableresourcethatchangesthebackgroundofthebuttontothesamecolorastheborderwhenthestateofthebuttonis"pressed".Youshouldalsosetthecolorofthetextinsidethebuttonstoaselectorthatmakesitwhitewhenthebuttonis"pressed".

SummaryAShapeDrawableisaprimitivegeometricshapedefinedinanxmlfilebyanumberofattributesincludingcolor,shape,paddingandmore.

Drawablesenhancethelookofanapplication.AStylecanspecifycommonpropertiessuchasheight,padding,fontcolor,fontsize,backgroundcolor,etal.

UsingstylescanreducetheamountofcommoncodeforyourUIcomponents.Styleshouldnotincludelayout-relatedinformation.StylescanbeappliedtoView,ActivitiesorApplications.

StyleappliedtoActivitiesorApplicationsmustbedefinedintheAndroidManifestXMLfile.StylescanbeinheritedbyidentifyingtheparentstyleusingXML.

WhenyouapplyastyletoacollectionofViewsinanActivityorinyourentireapplication,thatisknownasaThemeAndroid:themeistheattributeyouneedtosetastyleonacollectionofViewsinanActivityorApplication.TheAndroidplatformsuppliesalargecollectionofstylesandthemes.

RelatedconceptsTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

Drawables,StylesandThemes

LearnmoreDeveloperDocumentation:

LinearLayoutGuideDrawableResourceGuideStylesandThemesGuideDayNightThemeGuide

Videos

Udacity-ThemesandStyles

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5.2:MaterialDesign:Lists,CardsandColorsContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1:DownloadthestartercodeTask2:AddaCardViewandimagesTask3:MakeyourCardViewswipeable,movable,andclickableTask4:AddtheFABandchooseaMaterialDesigncolorpaletteCodingchallengeSummaryRelatedconceptLearnmore

ThischapterintroducesconceptsfromGoogle'sMaterialDesignguidelines,aseriesofbestpracticesforcreatingvisuallyappealingandintuitiveapplications.YouwilllearnhowtoaddandusetheCardViewandFloatingActionButtonViews,efficientlyuseimages,aswellasemploydesignbestpracticestomakeyouruser'sexperiencedelightful.

WhatyoushouldalreadyKNOWFromthepreviouschaptersyoushouldbeableto:

CreateandrunappsinAndroidStudio.CreateandeditelementsusingtheLayoutEditor,XML,andprogrammatically.UseaRecyclerViewtodisplayalist.

WhatyouwillLEARNRecommendeduseofmaterialwidgets(FloatingActionButton,CardView).Howtoefficientlyuseimagesinyourapp.Recommendedbestpracticesfordesigningintuitivelayoutsusingboldcolors.

WhatyouwillDOModifyanapplicationtofollowMaterialDesignguidelines.AddimagesandstylingtoaRecyclerViewlist.ImplementanItemTouchHelpertoaddDragandDropfunctionalitytoyourapp.

AppoverviewThe"MaterialMe!"appisamocksportsnewsapplicationwithverypoordesignimplementation.Youwillfixituptomeetthedesignguidelinestocreateadelightfuluserexperience!BelowaresomescreenshotsoftheappbeforeandaftertheMaterialDesignimprovements.

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Task1:DownloadthestartercodeThecompletestarterappprojectforthispracticalisavailableatMaterialMe-Starter.InthistaskyouwillloadtheprojectintoAndroidStudioandexploresomeoftheapp'skeyfeatures.

1.1OpenandruntheMaterialMeproject

1. DownloadandunziptheMaterialMe-Starterfile.2. OpentheappinAndroidStudio.3. Buildandruntheapp.

Theappshowsalistofsportsnameswithsomeplaceholdernewstextforeachsport.Thecurrentlayoutandstyleoftheappmakesitnearlyunusable:eachrowofdataisnotclearlyseparatedandthereisnoimageryorcolortoengagetheuser.

1.2Exploretheapp

1. Beforemakingmodificationstotheapp,exploreitscurrentstructure.Itcontainsthefollowingelements:

Sport.java

ThisclassrepresentsthedatamodelforeachrowofdataintheRecyclerView.Rightnowitcontainsafieldforthetitleofthesportandafieldforsomeinformationaboutthesport.

SportsAdapter.java

ThisistheadapterfortheRecyclerView.ItusesanArrayListofSportobjectsasitsdataandpopulateseachrowwiththisdata.

MainActivity.java

TheMainActivityinitializestheRecyclerViewandadapter,andcreatesthedatafromresourcefiles.

strings.xml

Thisresourcefilecontainsallofthedatafortheapplication,includingthetitlesandinformationforeachsport.

list_item.xml

ThislayoutfiledefineseachrowoftheRecyclerView.ItconsistsofthreeTextViews,oneforeachpieceofdata(thetitleandtheinfoforeachsport)andoneusedasalabel.

Task2:AddaCardViewandimagesOneofthefundamentalprinciplesofMaterialDesignistheuseofboldimagerytoenhancetheuserexperience.AddingimagestotheRecyclerViewlistitemsisagoodstartforcreatingadynamicandcaptivatinguserexperience.

Whenpresentinginformationthathasmixedmedia(likeimagesandtext),theMaterialDesignguidelinesrecommendusingaCardView,whichisaFrameLayoutwithsomeextrafeatures(suchaselevationandroundedcorners)thatgiveitaconsistentlookandfeelacrossmanydifferentapplicationsandplatforms.CardViewisaUIcomponentfoundintheAndroidSupportLibraries.

Inthissection,youwillmoveeachlistitemintoaCardViewandaddanImagetomaketheappcomplywithMaterialguidelines.

2.1AddtheCardView

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CardViewisnotincludedinthedefaultAndroidSDK,soyoumustbeadditasabuild.gradledependency.Dothefollowing:

1. Inyourapplevelbuild.gradlefile,addthefollowinglinetothedependenciesblock:

compile'com.android.support:cardview-v7:24.1.1'

Note:Theversionofthesupportlibrarymayhavechangedsincethewritingofthispractical.Updateittoit'smostcurrentversionandsyncyourgradlefiles.

2. Inthelist_item.xmlfile,surroundtherootLinearLayoutwithaCardViewwiththefollowingattributes:

Attribute Value

android:layout_width "match_parent"

android:layout_height "wrap_content"

android:layout_margin "8dp"

Note:Youwillneedtomovetheschemadeclaration(xmlns:android="http://schemas.android.com/apk/res/android")fromtheLinearLayouttotheCardviewwhichisnowthetoplevelViewofyourlayoutfile.

3. Runtheapp.NoweachrowitemiscontainedinsideaCardView,whichiselevatedabovethebottomlayerandcastsashadow.

2.2Downloadtheimages

TheCardViewisnotintendedtobeusedexclusivelywithplaintext:itisbestfordisplayingamixtureofcontent.Youhaveisagoodopportunitytomakethissportsinformationappmoreexcitingbyaddingbannerimagestoeveryrow!

Usingimagesisresourceintensiveforyourapp:theAndroidframeworkhastoloadtheentireimageintomemoryatfullresolution,eveniftheapponlydisplaysasmallthumbnailoftheimage.

InthissectionyouwilllearnhowtousetheGlidelibrarytoloadlargeimagesefficiently,withoutdrainingyourresourcesorevencrashingyourappdueto'OutofMemory'exceptions.

1. Downloadthebannerimageszipfile.2. Copythesefilesintotheres>drawabledirectoryofyourapp.

Note:Copythefilesusingyourfileexplorer,notAndroidStudio.NavigatetothedirectorywhereallyourAndroidProjectsarestored(It'scalled/AndroidStudioProjects),andgotoMaterialMe/app/src/main/res/drawableandpastetheimageshere.YouwillneedanarraywiththepathtoeachimagesothatyoucanincludeitintheSportsjavaobject.Todothis:

3. Defineanarraythatcontainsallofthepathstothedrawablesasitemsinyourstring.xmlfile.Besuretothattheyareinthesameorderasthesportstitlesarray:

<arrayname="sports_images">

<item>@drawable/img_baseball</item>

<item>@drawable/img_badminton</item>

<item>@drawable/img_basketball</item>

<item>@drawable/img_bowling</item>

<item>@drawable/img_cycling</item>

<item>@drawable/img_golf</item>

<item>@drawable/img_running</item>

<item>@drawable/img_soccer</item>

<item>@drawable/img_swimming</item>

<item>@drawable/img_tabletennis</item>

<item>@drawable/img_tennis</item>

</array>

2.3ModifytheSportobject

TheSport.javaobjectwillneedtoincludethedrawableresourcethatcorrepsondstothesport.Toachievethat:

1. AddanintegermembervariabletotheSportobjectthatwillcontainthedrawableresource:

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privatefinalintimageResource;

2. Modifytheconstructorsothatittakesanintegerasaparameterandassignsittothemembervariable:

publicSport(Stringtitle,Stringinfo,intimageResource){

this.title=title;

this.info=info;

this.imageResource=imageResource;

}

3. Createagetterfortheresourceinteger:

publicintgetImageResource(){

returnimageResource;

}

2.4FixtheinitializeData()method

InMainActivity.java,theinitializeData()methodisnowbroken,becausetheconstructorfortheSportobjectdemandstheimageresourceasthethirdparameter.

AconvenientdatastructuretousewouldbeaTypedArray.ATypedArrayallowsyoutostoreanarrayofotherXMLresources.ByusingaTypedArray,youwillbeabletoobtaintheimageresourcesaswellasthesportstitleandinformationbyusingindexinginthesameloop.

1. IntheinitializeData()method,gettheTypedArrayofresourceid'sbycallinggetResources().obtainTypedArray(),passinginthenameofthearrayofdrawableresourcesyoudefinedinyourstrings.xmlfile:

TypedArraysportsImageResources=

getResources().obtainTypedArray(R.array.sports_images);

YoucanaccessanelementatindexiintheTypedArraybyusingtheappropriate"get"method,dependingonthetypeofresourceinthearray.Inthisspecificcase,itcontainsresourceID's,soyouusethegetResourceId()method.

2. FixthecodeintheloopthatcreatestheSportsobjects,addingtheappropriatedrawableresourceIDasthethirdparameterbycallinggetResourceId()ontheTypedArray:

for(inti=0;i<sportsList.length;i++){

mSportsData.add(newSport(sportsList[i],sportsInfo[i],

sportsImageResources.getResourceId(i,0)));

}

3. CleanupthedatainthetypedarrayonceyouhavecreatedtheSportdataArrayList:

sportsImageResources.recycle();

2.5AddanImageViewtothelistitems

1. ChangetheLinearLayoutinsidethelist_item.xmlfiletoaRelativeLayout,anddeletetheorientationattribute.2. AddanImageViewwiththefollowingattributes:

Attribute Value

android:layout_width "match_parent"

android:layout_height "wrap_content"

android:id "@+id/sportsImage"

android:adjustViewBounds "true"

TheadjustViewBoundsattributemakestheImageViewadjustitsboundariestopreservetheaspectratiooftheimage.

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3. AddthefollowingattributestotheexistingTextViews:

TextViewid:title Attribute Value

android:layout_alignBottom "@id/sportsImage"

android:theme "@style/ThemeOverlay.AppCompat.Dark"

TextViewid:newsTitle Attribute Value

android:layout_below "@id/sportsImage"

android:textColor "?android:textColorSecondary"

TextViewid:subTitle android:layout_below "@id/newsTitle"

Note:ThequestionmarkintheabovetextColorattribute("?android:textColorSecondary")meansthattheframeworkwillapplythevaluefromthecurrentlyappliedtheme.Inthiscase,thisattributeisinheritedfromthe"Theme.AppCompat.Light.DarkActionBar"theme,whichdefinesitasalightgraycolor,oftenusedforsubheadings.

2.6LoadtheimagesusingGlide

AfterdownloadingtheimagesandsettinguptheImageView,thenextstepistomodifytheSportsAdaptertoloadanimageintotheImageViewinonBindViewHolder().Ifyoutakethisapproach,youwillfindthatyourappcrashesdueto"OutofMemory"errors.TheAndroidframeworkhastoloadtheimageintomemoryeachtimeatfullresolution,nomatterwhatthedisplaysizeoftheImageViewis.

Thereareanumberofwaystoreducethememoryconsumptionwhenloadingimages,butoneoftheeasiestapproachesistouseanImageLoadingLibrarylikeGlide,whichyouwilldointhisstep.Glideusesbackgroundprocessing,aswellsomeothercomplexprocessing,toreducethememoryrequirementsofloadingimages.Italsoincludessomeusefulfeatureslikeshowingplaceholderimageswhilethedesiredimagesareloaded.

Note:YoucanlearnmoreaboutreducingmemoryconsumptioninyourappintheDisplayingBitmapsguide.1. AddthefollowingdependencyforGlide,inyourapplevelbuild.gradlefile:

compile'com.github.bumptech.glide:glide:3.5.2'

2. AddavariableintheSportsAdapterclass,ViewHolderclassfortheImageView,andinitializeitintheViewHolderconstructor:

mSportsImage=(ImageView)itemView.findViewById(R.id.sportsImage);

3. AddthefollowinglineofcodetoonBindViewHolder()togettheimageresourcefromtheSportobjectandloaditintotheImageViewusingGlide:

Glide.with(mContext).load(currentSport.getImageResource()).into(holder.mSportsImage);

That'salltakestoloadanimagewithGlide.Glidealsohasseveraladditionalfeaturesthatletyouresize,transformandloadimagesinavarietyofways.HeadovertotheGlidegithubpagetolearnmore.

4. Runtheapp,yourlistitemsshouldnowhaveboldgraphicsthatmaketheuserexperiencedynamicandexciting!

Task3:MakeyourCardViewswipeable,movable,andclickableWhenusersseecardsinanapp,theyhaveexpectationsaboutthewaythecardsbehave.TheMaterialDesignguidelinessaythat:

Acardcanbedismissed,usuallybyswipingitaway.Alistofcardscanbereorderedbyholdingdownanddraggingthecards.

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Tappingoncardwillprovidefurtherdetails.

Youwillnowimplementthesebehaviorsinyourapp.

3.1Implementswipetodismiss

TheAndroidSDKincludesaclasscalledItemTouchHelperthatisusedtodefinewhathappenstoRecyclerViewlistitemswhentheuserperformsvarioustouchactions,suchasswipe,ordraganddrop.SomeofthecommonusecasesarealreadyimplementedinasetofmethodsinItemTouchHelper.SimpleCallback.

ItemTouchHelper.SimpleCallbackletsyoudefinewhichdirectionsaresupportedforswipingandmovinglistitems,andimplementtheswipingandmovingbehavior.

Dothefollowing:

1. CreateanewItemTouchHelperobject,intheonCreate()methodofMainActivity.java.Foritsargument,createanewinstanceofItemTouchHelper.SimpleCallbackandpressEntertomakeAndroidStudiofillintherequiredmethods:onMove()andonSwiped().

Note:Iftherequiredmethodswerenotautomaticallyadded,clickontheredlightbulbandselectImplementmethods.

2. TheSimpleCallbackconstructorwillbeunderlinedinredbecauseyouhavenotyetprovidedtherequiredparameters:thedirectionthatyouplantosupportformovingandswipinglistitems,respectively.

Becauseweareonlyimplementingswipetodismissatthemoment,youshouldpassin0forthesupportedmovedirectionsandItemTouchHelper.LEFT|ItemTouchHelper.RIGHTforthesupportedswipedirections:

ItemTouchHelperhelper=newItemTouchHelper(newItemTouchHelper

.SimpleCallback(0,ItemTouchHelper.LEFT|ItemTouchHelper.RIGHT){}

3. YoumustnowimplementthedesiredbehaviorinonSwiped().Inthiscase,swipingthecardleftorrightshoulddeleteitfromthelist.Callremove()onthedataset,passingintheappropriateindexbygettingthepositionfromtheViewHolder:

mSportsData.remove(viewHolder.getAdapterPosition());

4. ToallowtheRecyclerViewtoanimatethedeletionproperly,youmustalsocallnotifyItemRemoved(),againpassingintheappropriateindexbygettingthepositionfromtheViewHolder:

mAdapter.notifyItemRemoved(viewHolder.getAdapterPosition());

5. AftercreatingthenewItemTouchHelperobjectintheMainActivity'sonCreate()method,callattachToRecyclerView()ontheItemTouchHelperinstancetoaddittoyourRecyclerView:

helper.attachToRecyclerView(mRecyclerView);

6. Runyourapp,youcannowswipelistitemsleftandrighttodeletethem!

3.2ImplementdraganddropYoucanalsoimplementdraganddropfunctionalityusingthesameSimpleCallback.ThefirstargumentoftheSimpleCallbackdetermineswhichdirectionstheItemTouchHelpersupportsformovingtheobjectsaround.Dothefollowing:

1. ChangethefirstargumentoftheSimpleCallbackfrom0toincludeeverydirection,sincewewanttobeabletodraganddropanywhere:

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ItemTouchHelperhelper=newItemTouchHelper(newItemTouchHelper

.SimpleCallback(ItemTouchHelper.LEFT|ItemTouchHelper.RIGHT|

ItemTouchHelper.DOWN|ItemTouchHelper.UP,ItemTouchHelper.LEFT|

ItemTouchHelper.RIGHT){}

2. IntheonMove()method,gettheoriginalandtargetindexfromthe2ndand3rdargumentpassedin(correspondingtotheoriginalandtargetviewholders).

intfrom=viewHolder.getAdapterPosition();

intto=target.getAdapterPosition();

3. SwaptheitemsinthedatasetbycallingCollections.swap()andpassinthedataset,andtheinitialandfinalindexes:

Collections.swap(mSportsData,from,to);

4. Notifytheadapterthattheitemwasmoved,passingintheoldandnewindexes:

mAdapter.notifyItemMoved(from,to);

5. Runyourapp.Youcannowdeleteyourlistitemsbyswipingthemleftorright,orreorderthemusingalongpresstoactivateDragandDropmode.

3.3Implementthedetailview

AccordingtoMaterialDesignguidelines,acardisusedtoprovideanentrypointtomoredetailedinformation.Youmayfindyourselftappingonthecardstoseemoreinformationaboutthesports,becausethatishowyouexpectcardstobehave.Inthissection,youwilladdadetailactivitythatwillbelaunchedwhenanylistitemispressed.Forthispractical,thedetailactivitywillcontainthenameandimageofthelistitemyouclicked,butwillcontainonlygenericplaceholderdetailtext,soyoudon'thavetocreatecustomdetailforeachlistitem.

1. CreateanewactivitybygoingtoFile>New>Activity>EmptyActivity.2. CallitDetailActivity,acceptallofthedefaults.3. Inthenewlycreatedlayoutfile:

i. ChangetherootviewgrouptoRelativeLayout,asyou'vedoneinpreviousexercises.ii. RemovethepaddingfromtheRelativeLayoutelement.

4. CopyalloftheTextViewandImageViewviewsfromthelist_item.xmlfiletotheactivity_detail.xmlfile.5. Addtheword"Detail"toeveryreferencetoanid,inordertodifferentiateitfromlist_itemids.Forexample,changethe

ImageViewIDfromsportsImagetosportsImageDetail,aswellasanyreferencestothisIDforrelativeplacementsuchlayout_below.

6. ForthesubTitleDetailtextview,removetheplaceholdertextstringandpasteaparagraphofgenerictexttosubstitutedetailtext(Forexample,afewparagraphsofLoremIspum).

7. ChangethepaddingontheTextViewsto16dp.8. Wraptheentireactivity_detail.xmlinaScrollViewandchangethelayout_heightattributeoftheRelativeLayoutto

"wrap_content".

Note:TheattributesfortheScrollViewmightappearredatfirst.ThisisbecauseyoumustfirstaddanattributethatdefinestheAndroidnamespace.Thisistheattributethatshowsupinallofyourlayoutfilesbydefault:xmlns:android="http://schemas.android.com/apk/res/android".Simplymovethisdeclarationtothetoplevelviewandtheredshouldgoaway.

9. IntheSportsAdapterclass,maketheViewHolderinnerclassimplementView.OnClickListener,andimplementtherequiredmethod(onClick()).

10. SettheOnClickListenertotheitemviewintheconstructor:

itemView.setOnClickListener(this);

11. IntheonClick()method,gettheSportobjectfortheitemthatwasclickedusinggetAdapterPosition():

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SportcurrentSport=mSportsData.get(getAdapterPosition());

12. CreateanIntentthatlaunchestheDetailactivity,andputthetitleandimageresourceasextrasintheIntent:

IntentdetailIntent=newIntent(mContext,DetailActivity.class);

detailIntent.putExtra("title",currentSport.getTitle());

detailIntent.putExtra("image_resource",currentSport.getImageResource());

13. CallstartActivity()onthemContextvariable,passinginthenewIntent.14. InDetailActivity.java,initializetheImageViewandtitleTextViewinonCreate():

TextViewsportsTitle=(TextView)findViewById(R.id.titleDetail);

ImageViewsportsImage=(ImageView)findViewById(R.id.sportsImageDetail);

15. GetthetitlefromtheincomingIntentandsetittotheTextView:

sportsTitle.setText(getIntent().getStringExtra("title"));

16. UseGlidetoloadtheimageintotheImageView:

Glide.with(this).load(getIntent().getIntExtra("image_resource",0))

.into(sportsImage);

17. Runtheapp.Tappingonalistitemnowlaunchesthedetailactivity.

Task4:AddtheFABandchooseaMaterialDesigncolorpaletteOneoftheprinciplesbehindMaterialDesignisusingconsistentelementsacrossapplicationsandplatformssothatusersrecognizepatternsandknowhowtousethem.Youhavealreadyusedonesuchelement:theFloatingActionButton.TheFABisacircularbuttonthatfloatsabovetherestoftheUI.Itisusedtopromoteaparticularactiontotheuser,onethatisverylikelytobeusedinagivenactivity.Inthistask,youwillcreateaFABthatresetsthedatasettoit'soriginalstate.

4.1AddtheFAB

TheFloatingActionButtonispartoftheDesignSupportLibrary.

1. Addthefollowinglineofcodetotheapplevelbuild.gradlefiletoaddthedesignsupportlibrarydependency:

compile'com.android.support:design:24.2.1'

2. UsethevectorassetstudiotodownloadanicontouseintheFAB.Thebuttonwillresetthecontentsofthe

RecyclerViewsothisiconshoulddo: .Changethenametoic_reset.3. Inactivity_main.xml,addaFloatingActionButtonviewwiththefollowingparameters:

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Attribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:layout_alignParentBottom "true"

android:layout_alignParentRight "true

android:layout_margin "16dp"

android:src "@drawable/ic_reset"

android:onClick resetSports

4. DefinetheresetSports()methodinMainActivity.javatosimplycallinitializeData()toresetthedata.5. Runtheapp.YoucannowresetthedatabypushingtheFAB.

Note:Becausetheactivityisdestroyedandrecreatedwhentheconfigurationchanges,rotatingthedeviceresetsthedatainthisimplementation.Inorderforthechangestobepersistent(asinthecaseofreorderingorremovingdata),youwouldhavetoimplementonSaveInstanceState()orwritethechangestoapersistentsource(likeadatabaseorSharedPreferences).

4.2ChooseaMaterialDesignpalette

IfyourunyourappyoumaynoticethattheFABhasacolorthatyoudidn'tdefineanywhere.Also,theAppbar(thebarthatcontainsthetitleofyourapp)hasacolorthatyoudidnotexplicitlyset.Wherearethesecolorsdefined?

1. Navigatetoyourstyles.xmlfile(locatedinthevaluesdirectory).TheAppThemestyledefinesthreecolorsbydefault:colorPrimary,colorPrimaryDarkandcolorAccent.Thesestylesaredefinedbyvaluesfromthecolors.xmlfile.MaterialDesignrecommendspickingatleastthesethreecolorsforyourapp:

2. Aprimarycolor.ThisoneisautomaticallyusedtocoloryourAppbar.3. Aprimarydarkcolor.Adarkershadeofthesamecolor.Thisisusedforthestatusbarabovetheappbar,amongother

things.4. Anaccentcolor.Acolorthatcontrastswellwiththeprimarycolor.Thisisusedforvarioushighlights,butitisalsothe

defaultcoloroftheFAB.YoucanusetheMaterialColorGuidetopicksomecolorstoexperimentwith.5. Pickacolorfromtheguidetouseasyourprimarycolor.Itshouldbewithinthe300-700rangesothatyoucanstillpick

aproperaccentanddarkcolor.ModifythecolorPrimaryhexvalueinyourcolors.xmlfiletomatchthecoloryoupicked.6. Pickadarkershadeofthesamecolortouseasyourprimarydarkcolor.Again,modifythecolors.xmlhexvaluefor

colorPrimaryDarktomatch.7. PickanaccentcolorforyourFABfromthecolorswhosevaluesstartwithanA,andwhosecolorcontrastswellwiththe

primarycolor(likeOrangeA200).ChangethecolorAccentvalueincolors.xmltomatch.8. Addtheandroid:tintattributetotheFABandsetitequalto#FFFFFF(white)inordertochangetheiconcolortowhite.9. Runtheapp.TheAppBarandFABchangedtoreflectthenewcolorpalette!

Note:IfyouwanttochangethecoloroftheFABtosomethingotherthanthemecolors,usetheapp:backgroundTintattribute.Notethatthisusestheapp:namespaceandAndroidStudiowillpromptyoutoaddastatementtodefinethenamespace.

SolutioncodeAndroidStudioproject:MaterialMe

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

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Challenge1:Thischallengeconsistsofseveralsmallimprovementstoyourapplication:

AddrealdetailstotheSportobjectandpassthedetailstothedetailview.Implementawaytoensurethatthestateoftheappispersistentacrossorientationchanges.

Challenge2:Createanapplicationwith4imagesarrangedinagridinthecenterofyourlayout.Makethefirstthreesolidcoloredbackgroundswithdifferentshapes(square,circle,line),andthefourththeAndroidMaterialDesignIcon.Makeeachoftheseimagesrespondtoclicksasfollows:

1. OneofthecoloredblocksrelaunchestheActivityusingtheExplodeanimationforboththeenterandexittransitions.2. RelaunchtheActivityfromanothercoloredblock,thistimeusingtheFadetransition.3. Touchingthethirdcoloredblockstartsaninplaceanimationoftheview(suchasarotation).4. Finally,touchingtheandroidiconstartsasecondaryactivitywithaSharedElementTransitionswappingtheAndroid

blockwithoneoftheotherblocks.

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Note:YoumustsetyourminimumSDKlevelto21orhigherinordertoimplementsharedelementtransitions.

SummaryACardViewisagoodlayoutwhenpresentinginformationthathasmixedmedia(suchasimagesandtext)CardViewisaUIcomponentfoundintheAndroidSupportLibrariesCardViewwasnotdesignedjustfortextchildViews.LoadingimagesdirectlyintoImageViewisverymemoryintensive.Allimagesareloadedatfull-resolution.Useanimageloadinglibrary,suchasGlide,toefficientlyloadimagesintoyourappTheAndroidSDKhasaclasscalledItemTouchHelperwhichassistsinobtainingtap,swipeordrag-and-dropinformationforyourUI.AFloatingActionButton(FAB)focusestheuseronaparticularactionand"floats"aboutyourUI.MaterialDesignsuggest3colorsforyourapp:aprimarycolor,aprimarydarkcolorandanaccentcolor.TheMaterialDesignguidelinesareasetofguidingprinciplesthataimtocreateconsistent,intuitiveandplayfulapplications.MaterialDesignpromotestheuseofboldimageryandcolorstoenhanceuserexperience.Italsopromotesconsistentelementsacrossplatforms(suchasCardViewandtheFAB).MaterialDesignshouldbeusedformeaningful,intuitivemotionlikedismissableorrearrangeablecards.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

MaterialDesign

LearnmoreMaterialDesignGuidelinesMaterialPaletteGeneratorCardsandListsGuideFloatingActionButtonReferenceDefiningCustomAnimationsViewAnimation

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5.3:SupportingLandscape,MultipleScreenSizesandLocalizationContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1:SupportLandscapeOrientationTask2:SupportTabletsTask3:LocalizeyourAppCodingchallengesSummaryRelatedconceptLearnmore

AfterusingtheMaterialMe!applicationyoucreatedinthelastpractical,youmaynoticethatitisnotoptimizedforusewhentheorientationforthedeviceisrotatedfromportraitmodetolandscapemode.Likewise,ifyouaretestingonatablet,thefont-sizesaretoosmallandthespaceisnotusedefficiently.TheAndroidframeworkhasawaytosolvebothoftheseissues.ResourcequalifiersallowtheAndroidRuntimetousealternateresourcefiles(.xml)dependingonthedeviceconfiguration,suchas,theorientation,thelocaleandother"qualifiers".Forafulllistofavailablequalifiers,visittheProvidingResourcesguide.InthispracticalyouwilloptimizetheuseofspaceintheMaterialsportsappsothatyourappworkswellinlandscapemode,aswellasonatablet.

WhatyoushouldalreadyKNOWFromthepreviouschaptersyoushouldbeableto:

Locateandeditresourcefiles.Extractresources.Instantiateavirtualphoneortabletusingtheemulator.

WhatyouwillLEARNInthispractical,youwilllearnto:

Providealternateresourcesforlandscapemode.Providealternateresourcesfortablets.Providealternateresourcesfordifferentlocales.

WhatyouwillDOInthispracticalyouwill:

UpdatetheMaterialMe!applicationforbetteruseofspaceinlandscapemode.Addanalternativelayoutfortablets.Localizethecontentofyourapp.

AppOverview

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TheimprovedMaterialMe!applicationwillincludeimprovedlayoutswhenusedinlandscapemode,onatablet,andofferlocalizedcontentforusersoutsideoftheUS.

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Thispracticalbuildsonthe"MaterialMe!"appfromthepreviouspractical.

1. Continueonyourversionofthe"MaterialMe!"application,ordownloadithere.

Task1:SupportLandscapeOrientation

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Youmayrecallthatwhentheuserchangestheorientationofthedevice,theAndroidframeworkdestroysandrecreatesthecurrentactivity.Theneworientationoftenhasdifferentlayoutrequirementsthantheoriginalone.Forexample,theMaterialMe!applicationlooksgoodinportraitmode,butdoesnotmakeoptimaluseofthescreeninlandscapemode.Withthelargerwidthinlandscapemode,theimageineachlistitemoverwhelmsthetextprovidingapooruserexperience.

Inthistask,youwillcreateanalternativeresourcefilethatwillchangetheappearanceoftheappwhenitisusedinlandscapeorientation.

1.1ChangetoaGridLayoutManagerLayoutsthatcontainlistitemsoftenlookunbalancedinlandscapemodewhenthelistitemsincludefull-widthimages.Onegoodsolutionistouseagrid,insteadofalinearlistwhendisplayingtheCardViewsinlandscapemode.RecallthattheitemsinaRecyclerViewlistareplacedusingaLayoutManager;untilnow,youhavebeenusingtheLinearLayoutManagerwhichlaysouteachiteminaverticalorhorizontalscrollinglist.GridLayoutManagerisanotherlayoutmanagerthatdisplaysitemsinagrid,ratherthanalist.WhenyoucreateaGridLayoutManager,yousupplytwoparameters:theapplicationcontext,andanintegerrepresentingthenumberofcolumns.Youcanchangethenumberofcolumnsprogrammatically,whichgivesyouflexibilityindesigningresponsivelayouts.Inthiscase,thenumberofcolumnsintegershouldbe1inportraitorientation(singlecolumn)and2wheninlandscapemode.Noticewhenthenumberofcolumnsis1,aGridLayoutManagerbehavessimilartoaLinearLayoutManager.

1. Createanewresourcesfilecalledintegers.xml.Navigatetoyourresourcesdirectory,right-clickonthevaluesdirectorynameandselectNew>Valuesresourcefile.

2. Namethefileintegers.xmlandclickOK.3. Createanintegerconstantbetweenthe<resources>tagscalled"grid_column_count"andsetitequalto1:

<integername="grid_column_count">1</integer>

4. Createanothervaluesresourcefile,againcalledintegers.xmlbutwithdifferentcharacteristics.

Notethe"Availablequalifiers"optioninthedialogforcreatingtheresourcefile.Thesecharacteristicsarecalled"resourcequalifiers"andareusedtolabelresourceconfigurationsforvarioussituations.

5. SelectOrientation,andpressthe>>symbolinthemiddleofthedialogtoaccessthisqualifier.6. ChangetheScreenorientationselectortoLandscape,andnoticehowthedirectoryname"values-land"is

automaticallychanged.Thisistheessenceofresourcequalifiers:thedirectorynametellsAndroidwhentousethatspecificlayoutfile.Inthiscase,thatiswhenthephoneisrotatedtolandscapemode.

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7. ClickOKtogeneratethenewlayoutfile.8. Copytheintegerconstantyoucreatedintothisnewresourcefile,butchangethevalueto2.

Youshouldnowhavetwoindividualintegers.xmlfiles.Inthe"Android"projectviewinAndroidStudio,theseshouldbegroupedintoan"integers.xml"folder,witheachfileinsidelabeledwiththequalifieryouselected("land"inthiscase).

1.2ModifyMainActivity

1. InonCreate()inMainActivity,gettheintegerfromtheintegers.xmlresourcefile:

intgridColumnCount=getResources().getInteger(R.integer.grid_column_count);

TheAndroidRuntimewilltakecareofdecidingwhichintegers.xmlfiletouse,dependingonthestateofthedevice.

2. ChangetheLinearLayoutManagertoaGridLayoutManager,passinginthecontextandthenewlycreatedinteger:

mRecyclerView.setLayoutManager(newGridLayoutManager(this,gridColumnCount));

3. Runtheappandrotatethedevice.Thenumberofcolumnschangesautomaticallywiththeorientationofthedevice.

Whenusingtheapplicationinlandscapemode,youwillnoticethattheswipetodismissfunctionalityisnolongerintuitive,sincetheitemsarenowinagridandnotalist.YoucanusethegridColumnCountvariabletodisabletheswipeactionwhenthereismorethanonecolumn:

intswipeDirs;

if(gridColumnCount>1){

swipeDirs=0;

}else{

swipeDirs=ItemTouchHelper.LEFT|ItemTouchHelper.RIGHT;

}

ItemTouchHelperhelper=newItemTouchHelper(newItemTouchHelper.SimpleCallback

(ItemTouchHelper.LEFT|ItemTouchHelper.RIGHT|ItemTouchHelper.DOWN

|ItemTouchHelper.UP,swipeDirs)

Task2:SupportTablets

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2.1MaketheLayoutAdapttoTablets

Inthisstep,youwillcreatedifferentresourcequalifierstomaximizescreenusefortabletsizeddevices,increasingthecolumncountto2forportraitorientationand3forlandscapeorientation.Theresourcequalifieryouneeddependsonyourspecificrequirements.Thereareseveralqualifiersthatyoucanusetoselectthecorrectconditions:

"smallestwidth"-Thisqualifierisusedmostfrequentlytoselectfortablets.Itisdefinedbythesmallestwidthofthedevice(regardlessoforientation),whichremovestheambiguitywhentalkingabout"height"and"width"sincesomedevicesaretraditionallyheldinlandscapemode,andothersinportrait.Anythingwithasmallestwidthofatleast600dpisconsideredatablet."availablewidth"-Theavailablewidthistheeffectivewidthofthedevice,regardlessoftheorientation.Theavailablewidthchangeswhenthedeviceisrotated,sincetheeffectiveheightandwidthofthedeviceareswitched."availableheight"-Sameas"availablewidth",exceptitusestheeffectiveheightinsteadoftheeffectivewidth.

Tostartthistask:

1. Createanintegers.xmlfilewhichusesthe"smallestwidth"qualifierwiththevaluesetto600.Androidusesthisfilewhenevertheapprunsonatablet.

2. Copythecodefromtheintegers.xmlfilewiththelandscaperesourcequalifier(ithasagridcountof2)andpasteitinthenewintegers.xmlfile.

3. Createathirdintegers.xmlfilethatincludesboththesmallestscreenwidthof600dpqualifier,andthelandscapeorientationqualifier.Androidusesthisfilewhentheapprunsonatabletinlandscapemode.

Note:Androidwilllookfortheresourcefilewiththemostspecificresourcequalifierfirst,thenmoveontoamoregenericone.Forexample,ifavalueisdefinedintheintegers.xmlfilewithboththelandscapeandsmallestwidthqualifier,itwilloverridethevalueintheintegers.xmlfilewithjustthelandscapequalifier.Formoreinformationaboutresourcequalifiers,visittheProvidingResourcesGuide.

4. Changethegrid_column_countvariableto3inthelandscape,tabletintegers.xmlfile.

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genericone.Forexample,ifavalueisdefinedintheintegers.xmlfilewithboththelandscapeandsmallestwidthqualifier,itwilloverridethevalueintheintegers.xmlfilewithjustthelandscapequalifier.Formoreinformationaboutresourcequalifiers,visittheProvidingResourcesGuide.

4. Changethegrid_column_countvariableto3inthelandscape,tabletintegers.xmlfile.

5. Createavirtualtabletemulator.Runtheapponatabletemulatoraswellasaphoneemulatorandrotatebothofthedevicesintolandscapemode.Withtheseresourcequalifierfiles,theappusesthescreenrealestatemuchmoreeffectively.

2.2Updatethetabletlistitemstyles

Atthispoint,yourappchangesthenumberofcolumnsinaGridLayoutManagertofittheorientationofthedeviceandmaximizetheuseofthescreen.However,alltheTextViewsthatappearedcorrectly-sizedonaphone'sscreennowappeartoosmallforthelargerscreenofatablet.Tofixthis,youwillextracttheTextAppearancestylesfromthelayoutresourcefilesintothestylesresourcefile.Youwillalsocreateadditionalstyles.xmlfilesfortabletsusingresourcequalifiers.

Note:Youcouldalsocreatealternativelayoutfileswiththeproperresourcequalifiers,andchangethestylesoftheTextViewsinthose.However,thiswouldrequiremorecodeduplication,sincemostofthelayoutinformationisthesamenomatterwhatdeviceyouuse,soyouwillonlyextracttheattributesthatwillchange.CreatetheStyles

1. Inthestyles.xmlfile,createthefollowingstyles:

Name Parent

SportsTitle TextAppearance.AppCompat.Headline

SportsDetailText TextAppearance.AppCompat.Subhead

Createastyles.xmlfilefortablets

Nowyouwillcreatethefilewhereyouwilldefinestylesfortablets.

1. Createanewstyles.xmlresourcefilethatusestheSmallestScreenWidthqualifierwithavalueof600.2. Copythe"SportsTitle"and"SportsDetailText"stylesfromtheoriginalstyles.xmlfileintothenew,qualifiedstyles.xml

file.3. Changetheparentofthe"SportsTitle"styleto"TextAppearance.AppCompat.Display1"4. TheAndroidpre-definedDisplay1styleusesthetextColorSecondaryvaluefromthecurrenttheme

(ThemeOverlay.AppCompat.Dark),whichinthiscaseisalightgraycolor.Thelightgraycolordoesnotshowupwellonthebannerimagesinyourapp.Tocorrectthisaddan"android:textColor"attributetothe"SportsTitle"styleandsetitto"?android:textColorPrimary".'

Note:ThequestionmarktellsAndroidRuntimetofindthevalueinthethemeappliedtotheView.InthisexamplethethemeisThemeOverlay.AppCompat.DarkinwhichthetextColorPrimaryattributeiswhite.

5. Changetheparentof"SportsDetailText"styleto"TextAppearance.AppCompat.Headline".

Updatethestyleofthetextviewsinlist_item.xml

1. Backinthelist_item.xmlfile,changethestyleattributeofthe"title"Textviewto"@style/SportsDetailTitle"2. Changethestyleattributeofthe"newsTitle"and"subTitle"TextViewsto"@style/SportsDetailText".3. Runyourapp.Eachlistitemnowhasalargertextsizeonthetablet.

2.3UpdatethetabletsportsdetailstylesYouhavenowfixedthedisplayfortheMainActivity,whichlistsalltheSportsCardViews.TheDetailActivitystillhasthesamefontsizesontabletsandphones.

1. Createthefollowingstyleineachstyles.xmlfile:

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styles.xml(sw600dp)

Name Parent

SportsDetailTitle TextAppearance.AppCompat.Display3

styles.xml(notqualified)

Name Parent

SportsDetailTitle TextAppearance.AppCompat.Headline

2. Changethestyleofboththe"newsTitleDetail"and"subTitleDetail"TextViewsintheactivity_detail.xmllayoutfiletothe"SportsDetailText"styleyoucreatedinthepreviousstep.

3. Runyourapp.Allofthetextisnowlargeronthetablet,whichgreatlyimprovestheuserexperienceofyourapplication.

Task3:LocalizeyourAppA"locale"representsaspecificgeographic,politicalorculturalregionoftheworld.Resourcequalifierscanbeusedtoprovidealternateresourcesbasedontheusers'locale.Justasfororientationandscreenwidth,Androidprovidestheabilitytoincludeseparateresourcefilesfordifferentlocales.Inthisstep,youwillmodifyyourstrings.xmlfiletobealittlemoreinternational.

3.1Addalocalizedstrings.xmlfile

YoumayhavenoticedthatthesportsinformationcontainedinthisappisdesignedforusersfromtheUS.Itusestheterm"soccer"torepresentasportknownas"football"everywhereelseintheworld.Inordertomakeyourappmoreinternationalized,youcanprovidealocalespecificstrings.xmlfiletotheUSuserswhichuses"soccer",whileallotherlocaleswilluse"football".

1. Createanewvaluesresourcefile.2. Callthefilestrings.xmlandselectLocalefromthelistofavailablequalifiers.3. Inthe"Language:"section,selecten:English.4. Inthe"SpecificRegionOnly:"section,selectUS:UnitedStates.ThiswillcreateaspecificvaluesdirectoryfortheUS

locale,called"values-en-rUS".5. Copytheentiretyofthegenericstrings.xmlfiletothenewlocalespecificstrings.xmlfile.6. Inthegenericstrings.xmlfile,changethe"Soccer"iteminthesports_titlesarrayto"Football",aswellaschangingthe

relevantitemin"sports_info"array.7. Runtheapp.Dependingonthelanguagesettingonyourdevice,youwillseeeither"Soccer"or"Football".

Note:Tochangethelocalesettingonyourdevice,gotothedevicesettings,thenchooseLanguage&inputandchangetheLanguagesetting.IfyoupickEnglish(UnitedStates)theappwillhave"Soccer"asthestring,otherwiseitwillsay"Football".

SolutioncodeAndroidStudioproject:MaterialMe-Resource

CodingchallengesNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge1:ItturnsoutthatseveralcountriesotherthantheUSuse"soccer"insteadof"football".Researchthesecountriesandaddlocalizedstringsresourcesforthem.

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Challenge2:UsethelocalizationtechniquesyoulearnedinTask3incombinationwithGoogletranslatetotranslateallofthestringsinyourappintoadifferentlanguage.

SummaryGridLayoutManagerisalayoutmanagerthathandles2-dimensionalscrollinglists.YoucandynamicallychangethenumberofcolumnsinaGridLayoutManager.TheAndroidRuntimeusesalternativeconfigurationfilesforvariousruntimeenvironmentssuchasdevicelayout,screendimensions,locale,country,keyboard,etc.Alternativeresourcesarelocatedinfilesnamedwithresourcequalifiersaspartoftheirnames.Theformatforthesedirectoriesis<resources_name>-<qualifier>.Anyfileinyour"res"directorycanbequalifiedthisway.Somecommonqualifiersare:

orientation:land,portraitsmallestwidth:sw600dplocale:en-rGB,frscreendensity:ldpi,mpdi,xhdpi,xxhdpi,xxxhdpimobilecountrycode:mcc310(US),mcc208(France)andmore!

RelatedconceptsTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

ProvidingResourcesforAdaptiveLayouts

LearnmoreDeveloperDocumentation:

SupportingMultipleScreensProvidingResources

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6.1:UseEspressototestyourUIContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppOverviewTask1:SetupEspressoinyourprojectTask2:TestforswitchingactivitiesandenteringtextTask3:TestthedisplayofspinnerselectionsTask4:RecordatestofaRecyclerViewCodingchallengeSummaryRelatedconceptLearnmore

Whenyou,asadeveloper,testuserinteractionswithinyourapp,ithelpstoensurethatyourapp'susersdon'tencounterunexpectedresultsorhaveapoorexperiencewheninteractingwithyourapp.

Youcantesttheuserinterfaceforacomplexappmanuallybyrunningtheappandtryingtheuserinterface.Butyoucan'tpossiblycoverallpermutationsofuserinteractionsandalloftheapp'sfunctionality.Youwouldalsohavetorepeatthesemanualtestsonmanydifferentdeviceconfigurationsinanemulator,andonmanydifferenthardwaredevices.

WhenyouautomatetestsofUIinteractions,youfreeyourselfupforotherwork.YoucanusesuitesofautomatedteststoperformalloftheUIinteractionsautomatically,whichmakesiteasiertoruntestsfordifferentdeviceconfigurations.Itisagoodideatogetintothehabitofcreatinguserinterface(UI)testsasyoucodetoverifythattheUIofyourappisfunctioningcorrectly.

EspressoisatestingframeworkforAndroidthatmakesiteasytowritereliableuserinterface(UI)testsforanapp.Theframework,whichispartoftheAndroidSupportRepository,providesAPIsforwritingUIteststosimulateuserinteractionswithintheapp—everythingfromclickingbuttonsandnavigatingviewstochoosingmenuselectionsandenteringdata.

WhatyoushouldalreadyKNOWYoushouldbeableto:

CreateandrunappsinAndroidStudio.CreateandeditUIelementsusingtheLayoutEditor,enteringXMLcodedirectly,andaccessingUIelementsfromyourJavacode.AddonClickfunctionalitytoabutton.BuildtheTwoActivitiesappfromapreviouslesson.BuildthePhoneNumberSpinnerappfromapreviouslesson.BuildtheRecyclerViewappfromapreviouslesson.

WhatyouwillLEARNDuringthispractical,youwilllearnto:

SetupEspressoinyourappproject.WriteanEspressotestthattestsforuserinputandchecksforthecorrectoutput.WriteanEspressotesttofindaspinner,clickoneofitsitems,andcheckforthecorrectoutput.UsetheRecordEspressoTestfunctioninAndroidStudio.

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WhatyouwillDOInthispracticalapplicationyouwill:

ModifyaprojecttocreateEspressotests.Testtheapp'stextinputandoutput.Testclickingaspinneritemandcheckitsoutput.RecordanEspressotestofaRecyclerView.

AppOverviewYouwillmodifytheTwoActivitiesprojecttosetupEspressointheprojectfortesting.Youwillthentesttheapp’sfunctionality,whichenablesausertoentertextintoatextfieldandclicktheSendbutton,asshownontheleftsideofthefigurebelow,andviewthattextinasecondactivity,asshownontherightsideofthefigurebelow.

Tip:ForanintroductiontotestingAndroidapps,seeTestYourApp.

AndroidStudioproject:TwoActivities

Task1:SetupEspressoinyourprojectTouseEspresso,youmustalreadyhavetheAndroidSupportRepositoryinstalledwithAndroidStudio.YoumustalsoconfigureEspressoinyourproject.

Inthistaskyouchecktoseeiftherepositoryisinstalled.Ifitisnot,youwillinstallit.YouthenwillconfigureEspressointheTwoActivitiesprojectcreatedpreviously.

1.1CheckfortheAndroidSupportRepository

1. StartAndroidStudio,andchooseTools>Android>SDKManager.2. ClicktheSDKToolstab,andlookfortheSupportRepository.

If"Installed"appearsintheStatuscolumn,you'reallset.ClickCancel.If"Notinstalled"appears,oranupdateisavailable:

i. ClickthecheckboxnexttoAndroidSupportRepository.Adownloadiconshouldappearnexttothecheckbox.

ii. Clickoneofthefollowing:

ApplytostartinstallingtherepositoryandremaininSDKManagertomakeotherchanges.OKtoinstalltherepositoryandquittheSDKManager.

1.2ConfigureEspressofortheprojectWhenyoustartaprojectforthephoneandtabletformfactorusingAPI15:Android4.0.3(IceCreamSandwich)astheminimumSDK,AndroidStudioversion2.2andnewerautomaticallyincludesthedependenciesyouneedtouseEspresso.Toexecutetests,EspressoandUIAutomatoruseJUnitastheirtestingframework.JUnitisthemostpopularand

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widely-usedunittestingframeworkforJava.YourtestclassusingEspressoorUIAutomatorshouldbewrittenasaJUnit4testclass.IfyoudonothaveJUnit,youcangetitathttp://junit.org/junit4/.

Note:ThemostcurrentJunitrevisionisJUnit5.HoweverforthepurposesofusingEspressoorUIAutomator,version4.12isrecommended.IfyouhavecreatedyourprojectinapreviousversionofAndroidStudio,youmayhavetoaddthedependenciesandinstrumentationyourself.Toaddthedependenciesyourself,followthesesteps:

1. OpentheTwoActivitiesproject,orifyouprefer,makeacopyoftheprojectfirstandthenopenthecopy.SeeCopyandrenameaprojectintheAppendixforinstructions.

2. Openyourbuild.gradle(Module:app)file.

Note:Donotmakechangestothebuild.gradle(Project:yourappname)file.3. Checkifthefollowingisincluded(alongwithotherdependencies)inthedependenciessectionoftheproject's

build.gradle(Module:app)file:

androidTestCompile

('com.android.support.test.espresso:espresso-core:2.2.2',{

excludegroup:'com.android.support',module:'support-annotations'

})

testCompile'junit:junit:4.12'

Note:Ifthefiledoesn'tincludetheabovedependencystatements,enterthemintothedependenciessection.4. AndroidStudio2.2alsoaddsthefollowinginstrumentationstatementtotheendofthedefaultConfigsectionofanew

project:

testInstrumentationRunner

"android.support.test.runner.AndroidJUnitRunner"

Note:Ifthefiledoesn'tincludetheaboveinstrumentationstatement,enteritattheendofthedefaultConfigsection.Instrumentationisasetofcontrolmethods,orhooks,intheAndroidsystem.ThesehookscontrolanAndroidcomponentindependentlyofthecomponent'snormallifecycle.TheyalsocontrolhowAndroidloadsapps.Usinginstrumentationmakesitpossibleforteststoinvokemethodsintheapp,andmodifyandexaminefieldsintheapp,independentlyoftheapp'snormallifecycle.

5. Ifyoumodifiedthebuild.gradle(Module:app)file,clicktheSyncNowlinkinthenotificationaboutGradlefilesintoprightcornerofthewindow.

1.3Turnoffanimationsonyourtestdevice

ToletAndroidStudiocommunicatewithyourdevice,youmustfirstturnonUSBDebuggingonyourdevice,asdescribedinanearlierchapter.

Androidphonesandtabletsdisplayanimationswhenmovingbetweenappsandscreens.Theanimationsareattractivewhenusingthedevice,buttheyslowdownperformance,andmayalsocauseunexpectedresultsormayleadyourtesttofail.Soit'sagoodideatoturnoffanimationsonyourphysicaldevice.Toturnoffanimationsonyourtestdevice,tapontheSettingsicononyourphysicaldevice.LookforDeveloperOptions.NowlookfortheDrawingsection.Inthissection,turnoffthefollowingoptions:

WindowanimationscaleTransitionanimationscaleAnimatordurationscale

Tip:Youshouldalsokeepinmindthatinstrumentingasystem,suchasinexecutingunittests,canalterthetimingofspecificfunctions.Forthisreason,itisusefultokeepunittestingandactualdebuggingseparate.UnittestingusesanAPIbasedEspressoFrameworkwithhooksforinstrumentation.Debuggingusesbreakpointsandothermethodsintheactualcodingstatementswithinyourapp'scode,asdescribedinapreviouslesson.</div>

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Task2:TestforswitchingactivitiesandenteringtextYouwriteEspressotestsbasedonwhatausermightdowhileinteractingwithyourapp.TheEspressotestsareclassesthatareseparatefromyourapp'scode.Youcancreateasmanytestsasyouneed,inordertointeractwiththeviewsinyourUIthatyouwanttotest.

TheEspressotestislikearobotthatmustbetoldwhattodo.Itmustfindtheviewyouwantittofindonthescreen,anditmustinteractwithit,suchasclickingtheview,andcheckingthecontentsoftheview.Ifitfailstodoanyofthesethingsproperly,oriftheresultisnotwhatyouexpected,thetestfails.

WithEspresso,youcreatewhatisessentiallyascriptofactionstotakeoneachviewandcheckagainstexpectedresults.ThekeyconceptsarelocatingandtheninteractingwithUIelements.Thesearethebasicsteps:

1. Matchaview:Findaview.2. Performanaction:Performaclickorotheractionthattriggersaneventwiththeview.3. Assertandverifytheresult:Checktheview'sstatetoseeifitreflectstheexpectedstateorbehaviordefinedbythe

assertion.

Hamcrest(ananagramof"matchers")isaframeworkthatassistswritingsoftwaretestsinJava.Tocreateatest,youcreateamethodwithinthetestclassthatusesHamcrestexpressions.

Tip:FormoreinformationabouttheHamcrestmatchers,seeTheHamcrestTutorial.

WithEspressoyouusethefollowingtypesofHamcrestexpressionstohelpfindviewsandinteractwiththem:

ViewMatchers:HamcrestmatcherexpressionsintheViewMatchersclassthatletsyoufindaviewinthecurrentviewhierarchysothatyoucanexaminesomethingorperformsomeaction.ViewActions:HamcrestactionexpressionsintheViewActionsclassthatletsyouperformanactiononaviewfoundbyaViewMatcher.ViewAssertions:HamcrestassertionexpressionsintheViewAssertionsclassthatletsyouassertorcheckthestateofaviewfoundbyaViewMatcher.

Thefollowingshowshowallthreeexpressionsworktogether:

1. UseaViewMatchertofindaview:

onView(withId(R.id.my_view))

2. UseaViewActiontoperformanaction:

.perform(click())

3. UseaViewAssertiontocheckiftheresultoftheactionmatchesanassertion:

.check(matches(isDisplayed()));

Thefollowingshowshowtheaboveexpressionsareusedtogetherinastatement:

onView(withId(R.id.my_view))

.perform(click())

.check(matches(isDisplayed()));

2.1DefineaclassforatestandsetuptheactivityAndroidStudiocreatesablankEspressotestclassforyouinthesrc/androidTest/java/com.example.packagefolder:

1. Expandcom.example.android.twoactivities(androidTest),andopenExampleInstrumentedTest.2. Tomakethetestmoreunderstandableanddescribewhatitdoes,renametheclassfromExampleInstrumentedTestto

thefollowing:

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publicclassActivityInputOutputTest

3. Changetheclassdefinitiontothefollowing:

@RunWith(AndroidJUnit4.class)

publicclassActivityInputOutputTest{

@Rule

publicActivityTestRulemActivityRule=newActivityTestRule<>(

MainActivity.class);

}

Theclassdefinitionnowincludesseveralannotations:

@RunWith:TocreateaninstrumentedJUnit4testclass,addthe@RunWith(AndroidJUnit4.class)annotationatthebeginningofyourtestclassdefinition.@Rule:The@Ruleannotationletsyouaddorredefinethebehaviorofeachtestmethodinareusableway,usingoneofthetestruleclassesthattheAndroidTestingSupportLibraryprovides,suchasActivityTestRuleorServiceTestRule.TheruleaboveusesanActivityTestRuleobject,whichprovidesfunctionaltestingofasingleActivity—inthiscase,MainActivity.class.DuringthedurationofthetestyouwillbeabletomanipulateyourActivitydirectly,usingViewMatchers,ViewActions,andViewAssertions.

Intheabovestatement,ActivityTestRulemayturnredatfirst,butthenAndroidStudioaddsthefollowingimportstatementautomatically:

importandroid.support.test.rule.ActivityTestRule;

2.2Testswitchingactivities

TheTwoActivitiesapphastwoactivities:

Main:Includesthebutton_mainbuttonforswitchingtotheSecondactivityandthetext_header_replyviewthatservesasatextheadingfortheMainactivity.Second:Includesthebutton_secondbuttonforswitchingtotheMainactivityandthetext_headerviewthatservesasatextheadingfortheSecondactivity.

Whenyouhaveanappthatswitchesactivities,youshouldtestthatcapability.TheTwoActivitiesappprovidesatextentryfieldandaSendbutton(thebutton_mainid).ClickingSendlaunchestheSecondactivitywiththeenteredtextshowninthetext_headerviewoftheSecondactivity.

Butwhathappensifnotextisentered?WilltheSecondactivitystillappear?

TheActivityInputOutputTestclassoftestswillshowthattheviewsappearregardlessofwhethertextisentered.FollowthesestepstoaddyourteststoActivityInputOutputTest:

1. AddanactivityLaunch()methodtoActivityInputOutputTesttotestwhethertheviewsappearwhenclickingthebuttons,andincludethe@Testnotationonalineimmediatelyabovethemethod:

@Test

publicvoidactivityLaunch(){…}

The@TestannotationtellsJUnitthatthepublicvoidmethodtowhichitisattachedcanberunasatestcase.Atestmethodbeginswiththe@Testannotationandcontainsthecodetoexerciseandverifyasinglefunctioninthecomponentthatyouwanttotest.

2. AddacombinedViewMatcherandViewActionexpressiontotheactivityLaunch()methodtolocatetheviewcontainingthebutton_mainbutton,andincludeaViewActionexpressiontoperformaclick:

onView(withId(R.id.button_main)).perform(click());

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TheonView()methodletsyouuseViewMatcherargumentstofindviews.ItsearchestheviewhierarchytolocateacorrespondingViewinstancethatmeetssomegivencriteria—inthiscase,thebutton_mainview.The.perform(click())expressionisaViewActionexpressionthatperformsaclickontheview.

3. IntheaboveonViewstatement,onView,withID,andclickmayturnredatfirst,butthenAndroidStudioaddsimportstatementsforonView,withID,andclick.

4. AddanotherViewMatcherexpressiontotheactivityLaunch()methodtofindthetext_headerview(whichisintheSecondactivity),andaViewActionexpressiontoperformachecktoseeiftheviewisdisplayed:

onView(withId(R.id.text_header)).check(matches(isDisplayed()));

ThisstatementusestheonView()methodtolocatethetext_headerviewfortheSecondactivityandchecktoseeifitisdisplayedafterclickingthebutton_mainview.

5. IntheaboveonViewstatement,thecheck()methodmayturnredatfirst,butthenAndroidStudioaddsanimportstatementforit.

6. Addsimilarstatementstotestwhetherclickingthebutton_secondbuttonintheSecondactivityswitchestotheMainactivity:

onView(withId(R.id.button_second)).perform(click());

onView(withId(R.id.text_header_reply)).check(matches(isDisplayed()));

7. ReviewtheactivityLaunch()methodyoujustcreatedintheActivityInputOutputTestclass.Itshouldlooklikethis:

@Test

publicvoidactivityLaunch(){

onView(withId(R.id.button_main)).perform(click());

onView(withId(R.id.text_header)).check(matches(isDisplayed()));

onView(withId(R.id.button_second)).perform(click());

onView(withId(R.id.text_header_reply)).check(matches(isDisplayed()));

}

8. Torunthetest,right-click(orControl-click)ActivityInputOutputTestandchooseRunActivityInputOutputTestfromthepop-upmenu.Youcanthenchoosetorunthetestontheemulatororonyourdevice.

Asthetestruns,watchthetestautomaticallystarttheappandclickthebutton.TheSecondactivity'sviewappears.ThetestthenclickstheSecondactivity'sbutton,andtheMainactivityviewappears.

TheRunwindow(thebottompaneofAndroidStudio)showstheprogressofthetest,andwhenfinishes,itdisplays"Testsrantocompletion."IntheleftcolumnAndroidStudiodisplays"AllTestsPassed".

2.3TesttextinputandoutputWriteatestfortextinputandoutput.TheTwoActivitiesappusestheeditText_mainviewforinput,thebutton_mainbuttonforsendingtheinputtotheSecondactivity,andtheSecondactivityviewthatshowstheoutputinthefieldwiththeidtext_message.

1. Addanother@TestannotationandanewtextInputOutput()methodtotheApplicationTestclasstotesttextinputandoutput:

@Test

publicvoidtextInputOutput(){

onView(withId(R.id.editText_main)).perform(typeText("Thisisatest."));

onView(withId(R.id.button_main)).perform(click());

}

TheabovemethodusesaViewMatchertolocatetheviewcontainingtheeditText_mainview,andaViewActiontoenterthetext"Thisisatest."ItthenusesanotherViewMatchertofindtheviewwiththebutton_mainbutton,andanotherViewActiontoclickthebutton.

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2. AddaViewMatchertolocatetheSecondactivity'stext_messageview,andaViewAssertiontoseeiftheoutputmatchestheinputtotestthatthemessagewascorrectlysent:

onView(withId(R.id.text_message)).check(matches(withText("Thisisatest.")));

3. Runthetest.

Asthetestruns,theappstartsandthetextisautomaticallyenteredasinput;thebuttonisclicked,andthetextappearsonthesecondactivity'sscreen.

ThebottompaneofAndroidStudioshowstheprogressofthetest,andwhenfinished,itdisplays"Testsrantocompletion."IntheleftcolumnAndroidStudiodisplays"AllTestsPassed".Youhavesuccessfullytestedthetextinputfield,theSendbutton,andthetextoutputfield.

Solutioncode:

AndroidStudioProject:TwoActivitiesEspressoTest

SeeActivityInputOutputTest.java.

2.4Introduceanerrortoshowatestfailing

Introduceanerrorinthetesttoseewhatafailedtestlookslike.

1. Changethematchcheckonthetext_messageviewfrom"Thisisatest."to"Thisisafailingtest.":

onView(withId(R.id.text_message)).check(matches(withText("Thisisafailingtest.")));

2. Runthetestagain.Thistimeyouwillseethemessageinred,"1testfailed",abovethebottompane,andaredexclamationpointnexttotextInputOutputintheleftcolumn.Scrollthebottompanetothemessage"Testrunningstarted"andseethatalloftheresultsafterthatpointareinred.Theverynextstatementafter"Testrunningstarted"is:

android.support.test.espresso.base.DefaultFailureHandler$AssertionFailedWithCauseError:'withtext:is"Thisis

afailingtest."'doesn'tmatchtheselectedview.

Expected:withtext:is"Thisisafailingtest."

Got:"AppCompatTextView{id=2131427417,res-name=text_message...

Otherfatalerrormessagesappearaftertheabove,duetothecascadingeffectofafailureleadingtootherfailures.Youcansafelyignorethemandfixthetestitself.

Task3:TestthedisplayofspinnerselectionsTheEspressoonView()methodfindsaviewthatyoucantest.Thismethodwillfindaviewinthecurrentviewhierarchy.Butyouneedtobecareful—inanAdapterViewsuchasaspinner,theviewistypicallydynamicallypopulatedwithchildviewsatruntime.Thismeansthereisapossibilitytheviewthatyouwanttotestmaynotbeintheviewhierarchyatthattime.

TheEspressoAPIhandlesthisproblembyprovidingaseparateonData()entrypoint,whichisabletofirstloadtheadapteritemandbringitintofocuspriortolocatingandperformingactionsonanyofitschildren.

PhoneNumberSpinnerisanappfromapreviouslessonthatshowsaspinner,withtheidlabel_spinner,forchoosingthelabelofaphonenumber(Home,Work,Mobile,andOther).Theappdisplaysthechoiceinatextfield,concatenatedwiththeenteredphonenumber.

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wordscouldbeinadifferentlanguage.

AndroidStudioProject:PhoneNumberSpinner

3.1Createthetestmethod

1. OpenthePhoneNumberSpinnerproject,orifyouprefer,makeacopyoftheprojectfirstandthenopenthecopy.SeeCopyandrenameaprojectintheAppendixforinstructions.

2. ConfigureEspressoinyourprojectasdescribedpreviously.3. Expandcom.example.android.phonenumberspinner(androidTest),andopenExampleInstrumentedTest.4. RenameExampleInstrumentedTesttoSpinnerSelectionTestintheclassdefinition,andaddthefollowing:

@RunWith(AndroidJUnit4.class)

publicclassSpinnerSelectionTest{

@Rule

publicActivityTestRulemActivityRule=newActivityTestRule<>(

MainActivity.class);

}

5. CreatetheiterateSpinnerItems()methodaspublicreturningvoid.

3.2AccessthearrayusedforthespinneritemsYouwantthetesttoclickeachiteminthespinnerbasedonthenumberofelementsinthearray.Buthowdoyouaccessthearray?

1. AssignthearrayusedforthespinneritemstoanewarraytousewithintheiterateSpinnerItems()method:

publicvoiditerateSpinnerItems(){

String[]myArray=

mActivityRule.getActivity().getResources()

.getStringArray(R.array.labels_array);

}

Inthestatementabove,thetestaccessestheapplication'sarray(withtheidlabels_array)byestablishingthecontextwiththegetActivity()methodoftheActivityTestRuleclass,andgettingaresourcesinstanceintheapplication'spackageusinggetResources().

2. Assignthelengthofthearraytosize,andconstructaforloopusingthesizeasthemaximumnumberforacounter.

intsize=myArray.length;

for(inti=0;i<size;i++){

}

3.3Locatespinneritemsandclickonthem1. AddanonView()statementwithintheforlooptofindthespinnerandclickonit:

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3.3Locatespinneritemsandclickonthem

1. AddanonView()statementwithintheforlooptofindthespinnerandclickonit:

//Findthespinnerandclickonit.

onView(withId(R.id.label_spinner)).perform(click());

Ausermustclickthespinneritselfinorderclickanyiteminthespinner,soyourtestmustalsoclickthespinnerfirstbeforeclickingtheitem.

2. WriteanonData()statementtofindandclickaspinneritem:

//Findthespinneritemandclickonit.

onData(is(myArray[i])).perform(click());

Theabovestatementmatchesiftheobjectisaspecificiteminthespinner,asspecifiedbythemyArray[i]arrayelement.

IfonDataappearsinred,clicktheword,andthenclicktheredlightbulbiconthatappearsintheleftmargin.Choosethefollowinginthepop-upmenu:

Staticimportmethod'android.support.test.espresso.Espresso.onData'

Ifisappearsinred,clicktheword,andthenclicktheredlightbulbiconthatappearsintheleftmargin.Choosethefollowinginthepop-upmenu:

Staticimportmethod…>Matchers.is(org.hamcrest)

3. AddtwomoreonView()statementstotheforloop:

//FindtheSubmitbuttonandclickonit.

onView(withId(R.id.button_main)).perform(click());

//Findthetextviewandcheckthatthespinneritem

//ispartofthestring.

onView(withId(R.id.text_phonelabel))

.check(matches(withText(containsString(myArray[i]))));

Thefirststatementlocatesthebutton_mainandclicksit.Thesecondstatementcheckstoseeiftheresultingtext_phonelabelmatchesthespinneritemspecifiedbymyArray[i].

IfcontainsStringappearsinred,clicktheword,andthenclicktheredlightbulbiconthatappearsintheleftmargin.Choosethefollowinginthepop-upmenu:

Staticimportmethod…>Matchers.containsString(org.hamcrest)

4. Torunthetest,right-click(orControl-click)SpinnerSelectionTestandchooseRunSpinnerSelectionTestfromthepop-upmenu.Youcanthenchoosetorunthetestontheemulatororonyourdevice.

Thetestrunstheapp,clicksthespinner,and"exercises"thespinner—itclickseachspinneritemfromtoptobottom,checkingtoseeiftheitemappearsinthetextfield.Itdoesn'tmatterhowmanyspinneritemsaredefinedinthearray,orwhatlanguageisusedforthespinner'sitems—thetestperformsallofthemandcheckstheiroutputagainstthearray.

ThebottompaneofAndroidStudioshowstheprogressofthetest,andwhenfinished,itdisplays"Testsrantocompletion."IntheleftcolumnAndroidStudiodisplays"AllTestsPassed".

Solutioncode:

AndroidStudioproject:PhoneNumberSpinnerEspressoTest

SeeSpinnerSelectionTest.java.

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YoulearnedhowtocreateaRecyclerViewinapreviouschapter.LikeanAdapterView(suchasaspinner),aRecyclerViewdynamicallypopulateschildviewsatruntime.ButaRecyclerViewisnotanAdapterView,soyoucan'tuseonData()tointeractwithlistitemsasyoudidintheprevioustaskwithaspinner.WhatmakesaRecyclerViewcomplicatedfromthepointofviewofEspressoisthatonView()can'tfindthechildviewifitisoffthescreen.

Fortunately,youhavetwohandytoolstocircumventthesecomplications:

AclasscalledRecyclerViewActionsthatexposesasmallAPItooperateonaRecyclerView.AnAndroidStudiofeature(inversion2.2andnewer)thatletsyourecordanEspressotest.Useyourappasanormaluser.AsyouclickthroughtheappUI,editabletestcodeisgeneratedforyou.Youcanalsoaddassertionstocheckifaviewholdsacertainvalue.

RecordingEspressotests,ratherthancodingthetestsbyhand,ensuresthatyourappgetsUItestcoverageonareasthatmighttaketoomuchtimeorbetoodifficulttocodebyhand.

Solutioncode:

AndroidStudioproject:RecyclerView

4.1Openandruntheapp

1. OpentheRecyclerViewproject,orifyouprefer,makeacopyoftheprojectfirstandthenopenthecopy.SeeCopyandrenameaprojectintheAppendixforinstructions.

2. ConfigureEspressoinyourprojectasdescribedpreviously.3. Runtheapptoensurethatitrunsproperly.YoucanusetheemulatororanAndroiddevice.

Theappletsyouscrollalistofwords.WhenyouclickonawordsuchasWord15thewordinthelistchangesto"Clicked!Word15".

4.2Recordthetest

1. ChooseRun>RecordEspressoTest,selectyourdeploymenttarget(anemulatororadevice),andclickOK.2. Scrollthewordlistintheappontheemulatorordevice,andtaponWord15.TheRecordYourTestwindowshowsthe

actionthatwasrecorded("TapRecyclerViewwithelementposition15").

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3. ClickAddAssertionintheRecordYourTestwindow.Ascreenshotoftheapp'sUIappearsinapaneontherightsideofthewindow.SelectClicked!Word15inthescreenshotastheUIelementyouwanttocheck.

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4. Choosetextisfromtheseconddrop-downmenu.Thetextyouexpecttoseeisalreadyenteredinthefieldbelowthedrop-downmenu.

5. ClickSaveAssertion,andthenclickCompleteRecording.

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6. Inthedialogthatappears,editthenameofthetesttoRecyclerViewTestsothatitiseasytounderstandthetest'spurpose.

7. AndroidStudiomaydisplayarequesttoaddmoredependenciestoyourGradleBuildfile.ClickYestoaddthedependencies.

8. Expandcom.example.android.recyclerview(androidTest)toseethetest,andrunthetest.Itshouldpass.

Thefollowingisthetest,asrecordedintheRecyclerViewTest.javafile:

Introduction

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@RunWith(AndroidJUnit4.class)

publicclassRecyclerViewTest{

@Rule

publicActivityTestRule<MainActivity>mActivityTestRule=

newActivityTestRule<>(MainActivity.class);

@Test

publicvoidrecyclerViewTest(){

ViewInteractionrecyclerView=onView(

allOf(withId(R.id.recyclerview),isDisplayed()));

recyclerView.perform(actionOnItemAtPosition(15,click()));

ViewInteractiontextView=onView(

allOf(withId(R.id.word),withText("Clicked!Word15"),

childAtPosition(

childAtPosition(

withId(R.id.recyclerview),

11),

0),

isDisplayed()));

textView.check(matches(withText("Clicked!Word15")));

}

privatestaticMatcher<View>childAtPosition(

finalMatcher<View>parentMatcher,finalintposition){

returnnewTypeSafeMatcher<View>(){

@Override

publicvoiddescribeTo(Descriptiondescription){

description.appendText("Childatposition"+position+"inparent");

parentMatcher.describeTo(description);

}

@Override

publicbooleanmatchesSafely(Viewview){

ViewParentparent=view.getParent();

returnparentinstanceofViewGroup&&parentMatcher.matches(parent)

&&view.equals(((ViewGroup)parent).getChildAt(position));

}

};

}

}

ThetestusesaRecyclerViewobjectoftheViewInteractionclass,whichistheprimaryinterfaceforperformingactionsorassertionsonviews,providingbothcheck()andperform()methods.Examinethetestcodetoseehowitworks:

Perform:Thecodebelowusestheperform()methodandtheactionOnItemAtPosition()methodoftheRecyclerViewActionsclasstoscrolltotheposition(15)andclicktheitem:

ViewInteractionrecyclerView=onView(

allOf(withId(R.id.recyclerview),isDisplayed()));

recyclerView.perform(actionOnItemAtPosition(15,click()));

Checkwhetheritmatchestheassertion:Thecodebelowcheckstoseeiftheclickeditemmatchestheassertionthatitshouldbe"Clicked!Word15":

ViewInteractiontextView=onView(

allOf(withId(R.id.word),withText("Clicked!Word15"),

childAtPosition(

childAtPosition(

withId(R.id.recyclerview),

11),

0),

isDisplayed()));

textView.check(matches(withText("Clicked!Word15")));

Introduction

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ThecodeaboveusesamethodcalledchildAtPosition(),whichisdefinedasacustomMatcher:

privatestaticMatcher<View>childAtPosition(

finalMatcher<View>parentMatcher,finalintposition){

//TypeSafeMatcher()returned

...

}

Implementacustommatcher:ThecustommatcherextendstheabstractTypeSaveMatcherclassandrequiresthatyouimplementthefollowing:

ThematchesSafely()method,shownbelow,todefinehowtocheckforaviewinaRecyclerView.ThedescribeTo()method,shownbelow,todefinehowEspressodescribestheoutput'smatcherintheRunpaneatthebottomofAndroidStudioifafailureoccurs.

...

//TypeSafeMatcher()returned

returnnewTypeSafeMatcher<View>(){

@Override

publicvoiddescribeTo(Descriptiondescription){

description.appendText("Childatposition"

+position+"inparent");

parentMatcher.describeTo(description);

}

@Override

publicbooleanmatchesSafely(Viewview){

ViewParentparent=view.getParent();

returnparentinstanceofViewGroup&&

parentMatcher.matches(parent)

&&view.equals(((ViewGroup)

parent).getChildAt(position));

}

};

}

}

YoucanrecordmultipleinteractionswiththeUIinonerecordingsession.Youcanalsorecordmultipletests,andedittheteststoperformmoreactions,usingtherecordedcodeasasnippettocopy,paste,andedit.

SolutioncodeAndroidStudioproject:RecyclerViewEspressoTest

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:WriteanEspressotextfortheScorekeeperappfromapreviouslessonthattestswhethertheDayModebuttonappearsafterclickingNightMode,andwhethertheNightModebuttonappearsafterclickingDayMode.

SummaryInthispractical,youlearnedhowtodothefollowing:

SetupEspressototestanAndroidStudioproject:CheckingforandInstallingtheAndroidSupportRepository.Addinginstrumentationanddependenciestothebuild.gradle(Module:app)file.

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313

Turningoffanimationsinyourtestdevice.Definingthetestclass.

Testtoseewhetheranactivityislaunched:UsingtheonView()methodwithViewMatcherargumentstofindviews.UsingaViewActionexpressiontoperformaclick.UsingaViewAssertionexpressiontocheckiftheviewisdisplayed.UsingaViewAssertionexpressiontoseeiftheoutputmatchestheinput.

Testaspinneranditsselections:UsingtheonData()methodwithaviewthatisdynamicallypopulatedbyanadapteratruntime.Gettingitemsfromanapp'sarraybyestablishingthecontextwithgetActivity()andgettingaresourcesinstanceusinggetResources().UsinganonData()statementtofindandclickeachspinneritem.UsingtheonView()methodwithaViewActionandViewAssertiontocheckiftheoutputmatchestheselectedspinneritem.

RecordatestofaRecyclerView:UsingtheRecyclerViewActionsclassthatexposesmethodstooperateonaRecyclerView.RecordinganEspressotesttoautomaticallygeneratethetestcode.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

TestingYourUserInterface

LearnmoreAndroidStudioDocumentation:

TestYourAppEspressobasicsEspressocheatsheet

AndroidDeveloperDocumentation:

BestPracticesforTestingGettingStartedwithTestingTestingUIforaSingleAppBuildingInstrumentedUnitTestsEspressoAdvancedSamplesTheHamcrestTutorialHamcrestAPIandUtilityClassesTestSupportAPIs

AndroidTestingSupportLibrary:

EspressodocumentationEspressoSamples

Videos

AndroidTestingSupport-AndroidTestingPatterns#1(introduction)AndroidTestingSupport-AndroidTestingPatterns#2(onViewviewmatching)AndroidTestingSupport-AndroidTestingPatterns#3(onDataandadapterviews)

Other:

GoogleTestingBlog:AndroidUIAutomatedTesting

Introduction

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AtomicObject:"Espresso–TestingRecyclerViewsatSpecificPositions"StackOverflow:"HowtoassertinsideaRecyclerViewinEspresso?"GitHub:AndroidTestingSamplesGoogleCodelabs:AndroidTestingCodelab

Introduction

315

7.1:CreateanAsyncTaskContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1:SetuptheSimpleAsyncTaskprojectTask2:CreatetheAsyncTasksubclassTask3:ImplementthefinalstepsCodingchallengeSummaryRelatedconceptLearnmore

Athreadisanindependentpathofexecutioninarunningprogram.WhenanAndroidprogramislaunched,theAndroidRuntimesystemcreatesathreadcalledthe"Main"thread.Asyourprogramruns,eachlineofcodeisexecutedinaserialfashion,linebyline.ThismainthreadishowyourapplicationinteractswithcomponentsfromtheAndroidUIToolkit,andit'swhythemainthreadissometimescalledthe"UIthread".However,sometimesanapplicationneedstoperformresource-intensivework,suchasdownloadingfiles,databasequeries,playingmedia,orcomputingcomplexanalytics.ThistypeofintensiveworkcanblocktheUIthreadifallofthecodeexecutesseriallyonasinglethread.Whentheappisperformingresourcesintensivework,theappdoesnotrespondtotheuserordrawonthescreenbecauseitiswaitingforthatworktobedone.Thiscanyieldpoorperformance,whichnegativelyaffectstheuserexperience.UsersmaygetfrustratedanduninstallyourAndroidappiftheperformanceoftheappisslow.

Tokeeptheuserexperience(UX)runningsmoothlyandrespondingquicklytousergestures,theAndroidFrameworkprovidesahelperclasscalledAsyncTaskwhichprocessesworkoffoftheUIthread.AnAsyncTaskisanabstractJavaclassthatprovidesonewaytomovethisintensiveprocessingontoaseparatethread,therebyallowingtheUIthreadtoremainveryresponsive.Sincetheseparatethreadisnotsynchronizedwiththecallingthread,itiscalledanasynchronousthread.AnAsyncTaskalsocontainsacallbackthatallowsyoutodisplaytheresultsofthecomputationbackintheUIthread.

Inthispractical,youwilllearnhowtoaddabackgroundtasktoyourAndroidappusinganAsyncTask.

WhatyoushouldalreadyKNOWYoushouldbeableto:

CreateanActivity.AddaTextViewtothelayoutfortheactivity.ProgrammaticallygettheidfortheTextViewandsetitscontent.UseButtonviewsandtheironClickfunctionality.

WhatyouwillLEARNDuringthispractical,youwilllearnto:

AddanAsyncTasktoyourappinordertorunataskinthebackground,offoftheUIthread.IdentifyandunderstandthebenefitsanddrawbacksofusingAsyncTaskforbackgroundtasks.

WhatyouwillDO

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Duringthispractical,youwill:

CreateasimpleapplicationthatexecutesabackgroundtaskusinganAsyncTask.Runtheappandseewhathappenswhenyourotatethescreen.

AppoverviewYouwillbuildanappthathasoneTextViewandonebutton.Whentheuserclicksthebutton,theappsleepsforarandomamountoftime,andthendisplaysamessageintheTextViewwhenitwakesup.

Here'swhatthefinishedappwilllooklike:

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Task1.SetuptheSimpleAsyncTaskprojectTheSimpleAsyncTaskUIisstraightforward.ItcontainsabuttonthatlaunchestheAsyncTask,andaTextViewthatdisplaysthestatusoftheapplication.

1.1Createthelayout

1. CreateanewprojectcalledSimpleAsyncTaskusingtheEmptyActivitytemplate.(Acceptthedefaultsfortheotheroptions.)

2. Opentheactivity_main.xmllayoutfile.

i. ChangetherootviewtoLinearLayout.ii. Inthe"HelloWorld"TextViewelement,removethelayout_constraintattributes,iftheyarepresent.iii. AddthefollowingessentialUIelementstothelayout:

View Attributes Values

LinearLayout android:orientation vertical

TextViewandroid:textandroid:id

Iamreadytostartwork!@+id/textView1

Buttonandroid:textandroid:onClick

StartTaskstartTask

Note:Youcansetthelayoutheightandwidthofeachviewtowhateveryouwant,aslongtheviewsremainonthescreenindependentofthescreensize(usingwrap_contentensuresthatthisisthecase).

3. TheonClickattributeforthebuttonwillbehighlightedinyellow,sincethestartTask()methodisnotyetimplementedintheMainActivity.Placeyourcursorinthehighlightedtext,pressAlt+Enter(Option+EnteronaMac)andchooseCreate'startTask(View)in'MainActivity'tocreatethemethodstubinMainActivity.

DependingonyourversionofAndroidStudio,theactivity_main.xmllayoutfilewilllooksomethinglikethefollowing:

<?xmlversion="1.0"encoding="utf-8"?>

<LinearLayoutxmlns:android="http://schemas.android.com/apk/res/android"

android:layout_width="match_parent"

android:layout_height="match_parent"

android:paddingLeft="@dimen/activity_horizontal_margin"

android:paddingRight="@dimen/activity_horizontal_margin"

android:paddingTop="@dimen/activity_vertical_margin"

android:paddingBottom="@dimen/activity_vertical_margin"

android:orientation="vertical">

<TextView

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/ready_to_start"

android:id="@+id/textView1"

android:textSize="24sp"/>

<Button

android:layout_width="wrap_content"

android:layout_height="wrap_content"

android:text="@string/start_task"

android:id="@+id/button"

android:layout_marginTop="56dp"

android:onClick="startTask"/>

</LinearLayout>

Task2.CreatetheAsyncTasksubclass

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319

SinceAsyncTaskisanabstractclass,youneedtosubclassitinordertouseit.InthisexampletheAsyncTaskwillexecuteaverysimplebackgroundtask:itjustsleepsforarandomamountoftime.Inarealapp,thebackgroundtaskcouldperformallsortsofwork,fromqueryingadatabase,toconnectingtotheInternet,tocalculatingthenextGomovesothatyoucanbeatthecurrentGochampion.

AnAsyncTaskhasthefollowingmethodsforperformingworkoffofthemainthread:

onPreExecute():ThismethodrunsontheUIthread,andisusedforsettingupyourtask(likeshowingaprogressbar).doInBackground():Thisiswhereyouimplementthecodetoexecutetheworkthatistobeperformedontheseparatethread.onProgressUpdate():ThisisinvokedontheUIthreadandusedforupdatingprogressintheUI(suchasfillingupaprogressbar)onPostExecute():AgainontheUIthread,thisisusedforupdatingtheresultstotheUIoncetheAsyncTaskhas

finishedloading.Note:AbackgroundorworkerthreadisanythreadwhichisnotthemainorUIthread.

WhenyoucreateanAsyncTask,youmayneedtogiveitinformationabouttheworkwhichitistoperform,whetherandhowtoreportitsprogress,andinwhatformtoreturntheresult.

InthisexerciseyouwilluseanAsyncTasksubclasstodefineworkthatwillruninadifferentthreadthantheUIthread,whichwillavoidanyperformanceissues.

WhenyoucreateanAsyncTask,youcanconfigureitusingtheseparameters:

Params:ThedatatypeoftheparameterssenttothetaskuponexecutingthedoInBackground()overridemethod.Progress:ThedatatypeoftheprogressunitspublishedusingtheonProgressUpdated()overridemethod.Result:ThedatatypeoftheresultdeliveredbytheonPostExecute()overridemethod.

Forexample,anAsyncTaskwiththefollowingclassdeclarationwouldtakeaStringasaparameterindoInBackground()(touseinaquery,forexample),anIntegerforonProgressUpdate()(percentageofjobcomplete),andaBitmapforthetheresultinonPostExecute()(thequeryresult):

publicclassMyAsyncTaskextendsAsyncTask<String,Integer,Bitmap>{}

2.1SubclasstheAsyncTaskInyourfirstAsyncTaskimplementation,theAsyncTasksubclasswillbeverysimple.Itdoesnotrequireaqueryparameterorpublishitsprogress.YouwillonlybeusingthedoInBackground()andonPostExecute()methods.

1. CreateanewJavaclasscalledSimpleAsyncTaskthatextendsAsyncTaskandtakesthreegenerictypeparameters:Voidfortheparams,sincethisAsyncTaskdoesnotrequireanyinputs.Voidfortheprogresstype,sincetheprogressisnotpublished.AStringastheresulttype,sinceyouwillupdatetheTextViewwithastringwhentheAsyncTaskhascompleted

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320

execution.

publicclassSimpleAsyncTaskextendsAsyncTask<Void,Void,String>{}

Note:Theclassdeclarationwillbeunderlinedinred,sincetherequiredmethoddoInBackground()hasnotyetbeenimplemented.TheAsyncTaskwillneedtoupdatetheTextViewonceithascompletedsleeping.TheconstructorwillthenneedtoincludetheTextView,sothatitcanbeupdatedinonPostExecute().

2. DefineamembervariablemTextView.3. ImplementaconstructorforAsyncTaskthattakesaTextViewandsetsmTextViewtotheonepassedinTextView:

publicSimpleAsyncTask(TextViewtv){

mTextView=tv;

}

2.2ImplementdoInBackground()1. AddtherequireddoInBackground()method.Placeyourcursoronthehighlightedclassdeclaration,pressAlt+Enter

(Option+EnteronaMac)andselectImplementmethods.ChoosedoInBackground()andclickOK:

@Override

protectedStringdoInBackground(Void...voids){

returnnull;

}

2. ImplementdoInBackground()to:

Generatearandomintegerbetween0and10Multiplythatnumberby200Putthecurrentthreadtosleep.(UseThread.sleep())inatry/catchblock.ReturntheString"Awakeatlastafterxxmilliseconds"(wherexxisthenumberofmillisecondstheappslept)

@Override

protectedStringdoInBackground(Void...voids){

//Generatearandomnumberbetween0and10

Randomr=newRandom();

intn=r.nextInt(11);

//Makethetasktakelongenoughthatwehave

//timetorotatethephonewhileitisrunning

ints=n*200;

//Sleepfortherandomamountoftime

try{

Thread.sleep(s);

}catch(InterruptedExceptione){

e.printStackTrace();

}

//ReturnaStringresult

return"Awakeatlastaftersleepingfor"+s+"milliseconds!";

}

2.3ImplementonPostExecute()WhenthedoInBackground()methodcompletes,thereturnvalueisautomaticallypassedtotheonPostExecute()callback.

1. ImplementonPostExecute()totakeaStringargument(thisiswhatyoudefinedinthethirdparameterofAsyncTaskandwhatyourdoInBackground()methodreturned)anddisplaythatstringintheTextView:

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protectedvoidonPostExecute(Stringresult){

mTextView.setText(result);

}

Note:YoucanupdatetheUIinonPostExecute()becauseitisrunonthemain(UI)thread.YoucannotcallmTextView.setText()indoInBackground(),becausethatmethodisexecutedonaseparatethread.

Task3.Implementthefinalsteps

3.1ImplementthemethodthatstartstheAsyncTaskYourappnowhasanAsyncTaskthatperformsworkinthebackground(oritwouldifyoudidn'tcallsleep()asthesimulatedwork.)YoucannowimplementthemethodthatgetscalledwhentheStartTaskbuttonisclicked,totriggerthebackgroundtask.

1. IntheMainActivity.javafile,addamembervariabletostoretheTextView.

privateTextViewmTextView;

2. IntheonCreate()method,initializemTextViewtotheTextViewintheUI.3. AddcodetothestartTask()methodtocreateaninstanceofSimpleAsyncTask,passingtheTextViewmTextViewto

theconstructor.4. Callexecute()onthatSimpleAsyncTaskinstance.

Note:Theexecute()methodiswhereyoupassintheparameters(separatedbycommas)thatarethenpassedintodoInBackground()bythesystem.SincethisAsyncTaskhasnoparameters,youwillleaveitblank.

5. UpdatetheTextViewtoshowthetext"Napping…"

publicvoidstartTask(Viewview){

//Putamessageinthetextview

mTextView.setText("Napping...");

//StarttheAsyncTask.

//TheAsyncTaskhasacallbackthatwillupdatethetextview.

newSimpleAsyncTask(mTextView).execute();

}

SolutioncodeforMainActivity:

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packageandroid.example.com.simpleasynctask;

importandroid.os.Bundle;

importandroid.support.v7.app.AppCompatActivity;

importandroid.view.View;

importandroid.widget.TextView;

publicclassMainActivityextendsAppCompatActivity{

//TheTextViewwherewewillshowresults

TextViewmTextView;

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

//InitializemTextView

mTextView=(TextView)findViewById(R.id.textView1);

}

publicvoidstartTask(Viewview){

//Putamessageinthetextview

mTextView.setText("Napping...");

//StarttheAsyncTask.

//TheAsyncTaskhasacallbackthatwillupdatethetextview.

newSimpleAsyncTask(mTextView).execute();

}

}

3.2ImplementonSaveInstanceState()1. RuntheappandclicktheStartTaskbutton.Howlongdoestheappnap?2. ClicktheStartTaskbuttonagain,andwhiletheappisnapping,rotatethedevice.Ifthebackgroundtaskcompletes

beforeyoucanrotatethephone,tryagain.Alternatively,youcanupdatethecodeandmakeitsleepforalongertimeperiod.

Note:You'llnoticethatwhenthedeviceisrotated,theTextViewresetstoitsinitialcontentandtheAsyncTaskdoesn'tseemabletoupdatetheTextView.Thereareseveralthingsgoingonhere:

Whenyourotatethedevice,thesystemrestartstheapp,callingonDestroy()andthenonCreate(),whichrestartstheactivitylifecycle.SincetheAsyncTasksarenolongerconnectedtothelifecycleofyourapp,andcannotreconnecttotheactivity.TheAsyncTaskswillcontinuerunningtocompletioninthebackground,consumingsystemresources,butnevershowingtheresultsintheUI,whichgetsresetinonCreate().ItwillneverbeabletoupdatetheTextViewthatwaspassedtoit,sincethatparticularTextViewhasalsobeendestroyed.Eventually,thesystemrunoutofresources,andwillfail.EvenwithouttheAsyncTask,therotationofthedeviceresetsalloftheUIelementstotheirdefaultstate,whichfortheTextViewimpliesaparticularstringthatyousetintheactivity_main.xmlfile.

Forthesereasons,AsyncTasksarenotwellsuitedtotaskswhichmaybeinterruptedbythedestructionoftheActivity.InusecaseswherethisiscriticalyoucanuseadifferenttypeofclasscalledaLoader,whichyouwillimplementinalaterpractical.

InordertopreventtheTextViewfromresettingtotheinitialstring,youneedtosaveitsstate.You'vealreadylearnedhowtomaintainthestateofviewsinapreviouspractical,usingtheSavedInstanceStateclass.

YouwillnowimplementonSaveInstanceState()topreservethecontentofyourTextViewwhentheactivityisspontaneouslydestroyed.

Note:NotallusesofAsyncTaskrequireyoutohandlethestateoftheviewsonrotation.ThisappusesaTextViewto

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323

displaytheresultsoftheapp,sopreservingthestateisuseful.Inothercases,suchasuploadingafile,youmaynotneedanypersistentinformationintheUI,soretainingthestateisnotcritical.

3. OverridetheonSaveInstanceState()methodinMainActivitytopreservethetextinsidetheTextViewwhentheactivityisdestroyed:

outState.putString(TEXT_STATE,mTextView.getText().toString());

4. RetrievethevalueoftheTextViewwhentheactivityisrestoredintheonCreate()method.

//RestoreTextViewifthereisasavedInstanceState

if(savedInstanceState!=null){

mTextView.setText(savedInstanceState.getString(TEXT_STATE));

}

SolutioncodeforMainActivity:

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packageandroid.example.com.simpleasynctask;

importandroid.os.Bundle;

importandroid.support.v7.app.AppCompatActivity;

importandroid.view.View;

importandroid.widget.TextView;

/**

*TheSimpleAsyncTaskappcontainsabuttonthatlaunchesanAsyncTask

*whichsleepsintheasynchronousthreadforarandomamountoftime.

*/

publicclassMainActivityextendsAppCompatActivity{

//KeyforsavingthestateoftheTextView

privatestaticfinalStringTEXT_STATE="currentText";

//TheTextViewwherewewillshowresults

privateTextViewmTextView=null;

/**

*Initializestheactivity.

*@paramsavedInstanceStateThecurrentstatedata

*/

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

//InitializemTextView

mTextView=(TextView)findViewById(R.id.textView1);

//RestoreTextViewifthereisasavedInstanceState

if(savedInstanceState!=null){

mTextView.setText(savedInstanceState.getString(TEXT_STATE));

}

}

/**`

*HandlestheonCLickforthe"StartTask"button.LaunchestheAsyncTask

*whichperformsworkoffoftheUIthread.

*

*@paramviewTheview(Button)thatwasclicked.

*/

publicvoidstartTask(Viewview){

//Putamessageinthetextview

mTextView.setText(R.string.napping);

//StarttheAsyncTask.

//TheAsyncTaskhasacallbackthatwillupdatethetextview.

newSimpleAsyncTask(mTextView).execute();

}

/**

*SavesthecontentsoftheTextViewtorestoreonconfigurationchange.

*@paramoutStateThebundleinwhichthestateoftheactivityissavedwhenitisspontaneouslydestroye

d.

*/

@Override

protectedvoidonSaveInstanceState(BundleoutState){

super.onSaveInstanceState(outState);

//SavethestateoftheTextView

outState.putString(TEXT_STATE,mTextView.getText().toString());

}

}

SolutioncodeAndroidStudioproject:SimpleAsyncTask

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325

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:AsyncTaskprovidesanotherveryusefuloverridemethod:onProgressUpdate(),whichallowsyoutoupdatetheUIwhiletheAsyncTaskisrunning.UsethismethodtoupdatetheUIwiththecurrentsleeptime.LooktotheAsyncTaskdocumentationtoseehowonProgressUpdate()isproperlyimplemented.RememberthatintheclassdefinitionofyourAsyncTask,youwillneedtospecifythedatatypetobeusedintheonProgressUpdate()method.

SummaryAvoidresource-intensiveworkintheUIthreadwhichmaymakeyourUIsluggishorerratic.

AnycodethatdoesnotinvolvedrawingtheUIorrespondingtotheuserinputshouldbemovedfromtheUIthreadtoanother,separatethread.

AnAsyncTaskisanabstractJavaclassthatmovesintensiveprocessingontoaseparatethread.AsyncTaskmustbesubclassedtobeused.AsyncTaskhas4usefulmethods:onPreExecute(),doInBackground(),onPostExecute()andonProgressUpdate().

doInBackground()istheonlymethodthatisrunonaseparateworkerthread.YoushouldnotcallUImethodsinyourAsyncTaskmethod.TheothermethodsofAsyncTaskrunintheUIthreadandallowcallingmethodsofUIcomponents.

RotatinganAndroiddevicedestroysandrecreatesanActivity.ThiscandisassociatetheUIfromthebackgroundthread,whichwillcontinuetorun.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

AsyncTaskandAsyncTaskLoader

LearnmoreAndroiddeveloperdocumentation:

ProcessesandThreadsProcessingbitmapsofftheUIthreadusingAsyncTaskAsyncTask

Otherresources:

https://realm.io/news/android-threading-background-tasks/

Videos:

ThreadingPerformance101byPerformanceGuruColtMcAnlis.Learnmoreaboutthemainthreadandwhyit'sbadtorunlong-runningtasksonthemainthread.GoodAsyncTaskHuntingbyColtMcAnlis.LearnmoreaboutAsyncTasks.

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7.2:ConnecttotheInternetwithAsyncTaskandAsyncTaskLoaderContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOTask1.ExploretheBooksAPITask2.Createthe"WhoWroteIt?"appTask3.ImplementUIbestpracticesTask4.MigratetoAsyncTaskLoaderCodingchallengesSummaryRelatedconceptLearnmore

InthispracticalyouwilluseanAsyncTasktostartabackgroundtaskwhichgetsdatafromtheInternetusingasimpleRESTAPI.YouwillusetheGoogleAPIExplorertolearnhowtoquerytheBookSearchAPI,implementthisqueryinaworkerthreadusingAsyncTask,anddisplaytheresultinyourUI.ThenyouwillreimplementthesamebackgroundtaskusingAsyncTaskLoader,whichwillbemoreefficientinupdatingyourUI,handlingperformanceissues,andimprovingtheoverallUX.

WhatyoushouldalreadyKNOWFromthepreviouspracticalsyoushouldbeableto:

Createanactivity.AddaTextViewtothelayoutfortheactivity.ImplementonClickfunctionalitytoabuttoninyourlayout.ImplementanAsyncTaskanddisplaytheresultinyourUI.Passinformationbetweenactivitiesasextras.

WhatyouwillLEARNInthispractical,youwilllearnto:

UsetheGoogleAPIExplorertoinvestigateGoogleAPIsandtoviewJSONresponsestohttprequests.UsetheBooksAPIasanexampleAPIretrievingdataovertheInternetandkeeptheUIfastandresponsive.Youwon'tlearntheBooksAPIindetailinthispractical.Yourappwillonlyusethesimplebooksearchfunction.TolearnmoreabouttheBooksAPIseetheBooksAPIreferencedocumentation.ParsetheJSONresultsreturnedfromyourAPIquery.ImplementanAsyncTaskLoaderthatpreservesdatauponconfigurationchanges.UpdateyourUIusingtheLoadercallbacks.

WhatyouwillDOInthispractical,youwill:

UsetheGoogleAPIExplorertolearnaboutthesimplesearchfeatureoftheBooksAPI.Createthe"WhoWroteIt?"applicationthatqueriestheBooksAPIusingaworkerthreadanddisplaystheresultinthe

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327

UI.Modifythe"WhoWroteit?"apptouseanAsyncTaskLoaderinsteadofanAsyncTask.

AppOverviewYouwillbuildanappthatcontainsanEditTextfieldandaButton.TheuserentersthenameofthebookintheEditTextfieldandclicksthebutton.ThebuttonexecutesanAsyncTaskwhichqueriestheGoogleBookSearchAPItofindtheauthorandtitleofthebooktheuserislookingfor.TheresultsareretrievedanddisplayedinaTextViewfieldbelowthebutton.Oncetheappisworking,youwillthenmodifytheapptouseAsyncTaskLoaderinsteadoftheAsyncTaskclass.

Introduction

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Introduction

329

Task1.ExploretheBooksAPIInthispracticalyouwillusetheGoogleBooksAPItosearchforinformationaboutabook,suchastheauthor(s)andthetitle.TheGoogleBooksAPIprovidesprogrammaticaccesstotheGoogleBookSearchserviceusingRESTAPIs.ThisisthesameserviceusedbehindthesceneswhenyoumanuallyexecuteasearchonGoogleBooks.YoucanusetheGoogleAPIExplorerandGoogleBookSearchinyourbrowsertoverifythatyourAndroidappisgettingtheexpectedresults.

1.1SendaBooksAPIRequest

1. GototheGoogleAPIsExplorer(foundathttps://developers.google.com/apis-explorer/).2. ClickBooksAPI.3. Find(Ctrl-ForCmd-F)books.volumes.listandclickthatfunctionname.Youshouldseeawebpagethatliststhe

variousparametersoftheBooksAPIfunctionthatperformsthebooksearches.4. Intheqfieldenterabookname,orpartialbookname.Theqparameteristheonlyrequiredfield.5. UsethemaxResultsandprintTypefieldstolimittheresultstothetop10matchingbooksthatwereprinted.The

maxResultsfieldtakesanintegervaluethatlimitstheamountofresultsperquery.TheprintTypefieldtakesoneofthreestringarguments:all,whichdoesnotlimittheresultsbytypeatall;books,whichreturnsonlybooksinprint;andmagazineswhichreturnsonlymagazines.

6. Makesurethatthe"AuthorizerequestsusingOAuth2.0"switchatthetopoftheformisturnedoff.ClickExecutewithoutOAuthatthebottomoftheform.

7. ScrolldowntoseetheRequestandResponse.

TheRequestfieldisanexampleofaUniformResourceIdentifier(URI).AURIisastringthatnamesorlocatesaparticularresource.URLsareacertaintypeofURIforidentifyingandlocatingawebresource.FortheBooksAPI,therequestisaURLthatcontainsyoursearchasaparameter(followingtheqparameter).NoticetheAPIkeyfieldafterthequeryfield.Forsecurityreasons,whenaccessingapublicAPI,youusuallyneedtogetanAPIkeyandincludeitinyourRequest.However,thisspecificAPIdoesnotrequireakey,soyoucanleaveoutthatportionoftheRequestURIinyourapp.

1.2AnalyzetheBooksAPIResponse

TowardsthebottomofthepageyoucanseetheResponsetothequery.TheresponseusestheJSONformat,whichisacommonformatforAPIqueryresponses.IntheAPIExplorerwebpage,theJSONcodeisnicelyformattedsothatitishumanreadable.Inyourapplication,theJSONresponsewillbereturnedfromtheAPIserviceasasinglestring,andyouwillneedtoparsethatstringtoextracttheinformationyouneed.

1. IntheResponsesection,findthevalueforthe"title"key.Noticethatthisresulthasasinglekeyandvalue.2. Findthevalueforthe"authors"key.Noticethatthisonecancontainanarrayofvalues.3. Inthispractical,youwillonlyreturnthetitleandauthorsofthefirstitem.

Task2.Createthe"WhoWroteIt?"AppNowthatyouarefamiliarwiththeBooksAPImethodthatyouwillbeusing,it'stimetosetupthelayoutofyourapplication.

2.1Createtheprojectanduserinterface1. CreateanappprojectcalledWhoWroteIt?withoneActivity,usingtheEmptyActivityTemplate.2. AddthefollowingUIelementsintheXMLfile,usingaverticalLinearLayoutasrootview—theviewthatcontainsallthe

otherviewsinsidealayoutXMLfile.MakesuretheLinearLayoutusesandroid:orientation="vertical":

Introduction

330

View Attributes Values

TextView

android:layout_width

android:layout_height

android:id

android:text

android:textAppearance

wrap_content

wrap_content

@+id/instructions

@string/instructions

@style/TextAppearance.AppCompat.Title

EditText

android:layout_width

android:layout_height

android:id

android:inputType

android:hint

match_parent

wrap_content

@+id/bookInput

text

@string/input_hint

Button

android:layout_width

android:layout_height

android:id

android:text

android:onClick

wrap_content

wrap_content

@+id/searchButton

@string/button_text

searchBooks

TextView

android:layout_width

android:layout_height

android:id

android:textAppearance

wrap_content

wrap_content

@+id/titleText

@style/TextAppearance.AppCompat.Headline

TextView

android:layout_width

android:layout_height

android:id

android:textAppearance

wrap_content

wrap_content

@+id/authorText

@style/TextAppearance.AppCompat.Headline

3. Inthestrings.xmlfile,addthesestringresources:

<stringname="instructions">Enterabookname,orpartofa

bookname,orjustsometextfromabooktofind

thefullbooktitleandwhowrotethebook!</string>

<stringname="button_text">SearchBooks</string>

<stringname="input_hint">EnteraBookTitle</string>

4. CreateamethodcalledsearchBooks()inMainActivity.javatohandletheonClickbuttonaction.AswithallonClickmethods,thisonetakesaViewasaparameter.

2.2SetuptheMainActivityToquerytheBooksAPI,youneedtogettheuserinputfromtheEditText.

1. InMainActivity.java,createmembervariablesfortheEditText,theauthorTextViewandthetitleTextView.2. InitializethesevariablesinonCreate().3. InthesearchBooks()method,getthetextfromtheEditTextwidgetandconverttoaString,assigningittoastring

variable.

StringqueryString=mBookInput.getText().toString();

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Note:mBookInput.getText()returnsan"Editable"datatypewhichneedstobeconvertedintoastring.

2.3CreateanemptyAsyncTask

YouarenowreadytoconnecttotheInternetandusetheBookSearchRESTAPI.Networkconnectivitycanbesometimesbesluggishorexperiencedelays.Thismaycauseyourapptobehaveerraticallyorbecomeslow,soyoushouldnotmakeanetworkconnectionontheUIthread.IfyouattemptanetworkconnectionontheUIthread,theAndroidRuntimemayraiseaNetworkOnMainThreadExceptiontowarnyouthatit'sabadidea.

UseanAsyncTasktomakenetworkconnections:

1. CreateanewJavaclasscalledFetchBookinapp/javathatextendsAsyncTask.AnAsyncTaskrequiresthreearguments:

Theinputparameters.Theprogressindicator.Theresulttype.

Thegenerictypeparametersforthetaskwillbe<String,Void,String>sincetheAsyncTasktakesaStringasthefirstparameter(thequery),Voidsincethereisnoprogressupdate,andStringsinceitreturnsastringasaresult(theJSONresponse).

2. Implementtherequiredmethod,doInBackground(),byplacingyourcursorontheredunderlinedtext,pressingAlt+Enter(Opt+EnteronaMac)andselectingImplementmethods.ChoosedoInBackground()andclickOK.Makesuretheparametersandreturntypesarethecorrecttype(IttakesaStringarrayandreturnsaString).i. ClicktheCodemenuandchooseOverridemethods(orpressCtrl+O).SelecttheonPostExecute()method.TheonPostExecute()methodtakesaStringasaparameterandreturnsvoid.

3. TodisplaytheresultsintheTextViews,youmusthaveaccesstothoseTextViewsinsidetheAsyncTask.CreatemembervariablesintheFetchBookAsyncTaskforthetwoTextViewsthatshowtheresults,andinitializetheminaconstructor.YouwillusethisconstructorinyourMainActivitytopassalongtheTextViewstoyourAsyncTask.

SolutioncodeforFetchBook:

publicclassFetchBookextendsAsyncTask<String,Void,String>{

privateTextViewmTitleText;

privateTextViewmAuthorText;

publicFetchBook(TextViewmTitleText,TextViewmAuthorText){

this.mTitleText=mTitleText;

this.mAuthorText=mAuthorText;

}

@Override

protectedStringdoInBackground(String...params){

returnnull;

}

@Override

protectedvoidonPostExecute(Strings){

super.onPostExecute(s);

}

}

2.4CreatetheNetworkUtilsclassandbuildtheURI

Inthisstep,youwillopenanInternetconnectionandquerytheBooksAPI.Thissectionhasquitealotofcode,soremembertovisitthedeveloperdocumentationforConnectingtotheNetworkifyougetstuck.YouwillwritethecodeforconnectingtotheinternetinahelperclasscalledNetworkUtils.

1. CreateanewJavaclasscalledNetworkUtilsbyclickingFile>New>JavaClassandonlyfillinginthe"Name"field.2. CreateauniqueLOG_TAGvariabletousethroughoutNetworkUtilsclassforlogging:

Introduction

332

privatestaticfinalStringLOG_TAG=NetworkUtils.class.getSimpleName();

3. CreateanewstaticmethodcalledgetBookInfo()thattakesaStringasaparameter(whichwillbethesearchterm)andreturnsaString(theJSONStringresponsefromtheAPIyouexaminedearlier).

staticStringgetBookInfo(StringqueryString){}

4. CreatethefollowingtwolocalvariablesingetBookInfo()thatwillbeneededlatertohelpconnectandreadtheincomingdata.

HttpURLConnectionurlConnection=null;

BufferedReaderreader=null;

5. CreateanotherlocalvariableattheendofgetBookInfo()tocontaintherawresponsefromthequeryandreturnit:

StringbookJSONString=null;

returnbookJSONString;

IfyouremembertherequestfromtheBooksAPIwebpage,youwillnoticethatalltherequestsbeginwiththesameURI.Tospecifythetypeofresource,youappendqueryparameterstothebaseURI.Itiscommonpracticetoseparateallofthesequeryparametersintoconstants,andcombinethemusingaUri.BuildersotheycanbereusedfordifferentURI's.TheUriclasshasaconvenientmethod,Uri.buildUpon()thatreturnsaURI.Builderthatwecanuse.

Forthisapplication,youwilllimitthenumberandtypeofresultsreturnedtoincreasethequeryspeed.Torestrictthequery,youwillonlylookforbooksthatareprinted.

6. CreatethefollowingmemberconstantsintheNetworkUtilsclass:

privatestaticfinalStringBOOK_BASE_URL="https://www.googleapis.com/books/v1/volumes?";//BaseURIforthe

BooksAPI

privatestaticfinalStringQUERY_PARAM="q";//Parameterforthesearchstring

privatestaticfinalStringMAX_RESULTS="maxResults";//Parameterthatlimitssearchresults

privatestaticfinalStringPRINT_TYPE="printType";//Parametertofilterbyprinttype

7. Createaskeletontry/catch/finallyblockingetBookInfo().ThisiswhereyouwillmakeyourHTTPrequest.ThecodetobuildtheURIandissuethequerywillgointhetryblock.ThecatchblockisusedtohandleanyproblemswithmakingtheHTTPrequestandthefinallyblockisforclosingthenetworkconnectionafteryou'vefinishedreceivingtheJSONdataandreturningtheresult.

try{

...

}catch(Exceptionex){

...

}finally{

returnbookJSONString;

}

8. BuildupyourrequestURIinthetryblock:

//BuildupyourqueryURI,limitingresultsto10itemsandprintedbooks

UribuiltURI=Uri.parse(BOOK_BASE_URL).buildUpon()

.appendQueryParameter(QUERY_PARAM,queryString)

.appendQueryParameter(MAX_RESULTS,"10")

.appendQueryParameter(PRINT_TYPE,"books")

.build();

9. ConvertyourURItoaURL:

URLrequestURL=newURL(builtURI.toString());

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333

2.5MaketheRequest

ItisfairlycommontomakeanAPIrequestviatheinternet.Sinceyouwillprobablyusethisfunctionalityagain,youmaywanttocreateautilityclasswiththisfunctionalityordevelopausefulsubclassforyourownconvenience.ThisAPIrequestusestheHttpURLConnectionclassincombinationwithanInputStreamandaStringBuffertoobtaintheJSONresponsefromtheweb.IfatanypointtheprocessfailsandInputStreamorStringBufferareempty,itreturnsnullsignifyingthatthequeryfailed.

1. InthetryblockofthegetBookInfo()method,opentheURLconnectionandmaketherequest:

urlConnection=(HttpURLConnection)requestURL.openConnection();

urlConnection.setRequestMethod("GET");

urlConnection.connect();

2. ReadtheresponseusinganInputStreamandaStringBuffer,thenconvertittoaString:

InputStreaminputStream=urlConnection.getInputStream();

StringBufferbuffer=newStringBuffer();

if(inputStream==null){

//Nothingtodo.

returnnull;

}

reader=newBufferedReader(newInputStreamReader(inputStream));

Stringline;

while((line=reader.readLine())!=null){

/*Sinceit'sJSON,addinganewlineisn'tnecessary(itwon'taffect

parsing)butitdoesmakedebugginga*lot*easierifyouprintoutthe

completedbufferfordebugging.*/

buffer.append(line+"\n");

}

if(buffer.length()==0){

//Streamwasempty.Nopointinparsing.

returnnull;

}

bookJSONString=buffer.toString();

3. Closethetryblockandlogtheexceptioninthecatchblock.

catch(IOExceptione){

e.printStackTrace();

returnnull;

}

4. CloseboththeurlConnectionandthereadervariablesinthefinallyblock:

finally{

if(urlConnection!=null){

urlConnection.disconnect();

}

if(reader!=null){

try{

reader.close();

}catch(IOExceptione){

e.printStackTrace();

}

}

}

Note:Eachtimetheconnectionfails,thiscodereturnsnull.ThismeansthatonPostExecute()willhavetocheckitsinputparameterforanullstringandlettheuserknowtheconnectionfailed.Thiserrorhandlingstrategyissimplistic,astheuserhasnoideawhytheconnectionfailed.Abettersolutionforaproductionapplicationwouldbetohandleeachpointoffailuredifferentlysothattheusercangettheappropriatefeedback.

5. LogthevalueofthebookJSONStringvariablebeforereturningit.YouarenowdonewiththegetBookInfo()method.

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334

Log.d(LOG_TAG,bookJSONString);

6. InyourAsyncTaskdoInBackground()method,callthegetBookInfo()method,passinginthesearchtermwhichyouobtainedfromtheparamsargumentpassedinbythesystem(itisthefirstvalueintheparamsarray).ReturntheresultofthismethodinthedoInBackground()method:

returnNetworkUtils.getBookInfo(params[0]);

7. NowthatyourAsyncTaskissetup,youneedtolaunchitfromtheMainActivityusingtheexecute()method.AddthefollowingcodetoyoursearchBooks()methodinMainActivity.javatolaunchtheAsyncTask:

newFetchBook(mTitleText,mAuthorText).execute(mQueryString);

8. Runyourapp.Executeasearch.Yourappwillcrash.LookatyourLogstoseewhatiscausingtheerror.Youshouldseethefollowingline:

Causedby:java.lang.SecurityException:Permissiondenied(missingINTERNETpermission?)

ThiserrorindicatesthatyouhavenotincludedthepermissiontoaccesstheinternetinyourAndroidManifest.xmlfile.Connectingtotheinternetintroducesnewsecurityconcerns,whichiswhyyourappsdonothaveconnectivitybydefault.Youmustaddpermissionsmanuallyintheformofa<uses-permission>;tagintheAndroidManifest.xml.

2.6AddtheInternetpermissions

1. OpentheAndroidManifest.xmlfile.2. AllpermissionsofyourappneedtobeputintheAndroidManifest.xmlfileoutsideofthe<application>;tag.You

shouldbesuretofollowtheorderinwhichtagsaredefinedinAndroidManifest.xml.3. Addthefollowingxmltagsoutsideofthe<application>tag:

<uses-permissionandroid:name="android.permission.INTERNET"/>

<uses-permissionandroid:name="android.permission.ACCESS_NETWORK_STATE"/>

4. Buildandrunyourappagain.RunningaqueryshouldnowresultinaJSONstringbeingprintedtotheLog.

2.7ParsetheJSONstring

Nowthatyouhavethecorrectresponsetoyourquery,youmustparsetheresultstoextracttheinformationyouwanttodisplayintheUI.Fortunately,JavahasexistingclassesthataidsintheparsingandhandlingofJSONtypedata.Thisprocess,aswellasupdatingtheUI,willhappenintheonPostExecute()method.

ThereischancethatthedoInBackground()methodmightnotreturntheexpectedJSONstring.Forexample,thetrycatchmightfailandthrowanexception,thenetworkmighttimeoutorotherunhandlederrorsmightoccur.Inthosecases,theJavaJSONmethodswillfailtoparsethedataandwillthrowexceptions.Thisiswhyyouhavetodotheparsinginthetryblock,andthecatchblockmusthandlethecasewhereincorrectorincompletedataisreturned.

ToparsetheJSONdataandhandlepossibleexceptions,dothefollowing:

1. InonPostExecute(),addatry/catchblockbelowthecalltosuper.2. Usethebuilt-inJavaJSONclasses(JSONObjectandJSONArray)toobtaintheJSONarrayofresultsitemsinthetry

block.

JSONObjectjsonObject=newJSONObject(s);

JSONArrayitemsArray=jsonObject.getJSONArray("items");

3. IteratethroughtheitemsArray,checkingeachbookfortitleandauthorinformation.Ifbotharenotnull,exittheloopandupdatetheUI;otherwisecontinuelookingthroughthelist.Thisway,onlyentrieswithbothatitleandauthorswillbedisplayed.

Introduction

335

//Iteratethroughtheresults

for(inti=0;i<itemsArray.length();i++){

JSONObjectbook=itemsArray.getJSONObject(i);//Getthecurrentitem

Stringtitle=null;

Stringauthors=null;

JSONObjectvolumeInfo=book.getJSONObject("volumeInfo");

try{

title=volumeInfo.getString("title");

authors=volumeInfo.getString("authors");

}catch(Exceptione){

e.printStackTrace();

}

//Ifbothatitleandauthorexist,updatetheTextViewsandreturn

if(title!=null&&authors!=null){

mTitleText.setText(title);

mAuthorText.setText(authors);

return;

}

}

4. Iftherearenoresultswhichmeetthecriteriaofhavingbothavalidauthorandatitle,andtheloophasstopped,setthetitleTextViewtoread"NoResultsFound",andcleartheauthorsTextView.

5. Inthecatchblock,printtheerrortothelog,setthetitleTextViewto"NoResultsFound",andcleartheauthorsTextView.

Solutioncode:

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336

//MethodforhandlingtheresultsontheUIthread

@Override

protectedvoidonPostExecute(Strings){

super.onPostExecute(s);

try{

JSONObjectjsonObject=newJSONObject(s);

JSONArrayitemsArray=jsonObject.getJSONArray("items");

for(inti=0;i<itemsArray.length();i++){

JSONObjectbook=itemsArray.getJSONObject(i);

Stringtitle=null;

Stringauthors=null;

JSONObjectvolumeInfo=book.getJSONObject("volumeInfo");

try{

title=volumeInfo.getString("title");

authors=volumeInfo.getString("authors");

}catch(Exceptione){

e.printStackTrace();

}

if(title!=null&&authors!=null){

mTitleText.setText(title);

mAuthorText.setText(authors);

return;

}

}

mTitleText.setText("NoResultsFound");

mAuthorText.setText("");

}catch(Exceptione){

mTitleText.setText("NoResultsFound");

mAuthorText.setText("");

e.printStackTrace();

}

}

Task3.ImplementUIBestPracticesYounowhaveafunctioningappthatusestheBooksAPItoexecuteabooksearch.However,thereareafewthingsthattodonotbehaveasexpected:

WhentheuserclicksSearchBooks,thekeyboarddoesnotdisappear,andthereisnoindicationtotheuserthatthequeryisactuallybeingexecuted.Ifthereisnonetworkconnection,orthesearchfieldisempty,theappstilltriestoquerytheAPIandfailswithoutproperlyupdatingtheUI.Ifyourotatethescreenduringaquery,theAsyncTaskbecomesdisconnectedfromtheActivity,anditisnotabletoupdatetheUIwiththeresults.

Youwillfixtheseissuesinthefollowingsection.

3.1HidetheKeyboardandUpdatetheTextView

Theuserexperienceofsearchingisnotintuitive.Whenthebuttonispushed,thekeyboardremainsvisibleandthereisnowaytoknowthatthequeryisinprogress.OnesolutionistoprogrammaticallyhidethekeyboardandupdateoneoftheresultTextViewstoread"Loading…"whilethequeryisbeingperformed.Tousethissolution,youcan:

1. AddthefollowingcodetothesearchBooks()methodtohidethekeyboardwhenthebuttonispressed:

Introduction

337

InputMethodManagerinputManager=(InputMethodManager)

getSystemService(Context.INPUT_METHOD_SERVICE);

inputManager.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(),

InputMethodManager.HIDE_NOT_ALWAYS);

2. AddalineofcodebeneaththecalltoexecutetheFetchBooktaskthatchangesthetitleTextViewtoread"Loading…"andclearstheauthorTextView.

3. ExtractyourStringresources.

3.2Managethenetworkstateandtheemptysearchfieldcase

Wheneveryourapplicationusesthenetwork,itneedstohandlethepossibilitythatanetworkconnectionisunavailable.BeforeattemptingtoconnecttothenetworkinyourAsyncTaskorAsyncTaskLoader,yourappshouldcheckthestateofthenetworkconnection.

1. ModifyyoursearchBooks()methodtocheckboththenetworkconnectionandifthereisanytextinthesearchfieldbeforeexecutingtheFetchBooktask.

2. UpdatetheUIinthecasethatthereisnointernetconnectionornotextinthesearchfield.DisplaythecauseoftheerrorintheTextView.

Solutioncode:

publicvoidsearchBooks(View,view){

StringqueryString=mBookInput.getText().toString();

InputMethodManagerinputManager=(InputMethodManager)

getSystemService(Context.INPUT_METHOD_SERVICE);

inputManager.hideSoftInputFromWindow(getCurrentFocus().getWindowToken(),

InputMethodManager.HIDE_NOT_ALWAYS);

ConnectivityManagerconnMgr=(ConnectivityManager)

getSystemService(Context.CONNECTIVITY_SERVICE);

NetworkInfonetworkInfo=connMgr.getActiveNetworkInfo();

if(networkInfo!=null&&networkInfo.isConnected()&&queryString.length()!=0){

newFetchBook(mTitleText,mAuthorText).execute(queryString);

mAuthorText.setText("");

mTitleText.setText(R.string.loading);

}

else{

if(queryString.length()==0){

mAuthorText.setText("");

mTitleText.setText("Pleaseenterasearchterm");

}else{

mAuthorText.setText("");

mTitleText.setText("Pleasecheckyournetworkconnectionandtryagain.");

}

}

}

Task4.MigratetoAsyncTaskLoaderWhenusinganAsyncTask,itcannotupdatetheUIifaconfigurationchangeoccurswhilethebackgroundtaskisrunning.Toaddressthissituation,theAndroidSDKprovidesasetofclassescalledloadersdesignedspecificallyforloadingdataintotheUIasynchronously.Ifyouusealoader,youdon'thavetoworryabouttheloaderlosingtheabilitytoupdatetheUIintheactivitythatinitiallycreatedit.TheLoaderframeworkdoestheworkforyoubyreassociatingtheloaderwiththeappropriateActivitywhenthedevicechangesitsconfiguration.Thismeansthatifyourotatethedevicewhilethetaskisstillrunning,theresultswillbedisplayedcorrectlyintheActivityoncethedataisreturned.

Introduction

338

InthistaskyouwilluseaspecificloadercalledanAsyncTaskLoader.AnAsyncTaskLoaderisanabstractsubclassofLoaderandusesanAsyncTasktoefficientlyloaddatainthebackground.

Note:WhenyouusedanAsyncTask,youimplementedtheonPostExecute()methodintheAsyncTasktodisplaytheresultsonthescreen.WhenyouuseanAsyncTaskLoader,youdefinecallbackmethodsintheActivitytodisplaytheresults.LoadersprovidealotofadditionalfunctionalitybeyondjustrunningtasksandreconnectingtotheActivity.Forexample,youcanattachaloadertoadatasourceandhaveitautomaticallyupdatetheUIelementswhentheunderlyingdatachanges.Loaderscanalsobeprogrammedtoresumeloadingifinterrupted.

SowhyshouldyouuseanAsyncTaskifanAsyncTaskLoaderissomuchmoreuseful?Theansweristhatitdependsonthesituation.Ifthebackgroundtaskislikelytofinishbeforeanyconfigurationchangesoccur,anditisnotcrucialthatitupdatestheUI,anAsyncTaskmaybesufficient.TheLoaderframeworkactuallyusesanAsyncTaskbehindthescenestoworkitsmagic.

AgoodruleofthumbistouseanAsyncTaskLoaderinsteadofanAsyncTaskiftheusermightrotatethescreenwhilethejobisrunning,orwhenit'scriticaltoupdatetheUIwhenthejobfinishes.

InthisexerciseyouwilllearnhowtouseaAsyncTaskLoaderinsteadofanAsyncTasktorunyourBooksAPIquery.Youwilllearnmoreabouttheusesofotherloadersinalaterlesson.

ImplementingaLoaderrequiresthefollowingcomponents:

AclassthatextendsaLoaderclass(inthiscase,AsyncTaskLoader).AnActivitythatimplementstheLoaderManager.LoaderCallbacksclass.AninstanceoftheLoaderManager.

1. TheActivity.2. TheLoaderManager.LoaderCallbacks.3. TheLoadersubclass.4. TheLoaderImplementation.

TheLoaderManagerautomaticallymovestheloaderthroughitslifecycledependingonthestateofthedataandtheActivity.Forexample,theLoaderManagercallsonStartLoading()whentheloaderisinitializedanddestroystheloaderwhentheActivityisdestroyed.

TheLoaderManager.LoaderCallbacksareasetofmethodsintheActivitythatarecalledbytheLoaderManagerwhenloaderisbeingcreated,whenthedatahasfinishedloading,andwhentheloaderisreset.TheLoaderCallbackscantaketheresultsofthetaskandpassthembacktotheActivity'sUI.

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TheLoadersubclasscontainsthedetailsofloadingthedata,usuallyoverridingatleastonStartLoading().Itcanalsocontainadditionalfeaturessuchasobservingthedatasourceforchangesandcachingdatalocally.

YourLoadersubclassimplementsLoaderlifecyclecallbackmethodssuchasonStartLoading(),onStopLoading()andonReset().TheloadersubclassalsocontainstheforceLoad()methodwhichinitiatestheloadingofthedata.Thismethodisnotcalledautomaticallywhentheloaderisstartedbecausesomesetupisusuallyrequiredbeforealoadisperformed.ThesimplestimplementationwouldcallforceLoad()inonStartLoading()whichresultsinaloadeverytimetheLoaderManagerstartstheloader.

4.1CreateanAsyncTaskLoader

1. CopytheWhoWroteItproject,inordertopreservetheresultsofthepreviouspractical.RenamethecopiedprojectWhoWroteItLoader.

2. CreateanewclassinyourJavadirectorycalledBookLoader.3. HaveyourBookLoaderclassextendAsyncTaskLoaderwithparameterizedtype<String>.4. Makesureyouimporttheloaderfromthev4SupportLibrary.5. Implementtherequiredmethod(loadInBackground()).Noticethesimilaritybetweenthismethodandtheinitial

doInBackground()methodfromAsyncTask.6. Createtheconstructorforyournewclass.InAndroidStudio,it'slikelytheclassdeclarationwillstillbeunderlinedinred

becauseyourconstructordoesnotmatchthesuperclassimplementation.Withyourtextcursorontheclassdeclarationline,pressAlt+Enter(Option+EnteronaMac)andchooseCreateconstructormatchingsuper.Thiswillcreateaconstructorwiththecontextasaparameter.

DefineonStartLoading()

1. PressCtrl+OtoopentheOverridemethodsmenu,andselectonStartLoading.Thismethodiscalledbythesystemwhenyoustartyourloader.

2. TheloaderwillnotactuallystartloadingthedatauntilyoucalltheforceLoad()method.InsidetheonStartLoading()methodstub,callforceLoad()tostarttheloadInBackground()methodoncetheLoaderiscreated.

DefineloadInBackground()

1. CreateamembervariablemQueryStringthatwillholdthequeryString,andmodifytheconstructortotakeaStringasanargumentandassignittothemQueryStringvariable.

2. IntheloadInBackground()method,callthegetBookInfo()methodpassinginmQueryString,andreturntheresulttodownloadtheinformationfromtheBooksAPI:

@Override

publicStringloadInBackground(){

returnNetworkUtils.getBookInfo(mQueryString);

}

4.2ModifyMainActivityYoumustnowimplementtheLoaderCallbacksinyourMainActivitytohandletheresultsoftheloadInBackground()AsyncTaskLoadermethod.

1. AddtheLoaderManager.LoaderCallbacksimplementationtoyourMainActivityclassdeclaration,parameterizedwiththeStringtype:

publicclassMainActivityextendsAppCompatActivity

implementsLoaderManager.LoaderCallbacks<String>{

2. Implementalltherequiredmethods:onCreateLoader(),onLoadFinished(),onLoaderReset().PlaceyourtextcursorontheclasssignaturelineandenterAlt+Enter(Option+EnteronaMac).Makesureallthemethodsareselected.

Note:IftheimportsforLoaderandLoaderManagerinMainActivitydonotmatchtheimportfortheAsyncTaskLoaderfortheBookLoaderclass,youwillhavesometypeerrorsinthecallbacks.Makesurethatallimportsarefromthe

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AndroidSupportLibrary.

LoadersusetheBundleclasstopassinformationfromthecallingactivitytotheLoaderCallbacks.YoucanaddprimitivedatatoabundlewiththeappropriateputType()method.

Tostartaloader,youhavetwooptions:

initLoader():Thismethodcreatesanewloaderifonedoesnotexistalready,andpassesintheargumentsBundle.Ifaloaderexists,thecallingActivityisre-associatedwithitwithoutupdatingtheBundle.restartLoader():ThismethodisthesameasinitLoader()exceptthatifitfindsanexistingloader,itdestroysandrecreatesitwiththenewBundle.

BothofthesemethodsaredefinedintheLoaderManager,whichmanagesalltheLoaderinstancesusedinanActivity(orFragment).EachActivityhasexactlyoneLoaderManagerinstancethatisresponsibleforthelifecycleoftheLoadersthatitmanages.

Currently,theFetchBookAsyncTaskistriggeredwhentheuserpressesthebutton.You'llwanttostartyourloaderwithanewBundleeachtimethebuttonispressed.Todothis,youneedtoedittheonClickmethodforthebutton.

1. InthesearchBooks()method,whichistheonClickmethodforthebutton,replacethecalltoexecutetheFetchBooktaskwithacalltorestartLoader(),passinginthequerystringyougotfromtheEditTextintheBundle:

BundlequeryBundle=newBundle();

queryBundle.putString("queryString",queryString);

getSupportLoaderManager().restartLoader(0,queryBundle,this);

TherestartLoader()methodtakesthreearguments:

Aloaderid(usefulifyouimplementmorethanoneloaderinyouractivity).AnargumentsBundle(thisiswhereanydataneededbytheloadergoes).TheinstanceofLoaderCallbacksyouimplementedinyouractivity.IfyouwanttheloadertodelivertheresultstotheMainActivity,specifythisasthethirdargument.

2. ExaminetheOverridemethodsintheLoaderCallbacksclass.Thesemethodsare:

onCreateLoader():CalledwhenyouinstantiateyourLoader.onLoadFinished():Calledwhentheloader'staskfinishes.ThisiswhereyouaddthecodetoupdateyourUIwiththeresults.onLoaderReset():Cleansupanyremainingresources.

Youwillonlybedefiningthefirsttwomethods,sinceyourcurrentdatamodelisasimplestringthatdoesnotneedextracarewhentheloaderisreset.

ImplementonCreateLoader()

1. InonCreateLoader(),returnaninstanceoftheBookLoaderclass,passinginthequeryStringobtainedfromtheargumentsBundle:

returnnewBookLoader(this,args.getString("queryString"));

ImplementonLoadFinished()

1. UpdateonLoadFinished()toprocessyourresult,whichistherawJSONStringresponsefromtheBooksAPI.i. CopythecodefromonPostExecute()inyourFetchBookclasstoonLoadFinished()inyourMainActivity,excludingthecalltosuper.onPostExecute().

ii. ReplacetheargumenttotheJSONObjectconstructorwiththepassedindataString.2. Runyourapp.

Youshouldhavethesamefunctionalityasbefore,butnowinaLoader!Onethingstilldoesnotwork.Whenthedeviceisrotated,theViewdataislost.ThatisbecausewhentheActivityiscreated(orrecreated),theActivitydoesnotknowthereisaloaderrunning.AninitLoader()methodisneededinonCreate()ofMainActivitytoreconnecttothe

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loader.

3. AddthefollowingcodeinonCreate()toreconnecttotheLoaderifitalreadyexists:

if(getSupportLoaderManager().getLoader(0)!=null){

getSupportLoaderManager().initLoader(0,null,this);

}

Note:Iftheloaderexists,initializeit.YouonlywanttoreassociatetheloadertotheActivityifaqueryhasalreadybeenexecuted.Intheinitialstateoftheapp,nodataisloadedsothereisnonetopreserve.

4. Runyourappagainandrotatethedevice.TheLoaderManagernowpreservesyourdataacrossdeviceconfigurations!

5. RemovetheFetchBookclassasitisnolongerused.

SolutioncodeAndroidStudioproject:WhoWroteItLoader

CodingchallengesNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge1:ExplorethethespecificAPIyouareusingingreaterdetailandfindasearchparameterthatrestrictstheresultstobooksthataredownloadableintheepubformat.Addthisparametertoyourrequestandviewtheresults.

Challenge2:TheresponsefromtheBooksAPIcontainsasmanyresultsasyousetwiththemaxResultsparameter,butinthisimplementationyouareonlyreturningthefirstvalidBookresult.ModifyyourappsothatthedataisdisplayedinaRecyclerViewthathasamaxResultsamountofentries.

SummaryTasksthatconnecttothenetwork,orrequireextratimeprocessing,shouldnotbeexecutedontheUIthread.

TheAndroidRuntimeusuallydefaultstoStrictModewhichwillraiseanexceptionifyouattemptnetworkconnectivityorfileaccessontheUIthread.

TheGoogleAPIExplorerisatoolthathelpsyouexplorenumerousGoogleAPIsinteractively.TheBooksSearchAPIisasetofRESTfulAPIstoaccessGoogleBooksprogrammatically.AnAPIrequesttoGoogleBooksisintheformofaURL.TheresponsetothatAPIrequestreturnsaJSONstring.

UsegetText()toretrievetextfromanEditTextview.ItcanbeconvertedintoasimpleStringbyusingtoString().TheURIclasshasaconvenientmethod,Uri.buildUpon()thatreturnsaURI.BuilderthatcanbeusedtoconstructaURIstring.AnAsyncTaskisaclassthatallowsyoutoruntasksinthebackground,asynchronously,insteadofontheUIthread.

AnAsyncTaskcanbestartedviaexecute().AnAsyncTaskwillnotbeabletoupdatetheUIiftheActivityitiscontrollingterminates(suchasinaconfigurationchangeonthedevice).AnAsyncTaskmustbesubclassedtobeused.ThesubclasswilloverrideatleastonemethoddoInBackground(Params),andmostoftenwilloverrideasecondoneonPostExecute(Result)aswell.

WheneveranAsyncTaskisexecuted,itgoesthroughthefollowing4steps:

1. onPreExecute().InvokedontheUIthreadbeforethetaskisexecuted.Thisstepisnormallyusedtosetupthetask.

2. doInBackground(Params).InvokedonthebackgroundthreadimmediatelyafteronPreExecute()finishesexecuting.Thisstepisusedtoperformbackgroundcomputationthatcantakealongtime.

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3. onProgressUpdate(Progress).InvokedontheUIthreadafteryouacallindoInBackgroundtopublishProgress(Progress).

4. onPostExecute(Result).InvokedontheUIthreadafterthebackgroundcomputationhasfinished.Theresultofthebackgroundcomputationgetspassedintothismethodasaparameter.

AsyncTaskLoaderistheLoaderequivalentofanAsyncTask.Itprovidesamethod,loadInBackground(),thatrunsonaseparatethreadandwhoseresultsareautomaticallydeliveredtotheUIthread(totheonLoadFinished()LoaderManagercallback).YoumustconfigurenetworkpermissionsintheAndroidmanifestfiletoconnecttotheInternet:

<uses-permissionandroid:name="android.permission.INTERNET">

UsethebuiltinJavaJSONclasses(JSONObjectandJSONArray)tocreateandparseJSONstrings.

ALoaderallowsasynchronousloadingofdatainanActivity.ALoadercanbeusedtore-establishcommunicationtotheUIwhenanActivityisterminatedbeforethetaskfinishes(suchasbydevicerotation).AnAsyncTaskLoaderisaLoaderthatusesanAsyncTaskhelperclassbehindthescenestodoworkinthebackgroundoffthemainthread.LoadersaremanagedbyaLoaderManager;oneormoreLoaderscanbeassignedandmanagedbyasingleLoadManager.TheLoaderManagerallowsyoutoassociateanewlycreatedActivitywithaLoaderusinggetSupportLoaderManager().initLoader().

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

ConnecttotheInternetwithAsyncTaskandAsyncTaskLoader

LearnmoreAndroidDeveloperDocumentation

Guides

ConnectingtotheNetworkManagingNetworkStateLoaders

Reference

AsyncTaskAsyncTaskLoader

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7.3:BroadcastReceiversContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOTask1.SetupthePowerReceiverProjectTask2.SendandReceiveaCustomBroadcastCodingchallengeSummaryRelatedconceptLearnmore

CertaineventsthatcanhappenintheAndroidsystemmightaffectthefunctionalityofapplicationsinstalledonthedevice.Forexample,ifthesystemhasfinishedbooting,youmightlikeyourweatherapptoupdateitsinformation.TheAndroidframeworkhandlesthisbysendingoutsystembroadcastscontainingIntentsthataremeanttobereceivedusingBroadcastReceivers.ABroadcastReceiveristhebaseclassforcodethatwillreceiveIntentssentbysendBroadcast().Therearetwomajorclassesofbroadcaststhatcanbereceived:

Normalbroadcasts(sentwithContext.sendBroadcast())arecompletelyasynchronous.Allreceiversofthebroadcastareruninanundefinedorder,oftenatthesametime.Thisismoreefficient,butmeansthatreceiverscannotusetheresultorabortAPIsincludedhere.Orderedbroadcasts(sentwithContext.sendOrderedBroadcast)aredeliveredtoonereceiveratatime.Aseachreceiverexecutesinturn,itcanpropagatearesulttothenextreceiver,oritcancompletelyabortthebroadcastsothatitwon'tbepassedtootherreceivers.Theorderreceiversrunincanbecontrolledwiththeandroid:priorityattributeofthematchingintent-filter;receiverswiththesameprioritywillberuninanarbitraryorder.

Eveninthecaseofnormalbroadcasts,thesystemmayinsomesituationsreverttodeliveringthebroadcastonereceiveratatime.Inparticular,forreceiversthatmayrequirethecreationofaprocess,onlyonewillberunatatimetoavoidoverloadingthesystemwithnewprocesses.Inthissituation,however,thenon-orderedsemanticshold:thesereceiversstillcannotreturnresultsoraborttheirbroadcast.

Additionally,youcancreateIntentswithcustomactionsandbroadcastthemyourselffromyourapplicationusingthesendBroadcast()method.ThebroadcastwillbereceivedbyallapplicationswithaBroadcastReceiverregisteredforthataction.TolearnmoreaboutbroadcastIntentsandBroadcastreceivers,visittheIntentdocumentation.

ItisusefultonotethatwhiletheIntentclassisusedforsendingandreceivingbroadcasts,theIntentbroadcastmechanismiscompletelyseparatefromIntentsthatareusedtostartActivities.

Inthispractical,you'llcreateanappthatrespondstoachangeinthechargingstateofyourdevice,aswellassendsandreceivesacustomBroadcastIntent.

WhatyoushouldalreadyKNOWPriortothispractical,youshouldbeableto:

IdentifykeypartsoftheAndroidManifest.xmlfile.CreateImplicitIntents.

WhatyouwillLEARNDuringthispractical,youwilllearnto:

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SubclassandimplementaBroadcastReceiver.RegisterforsystemBroadcastintents.CreateandsendcustomBroadcastintents.

WhatyouwillDOInthispractical,youwill:

SubclassaBroadcastReceivertoshowaToastwhenabroadcastisreceived.Registeryourreceivertolistentosystembroadcasts.Sendandreceiveacustombroadcastintent.

AppoverviewThePowerReceiverapplicationwillregisteraBroadcastReceiverthatdisplaysaToastmessagewhenthedeviceisconnectedordisconnectedfrompower.ItwillalsosendandreceiveacustomBroadcastIntenttodisplayadifferentToastmessage.

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Task1.SetupthePowerReceiverProject

1.1CreatetheProject1. CreateanewprojectcalledPowerReceiver,acceptthedefaultoptionsandusetheEmptytemplate.2. CreateanewBroadcastReceiver.SelectthepackagenameintheAndroidProjectViewandnavigatetoFile>New>

Other>BroadcastReceiver.3. NametheclassCustomReceiverandmakesure"Exported"and"Enabled"arechecked.

Note:The"Exported"featureallowsyourapplicationtorespondtooutsidebroadcasts,while"Enabled"allowsittobeinstantiatedbythesystem.

4. NavigatetoyourAndroidmanifestfile.NotethatAndroidStudioautomaticallygeneratesa<receiver>tagwithyourchosenoptionsasattributes.BroadcastReceiverscanalsoberegisteredprogrammatically,butitiseasiesttodefinetheminthemanifest.

1.2RegisteryourReceiverforsystembroadcasts

Inordertoreceiveanybroadcasts,youmustfirstdeterminewhichbroadcastintentsyouareinterestedin.IntheIntentdocumentation,under"StandardBroadcastActions",youcanfindsomeofthecommonbroadcastintentssentbythesystem.Inthisapp,youwillbeinterestedintwoparticularbroadcasts:ACTION_POWER_CONNECTEDandACTION_POWER_DISCONNECTED.BroadcastReceiversregisterforbroadcastthesamewayyouregisteredyouractivitiesforimplicitIntents:youuseanintentfilter.Youlearnedaboutimplicitintentsinanearlierpractical.

1. IntheAndroidManifest.xmlfile,addthefollowingcodebetweenthe<receiver>tagstoregisteryourReceiverforthesystemIntents:

<intent-filter>

<actionandroid:name="android.intent.action.ACTION_POWER_CONNECTED"/>

<actionandroid:name="android.intent.action.ACTION_POWER_DISCONNECTED"/>

</intent-filter>

1.3ImplementonReceive()inyourBroadcastReceiver

OncetheBroadcastReceiverinterceptsabroadcastthatitisregisteredfor,theIntentisdeliveredtothereceiver'sonReceive()method,alongwiththecontextinwhichthereceiverisrunning.

1. NavigatetoyourCustomReceiverfile,anddeletethedefaultimplementationinsidetheonReceive()method.2. ObtaintheactionfromtheintentandstoreitinaStringvariablecalledintentAction:

@Override

publicvoidonReceive(Contextcontext,Intentintent){

StringintentAction=intent.getAction();

}

3. CreateaswitchstatementwiththeintentActionstring,sothatyourappcandisplayadifferenttoastmessageforeachspecificactionyourreceiverisregisteredfor:

switch(intentAction){

caseIntent.ACTION_POWER_CONNECTED:

break;

caseIntent.ACTION_POWER_DISCONNECTED:

break;

}

4. InitializeaStringvariablecalledtoastMessagebeforetheswitchstatement,andmakeit'svaluenullsothatitcanbesetdependingonthebroadcastactionyoureceive.

5. AssigntoastMessageto"Powerconnected!"iftheactionisACTION_POWER_CONNECTED,and"Powerdisconnected!"ifitis

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ACTION_POWER_DISCONNECTED.Extractyourstringresources.6. Displayatoastmessageforashortdurationaftertheswitchstatement:

Toast.makeText(context,toastMessage,Toast.LENGTH_SHORT).show();

7. Runyourapp.Afteritisinstalled,unplugyourdevice.Itmaytakeamomentthefirsttime,butsureenough,atoastisdisplayedeachtimeyouplugin,orunplugyourdevice.Note:Ifyouareusinganemulator,youcantogglethepowerconnectionstatebyselectingtheellipsesiconforthemenu,chooseBatteryontheleftbar,andtoggleusingtheChargerconnectionsetting.

1.4RestrictyourBroadcastReceiver

BroadcastReceiversarealwaysactive,andthereforeyourappdoesnotevenneedtoberunningforitsonReceive()methodtobecalled.

1. Goahead,tryitout:closeyourapp,andplugorunplugyourdevice.

Thetoastmessageisstilldisplayed!

Thereisalotofresponsibilityonyou,asthedeveloper,tonotoverwhelmyouruserwithnotificationsorunwantedfunctionalityeverytimeabroadcastoccurs.Inthisexample,havingaToastmessagepopupeverytimethepowerstatechangescouldquicklyannoytheuser.Tolimitthis,youwilladdsomecodetoensurethatthebroadcastreceiverisonlyactivewhentheappisshowing.

ThePackageManagerclassisresponsibleforenablinganddisablingaparticularandroidcomponent(suchasaservice,activityorbroadcastreceiver).ThisisaccomplishedusingthesetComponentEnabledSetting()methodwhichtakesthreearguments:

TheComponentName(anidentifierforthecomponentyouwanttoenableordisable).OneofthePackageManagerclassconstantsthatrepresenttheenabledstateofacomponent.InthisappwewillusePackageManager.COMPONENT_ENABLED_STATE_ENABLEDandPackageManager.COMPONENT_ENABLED_STATE_DISABLED.SeethePackageManagerreferencefortheotherconstants.Anoptionalflagconstantthattellsthesystemnottokilltheappwhenchangingthestateofthecomponent:PackageManager.DONT_KILL_APP.

2. Forthebroadcastreceivertoonlybeactivewhentheappisshowing,enableitinonStart()anddisableitinonStop().

3. Createtwomembervariables:aPackageManagerandaComponentName.4. InitializebothoftheminonCreate().

InstantiatethePackageManagerwithgetPackageManager().TheconstructorforComponentNametakestheapplicationcontextandtheclassnameofthecomponent:

mReceiverComponentName=newComponentName(this,CustomReceiver.class);

mPackageManager=getPackageManager();

5. OverridebothonStart()andonStop():

@Override

protectedvoidonStart(){

super.onStart();

}

@Override

protectedvoidonStop(){

super.onStop();

}

6. CallsetComponentEnabledSetting()onthePackageManagerinonStart().PassintheComponentname,thePackageManager.COMPONENT_ENABLED_STATE_ENABLEDconstant,andtheDONT_KILL_APPflag:

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mPackageManager.setComponentEnabledSetting

(mReceiverComponentName,PackageManager.COMPONENT_ENABLED_STATE_ENABLED,

PackageManager.DONT_KILL_APP);

7. InonStop(),usethePackageManagertodisabletheCustomReceiver,usingthePackageManager.COMPONENT_ENABLED_STATE_DISABLEDconstant:

mPackageManager.setComponentEnabledSetting

(mReceiverComponentName,PackageManager.COMPONENT_ENABLED_STATE_DISABLED,

PackageManager.DONT_KILL_APP);

Task2.SendandReceiveaCustomBroadcastInadditiontorespondingtosystembroadcasts,yourapplicationcanalsosendandreceivecustomBroadcastIntents.AcustombroadcastintentisexactlythesameasystemoneexceptyoumustdefineyourownIntentactionforit(auniquestring)andit'sdeliveredusingthesendBroadcast()method.Inthistask,youwilladdabuttontoyouractivitythatsendsacustomBroadcastIntent,whichwillberegisteredbyyourreceiveranddisplayedinaToastmessage.

2.1DefineyourcustomBroadcastActionstringBoththesenderandreceiverofacustombroadcastmustagreeonauniqueactionstringfortheBroadcastIntent.ItisacommonpracticetocreateuniqueactionstringsbyprependingyourActionNamewithyourpackagename.

1. CreateaconstantStringvariableinbothyourMainActivityandyourCustomReceiverclasstobeusedastheBroadcastIntentAction(thisisyourcustomactionstring):

privatestaticfinalStringACTION_CUSTOM_BROADCAST=

"com.example.android.powerreceiver.ACTION_CUSTOM_BROADCAST";

2.2Adda"SendCustomBroadcast"Button

1. Inyouractivity_main.xmlfile,addaButtonviewwiththefollowingattributes:

Attribute Value

android:id "@+id/sendBroadcast"

android:layout_width wrap_content

android:layout_height wrap_content

android:text "SendCustomBroadcast"

android:layout_margin "8dp"

android:onClick "sendCustomBroadcast"

2. Extractyourstringresources.3. CreatethestubforthesendCustomBroadcast()method:ClickintheyellowhighlightedonClickmethodname.Press

Alt(OptionforMacusers)+Enterandchoose'Create'sendCustomBroadcast(View)'in'MainActivity'.

2.3ImplementsendCustomBroadcast()

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Becausethisbroadcastismeanttobeusedsolelybyyourapplication,youshoulduseLocalBroadcastManagertomanagethebroadcastsinyourapplication.LocalBroadcastManagerisaclassthatallowsyoutoregisterforandsendbroadcastsofIntentstolocalobjectswithinyourapp.Bykeepingbroadcastslocal,yourapplicationdatawillnotbesharedwithotherAndroidapplications,keepingyourinformationmoresecureandmaintainingsystemefficiency.

1. InthesendCustomBroadcast()methodinMainActivity,createanewIntent,withyourcustomactionstringastheargument.

IntentcustomBroadcastIntent=newIntent(ACTION_CUSTOM_BROADCAST);

2. SendthebroadcastusingtheLocalBroadcastManagerclass:LocalBroadcastManager.getInstance(this).sendBroadcast(customBroadcastIntent);

2.4RegisteryourCustomBroadcastForsystembroadcasts,youregisteredyourreceiverintheAndroidManifest.xmlfile.Itisalsopossibletoregisteryourreceiverforspecificactionsprogrammatically.ForbroadcastssentusingLocalBroadcastManager,staticregistrationsinthemanifestisnotallowed.

Ifyouprogrammaticallyregisterthebroadcastreceiver,youmustalsounregisterthereceiverwhenitisnolongerneeded.Inyourapplication,thereceiverwillonlyneedtorespondtothecustombroadcastwhenitisrunning,sowecanthereforeregistertheactioninonCreate()andunregisteritinonDestroy().

1. CreateamembervariableinMainActivityforyourReceiverandinitializeit:

privateCustomReceivermReceiver=newCustomReceiver();

2. InonCreate(),getaninstanceofLocalBroadcastManagerandregisteryourreceiverwiththecustomintentaction:

LocalBroadcastManager.getInstance(this)

.registerReceiver(mReceiver,newIntentFilter(ACTION_CUSTOM_BROADCAST));

3. OverridetheonDestroy()methodandunregisteryourreceiverfromtheLocalBroadcastManager:

@Override

protectedvoidonDestroy(){

LocalBroadcastManager.getInstance(this).unregisterReceiver(mReceiver);

super.onDestroy();

}

2.5RespondtotheCustomBroadcast1. InonReceive()inyourCustomReceiverclass,addacasestatementforthecustomIntentAction.2. Modifythetoastmessageto"CustomBroadcastReceived",extractitintoyourstrings.xmlandcallit

custom_broadcast_toast(pressAlt+EnterorOption+EnteronaMacandchooseextractstringresource):

caseACTION_CUSTOM_BROADCAST:

toastMessage=context.getString(R.string.custom_broadcast_toast);

break;

Note:BroadcastReceiversthatareregisteredprogrammaticallyarenotaffectedbytheenablingordisablingdonebythePackageManagerclass,whichismeantforcomponentslistedintheAndroidManifestfile.Enablingordisablingsuchreceiversisdonebyregisteringorunregisteringthem,respectively.Inthiscase,turningoffthe"ReceiverEnabled"togglewillstopthepowerconnectedordisconnectedtoastmessages,butnottheCustomBroadcastIntentToastmessages.

That'sit!YourappnowdeliverscustomBroadcastintentsandisabletoreceivebothsystemandcustomBroadcasts.

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SolutioncodeAndroidStudioproject:PowerReceiver

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:Acommonpatternforbroadcastreceiversisstartingsomeupdateoractiononcethedevicehasbooted.ImplementaBroadcastReceiverthatwillshowatoastmessagehalfanhourafterthedevicehasbooted.

SummaryBroadcastReceiversareoneofthefundamentalcomponentsofanandroidapplication.BroadcastReceiverscanreceiveIntentsbroadcastedbyboththesystemandapplication.TheIntentbroadcastmechanismiscompletelyseparatefromIntentsthatareusedtostartActivities.YouneedtosubclasstheBroadcastReceiverclassandimplementonReceive()toprocesstheincomingIntentassociatedwiththebroadcast.AbroadcastreceivercanberegisteredintheAndroidmanifestfileorprogrammatically.UseLocalBroadcastManagertoregisterandsendforBroadcaststhatareprivatetoyourapplication.LocalBroadcastManagerismoreefficientandsecurethansystembroadcasts.ForbroadcastssentusingLocalBroadcastManager,youcanonlyregisterinterestforspecificactionsprogrammatically.AcommonpracticetocreateuniqueIntentactionnamesforbroadcastsistoprependyourActionNamewithyourpackagename.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

BroadcastReceivers

LearnmoreAndroidDeveloperDocumentation

Guides

IntentsandIntentFiltersManipulatingBroadcastReceiversOnDemand

Reference

BroadcastReceiver

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8.1:NotificationsContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.CreateabasicnotificationTask2.UpdateandcancelyournotificationTask3.AddnotificationactionsCodingchallengeSummaryRelatedconceptLearnmore

Untilnow,theappsyouhavebuiltusedUIelementsthatarevisibleonlywhenyourappisrunning.TheonlyexceptiontothisistheBroadcastReceiveryouimplementedthatshowedaToastmessagewhenthedevicewasconnectedordisconnectedfrompower.Therearemanytimeswhenyouwanttoshowyouruserinformationevenwhenyourapplicationisnotrunning.Forexample,youmightletthemknowthatnewcontentisavailable,orupdatethemontheirfavoriteteamscore.TheAndroidframeworkprovidesamechanismforyourapptonotifyusersevenwhentheappisnotintheforeground:theNotificationframework.

ANotificationisamessageyoucandisplaytotheuseroutsideofyourapplication'snormalUI.WhenAndroidissuesanotification,itwillfirstappearasaniconinthenotificationareaofthedevice.Toseethespecificdetailsofthenotification,theuseropensthenotificationdrawer.Boththenotificationareaandthenotificationdraweraresystem-controlledareasthattheusercanviewatanytime.

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Inthispracticalyou'llcreateanappthattriggersanotificationwhenabuttonispressedandprovidestheabilitytoupdatethenotificationorcancelit.

WhatyoushouldalreadyKNOWForthispractical,youshouldbeableto:

ImplementtheonClick()methodforbuttons.CreateImplicitIntents.SendCustomBroadcastIntents.UseBroadcastReceivers.

WhatyouwillLEARNDuringthispractical,youwilllearnto:

CreateaNotificationusingtheNotificationBuilder.UsePendingIntentstorespondtoNotificationactions.UpdateorcancelexistingNotifications.

WhatyouwillDOInthispractical,youwill:

Sendanotificationwhenabuttonispushed.Updatethenotificationbothfromabuttonandanactionlocatedinthenotification.Launchanimplicitintenttoawebpagefromthenotification.

AppoverviewNotifyMe!isanapplicationthatcantrigger,updateandcancelanotification.Italsoexperimentswithnotificationstyles,actionsandpriorities.

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Task1.Createabasicnotification

1.1Createtheproject1. Createanewprojectcalled"NotifyMe!",acceptthedefaultoptions,andusetheemptytemplate.2. Inyouractivity_main.xmlfile,changetherootviewelementtoaverticalLinearLayoutwithitsgravityattributesetto

"center".3. AddabuttonwiththefollowingattributestoreplacethedefaultTextView:

Attribute Value

android:id "@+id/notify"

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:text "NotifyMe!"

android:layout_margin "4dp"

4. CreateamethodstubforthesendNotification()method.Themethodshouldtakenoargumentsandreturnvoid:

publicvoidsendNotification(){}

5. CreateamembervariablefortheNotifyButton.6. InitializethebuttoninonCreate()andcreateanonClickListenerforit:

mNotifyButton=(Button)findViewById(R.id.notify);

mNotifyButton.setOnClickListener(newView.OnClickListener(){

@Override

publicvoidonClick(Viewview){

}

});

7. CallsendNotification()fromtheonClickmethod.

1.2BuildyourfirstnotificationNotificationsarecreatedusingtheNotificationCompat.Builderclass,whichallowsyoutosetthecontentandbehavioroftheNotification.Anotificationmustcontainthefollowingelements:

Atitle,setbysetContentTitle().Detailtext,setbysetContentText().Anicon,setbysetSmallIcon().

AnAndroidNotificationisdeployedbytheNotificationManager.Ifyouneedtoupdateorcancelthenotificationinthefuture,youshouldassociateanotificationIDwithyourNotification.

CreatetheNotificationIcon

1. GotoFile>New>ImageAsset.2. FromtheIconTypedropdown,selectNotificationIcons.3. ClickontheiconnexttotheClipArtitemtoselectamaterialiconthatyouwilluseastheiconforyournotification.In

thisexample,youcanusetheAndroidicon.4. Renametheresourceic_androidandclickNextandFinish.Thiswillcreateanumberofdrawablefileswithdifferent

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resolutionsfordifferentAPIlevels.5. CreateamembervariableinMainActivitytostoretheNotificationManager:

privateNotificationManagermNotifyManager;

6. CreateaconstantvariableforthenotificationID.Sincetherewillbeonlyoneactivenotificationatatime,wecanusethesameIDforallnotifications:

privatestaticfinalintNOTIFICATION_ID=0;

7. InstantiatetheNotificationManagerinonCreateusinggetSystemService():

mNotifyManager=(NotificationManager)getSystemService(NOTIFICATION_SERVICE);

8. CreateandinstantiatetheNotificationBuilderinthesendNotification()method:

NotificationCompat.BuildernotifyBuilder=newNotificationCompat.Builder(this)

Note:MakesuretheNotificationCompatclassisimportedfromthev4supportlibrary.9. SettheNotificationTitleto"You'vebeennotified!".10. SettheNotificationTextto"Thisisyournotificationtext."11. SettheNotificationicontotheandroidiconyouadded.

NotificationCompat.BuildernotifyBuilder=newNotificationCompat.Builder(this)

.setContentTitle("You'vebeennotified!")

.setContentText("Thisisyournotificationtext.")

.setSmallIcon(R.drawable.ic_android);

12. Callnotify()ontheNotificationManagerattheendofthesendNotification()method,passinginthenotificationIDandthenotification:

NotificationmyNotification=notifyBuilder.build();

mNotifyManager.notify(NOTIFICATION_ID,myNotification);

13. Runyourapp.The"NotifyMe!"buttonnowissuesanotification(lookfortheiconinthestatusbar),butit'smissingsomeessentialfeatures:thereisnonotificationsoundorvibration,clickingonthenotificationdoesn'tdoanything.Let'saddsomeadditionalfunctionalitytothenotification.

1.3Addacontentintent

Inordertoimproveyournotification,youwilladdafewmorefeaturesavailablethroughtheNotificationCompat.Builderclass:

Acontentintent,whichislaunchedwhenthenotificationistapped,andissetbysetContentIntent().Apriority,whichdetermineshowthesystemdisplaysthenotificationwithrespecttoothernotifications,andissetbysetPriority().Thedefaultoptions,suchassounds,vibrationandLEDlights(ifavailable),andissetbysetDefaults().

TappinganotificationlaunchesanIntent.ContentIntentsfornotificationsareverysimilartotheIntentsyou'vebeenusingthroughoutthiscourse.Theycanbeexplicitintentstolaunchanactivity,implicitintentstoperformanaction,orbroadcastintentstonotifythesystemofasystemorcustomevent.ThemajordifferencewithanIntentinanotificationisthatitmustbewrappedinaPendingIntent,whichallowsthenotificationtoperformtheactionevenifyourapplicationisnotrunning.APendingIntentisgiventoanexternalcomponent(e.g.NotificationManager)whichallowstheexternalapplicationtouseyourapplication'spermissionstoexecuteapredefinedpieceofcode.Ineffect,itauthorizesthenotificationtosendtheintentontheapplication'sbehalf.

Forthisexample,thecontentintentofthenotification(thatis,theintentthatislaunchedwhenthenotificationispressed)willlaunchtheMainActivityoftheapplication(ifyouarealreadyintheapplicationthiswillhavenoeffect).

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1. CreateanexplicitintentinthesendNotification()methodtolaunchtheMainActivityclass:

IntentnotificationIntent=newIntent(this,MainActivity.class);

2. GetaPendingIntentusinggetActivity(),passinginthenotificationIDconstantfortherequestCodeandusingtheFLAG_UPDATE_CURRENTflag:

PendingIntentnotificationPendingIntent=PendingIntent.getActivity(this,

NOTIFICATION_ID,notificationIntent,PendingIntent.FLAG_UPDATE_CURRENT);

3. AddthePendingIntenttotheNotificationusingsetContentIntent()intheNotificationCompat.Builder:

.setContentIntent(notificationPendingIntent)

4. Runtheapp.ClicktheNotifyMe!buttontosendthenotification.Quittheapp.Nowviewthenotificationandclickit.NoticetheappwillopenbackupattheMainActivity.

1.4Addpriorityanddefaultstoyournotification

Whenyouruserclicksthe"NotifyMe!"button,thenotificationisissuedbuttheonlyvisualthattheuserseesistheiconinthenotificationbar.Inordertocatchtheuser'sattention,thenotificationdefaultsandprioritymustbeproperlyset.

PriorityisanintegervaluefromPRIORITY_MIN(-2)toPRIORITY_MAX(2)thatrepresentshowimportantyournotificationistotheuser.Notificationswithahigherprioritywillbesortedabovelowerpriorityonesinthenotificationdrawer.HIGHorMAXprioritynotificationswillbedeliveredas"Heads-Up"Notifications,whichdropdownontopoftheuser'sactivescreen.

1. AddthefollowinglinetotheNotificationBuildertosetthepriorityofthenotificationtoHIGH:

.setPriority(NotificationCompat.PRIORITY_HIGH)

2. ThedefaultsoptionintheBuilderisusedtosetthesounds,vibration,andLEDcolorpatternforyournotification(iftheuser'sdevicehasanLEDindicator).Inthisexample,youwillusethedefaultoptionsbyaddingthefollowinglinetoyourBuilder:

.setDefaults(NotificationCompat.DEFAULT_ALL)

3. Youneedtoquittheapplicationandstartitagaintoseethechanges.Note:Thehighprioritynotificationwillnotdropdowninfrontoftheactivescreenunlessboththepriorityandthedefaultsareset.Thepriorityaloneisnotenough.

Task2.UpdateandcancelyournotificationAfterissuinganotification,itisusefultobeabletoupdateorcancelthenotificationiftheinformationchangesorbecomesnolongerrelevant.

Inthistask,youwilllearnhowtoupdateandcancelyournotification.

2.1Addupdateandcancelbuttons

1. Inyourlayoutfile,createtwocopiesofthe"NotifyMe!"button.2. Changethetextattributeinthecopiesto"UpdateMe!"and"CancelMe!".3. Changetheid'sto"update"and"cancel",respectively.4. AddamembervariableforeachofthenewbuttonsandinitializetheminonCreate().5. CreatetwomethodsintheMainActivitythattakenoparametersandreturnvoid:

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publicvoidupdateNotification(){}

publicvoidcancelNotification(){}

6. CreateonClickListenersforthenewbuttonsandcallupdateNotification()in"update"buttononClickmethodandcancelNotification()inthe"cancel"buttononClickmethod.

2.2Implementthecancelandupdatenotificationmethods

CanceltheNotification

Cancelinganotificationisstraightforward:callcancel()ontheNotificationManager,passinginthenotificationID:

mNotifyManager.cancel(NOTIFICATION_ID);

UpdatetheNotification

Updatinganotificationismorecomplex.Androidnotificationscomewithalternativestylesthatcanhelpcondenseinformationorrepresentitmoreefficiently.Forexample,theGmailappuses"InboxStyle"notificationsifthereismorethanasingleunreadmessage,condensingtheinformationintoasinglenotification.

Inthisexample,youwillupdateyournotificationtousetheBigPictureStylenotification,whichallowsyoutoincludeanimageinyournotification.

1. Downloadthisimagetouseinyournotification,andrenameittomascot_1.2. Putitintheres/drawablefolder.3. InyourupdateNotification()method,convertyourdrawableintoabitmap:

BitmapandroidImage=BitmapFactory

.decodeResource(getResources(),R.drawable.mascot_1);

4. CopytheIntentandPendingIntentyoucreateinsendNotification()toupdateNotification(),asyouwillusethesamePendingIntentasaContentIntent.

5. CopytheNotificationCompat.BuildercodefromsendNotification()toupdateNotification(),tohavethesamebasicnotificationoptionsinyourupdatednotification.

6. ChangethestyleofyournotificationinthesameNotificationCompat.Builder,settingtheimageandthe"BigContentTitle":

.setStyle(newNotificationCompat.BigPictureStyle()

.bigPicture(androidImage)

.setBigContentTitle("NotificationUpdated!"));

Note:TheBigPictureStyleisasubclassofNotificationCompat.Stylewhichprovidesalternativelayoutsfornotifications.Seethedocumentationforotherdefinedsubclasses.

7. ChangethepriorityoftheBuildertothedefault,sothatyoudon'tgetanotherheadsupnotificationwhenitisupdated(headsupnotificationscanonlybeshowninthedefaultstyle).

.setPriority(NotificationCompat.PRIORITY_DEFAULT)

8. Callnotify()ontheNotificationManager,passinginthesamenotificationIDasbefore.

mNotifyManager.notify(NOTIFICATION_ID,notifyBuilder.build());

9. Runyourapp.Afterclickingupdate,checkthenotificationagain.Itnowhastheimageandupdatedtitle!Youcanshrinkbacktotheregularnotificationstylebypinchingontheextendedone.

2.3Togglethebuttonstate

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Inthisapplication,theusercangetconfusedbecausethestateofthenotificationisnottrackedinsidetheactivity.Forexample,theusermaytap"CancelMe!"whennonotificationisshowing.Youcanfixthisbyenablinganddisablingthevariousbuttonsdependingonthestateofthenotification.Whentheappisfirstrun,the"NotifyMe!"buttonshouldbetheonlyoneenabledasthereisnonotificationyettoupdateorcancel.Afteranotificationissent,thecancelandupdatebuttonsshouldbeenabled,andthenotificationbuttonshoulddisabledsincethenotificationhasalreadybeendelivered.Afterthenotificationisupdated,theupdateandnotifybuttonsshouldbedisabled,leavingonlythecancelbuttonenabled.Finally,ifthenotificationiscancelled,thebuttonsshouldreturntotheinitialconditionwiththenotifybuttonbeingtheonlyoneenabled.

Hereistheenabledstatetogglecodeforeachmethod:

onCreate():

mNotifyButton.setEnabled(true);

mUpdateButton.setEnabled(false);

mCancelButton.setEnabled(false);

sendNotification():

mNotifyButton.setEnabled(false);

mUpdateButton.setEnabled(true);

mCancelButton.setEnabled(true);

updateNotification():

mNotifyButton.setEnabled(false);

mUpdateButton.setEnabled(false);

mCancelButton.setEnabled(true);

cancelNotification():

mNotifyButton.setEnabled(true);

mUpdateButton.setEnabled(false);

mCancelButton.setEnabled(false);

Task3.AddnotificationactionsSometimes,anotificationrequiresimmediateinteraction:snoozinganalarm,replyingtoatextmessage,andsoon.Whenthesetypesofnotificationsoccur,theusermighttapyournotificationtorespondtotheevent.AndroidthenloadstheproperActivityinyourapplicationfortheusertorespond.Toavoidopeningyourapplication,thenotificationframeworkletsyouembedanotificationactiondirectlyinthenotificationitself.Thisallowstheusertoactonthenotificationwithoutopeningyourapplication.

Thecomponentsneededforanactionare:

Anicon,tobeplacedinthenotification.Alabelstring,placednexttotheicon.APendingIntent,tobesentwhenthenotificationactionisclicked.

Forthisexample,youwilladdtwoactionstoyournotification.Firstyou'lladda"LearnMore"actionwithanimplicitintentthatlaunchesawebpage,thenan"Update"actionwithabroadcastintentthatupdatesyournotificationwithoutlaunchingtheapplication.

3.1Implementthe"LearnMore"action

Asafirstexampleofnotificationactions,youwillimplementonethatlaunchesanimplicitintenttoopenawebsite.

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1. CreateamemberStringvariablethatcontainstheURLtotheMaterialDesignguidefornotifications:https://developer.android.com/design/patterns/notifications.html.

2. CreateanimplicitIntentthatopensthesavedURLinthesendNotification()methodbeforeyoubuildthenotification.3. CreateaPendingIntentfromtheimplicitintent,usingtheflagFLAG_ONE_SHOTsothatthePendingIntentcannotbe

reused:

IntentlearnMoreIntent=newIntent(Intent.ACTION_VIEW,Uri

.parse(NOTIFICATION_GUIDE_URL));

PendingIntentlearnMorePendingIntent=PendingIntent.getActivity

(this,NOTIFICATION_ID,learnMoreIntent,PendingIntent.FLAG_ONE_SHOT);

4. AddthisiconusingtheImageAssetStudio,andcallitic_learn_more:5. AddthefollowinglineofcodetoyourbuilderinbothsendNotification()andupdateNotification()toaddtheaction

toboththeoriginalandupdatednotification:

.addAction(R.drawable.ic_learn_more,"LearnMore",learnMorePendingIntent);

6. Runyourapp.Younotificationwillnowhaveaclickableiconthattakesyoutotheweb!

3.2Implementthe"Update"action

You'veseenthatanotificationactionusesaPendingIntenttorespondtouserinteraction.Inthelaststep,youaddedanactionthatusesaPendingIntentcreatedusingthegetActivity()method.YoucanalsocreateaPendingIntentwhichdeliversabroadcastintentbycallinggetBroadcast()onthePendingIntentclass.BroadcastIntentsareveryusefulinnotifications,sinceabroadcastreceivercanregisteritsinterestintheintentandrespondaccordingly,entirelywithoutlaunchingaspecificactivity.

YouwillnowimplementaBroadcastReceiverthatwillcalltheupdateNotification()methodwhenthe"Update"actioninthenotificationispressed.Itisacommonpatterntoaddfunctionalitytoanotificationthatalreadyexistsintheapp,sotheuserdoesnotneedtolaunchanyapptoperformtheaction.

1. SubclassaBroadcastReceiverasaninnerclassinMainActivityandoverridetheonReceive()method.Don'tforgettoincludeanemptyconstructor:

publicclassNotificationReceiverextendsBroadcastReceiver{

publicNotificationReceiver(){

}

@Override

publicvoidonReceive(Contextcontext,Intentintent){

}

}

2. IntheonReceive()method,callupdateNotification().3. CreateaconstantmembervariableinMainActivitytorepresenttheupdatenotificationactionforyourBroadcastIntent.

Makesureitbeginswithyourpackagenametoinsureit'suniqueness:

privatestaticfinalStringACTION_UPDATE_NOTIFICATION=

"com.example.android.notifyme.ACTION_UPDATE_NOTIFICATION";

4. Createamembervariableforyourreceiverandinitializeitusingthedefaultconstructor.5. IntheonCreate()method,registeryourBroadcastReceivertoreceivetheACTION_UPDATE_NOTIFICATIONintent:

registerReceiver(mReceiver,newIntentFilter(ACTION_UPDATE_NOTIFICATION));

6. OverridetheonDestroy()methodofyourActivitytounregisteryourreceiver:

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@Override

protectedvoidonDestroy(){

unregisterReceiver(mReceiver);

super.onDestroy();

}

Note:InthisexampleyouareregisteringyourBroadcastReceiverprogrammaticallybecauseyourreceiverisdefinedasaninnerclass.Whenreceiversaredefinedthisway,theycannotberegisteredintheAndroidManifestsincetheyaredynamicandhavethepossibilityofchangingduringthelifeoftheapplication.

ItmayseemthebroadcastsentbythenotificationonlyconcernsyourappandshouldbedeliveredwithaLocalBroadcastManager.However,theuseofPendingIntentsdelegatestheresponsibilityofdeliveringthenotificationtotheAndroidFramework.BecausetheAndroidruntimeishandlingthebroadcast,LocalBroadcastManagercannotbeused.

CreatetheUpdateAction

1. CreateabroadcastIntentinthesendNotification()methodusingthecustomupdateaction.2. GetaPendingIntentusinggetBroadcast():

IntentupdateIntent=newIntent(ACTION_UPDATE_NOTIFICATION);

PendingIntentupdatePendingIntent=PendingIntent.getBroadcast

(this,NOTIFICATION_ID,updateIntent,PendingIntent.FLAG_ONE_SHOT);

3. CreatethisiconusingtheImageAssetStudio,callitic_update.4. AddtheactiontothebuilderinthesendNotification()method,givingitthetitle"Update":

.addAction(R.drawable.ic_update,"Update",updatePendingIntent)

5. Runyourapp.Youcannowupdateyournotificationwithoutopeningtheapp!

SolutioncodeAndroidStudioproject:NotifyMe

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:Enablinganddisablingthevariousbuttonsisacommonwaytoensuretheuserdoesnotperformanyactionsthatarenotsupportedinthecurrentstateoftheapp(thinkofdisablinga"Sync"buttonwhenthereisnonetwork").Inthisapplication,however,thereisoneusecaseinwhichthestateofyourbuttonsdoesnotmatchthestateoftheapplication:whenauserdismissesanotificationbyswipingitawayorclearingthewholenotificationdrawer.Inthiscase,yourapphasnowayofknowingthatthenotificationwascancelled,andthatthebuttonstatemustbechanged.

Createanotherbroadcastintentthatwilllettheapplicationknowthattheuserhasdismissedthenotification,andtogglethebuttonstatesaccordingly.

Hint:CheckouttheNotificationCompat.BuilderclassforamethodthatdeliversanIntentwhenthenotificationhasbeendismissedbytheuser.

Summary

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ANotificationisamessageyoucandisplaytotheuseroutsideofyourapplication'snormalUI.Notificationsprovideawayforyourapptointeractwiththeuserevenwhentheappisnotrunning.WhenAndroidissuesanotification,itwillfirstappearasaniconinthenotificationareaofthedevice.TheUIandactionsforanotificationarespecifiedusingNotificationCompat.Builder.TocreateanotificationuseNotificationCompat.Builder.build().Toissuethenotification,passtheNotificationobjecttotheAndroidruntimesystemwithNotificationManager.notify().Toupdateorcancelanotification,youneedtoassociateanotificationIDwithyourNotification.AnIntentcanbepartofanotification(Explicit,ImplicitorBroadcast).Intentsinanotificationmustbe"wrapped"inaPendingIntent,whichreallyisn'tanIntent.APendingIntentisanimplementationofthedecoratorpattern.Therequiredcomponentsofanotificationare:smallicon(setSmallIcon()),title(setContentTitle())andsomedetailedtext(setContentText()).Someoptionalcomponentsofanotificationare:intent,expandedstyles,priority,etal.SeeNotificationCompat.Builderformoreinfo.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

Notifications

LearnmoreGuides

NotificationsNotificationDesignGuide

Reference

NotificationCompat.BuilderNotificationCompat.Style

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8.2:AlarmManagerContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.SetuptheStandUp!projectandviewsTask2.SetupthenotificationTask3.CreatetherepeatingalarmCodingchallengeSummaryRelatedconceptLearnmore

Inyourpreviouspracticals,you'velearnedhowtomakeyourapprespondtouserinteractionbypushingabuttonortappinganotification.You'vealsolearnedhowtomakeyourapprespondtosystemeventsusingBroadcastReceivers.Butwhatifyourappneedstotakeactionataspecifictime,suchasisthecasewithacalendarnotification?Inthatcase,youwoulduseAlarmManager,aclassthatallowsyoutolaunchandrepeataPendingIntentataspecifictimeandinterval.

Inthispractical,youwillcreateatimerthatwillremindyoutostandupifyouhavebeensittingfortoolong.

WhatyoushouldalreadyKNOWFrompreviouspracticals,youshouldbeableto:

ImplementonCheckChangedlistenersfortogglebuttons.Setupcustombroadcastintents.Usebroadcastreceivers.Sendnotifications.

WhatyouwillLEARNYouwilllearnto:

SchedulerepeatingalarmswithAlarmManager.CheckifanAlarmisalreadysetup.Cancelarepeatingalarm.

WhatyouwillDOSetarepeatingalarmtonotifyyoueveryfifteenminutes.UseaToggleButtontosetandkeeptrackofthealarm.UseToastmessagestonotifytheuserwhentheAlarmisturnedonoroff.

AppoverviewStandUp!isanappthathelpsyoustayhealthybyremindingyoutostandupandwalkaroundeveryfifteenminutes.Itusesanotificationtoletyouknowwhenfifteenminuteshavepassed.TheappincludesatogglebuttonthatcanturntheAlarmonandoff.

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Task1.SetuptheStandUp!projectandviews

1.1CreatetheStandUp!projectlayout1. Createanewprojectcalled"StandUp!",acceptthedefaultoptionsandusetheemptyactivitytemplate.2. Opentheactivity_main.xmllayoutfile.

i. ChangetherootviewtoRelativeLayout.ii. Removetheentire"HelloWorld"TextViewandaddthefollowingelements:

TextView Attribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:layout_above "@+id/alarmToggle"

android:layout_centerHorizontal "true"

android:layout_margin "8dp"

android:text "StandUpAlarm"

android:textAppearance "@style/TextAppearance.AppCompat.Headline"

ToggleButton Attribute Value

android:id "@+id/alarmToggle"

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:layout_centerHorizontal "true"

android:layout_centerVertical "true"

1.2SetupthesetOnCheckedChangeListener()methodTheStandUp!appincludesatogglebuttonthatisusedtosetandcancelthealarm,aswellasvisiblyrepresentthealarm'scurrentstatus.Tosetthealarmwhenthetoggleisturnedon,youwillusetheonCheckedChangeListener()method:

1. InyourMainActivityonCreate()method,findtheAlarmTogglebyid.2. CallsetOnCheckedChangeListener()onthetogglebuttoninstance,andbegintyping"newOnCheckedChangeListener".

AndroidStudiowillautocompletethemethodforyou,includingtherequiredonCheckedChanged()overridemethod.Thismethodhastwoparameters:theCompoundButtonthatwasclicked(inthiscaseit'stheAlarmTogglebutton),andabooleanrepresentingthecurrentstateoftheToggleButton(i.e.,whetherthetoggleisnowsetonoroff.

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alarmToggle.setOnCheckedChangeListener(

newCompoundButton.OnCheckedChangeListener(){

@Override

publicvoidonCheckedChanged(CompoundButtoncompoundButton,

booleanisChecked){

}

});

3. Itisusefulfortheusertohavesomefeedbackotherthanthetogglebuttonbeingturnedonandofftoindicatethealarmwasindeedset(youhaven'timplementedthealarmyet,youwilldothatinafurthersection).Setupanif/elseblockusingthebooleanparameterintheonCheckedChanged()methodthatdeliversatoastmessagetotelltheuseriftheAlarmwasturnedonoroff.Don'tforgettoextractyourstringresources.

StringtoastMessage;

if(isChecked){

//Setthetoastmessageforthe"on"case

toastMessage=getString(R.string.alarm_on_toast);

}else{

//Setthetoastmessageforthe"off"case

toastMessage=getString(R.string.alarm_off_toast);

}

//Showatoasttosaythealarmisturnedonoroff

Toast.makeText(MainActivity.this,toastMessage,Toast.LENGTH_SHORT)

.show();

Task2.SetupthenotificationThenextstepistocreatethenotificationthatwillremindtheusertostandupeveryfifteenminutes.Fornow,thenotificationwillbedeliveredimmediatelywhenthetoggleisset.

2.1Createthenotification

Inthisstep,youwillcreateadeliverNotification()methodthatwillposttheremindertostandupandwalkaround.

1. CreateamembervariableinMainActivitycalledmNotificationManageroftypeNotificationManager.2. InitializeitinonCreate()bycallinggetSystemService():

mNotificationManager=(NotificationManager)getSystemService(NOTIFICATION_SERVICE);

3. CreateamethodinMainActivitycalleddeliverNotification()thattakestheContextasanargumentanddoesnotreturnanything.

privatevoiddeliverNotification(Contextcontext){}

4. CreateamemberconstantinMainActivitycalledNOTIFICATION_IDandsetitto0.Yourappwillonlyhaveonenotificationatatime,soyouwillusethesamenotificationIDforallnotifications.Note:NotificationID'sareusedtodistinguishnotificationswithinyourapplication.TheNotificationManagerwillonlybeabletocancelnotificationsdeliveredfromyourappsoyoucanusethesameIDinindifferentapplications.

NotificationcontentIntent

1. CreateanIntentinonCreate()thatyouwilluseforthenotificationcontentIntent:

IntentcontentIntent=newIntent(context,MainActivity.class);

2. CreateaPendingIntentfromcontentIntentrightbelowthedefinitionofcontentIntentusingthegetActivity()method,passinginthenotificationIDandusingtheFLAG_UPDATE_CURRENTflag:

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PendingIntentcontentPendingIntent=PendingIntent.getActivity

(context,NOTIFICATION_ID,contentIntent,PendingIntent.FLAG_UPDATE_CURRENT);

Note:PendingIntentflagstellthesystemhowtohandlethesituationwhenmultipleinstancesofthesamePendingIntentarecreated(meaningtheycontainthesameintent).TheFLAG_UPDATE_CURRENTflagtellsthesystemtousetheoldIntentbutreplacetheextrasdata.Sinceyoudon'thaveanyextrasinthisIntent,youreusethesamePendingIntentoverandover.

Notificationtitleandtext

1. Createastringresourceinyourstrings.xmlfilecallednotification_title.Setitequalto"StandUpAlert".2. Createastringresourceinyourstrings.xmlfilecallednotification_text.Setitequalto"Youshouldstandupandwalk

aroundnow!".

Notificationicon

1. Addanimageassettouseasthenotificationicon(usetheImageAssetStudio).Chooseanyiconyoufindappropriate

forthisalarm:

Buildthenotification

1. UsetheNotificationCompat.BuildertobuildanotificationinthedeliverNotification()methodusingtheabovenotificationtitle,text,iconandcontentintent.

NotificationCompat.Builderbuilder=newNotificationCompat.Builder(context)

.setSmallIcon(R.drawable.ic_stand_up)

.setContentTitle(context.getString(R.string.notification_title))

.setContentText(context.getString(R.string.notification_text))

.setContentIntent(contentPendingIntent)

2. SettheNotificationprioritytoPRIORITY_HIGH:

.setPriority(NotificationCompat.PRIORITY_HIGH)

3. AddanoptiontothebuildertosetAutoCanceltotrue,andanotheroptiontousethedefaultlight,soundandvibrationpattern:

.setAutoCancel(true)

.setDefaults(NotificationCompat.DEFAULT_ALL);

Deliverthenotification

1. UsetheNotificationManagertodeliverthenotification:

mNotificationManager.notify(NOTIFICATION_ID,builder.build());

2. CalldeliverNotification()whenthealarmtogglebuttonisturnedon,passingintheactivitycontext:3. CallcancelAll()ontheNotificationManagerifthetoggleisturnedofftoremovethenotification.

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if(isChecked){

deliverNotification(MainActivity.this);

//Setthetoastmessageforthe"on"case

toastMessage=getString(R.string.alarm_on_toast);

}else{

//Cancelnotificationifthealarmisturnedoff

mNotificationManager.cancelAll();

//Setthetoastmessageforthe"off"case

toastMessage=getString(R.string.alarm_off_toast);

}

4. Runtheapp,andcheckthatthenotificationisdeliveredwithallthedesiredoptions.

Atthispointthereisnoalarmatall:thenotificationisimmediatelydeliveredwhenthealarmtoggleisturnedon.InthenextsectionyouwillimplementtheAlarmManagertoscheduleanddeliverthenotificationevery15minutes.

Task3.CreatetherepeatingalarmNowthatyourappcansendanotificationitistimetoimplementthemaincomponentofyourapplication:theAlarmManager.Thisistheclassthatwillberesponsibleforperiodicallydeliveringtheremindertostandup.AlarmManagerhasmanykindsofalarmsbuiltintoit,bothone-timeandperiodic,exactandinexact.Tolearnmoreaboutthedifferentkindsofalarms,seeSchedulingRepeatingAlarms.

AlarmManager,likenotifications,usesaPendingIntentthatitdeliverswiththespecifiedoptions.Becauseofthis,itcandelivertheIntentevenwhentheapplicationisnolongerrunning.Inthisapplication,yourPendingIntentwilldeliveranIntentbroadcastwithacustom"Notify"action.

Thebroadcastintentwillbereceivedbyabroadcastreceiverthattakestheappropriateaction(deliversthenotification).

TheAlarmManagercantriggerone-timeorrecurringeventswhichoccurevenwhenthedeviceisindeepsleeporyourapplicationisnotrunning.EventsmaybescheduledwithyourchoiceofcurrentTimeMillis()whenusingtherealtimeversion(RTC)orelapsedRealtime()whenusingtheelapsedtimeversion(ELAPSED_REALTIME),anddeliveraPendingIntentwhentheyoccur.Formoreinformationonthedifferentclocksavailableandinformationonhowtocontrolthetimingofevents,seetheSystemClockDeveloperReference.

3.1Setupthebroadcastpendingintent

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TheAlarmManagerisresponsiblefordeliveringyourPendingIntentataspecifiedinterval.ThisPendingIntentwilldeliverabroadcastintentlettingtheapplicationknowitistimetoupdatetheremainingtimeinthenotification.

1. CreateastringconstantasamembervariableinMainActivitytobeusedasthebroadcastintentactionwhichwilldeliverthenotification:

privatestaticfinalStringACTION_NOTIFY=

"com.example.android.standup.ACTION_NOTIFY";

Note:usethefully-qualifiedpackagenamefortheIntentstring,toensurethatyourBroadcastisunique,andcannotaccidentallybeusedbyotherapplicationswithsimilaractions.

2. CreateanIntentcallednotifyIntentinonCreate()withthecustomstringasitsaction:

IntentnotifyIntent=newIntent(ACTION_NOTIFY);

3. CreatethenotifyPendingIntentusingthecontext,theNOTIFICATION_IDvariable,thenewnotifyintent,andthePendingIntentflagUPDATE_CURRENT:

PendingIntentnotifyPendingIntent=PendingIntent.getBroadcast

(this,NOTIFICATION_ID,notifyIntent,PendingIntent.FLAG_UPDATE_CURRENT);

3.2Settherepeatingalarm

YouwillnowusetheAlarmManagertodeliverthisbroadcastIntentevery15minutes.Forthistask,theappropriatetypeofalarmisaninexact,repeatingalarmthatuseselapsedtimeandwillwakethedeviceupifitisasleep.Therealtimeclockisnotrelevanthere,sincewewanttodeliverthenotificationeveryfifteenminutes.

1. InitializetheAlarmManagerinonCreate()bycallinggetSystemService():

AlarmManageralarmManager=(AlarmManager)getSystemService(ALARM_SERVICE);

2. IntheonCheckedChanged()method,callsetInexactRepeating()onthealarmmanagerinstancewhentheuserclickstheAlarm"ON"(Thesecondparameteristrue).YouwillusethesetInexactRepeating()alarmsinceitismoreresourceefficienttouseinexacttiming(thesystemcanbundlealarmsfromdifferentappstogether)anditisacceptableforyouralarmtodeviatealittlebitfromtheexact15minuterepeatinterval.ThesetInexactRepeating()methodtakes4arguments:

3. Thealarmtype.Inthiscaseyouwillusetheelapsedtimesinceboottype,sinceonlytherelativetimeisimportant.Youalsowanttowakeupthedeviceifit'sasleep,sothealarmtypeisELAPSED_REALTIME_WAKEUP.

4. Thetriggertimeinmilliseconds.Forthis,usethecurrentelapsedtime,plus15minutes.Togetthecurrentelapsedtime,youcancallSystemClock.elapsedRealtime().Youcanthenuseabuilt-inAlarmManagerconstanttoadd15minutestotheelapsedtime:AlarmManager.INTERVAL_FIFTEEN_MINUTES.

5. Thetimeintervalinmilliseconds.Youwantthenotificationpostedevery15minutes.YoucanusetheAlarmManager.INTERVAL_FIFTEEN_MINUTESconstantagain.

6. ThePendingIntenttobedelivered.YoucreatedthePendingIntentintheprevioustask.

longtriggerTime=SystemClock.elapsedRealtime()

+AlarmManager.INTERVAL_FIFTEEN_MINUTES;

longrepeatInterval=AlarmManager.INTERVAL_FIFTEEN_MINUTES;

//IftheToggleisturnedon,settherepeatingalarmwitha15minuteinterval

alarmManager.setInexactRepeating(AlarmManager.ELAPSED_REALTIME_WAKEUP,

triggerTime,repeatInterval,notifyPendingIntent);

Note:BecauseyouareaccessingtheAlarmManagerandnotifyPendingIntentinstancesfromananonymousinnerclass,AndroidStudiomaymaketheseinstancesfinal.Ifitdoesn't,youhavetomakethemfinalyourself.

7. RemovethecalltodeliverNotification()intheonCheckedChanged()method.

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8. Ifthealarmtoggleisturnedoff(byclickingthetoggleintheONstate),cancelthealarmbycallingcancel()ontheAlarmManager,passinginthependingintentusedtocreatethealarm.

alarmManager.cancel(notifyPendingIntent);

KeepthecalltocancelAll()ontheNotificationManager,sinceturningthetoggleoffshouldstillremoveanyexistingnotification.

TheAlarmManagerwillnowstartdeliveringyourBroadcastIntentstartingfifteenminutesfromwhentheAlarmwasset,andeveryfifteenminutesafterthat.Yourapplicationneedstobeabletorespondtotheseintentsbydeliveringthenotification.InthenextstepyouwillsubclassaBroadcastReceivertoreceivethebroadcastintentsanddeliverthenotification.

3.3CreatetheBroadcastReceiverTheBroadcastReceiverisresponsibleforreceivingthebroadcastintentsfromtheAlarmManagerandreactingappropriately.

1. InAndroidStudio,clickonFile>New>Other>BroadcastReceiver.2. EnterAlarmReceiverforthename,makesuretheExportedcheckboxisunchecked(toensurethatotherappswillnot

beabletoinvokethisBroadcastReceiver).YoucanalsochangethissettingintheAndroidManifestbysettingtheandroid:exportedattributetofalse.AndroidStudiowillcreatethesubclassofBroadcastReceiverwiththerequiredmethod(onReceive()),aswellasaddthereceivertoyourAndroidManifest.YouneedtoaddanIntentFiltertoyourthe<receiver>tagintheAndroidManifesttoselecttheproperincomingBroadcastIntents.

3. IntheAndroidManifest,createan<intent-filter>openingandclosingtagbetweenthe<receiver>tags.Createan<action>itemintheintentfilterwithandroid:nameattributesettothecustomACTION_NOTIFYactionstringyoucreated:

<intent-filter>

<actionandroid:name="com.example.android.standup.ACTION_NOTIFY"/>

</intent-filter>

4. CutandpastethedeliverNotification()methodtotheonReceive()methodintheBroadcastReceiverandcallitfromonReceive().ThenotificationmanagerandnotificationIDhasnotbeeninitializedintheBroadcastReceiverclasssoitwillbehighlightedinred.

5. CopytheNOTIFICATION_IDvariablefromtheMainActivityintotheBroadcastReceiverclass.6. InitializetheNotificationManageratthebeginningoftheonReceive()method.YouhavetocallgetSystemService()

fromthepassedinContext:

NotificationManagernotificationManager=(NotificationManager)

context.getSystemService(Context.NOTIFICATION_SERVICE);

7. RemovethelinethatraisestheUnsupportedOperationException.8. Runyourapp.Ifyoudon'twanttowaitforfifteenminutestoseethenotification,youcanchangethetriggertimeto

SystemClock.elapsedRealtime()toseethenotificationimmediately.Youcanalsochangetheintervaltoashortertimetomakesurethattherepeatedalarmisworking.

Younowhaveanappthatcanscheduleandperformarepeatedoperation,eveniftheapplicationisnolongerrunning.Goahead,exittheapplicationcompletely,thenotificationwillstillbedelivered.Thereisonefinalcomponentmissingthatwouldensureaproperuserexperience:iftheapplicationisexited,thetogglebuttonwillresettotheoffstate,evenifthealarmhasalreadybeenset.Tofixthis,youwillneedtocheckthestateofthealarmeverytimetheapplicationislaunched.

3.5Checkthestateofthealarm

Totrackthestateofthealarm,youwillneedabooleanvariablethatistrueiftheAlarmalreadyexists,andfalseotherwise.Tosetthisboolean,youcancallPendingIntent.getBroadcast()withtheFLAG_NO_CREATEPendingIntentflag.Inthiscase,thePendingIntentisreturnedifitalreadyexists,otherwisethecallreturnsnull.Thisisextremelyusefulfor

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checkingwhetherthealarmhasalreadybeenset.

Note:WhenyoucreateaPendingIntent,thesystemusestheIntent.filterEquals()methodtodetermineifaPendingIntentwiththesameIntentalreadyexists.ThismeansthattohavetwodistinctPendingIntents,thecontainedIntentshavetodifferinoneofaction,data,type,class,orcategories.Intentextrasarenotincludedinthecomparison.

ThePendingIntentflagdetermineswhathappenswhenaPendingIntentwhoseIntentmatchestheoneyouaretryingtocreatealreadyexists.InthecaseoftheNO_CREATEflag,itwillreturnnullunlessaPendingIntentwithamatchingIntentalreadyexists.1. CreateabooleanthatistrueifPendingIntentisnotnull,andfalseotherwise,usingthisstrategy.Usethisbooleanto

correctlysetthestateoftheToggleButtonwhenyourappstarts.ThiscodehastocomebeforethePendingIntenthasbeencreated,otherwiseitwillalwaysreturntrue:

booleanalarmUp=(PendingIntent.getBroadcast(this,NOTIFICATION_ID,notifyIntent,

PendingIntent.FLAG_NO_CREATE)!=null);

2. SetthecheckedstateofthetogglerightafteryoudefinethealarmUpboolean:

alarmToggle.setChecked(alarmUp);

ThisensuresthatthetogglewillalwaysbeturnedoniftheAlarmisset,andoffotherwise.That'sit,Younowhavearepeatedscheduledalarmtoremindyoutostandupeveryfifteenminutes.

3. Runyourapp.Switchonthealarm.Exittheapp.Opentheappagain.Thealarmbuttonwillshowthatthealarmison.

Solutioncode**AndroidStudioproject:StandUp

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

TheAlarmManagerclassalsohandlesalarmclocksintheusualsense,thekindthatwakeyouupinthemorning.OndevicesrunningAPI21+,youcangetinformationaboutthenextalarmclockofthiskindbycallinggetNextAlarmClock()onthealarmmanager.

AddabuttontoyourapplicationthatdisplaysthetimeofnextalarmclockthattheuserhassetinaToastmessage.

SummaryAlarmManagerallowsyoutoscheduletasksbasedontherealtimeclockortheelapsedtimesinceboot.AlarmManagerprovidesavarietyofalarmtypes,bothperiodicandonetime,withoptionstowakeupyourdeviceifitisasleep.AlarmManagerismeantforsituationswhereprecisetimingiscritical(suchasacalendarevent).Otherwise,considertheJobSchedulerframeworkformoreresource-efficienttimingandscheduling.UsetheinexacttimingversionoftheAlarmManagerwheneverpossible,tominimizetheloadcausedbymultipleusers'devicesormultipleapplicationsperformingataskattheexactsametime.AlarmManagerusesPendingIntentstoperformtheoperations,soyoucanschedulebroadcasts,servicesandactivitiesusingtheappropriatePendingIntent.

Relatedconcept

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TherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

SchedulingAlarms

LearnmoreAndroiddeveloperdocumentation:

SchedulingRepeatingAlarmsAlarmManagerSystemClock

Otherresources:

BlogPostonchoosingthecorrectalarmtype

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8.3:JobSchedulerContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOTask1.ImplementaJobServiceTask2.ImplementthejobconditionsCodingchallengeSummaryRelatedconceptLearnmore

You'veseenthatyoucantriggereventsbasedonthereal-timeclock,ortheelapsedtimesincebootusingtheAlarmManagerclass.Mosttasks,however,donotrequireanexacttime,butshouldbescheduledbasedonacombinationofsystemanduserrequirements.Forexample,anewsappmightliketoupdatethenewsinthemorning,butcouldwaituntilthedeviceischargingandconnectedtowifitoupdatethenews,topreservetheuser'sdataandsystemresources.

TheJobSchedulerclassismeantforthiskindofscheduling;itallowsyoutosettheconditions,orparametersofrunningyourtask.Giventheseconditions,theJobSchedulercalculatesthebesttimetoscheduletheexecutionofthejob.Someexamplesoftheseparametersare:persistanceofthejobacrossreboots,theintervalthatthejobshouldrunat,whetherornotthedeviceispluggedin,orwhetherornotthedeviceisidle.

ThetasktoberunisimplementedasaJobServicesubclassandexecutedaccordingtothespecifiedconstraints.

JobSchedulerisonlyavailableondevicesrunningAPI21+,andiscurrentlynotavailableinthesupportlibrary.Forbackwardcompatibility,usetheGcmNetworkManager(soontobeFirebaseJobDispatcher).

Inthispractical,youwillcreateanappthatschedulesanotificationtobepostedwhentheparameterssetbytheuserarefulfilled,andthesystemrequirementsaremet.

WhatyoushouldalreadyKNOWFromthepreviouspracticals,youshouldbeableto:

Deliveranotification.GetanintegervaluefromaSpinnerview.UseSwitchviewsforuserinput.CreatePendingIntents.

WhatyouwillLEARNYouwilllearnto:

ImplementaJobService.ConstructaJobInfoobjectwithspecificconstraints.ScheduleaJobServicebasedontheJobInfoobject.

WhatyouwillDOInthispractical,youwill:

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ImplementaJobServicethatdeliversasimplenotificationtolettheuserknowthejobisrunning.Getuserinputtoconfiguretheconstraints(suchaswaitinguntilthedeviceischarging)ontheJobServiceyouarescheduling.SchedulethejobusingJobScheduler.

AppOverviewForthispracticalyouwillcreateanappcalled"NotificationScheduler".YourappwilldemonstratetheJobSchedulerframeworkbyallowingtheusertoselectconstraintsandscheduleajob.Whenthatjobisexecuted,itwillpostanotification(inthisapp,yournotificationiseffectivelyyour"job").

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TousetheJobScheduler,youneedtwoadditionalparts:JobServiceandJobInfo.AJobInfoobjectcontainsthesetofconditionsthatwilltriggerthejobtorun.AJobServiceistheimplementationofthejobthatistorununderthoseconditions.

Task1.ImplementaJobServiceTobeginwith,youmustcreateaservicethatwillberunatthetimedeterminedbytheconditions.TheJobServiceisautomaticallyexecutedbythesystem,andtheonlypartsyouneedtoimplementare:

onStartJob()callback

calledwhenthesystemdeterminesthatyourtaskshouldberun.Youimplementthejobtobedoneinthismethod.Note:onStartJob()isexecutedonthemainthread,andthereforeanylong-runningtasksmustbeoffloadedtoadifferentthread.Inthiscase,youaresimplypostinganotification,whichcanbedonesafelyonthemainthread.returnsabooleanindicatingwhetherthejobneedstocontinueonaseparatethread.Iftrue,theworkisoffloadedtoadifferentthread,andyourappmustcalljobFinished()explicitlyinthatthreadtoindicatethatthejobiscomplete.Ifthereturnvalueisfalse,theframeworkknowsthatthejobiscompletedbytheendofonStartJob()anditwillautomaticallycalljobFinished()onyourbehalf.

onStopJob()callback

callediftheconditionsarenolongermet,meaningthatthejobmustbestopped.returnsabooleanthatdetermineswhattodoifthejobisnotfinished.Ifthereturnvalueistrue,thejobwillberescheduled,otherwise,itwillbedropped.

1.1CreatetheProjectandtheNotificationJobService

VerifythattheminimumSDKyouareusingisAPI21.PriortoAPI21,JobSchedulerdoesnotwork,asitismissingsomeoftherequiredAPIs.

1. Usetheemptytemplate,andcreateanewprojectcalled"NotificationScheduler".2. CreateanewJavaclasscalledNotificationJobServicethatextendsJobService.3. Addtherequiredmethods:onStartJob()andonStopJob().4. InyourAndroidManfiest.xmlfile,registeryourJobServicewiththefollowingpermissioninsidethe<application>tag:

<service

android:name=".NotificationJobService"

android:permission="android.permission.BIND_JOB_SERVICE"/>

1.2ImplementonStartJob()

1. Addanotificationiconforthe"JobRunning"notification.2. InonStartJob(),createaPendingIntenttolaunchtheMainActivityofyourapptobeusedasthecontentintentfor

yournotification.3. InonStartJob(),constructanddeliveranotificationwiththefollowingattributes:

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Attribute Title

ContentTitle "JobService"

ContentText "YourJobisrunning!"

ContentIntent contentPendingIntent

SmallIcon R.drawable.ic_job_running

Priority NotificationCompat.PRIORITY_HIGH

Defaults NotificationCompat.DEFAULT_ALL

AutoCancel true

4. MakesureonStartJob()returnsfalse,becausealloftheworkiscompletedinthatcallback.5. MakeonStopJob()returntrue,sothatthejobisrescheduledifitfails.

@Override

publicbooleanonStartJob(JobParametersjobParameters){

//Setupthenotificationcontentintenttolaunchtheappwhenclicked

PendingIntentcontentPendingIntent=PendingIntent.getActivity

(this,0,newIntent(this,MainActivity.class),

PendingIntent.FLAG_UPDATE_CURRENT);

NotificationManagermanager=

(NotificationManager)getSystemService(NOTIFICATION_SERVICE);

NotificationCompat.Builderbuilder=newNotificationCompat.Builder(this)

.setContentTitle(getString(R.string.job_service))

.setContentText(getString(R.string.job_running))

.setContentIntent(contentPendingIntent)

.setSmallIcon(R.drawable.ic_job_running)

.setPriority(NotificationCompat.PRIORITY_HIGH)

.setDefaults(NotificationCompat.DEFAULT_ALL)

.setAutoCancel(true);

manager.notify(0,builder.build());

returnfalse;

}

Task2.ImplementthejobconditionsNowthatyouhaveyourJobService,itistimetoidentifythecriteriaforrunningthejob.Forthis,usetheJobInfocomponent.Youwillcreateaseriesofparameterizedconditionsforrunningajobusingavarietyofnetworkconnectivitytypesanddevicestatus.

Tobegin,youwillcreateagroupofradiobuttonstodeterminethenetworktyperequiredforthisjob.

2.1Implementthenetworkconstraint

OneofthepossibleconditionsforrunningaJobisthestatusofyourdevice'snetworkconnectivity.YoucanlimittheJobServicetobeexecutedonlywhencertainnetworkconditionsaremet.Theoptionsare:

NETWORK_TYPE_NONE:thejobwillrunwithorwithoutanetworkconnection.Thisisthedefaultvalue.NETWORK_TYPE_ANY:thejobwillrunaslongasanetwork(cellular,wifi)isavailable.NETWORK_TYPE_UNMETERED:thejobwillrunaslongasthedeviceisconnectedtowifithatdoesnotuseaHotSpot.

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Createthelayoutforyourapp

Createthelayoutforyourapptoshowthebuttonsfortheusertochoosethenetworkcriteria.

1. Inyouractivity_main.xmlfile,changetherootviewelementtoaverticalLinearLayout.2. ChangetheTextViewtohavethefollowingattributes:

Attribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:text "NetworkTypeRequired:"

android:textAppearance "@style/TextAppearance.AppCompat.Subhead"

android:layout_margin "4dp"

3. AddaRadioGroupcontainerelementbelowtheTextViewwiththefollowingattributes:

Attribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:orientation "horizontal"

android:id "@+id/networkOptions"

android:layout_margin "4dp"

Note:Usingaradiogroupensuresthatonlyoneofitschildrencanbeselectedatatime.FormoreinformationonRadioButtonsseethisguide.

4. AddthreeRadioButtonsaschildrentotheRadioGroupwiththeirlayoutheightandwidthsetto"wrap_content"andthefollowingattributes:

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RadioButton1

android:text "None"

android:id "@+id/noNetwork"

android:checked true

RadioButton2

android:text "Any"

android:id "@+id/anyNetwork"

RadioButton3

android:text "Wifi"

android:id "@+id/wifiNetwork"

5. Addtwobuttonsbelowtheradiobuttongroupwithheightandwidthsetto"wrapcontent"withthefollowingattributes:

Button1

android:text "ScheduleJob"

android:onClick "scheduleJob"

android:layout_gravity "center_horizontal"

android:layout_margin "4dp"

Button2

android:text "CancelJobs"

android:onClick "cancelJobs"

android:layout_gravity "center_horizontal"

android:layout_margin "4dp"

6. AddthemethodstubsforbothoftheonClick()methodsinMainActivity.

Gettheselectednetworkoption

1. InscheduleJob(),findtheRadioGroupbyidandsaveitinaninstancevariablecallednetworkOptions.2. Gettheselectednetworkidandsaveitinaintegervariable:

intselectedNetworkID=networkOptions.getCheckedRadioButtonId();

3. Createaselectednetworkoptionintegervariableandsetitequaltothedefaultnetworkoption(nonetworkrequired):

intselectedNetworkOption=JobInfo.NETWORK_TYPE_NONE;

4. Createaswitchstatementwiththeselectednetworkid,andaddacaseforeachofthepossibleid's:

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switch(selectedNetworkID){

caseR.id.noNetwork:

break;

caseR.id.anyNetwork:

break;

caseR.id.wifiNetwork:

break;

}

5. AssigntheselectednetworkoptiontheappropriateJobInfonetworkconstant,dependingonthecase:

switch(selectedNetworkID){

caseR.id.noNetwork:

selectedNetworkOption=JobInfo.NETWORK_TYPE_NONE;

break;

caseR.id.anyNetwork:

selectedNetworkOption=JobInfo.NETWORK_TYPE_ANY;

break;

caseR.id.wifiNetwork:

selectedNetworkOption=JobInfo.NETWORK_TYPE_UNMETERED;

break;

}

CreatetheJobSchedulerandtheJobInfoobject

1. InMainActivity,createamembervariablefortheJobScheduler,andinitializeitinscheduleJob()usinggetSystemService():

mScheduler=(JobScheduler)getSystemService(JOB_SCHEDULER_SERVICE);

2. CreateamemberconstantfortheJOB_ID,andsetitequalto0.3. CreateaJobInfo.BuilderobjectinscheduleJob().TheconstructorfortheJobInfo.Builderclasstakestwo

parameters:TheJOB_ID.TheComponentNamefortheJobServiceyoucreated.AComponentNameisusedtoidentifytheJobServicewiththeJobInfoobject.

ComponentNameserviceName=newComponentName(getPackageName(),

NotificationJobService.class.getName());

JobInfo.Builderbuilder=newJobInfo.Builder(JOB_ID,serviceName)

4. CallsetRequiredNetworkType()ontheJobInfo.Builderobject,passingintheselectednetworkoption:

.setRequiredNetworkType(selectedNetworkOption);

5. Callschedule()ontheJobSchedulerobject,passingintheJobInfoobjectwiththebuild()method:

JobInfomyJobInfo=builder.build();

mScheduler.schedule(myJobInfo);

6. ShowaToastmessage,lettingtheuserknowthejobwasscheduled.7. InthecancelJobs()method,checkiftheJobSchedulerobjectisnull,andifnot,callcancelAll()onittoremoveall

pendingjobs,resettheJobSchedulertobenull,andshowaToastmessagetolettheuserknowthejobwascanceled:

if(mScheduler!=null){

mScheduler.cancelAll();

mScheduler=null;

Toast.makeText(this,"JobsCanceled",Toast.LENGTH_SHORT).show();

}

8. Runtheapp.Youcannowsettasksthathavenetworkrestrictionsandseehowlongittakesforthemtobeexecuted.Inthiscase,thetaskistodeliveranotification.Todismissthenotification,eitherswipeitawayortaponittoopenthe

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notification.

Youmaynoticethatifyoudonotchangethenetworkconstrainttoeither"Any"or"Wifi",theappwillcrashwiththefollowingexception:

java.lang.IllegalArgumentException:

You'retryingtobuildajobwithnoconstraints,thisisnotallowed.

Thisisbecausethe"NoNetworkRequired"conditionisthedefaultanddoesnotactuallycountasaconstraint.TheJobSchedulerneedsatleastoneconstrainttoproperlyscheduletheJobService.Inthefollowingsectionyouwillcreateaconditionalthatistruewhenatleastoneconstraintisset,andfalseotherwise.Youwillthenschedulethetaskifit'strue,andshowaToasttotelltheusertosetaconstraintifitisn't.

2.2Checkforconstraints

JobSchedulerrequiresatleastoneconstrainttobeset.Inthistaskyouwillcreateabooleanthatwilltrackifthisrequirementhasbeenmet,sothatyoucannotifytheusertosetatleastoneconstraintiftheyhaven'talready.Asyoucreateadditionaloptionsinthefurthersteps,youwillneedtomodifythisbooleansoitisalwaystrueifatleastoneconstraintisset,andfalseotherwise.

1. CreateabooleanvariablecalledconstraintSetthatistrueifselectednetworkoptionisnotthedefaultJobInfo.NETWORK_TYPE_NONE:

booleanconstraintSet=selectedNetworkOption!=JobInfo.NETWORK_TYPE_NONE;

2. Createanif/elseblockusingtheconstraintSetboolean.3. MovethecodethatschedulesthetaskandshowstheToastmessageintotheifblock.4. IfconstraintSetisfalse,showaToastmessagetotheusertosetatleastoneconstraint.Don'tforgettoextract

yourstringresources:

if(constraintSet){

//Schedulethejobandnotifytheuser

JobInfomyJobInfo=builder.build();

mScheduler.schedule(myJobInfo);

Toast.makeText(this,R.string.job_scheduled,Toast.LENGTH_SHORT).show();

}else{

Toast.makeText(this,R.string.no_constraint_toast,Toast.LENGTH_SHORT).show();

}

2.3ImplementtheDeviceIdleandDeviceChargingconstraints

JobSchedulerincludestheabilitytowaituntilthedeviceischarging,orinanidlestate(thescreenisoff,andtheCPUhasgonetosleep)toexecuteyourJobService.YouwillnowaddswitchestoyourapptotoggletheseconstraintsonyourJobService.

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AddtheUIelementsforthenewconstraints

1. Inyouractivity_main.xmlfile,copythenetworktypelabelTextViewandpasteitbelowtheRadioGroup.2. Changetheandroid:textattributeto"Requires:".3. Belowthistextview,insertahorizontalLinearLayoutwitha4dpmargin.4. CreatetwoSwitchviewsaschildrentothehorizontalLinearLayoutwithheightandwidthsetto"wrap_content"andthe

followingattributes:

Switch1

android:text "DeviceIdle"

android:id "@+id/idleSwitch"

Switch2

android:text "DeviceCharging"

android:id "@+id/chargingSwitch"

Addthecodeforthenewconstraints

1. InMainActivity,createmembervariables,mDeviceIdleandmDeviceCharging,fortheswitchesandinitializetheminonCreate().

2. InthescheduleJob()method,addthefollowingcallstosettheconstraintsontheJobSchedulerbasedontheuserselectionintheswitches:

builder.setRequiresDeviceIdle(mDeviceIdle.isChecked());

builder.setRequiresCharging(mDeviceCharging.isChecked());

3. UpdatethecodethatsetsconstraintSettoconsiderthesenewconstraints:

booleanconstraintSet=(selectedNetworkOption!=JobInfo.NETWORK_TYPE_NONE)

||mDeviceChargingSwitch.isChecked()||mDeviceIdleSwitch.isChecked();

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4. Runyourapp,nowwiththeadditionalconstraints.Trythedifferencecombinationsofswitchestoseewhenthenotificationgetssent(thatindicatesthatthejobran).Youcantestthechargingstateconstraintinanemulatorbyopeningthemenu(theellipsesiconnexttotheemulateddevice),gototheBatterypaneandtoggletheBatteryStatusdropdown.ThereisnowaytomanuallyputtheemulatorinIdlemodeasofthewritingofthispractical.

Waitinguntilthedeviceisidleandpluggedinisacommonpatternforbatteryintensivetaskssuchasdownloadingoruploadinglargefiles.

2.4ImplementtheOverrideDeadlineconstraint

Uptothispoint,thereisnowaytoknowpreciselywhentheframeworkwillexecuteyourtask.Thesystemtakesintoaccounteffectiveresourcemanagementwhichmaydelayyourtaskdependingonthestateofthedevice,anddoesnotguaranteethatyourtaskwillrunontime.Forexample,anewsappmaywanttodownloadthelatestnewsonlywhenwifiisavailableandthedeviceispluggedinandcharging;butausermayinadvertentlyforgettoenabletheirwifiorchargetheirdevice.Ifyoudon'taddatimeparametertoyourscheduledJob,thatuserwillbedisappointedwhentheywakeuptoyesterday'snews.Forthisreason,theJobSchedulerAPIincludestheabilitytosetaharddeadlinethatwilloverridethepreviousconstraints.

AddthenewUIforsettingthedeadlinetorunthetask

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InthisstepyouwilluseanewUIcomponent,aSeekbar,toallowtheusertosetadeadlinebetween0and100secondstoexecuteyourtask.

TheusersetsthevaluebydraggingtheSeekBar.

1. CreateahorizontalLinearLayoutbelowtheexistingLinearLayoutwiththeswitches,whichwillcontainthelabelsfortheSeekBar.

2. TheSeekBarwillhavetwolabels:astaticonejustlikethelabelfortheRadioGroupofbuttons,andadynamiconethatwillbeupdatedwiththevaluefromtheSeekBar.AddtwoTextViewstotheLinearLayoutwiththefollowingattributes:

TextView1

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:text "OverrideDeadline:"

android:id "@+id/seekBarLabel"

android:textAppearance "@style/TextAppearance.AppCompat.Subhead"

TextView2

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:text "NotSet"

android:id "@+id/seekBarProgress"

android:textAppearance "@style/TextAppearance.AppCompat.Subhead"

3. AddaSeekBarviewbelowtheLinearLayoutwiththefollowingattributes:

Attribute Value

android:layout_width "match_parent"

android:layout_height "wrap_content"

android:id "@+id/seekBar"

android:layout_margin "4dp"

Writethecodeforaddingthedeadline

1. InMainActivity,createamembervariablefortheSeekBarandinitializeitinonCreate():

mSeekBar=(SeekBar)findViewById(R.id.seekBar);

2. CreatefinalvariablesforbothTextViews(theywillbeaccessedfromaninnerclass)andinitializetheminonCreate():

finalTextViewlabel=(TextView)findViewById(R.id.seekBarLabel);

finalTextViewseekBarProgress=(TextView)findViewById(R.id.seekBarProgress);

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3. InonCreate(),callsetOnSeekBarChangeListener()ontheSeekBar,passinginanewOnSeekBarChangeListener(AndroidStudioshouldgeneratetherequiredmethods):

mSeekBar.setOnSeekBarChangeListener(newSeekBar.OnSeekBarChangeListener(){

@Override

publicvoidonProgressChanged(SeekBarseekBar,inti,booleanb){}

@Override

publicvoidonStartTrackingTouch(SeekBarseekBar){}

@Override

publicvoidonStopTrackingTouch(SeekBarseekBar){}

});

4. ThesecondargumentofonProgressChanged()isthecurrentvalueoftheSeekBar.IntheonProgressChanged()callback,checkiftheintegervalueisgreaterthan0(meaningavaluehasbeensetbytheuser),andifitis,settheSeekBarprogresslabeltotheintegervalue,followedby"s"toindicateseconds:

if(i>0){

mSeekBarProgress.setText(String.valueOf(i)+"s");

}

5. Otherwise,settheTextViewtoread"NotSet":

else{

mSeekBarProgress.setText("NotSet");

}

6. TheoverridedeadlineshouldonlybesetiftheintegervalueoftheSeekBarisgreaterthan0.InthescheduleJob()method,createanintegertostoretheSeekBarprogressandabooleanvariablethatistrueiftheSeekBarhasanintegervaluegreaterthan0:

intseekBarInteger=mSeekBar.getProgress();

booleanseekBarSet=seekBarInteger>0;

7. Ifthisbooleanistrue,callsetOverrideDeadline()ontheJobInfo.Builder,passingintheintegervaluefromtheSeekBarmultipliedby1000(theparameterisinmilliseconds,youwanttheusertosetthedeadlineinseconds):

if(seekBarSet){

builder.setOverrideDeadline(seekBarInteger*1000);

}

8. ModifytheconstraintSetbooleantoincludethevalueofseekBarSetasapossibleconstraint:

booleanconstraintSet=selectedNetworkOption!=JobInfo.NETWORK_TYPE_NONE

||mDeviceChargingSwitch.isChecked()||mDeviceIdleSwitch.isChecked()

||seekBarSet;

9. Runtheapp.TheusercannowsetaharddeadlineinsecondsbywhichtimetheJobServicemustberun!

2.5ImplementthePeriodicconstraintJobScheduleralsoallowsyoutoschedulearepeatedtask,muchlikeAlarmManager.Thisoptionhasafewcaveats:

Thetaskisnotguaranteedtoruninagivenperiod(theotherconditionsmaynotbemet,ortheremightnotbeenoughsystemresources).Usingthisconstraintpreventsyoufromalsosettinganoverridedeadlineoraminimumlatency(),sincetheseoptionsdonotmakesenseforrepetitivetasks.SeeJobInfo.Builder)documentationformoreinformation.

AddthePeriodicSwitchtothelayout

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YouwilladdaSwitchtoallowtheusertoswitchbetweenhavingthejobrunonceorrepeatedlyatperiodicintervals.

1. Inactivity_main.xml,addaSwitchviewbetweenthetwohorizontalLinearLayouts.Usethefollowingattributes:

Attribute Value

android:layout_width "wrap_content"

android:layout_height "wrap_content"

android:text "Periodic"

android:id "@+id/periodicSwitch"

android:layout_margin "4dp"

2. CreateamembervariablefortheswitchandinitializeitinonCreate():

mPeriodicSwitch=(Switch)findViewById(R.id.periodicSwitch);

WritethecodetousethePeriodicSwitch

Theoverridedeadlineandperiodicconstraintsaremutuallyexclusive.YouwillusetheswitchtotogglethefunctionalityandlabeloftheSeekBartorepresenteithertheoverridedeadline,ortheperiodicinterval.

1. CallsetOnCheckedChangeListener()ontheperiodicswitch,passinginanewOnCheckedChangeListener.2. Ifchecked,setthelabelto"PeriodicInterval:",otherwiseto"OverrideDeadline:":

mPeriodicSwitch.setOnCheckedChangeListener(

newCompoundButton.OnCheckedChangeListener(){

@Override

publicvoidonCheckedChanged(CompoundButtoncompoundButton,booleanisChecked){

if(isChecked){

label.setText(R.string.periodic_interval);

}else{

label.setText(R.string.override_deadline);

}

}

});

AllthatremainsnowistoimplementthelogicinthescheduleJob()methodtoproperlysettheconstraintsontheJobInfoobject.

Iftheperiodicoptionison:

IftheSeekBarhasanon-zerovalue,settheconstraintbycallingsetPeriodic()ontheJobInfo.Builderobject.IftheSeekBarhasavalueof0,showaToastmessageaskingtheusertosetaperiodicintervalwiththeSeekBar.

Iftheperiodicoptionisoff:

IftheSeekBarhasanon-zerovalue,theuserhassetanoverridedeadline.ApplytheoverridedeadlineusingthesetOverrideDeadline()option.IftheSeekBarhasavalueof0,theuserhassimplynotspecifiedanoverridedeadlineoraperiodictask,soaddnothingtotheJobInfo.Builderobject.ReplacethecodethatsetstheoverridedeadlinetotheJobInfo.BuilderinscheduleJob()withthefollowingcodetoimplementthislogic:

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if(mPeriodicSwitch.isChecked()){

if(seekBarSet){

builder.setPeriodic(seekBarInteger*1000);

}else{

Toast.makeText(MainActivity.this,

"Pleasesetaperiodicinterval",Toast.LENGTH_SHORT).show();

}

}else{

if(seekBarSet){

builder.setOverrideDeadline(seekBarInteger*1000);

}

}

SolutioncodeAndroidStudioproject:NotificationScheduler

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge:Upuntilnow,yourtasksscheduledbytheJobServicefocusedondeliveringanotification.Mostofthetime,however,JobSchedulerisusedformorerobustbackgroundtaskssuchasupdatingtheweatherorsyncingwithadatabase.Sincebackgroundtaskscanbemorecomplexinnature,bothfromaprogrammaticandfromafunctionalitystandpoint,thejobofnotifyingtheframeworkwhenthetaskiscompletefallsonthedeveloper.Fortunately,thedevelopercandothisbycallingjobFinished().

1. ImplementaJobServicethatstartsanAsyncTaskwhenthegivenconstraintsaremet.TheAsyncTaskshouldsleepfor5seconds.ThiswillrequireyoutocalljobFinished()oncethetaskiscomplete.Iftheconstraintsarenolongermetwhilethethreadissleeping,showaToastmessagesayingthatthejobfailedandalsoreschedulethejob.

SummaryJobSchedulerprovidesaflexibleframeworktointelligentlyaccomplishbackgroundservices.JobSchedulerisonlyavailableondevicesrunningAPI21+TousetheJobScheduler,youneedtwoparts:JobServiceandJobInfo.JobInfoisasetofconditionsthatwilltriggerthejobtorun.JobServiceimplementsthejobtorunundertheconditionsspecifiedbyJobInfo.YouonlyhavetoimplementtheonStartJob()andonStopJob()callbackmethodsinyourJobService.Theimplementationofyourjoboccurs(orisstarted)inonStartJob().onStartJob()returnsabooleanthatindicateswhethertheserviceneedstoprocesstheworkinaseparatethread.IfonStartJob()returnstrue,youmustexplicitlycalljobFinished().IfonStartJob()returnsfalse,theruntimewillcalljobFinished()onyourbehalf.JobServiceisprocessedonthemainthread,soavoidlengthycalculationsorI/O.JobScheduleristhemanagerclassresponsibleforschedulingthetask.JobSchedulerbatchestaskstogethertomaximizetheefficiencyofsystemresources,whichmeansyoudonothaveexactcontrolofwhenitwillbeexecuted.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

TransferringDataEfficiently

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Learnmore

AndroidDeveloperDocumentation

Reference

JobSchedulerJobInfoJobInfo.BuilderJobServiceJobParameters

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9.1:SharedPreferencesContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.ExploreHelloSharedPrefsTask2.SaveandrestoredatatosharedpreferencesCodingchallengeSummaryRelatedconceptLearnmore

Sharedpreferencesallowyoutoreadandwritesmallamountsofprimitivedata(askey/valuepairs)toafileonthedevicestorage.TheSharedPreferenceclassprovidesAPIsforgettingahandletoapreferencefileandforreading,writing,andmanagingthisdata.ThesharedpreferencesfileitselfismanagedbytheAndroidframework,andaccessibleto(sharedwith)allthecomponentsofyourapp.Thatdataisnot,however,sharedwithoraccessibletoanyotherapps.

Thedatayousavetosharedpreferencesisdifferentfromthedatainthesavedactivitystateyoulearnedaboutinanearlierchapter.Thedataintheactivityinstancestateisretainedacrossactivityinstancesinthesameusersession.Sharedpreferencespersistacrossusersessions,evenifyourappiskilledandrestartedorifthedeviceisrebooted.

Usesharedpreferencesonlywhenyouneedtosaveasmallamountdataassimplekey/valuepairs.TomanagelargeramountsofpersistentappdatausetheothermethodssuchasSQLdatabases,whichyouwilllearnaboutinalaterchapter.

WhatyoushouldalreadyKNOWFromthepreviouspracticalsyoushouldbefamiliarwith:

Creating,building,andrunningappsinAndroidStudio.Designinglayoutswithbuttonsandtextviews.Usingstylesandthemes.Savingandrestoringactivityinstancestate.

WhatyouwillLEARNYouwilllearnto:

Identifywhatsharedpreferencesare.Createasharedpreferencesfileforyourapp.Savedatatosharedpreferences,andreadthosepreferencesbackagain.Clearthedatainthesharedpreferences.

WhatyouwillDOInthispractical,youwill:

Addtheabilitytosave,retrieve,andresetsharedpreferencestoanapp.

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AppOverviewTheHelloSharedPrefsappisanothervariationoftheHelloToastappyoucreatedinLesson1.Itincludesbuttonstoincrementthenumber,tochangethebackgroundcolor,andtoresetboththenumberandcolortotheirdefaults.Theappalsousesthemesandstylestodefinethebuttons.

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You'llstartwiththestarterappinthispracticalandaddsharedpreferencestothemainactivitycode.You'llalsoaddaresetbuttonthatsetsboththecountandthebackgroundcolortothedefault,andclearsthepreferencesfile.

Task1.ExploreHelloSharedPrefsThecompletestarterappprojectforthispracticalisavailableatHelloSharedPrefs-Start.InthistaskyouwillloadtheprojectintoAndroidStudioandexploresomeoftheapp'skeyfeatures.

1.1OpenandRuntheHelloSharedPrefsProject

1. DownloadtheHelloSharedPrefs-Startappandunzipthefile.2. OpentheappinAndroidStudio.3. BuildandruntheprojectinAndroidStudio.Trythesethings:

ClicktheCountbuttontoincrementthenumberinthemaintextview.Clickanyofthecolorbuttonstochangethebackgroundcolorofthemaintextview.Rotatethedeviceandnotethatbothbackgroundcolorandcountarepreserved.ClicktheResetbuttontosetthecolorandcountbacktothedefaults.

4. Force-quittheappusingoneofthesemethods:

InAndroidStudio,selectRun>Stop'app'orclicktheStopIcon inthetoolbar.Onthedevice,clicktheRecentsbutton(thesquarebuttoninthelowerrightcorner).SwipethecardfortheHelloSharedPrefsapptoquit,orclicktheXintherightcorner.Ifyouquittheappinthismanner,waitafewsecondsbeforestartingitagainsothesystemcancleanup.

5. Re-runtheapp.

Theapprestartswiththedefaultappearance--thecountis0,andthebackgroundcolorisgrey.

1.2ExploretheActivitycode1. OpenMainActivity(java/com.example.android.simplecalc/MainActivity).2. Examinethecodeandnotethesethings:

Thecount(mCount)isdefinedbyaninteger.ThecountUp()clickhandlermethodincrementsthisvalueandupdatesthemaintextview.Thecolor(mColor)isalsoanintegerthatisinitiallydefinedasgreyinthecolors.xmlresourcefileasdefault_background.ThechangeBackground()clickhandlermethodgetsthebackgroundcolorofthebuttonthatwasclickedandthensetsthebackgroundcolorofthemaintextview.BoththecountandcolorintegersaresavedtotheinstancestatebundleinonSaveInstanceState(),andrestoredinonCreate().Thebundlekeysforcountandcoloraredefinedbyprivatevariables(COUNT_KEY)and(COLOR_KEY).

Task2.SaveandrestoredatatoasharedpreferencesfileInthistaskyou'llsavethestateoftheapptoasharedpreferencesfile,andreadthatdatabackinwhentheappisrestarted.Becausethestatedatayou'resavingtothesharedpreferences(thecurrentcountandcolor)arethesamedatayoupreserveintheinstancestate,youdon'thavetodoittwice--youcanreplacetheinstancestatealtogetherwiththesharedpreferencestate.

2.1Initializethepreferences1. AddmembervariablestotheMainActivityclasstoholdthenameofthesharedpreferencesfile,andareferencetoa

SharedPreferencesobject.

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privateSharedPreferencesmPreferences;

privateStringsharedPrefFile="com.example.android.hellosharedprefs";

Youcannameyoursharedpreferencesfileanythingyouwantto,butconventionallyithasthesamenameasthepackagenameofyourapp.

2. IntheonCreate()method,initializethesharedpreferences.Makesureyouinsertthiscodebeforetheifstatement.:

mPreferences=getSharedPreferences(sharedPrefFile,MODE_PRIVATE);

ThegetSharedPreferences()methodopensthefileatthegivenfilename(sharedPrefFile)withthemodeMODE_PRIVATE.

Note:OlderversionsofAndroidhadothermodesthatallowedyoutocreateaworld-readableorworld-writablesharedpreferencesfile.ThesemodesweredeprecatedinAPI17,andarenowstronglydiscouragedforsecurityreasons.Ifyouneedtosharedatawithotherapps,useaserviceoracontentprovider.

SolutionCode(MainActivity-partial)

publicclassMainActivityextendsAppCompatActivity{

privateintmCount=0;

privateTextViewmShowCount;

privateintmColor;

privateSharedPreferencesmPreferences;

privateStringsharedPrefFile="com.example.android.hellosharedprefs";

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

mShowCount=(TextView)findViewById(R.id.textview);

mColor=ContextCompat.getColor(this,R.color.default_background);

mPreferences=getSharedPreferences(sharedPrefFile,MODE_PRIVATE);

//…

}

}

2.2SavepreferencesinonPause()

Savingpreferencesisalotlikesavingtheinstancestate--bothoperationssetasidethedatatoaBundleobjectasakey/valuepair.Forsharedpreferences,however,yousavethatdataintheonPause()lifecyclecallback,andyouneedasharededitorobject(SharedPreferences.Editor)towritetothesharedpreferencesobject.

1. ClickthelastlineoftheMainActivityclass,justbeforetheclosingbracket.2. SelectCode>Generate,thenselectOverrideMethods.3. Type"onPause",selectthemethodsignaturefortheonPause()method,andclickOK.

AskeletononPause()methodisaddedtotheinsertionpoint.

4. GetaneditorfortheSharedPreferencesobject:

SharedPreferences.EditorpreferencesEditor=mPreferences.edit();

Asharedpreferenceseditorisrequiredtowritetothesharedpreferencesobject.AddthislinetoonPause()afterthecalltosuper.onPause().

5. UsetheputInt()methodtoputboththemCountandmColorintegersintothesharedpreferenceswiththeappropriatekeys:

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preferencesEditor.putInt(COUNT_KEY,mCount);

preferencesEditor.putInt(COLOR_KEY,mColor);

TheSharedPreferences.Editorclassincludesmultipleputmethodsfordifferentdatatypes,includingputInt()andputString().

6. Callapply()tosavethepreferences:

preferencesEditor.apply();

Theapply()methodsavesthepreferencesasynchronously,offoftheUIthread.Thesharedpreferenceseditoralsohasacommit()methodtosynchronouslysavethepreferences.Thecommit()methodisdiscouragedasitcanblockotheroperations.

7. DeletetheentireonSaveInstanceState()method.Sincetheactivityinstancestatecontainsthesamedataasthesharedpreferences,youcanreplacetheinstancestatealtogether.

SolutionCode(MainActivity-onPause()method)

@Override

protectedvoidonPause(){

super.onPause();

SharedPreferences.EditorpreferencesEditor=mPreferences.edit();

preferencesEditor.putInt(COUNT_KEY,mCount);

preferencesEditor.putInt(COLOR_KEY,mColor);

preferencesEditor.apply();

}

2.3RestorepreferencesinonCreate()

Aswiththeinstancestate,yourappreadsanysavedsharedpreferencesintheonCreate()method.Again,sincethesharedpreferencescontainthesamedataastheinstancestate,wecanreplacethestatewiththepreferenceshereaswell.EverytimeonCreate()iscalled--whentheappstarts,onconfigurationchanges--thesharedpreferencesareusedtorestorethestateoftheview.

1. LocatethepartoftheonCreate()methodthattestsifthesavedInstanceStateargumentisnullandrestorestheinstancestate:

if(savedInstanceState!=null){

mCount=savedInstanceState.getInt(COUNT_KEY);

if(mCount!=0){

mShowCountTextView.setText(String.format("%s",mCount));

}

mColor=savedInstanceState.getInt(COLOR_KEY);

mShowCountTextView.setBackgroundColor(mColor);

}

2. Deletethatentireblock.3. IntheonCreate()method,inthesamespotwherethesaveinstancestatecodewas,getthecountfromthe

preferenceswiththeCOUNT_KEYkeyandassignittothemCountvariable.

mCount=mPreferences.getInt(COUNT_KEY,0);

Whenyoureaddatafromthepreferencesyoudon'tneedtogetasharedprefrenceseditor.Useanyofthegetmethodsonasharedpreferencesobjecttoretrievepreferencedata.

NotethatthegetInt()methodtakestwoarguments:oneforthekey,andtheotherforthedefaultvalueifthekeycannotbefound.Inthiscasethedefaultvalueis0,whichisthesameastheinitialvalueofmCount.

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4. Updatethevalueofthemaintextviewwiththenewcount.

mShowCountTextView.setText(String.format("%s",mCount));

5. GetthecolorfromthepreferenceswiththeCOLOR_KEYkeyandassignittothemColorvariable.

mColor=mPreferences.getInt(COLOR_KEY,mColor);

Asbefore,thesecondargumenttogetInt()isthedefaultvaluetouseincasethekeydoesn'texistinthesharedpreferences.InthiscaseyoucanjustreusethevalueofmColor,whichwasjustinitializedtothedefaultbackgroundfurtherupinthemethod.

6. Updatethebackgroundcolorofthemaintextview.

mShowCountTextView.setBackgroundColor(mColor);

7. Runtheapp.Clickthecountbuttonandchangethebackgroundcolortoupdatetheinstancestateandthepreferences.

8. Rotatethedeviceoremulatortoverifythatthecountandcoloraresavedacrossconfigurationchanges.9. Force-quittheappusingoneofthesemethods:

InAndroidStudio,selectRun>Stop'app.'Onthedevice,clicktheRecentsbutton(thesquarebuttoninthelowerrightcorner).SwipethecardfortheHelloSharedPrefsapptoquit,orclicktheXintherightcorner.

10. Re-runtheapp.Theapprestartsandloadsthepreferences,maintainingthestate.

SolutionCode(MainActivity-onCreate())

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

//Initializeviews,color,preferences

mShowCountTextView=(TextView)findViewById(R.id.count_textview);

mColor=ContextCompat.getColor(this,R.color.default_background);

mPreferences=getSharedPreferences(mSharedPrefFile,MODE_PRIVATE);

//Restorepreferences

mCount=mPreferences.getInt(COUNT_KEY,0);

mShowCountTextView.setText(String.format("%s",mCount));

mColor=mPreferences.getInt(COLOR_KEY,mColor);

mShowCountTextView.setBackgroundColor(mColor);

}

2.4Resetpreferencesinthereset()clickhandler

Theresetbuttoninthestarterappresetsboththecountandcolorfortheactivitytotheirdefaultvalues.Sincethepreferencesholdthestateoftheactivity,it'simportanttoalsoclearthepreferencesatthesametime.

1. Inthereset()clickhandlermethod,afterthecolorandcountarereset,getaneditorfortheSharedPreferencesobject:

SharedPreferences.EditorpreferencesEditor=mPreferences.edit();

2. Deleteallthesharedpreferences:

preferencesEditor.clear();

3. Applythechanges:

preferencesEditor.apply();

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SolutionCode(reset()method):

publicvoidreset(Viewview){

//Resetcount

mCount=0;

mShowCountTextView.setText(String.format("%s",mCount));

//Resetcolor

mColor=ContextCompat.getColor(this,R.color.default_background);

mShowCountTextView.setBackgroundColor(mColor);

//Clearpreferences

SharedPreferences.EditorpreferencesEditor=mPreferences.edit();

preferencesEditor.clear();

preferencesEditor.apply();

}

SolutioncodeAndroidStudioproject:HelloSharedPrefs

CodingchallengeNote:Allcodingchallengesareoptionalandnotprerequisiteforthematerialinthenextchapter.

Challenge:ModifytheHelloSharedPrefsappsothatinsteadofautomaticallysavingthestatetothepreferencesfile,addasecondactivitytochange,reset,andsavethosepreferences.AddabuttontotheappnamedSettingstolaunchthatactivity.Includetogglebuttonsandspinnerstomodifythepreferences,andSaveandResetbuttonsforsavingandclearingthepreferences.

SummaryTheSharedPreferencesclassallowsanapptostoresmallamountsofprimitivedataaskey-valuepairs.Sharedpreferencespersistacrossdifferentusersessionsofthesameapp.Towritetothesharedpreferences,getaSharedPreferences.Editorobject.Usethevariousput*methodsinaSharedPreferences.Editorobject,suchasputInt()orputString(),toputdataintothesharedpreferenceswithakeyandavalue.Usethevariousget*methodsinaSharedPreferencesobject,suchasgetInt()orgetString(),togetdataoutofthesharedpreferenceswithakey.Usetheclear()methodinaSharedPreferences.Editorobjecttoremoveallthedatastoredinthepreferences.Usetheapply()methodinaSharedPreferences.Editorobjecttosavethechangestothepreferencesfile.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

SharedPreferences

LearnmoreSavingData(AndroidGuides)StorageOptions(AndroidGuides)

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SavingKey-ValueSets(AndroidTraining)SharedPreferences(AndroidAPIReference)SharedPreferences.Editor(AndroidAPIReference)HowtouseSharedPreferencesinAndroidtostore,fetchandeditvalues(StackOverflow)onSavedInstanceStatevs.SharedPreferences(StackOverflow)

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9.2:AddingSettingstoanAppContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1:AddaswitchsettingtoanappTask2:UsingtheSettingsActivitytemplateCodingchallengesSummaryRelatedConceptLearnmore

Appsoftenincludesettingsthatallowuserstomodifyappfeaturesandbehaviors.Forexample,someappsallowuserstosettheirhomelocations,defaultunitsformeasurements,diningoptions,andothersettingsthatapplytotheentireapp.Settingsareusuallyaccessedinfrequently,becauseonceauserchangesasetting,suchasahomelocation,theyrarelyneedtogobackandchangeitagain.

UsersexpecttonavigatetoappsettingsbytappingSettingsinsidenavigation,suchasanavigationdrawerasshownontheleftsideofthefigurebelow,orintheoptionsmenuintheappbar,shownontherightsideofthefigurebelow.

Inthefigureabove:

1. Settingsinsidenavigation(anavigationdrawer)2. Settingsintheoptionsmenuoftheappbar

Inthispracticalyouwilladdasettingsactivitytoanapp.UserswillbeabletonavigatetotheappsettingsbytappingSettings,whichwillbelocatedintheoptionsmenuintheappbar.

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WhatyoushouldalreadyKNOWFromthepreviouspracticals,youshouldbeableto:

Addanactivitytoanapp.Designlayoutswithbuttonsandtextviews.Extractstringresourcesandeditstringandstringarrayvalues.Createanoptionsmenuintheappbar.Addandeditthemenuitemsintheoptionsmenu.Addtheeventhandlerformenuitemclicks.EdittheAndroidManifest.xmlfiletoaddUpnavigationforasecondactivity.ReadpreferencesfromsharedPreferences.

WhatyouwillLEARNYouwilllearnto:

Addanactivityandunderstandtheuseoffragmentsformanagingsettings.CreateanXMLresourcefileofsettingswiththeirattributes.Createnavigationtothesettingsactivity.Setthedefaultvaluesofsettings.Readthesettingsvalueschangedbytheuser.CustomizetheSettingsActivitytemplateforyourownuse.

WhatyouwillDOInthispractical,youwill:

CreateanappthatincludesSettingsintheoptionsmenu.Add"Settingsoption"asatoggleswitch.Addcodetosetthedefaultvalueforthesetting,andaccessthesettingvalueafterithaschanged.UseandcustomizetheAndroidStudioSettingsActivitytemplate.

AppoverviewAndroidStudioprovidesashortcutforsettingupanoptionsmenuwithSettings.IfyoustartanAndroidStudioprojectforasmartphoneortabletusingtheBasicActivitytemplate,thenewappincludesSettingsasshownbelow:

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Thetemplatealsoincludesafloatingactionbuttoninthelowerrightcornerofthescreenwithanenvelopeicon.Youcanignorethisbuttonforthispractical,asyouwon'tbeusingit.

You'llstartbycreatinganappnamedAppWithSettingsusingtheBasicActivitytemplate,andaddasettingsactivitythatprovidesonetoggleswitchsettingthattheusercanturnonoroff:

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Youwilladdcodetoreadthesettingandperformanactionbasedonitsvalue.Forthesakeofsimplicity,theactionwillbetodisplayatoastmessagewiththevalueofthesetting.

Inthesecondtask,youwilladdthestandardSettingsActivitytemplateprovidedbyAndroidStudiototheDroidCafeappyoucreatedinapreviouslesson.TheSettingsActivitytemplateispre-populatedwithsettingsyoucancustomizeforanapp,andprovidesadifferentlayoutforsmartphonesandtablets:

Smartphones:AmainSettingsscreenwithaheaderlinkforeachgroupofsettings,suchasGeneralforgeneralsettings,asshownbelow.

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Tablets:Amaster/detailscreenlayoutwithaheaderlinkforeachgroupontheleft(master)side,andthegroupofsettingsontheright(detail)side,asshowninthefigurebelow.

Allyouneedtodotocustomizethetemplateischangetheheaders,settingtitles,settingdescriptions,andvaluesforthesettings,andwritethecodeyouwouldnormallywritetousethevaluesofthesettings.

TheDroidCafeappwascreatedinapreviouslessonfromtheBasicActivitytemplate,whichprovidesanoptionsmenuintheappbarforplacingtheSettingsoption.YouwillcustomizethesuppliedSettingsActivitytemplatebychangingasinglesetting'stitle,description,values,anddefaultvalues.Youwilladdcodetoreadthesetting'svalueaftertheuserchangesit,anddisplaythatvalue.

Task1:AddaswitchsettingtoanappInthistask,youwill:

CreateanewprojectbasedontheBasicActivitytemplate(whichprovidesanoptionsmenu).AddatoggleswitchsettingwithattributesinapreferenceXMLfile.Addanactivityforsettingsandafragmentforaspecificsetting.YouwillusethePreferenceFragmentCompatversionofPreferenceFragmentinordertomaintaincompatibilitywithAppCompatActivity.Youwillalsoaddtheandroid.support:preference-v7library.ConnecttheSettingsitemintheoptionsmenutothesettingsactivity.

1.1Createtheprojectandaddthexmldirectoryandresourcefile

1. InAndroidStudio,createanewprojectwiththefollowingparameters:

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Attribute Value

ApplicationName AppWithSettings

CompanyName android.example.com(oryourowndomain)

PhoneandTabletMinimumSDK API15:Android4.0.3IceCreamSandwich

UseaFragment? Leaveunchecked

Template BasicActivity

2. Runtheapp,andtaptheoverflowiconintheappbartoseetheoptionsmenu,asshowninthefigurebelow.TheonlyitemintheoptionsmenuisSettings.

3. CreateanewresourcedirectorytoholdtheXMLfilecontainingthesettings:i. SelecttheresdirectoryintheProject:Androidview,andchooseFile>New>AndroidResourceDirectory.TheNewResourceDirectorydialogappears.

ii. IntheResourcetypedrop-downmenu,choosexml.TheDirectorynameautomaticallychangestoxml.iii. ClickOK.

4. ThexmldirectoryappearsintheProject:Androidviewinsidetheresdirectory.SelectthexmldirectoryandchooseFile>New>XMLresourcefile(orright-clickthexmldirectoryandchooseNew>XMLresourcefile).

5. EnterthenameoftheXMLfile,preferences,intheFilenamefield,andclickOK.Thepreferences.xmlfileappearsinsidethexmldirectory,andthelayouteditorappears,asshowninthefigurebelow.

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Inthefigureabove:

1. Thepreferences.xmlfileinsidethexmldirectory.2. Thelayouteditorshowingthepreferences.xmlcontents.

1.2AddtheXMLpreferenceandattributesforthesetting

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1. DragaSwitchPreferencefromthePalettepaneontheleftsidetothetopofthelayout,asshowninthefigurebelow.

2. ChangethevaluesinthePropertiespaneontherightsideofthelayouteditorasfollows(refertothefigurebelow):

i. defaultValue:trueii. key:example_switchiii. title:Settingsoptioniv. summary:Turnthisoptiononoroff

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3. ClicktheTexttabatthebottomofthelayouteditortoedittheXMLcode:

<PreferenceScreenxmlns:android="http://schemas.android.com/apk/res/android">

<SwitchPreference

android:defaultValue="true"

android:title="Settingsoption"

android:key="example_switch"

android:summary="Turnthisoptiononoroff"/>

</PreferenceScreen>

ThePropertiesvaluesyouenteredrepresentXMLattributes:

android:defaultValue:Thedefaultvalueofthesettingwhentheappstartsforthefirsttime.android:title:Thetitleofthesetting.ForaSwitchPreference,thetitleappearstotheleftofthetoggleswitch.android:key:Thekeytouseforstoringthesettingvalue.Eachsettinghasacorrespondingkey-valuepairthatthesystemusestosavethesettinginadefaultSharedPreferencesfileforyourapp'ssettings.android:summary:Thetextsummaryappearsunderneaththesetting.

4. Extractthestringresourcesfortheandroid:titleandandroid:summaryattributevaluesto@string/switch_titleand@string/switch_summary.

5. Change<SwitchPreferenceinthecodeto<android.support.v7.preference.SwitchPreferenceCompat:

<PreferenceScreenxmlns:android="http://schemas.android.com/apk/res/android">

<android.support.v7.preference.SwitchPreferenceCompat

.../>

</PreferenceScreen>

InordertousethePreferenceFragmentCompatversionofPreferenceFragment,youmustalsousetheandroid.support.v7versionofSwitchPreference(SwitchPreferenceCompat).

TheSwitchPreferenceCompatlineabovemayshowayellowlightbulbiconwithawarning,butyoucanignoreit.

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6. Openthestyles.xmlfile,andaddthefollowingpreferenceThemedeclarationtotheAppTheme:

<stylename="AppTheme"parent="Theme.AppCompat.Light.DarkActionBar">

...

<itemname="preferenceTheme">@style/PreferenceThemeOverlay</item>

</style>

InordertousethePreferenceFragmentCompatversionofPreferenceFragment,youmustalsodeclarepreferenceThemewiththePreferenceThemeOverlaystyletotheapptheme.

7. Openthebuild.gradle(Module:app)file,andaddthefollowingtothedependenciessection:

dependencies{

...

compile'com.android.support:preference-v7:25.0.1'

}

Theaboveaddstheandroid.support:preference-v7libraryinordertousethePreferenceFragmentCompatversionofPreferenceFragment.

1.3Addanactivityforsettingsandafragmentforaspecificsetting

1. InordertocreateaSettingsactivitythatprovidesaUIforsettings,addanEmptyActivitytotheapp:

i. SelectappatthetopoftheProject:Androidview.ii. ChooseNew>Activity>EmptyActivity.iii. NametheactivitySettingsActivity.iv. Unchecktheoptiontogeneratealayoutfile(youdon'tneedone).v. LeavecheckedtheBackwardsCompatibility(AppCompat)option.vi. ThePackagenameshouldalreadybesettocom.example.android.projectname,andtheTargetSourceSet

shouldbesettomain.Ifnot,maketheseselectionsinthedrop-downmenus.vii. ClickFinish.TheresultisthefollowingclassdefinitioninSettingsActivity:

publicclassSettingsActivityextendsAppCompatActivity{

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

}

}

2. Addablankfragmentforagroupofsimilarsettings(withoutalayout,factorymethods,orinterfacecallbacks)totheapp,inordertoswapthemintotheSettingsactivityscreenwhenneeded:

i. SelectappatthetopoftheProject:Androidviewagain.ii. ChooseNew>Fragment>Fragment(Blank).iii. NamethefragmentSettingsFragment.iv. Unchecktheoptiontogeneratealayoutfile(youdon'tneedone).v. Unchecktheoptiontoincludefragmentfactorymethods.vi. Unchecktheoptiontoincludeinterfacecallbacks.vii. ClickFinish.TheresultisthefollowingclassdefinitioninSettingsFragment:

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publicclassSettingsFragmentextendsFragment{

publicSettingsFragment(){

//Requiredemptypublicconstructor

}

@Override

publicViewonCreateView(LayoutInflaterinflater,

ViewGroupcontainer,BundlesavedInstanceState){

TextViewtextView=newTextView(getActivity());

textView.setText(R.string.hello_blank_fragment);

returntextView;

}

}

3. ChangetheclassdefinitionofSettingsFragmenttoextendPreferenceFragmentCompat:

publicclassSettingsFragmentextendsPreferenceFragmentCompat{

...

}

YouuseaspecializedFragmentsubclasstodisplayalistofsettings.ThebestpracticeistousearegularActivitythathostsaPreferenceFragmentthatdisplaystheappsettings.FragmentslikePreferenceFragmentprovideamoreflexiblearchitectureforyourapp,comparedtousingactivitiesalone.Afragmentislikeamodularsectionofanactivity—ithasitsownlifecycleandreceivesitsowninputevents,andyoucanaddorremoveafragmentwhiletheactivityisrunning.

UsethePreferenceFragmentCompatversionofPreferenceFragmentwithanactivitythatextendsAppCompatActivity.Inordertoextendthefragment,youmayhavetoaddthefollowingimportstatement:

importandroid.support.v7.preference.PreferenceFragmentCompat;

4. ReplacetheentireonCreateView()methodinthefragmentwiththisonCreate()method:

@Override

publicvoidonCreatePreferences(BundlesavedInstanceState,

StringrootKey){

}

ThereasonwhyyoureplaceonCreateView()withonCreatePreferences()inSettingsFragmentisbecauseyouwillbeaddingthisfragmenttotheexistingSettingsActivitytodisplaypreferences,ratherthanshowingaseparatefragmentscreen.Addingittotheexistingactivitymakesiteasytoaddorremoveafragmentwhiletheactivityisrunning.ThepreferencefragmentisrootedatthePreferenceScreenusingrootKey.

Youcansafelyremovetheemptyconstructorfromthefragmentaswell,sincethefragmentisnotdisplayedbyitself:

publicSettingsFragment(){

//Requiredemptypublicconstructor

}

5. AttheendoftheonCreatePreferences()methodinSettingsFragment,youneedtoassociatewiththisfragmentthepreferences.xmlsettingsresourceyoujustcreated.AddacalltosetPreferencesFromResource()passingtheidoftheXMLfile(R.xml.preferences)andtherootKeytoidentifythepreferencerootinPreferenceScreen:

setPreferencesFromResource(R.xml.preferences,rootKey);

TheonCreatePreferences()methodshouldnowlooklikethis:

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@Override

publicvoidonCreatePreferences(BundlesavedInstanceState,

StringrootKey){

setPreferencesFromResource(R.xml.preferences,rootKey);

}

6. AddthefollowingcodetotheendoftheSettingsActivityonCreate()methodsothatthefragmentisdisplayedasthemaincontent:

getSupportFragmentManager().beginTransaction()

.replace(android.R.id.content,newSettingsFragment())

.commit();

Theabovecodeisthetypicalpatternusedtoaddafragmenttoanactivitysothatthefragmentappearsasthemaincontentoftheactivity.Youuse:

getFragmentManager()iftheclassextendsActivityandthefragmentextendsPreferenceFragment.getSupportFragmentManager()iftheclassextendsAppCompatActivityandthefragmentextendsPreferenceFragmentCompat.

TheentireonCreate()methodinSettingsActivityshouldnowlooklikethefollowing:

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

getSupportFragmentManager().beginTransaction()

.replace(android.R.id.content,newSettingsFragment())

.commit();

}

1.4ConnecttheSettingsmenuitemtothesettingsactivity

UseanintenttolaunchtheSettingsActivityfromtheMainActivity.

1. FindtheifblockintheonOptionsItemSelected()methodinMainActivity,whichhandlesthetaponSettingsintheoptionsmenu:

if(id==R.id.action_settings){

returntrue;

}

2. AddanintenttotheifblocktolaunchtheSettingsActivity:

if(id==R.id.action_settings){

Intentintent=newIntent(this,SettingsActivity.class);

startActivity(intent);

returntrue;

}

3. AddUp-buttonnavigationtoSettingsActivitybyeditingitsdeclarationintheAndroidManifest.xmlfiletodefinetheactivity'sparentasMainActivity.i. FindtheSettingsActivitydeclarationinAndroidManifest.xml:

<activityandroid:name=".SettingsActivity"></activity>

ii. Changethedeclarationtothefollowing:

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<activityandroid:name=".SettingsActivity"

android:label="Settings"

android:parentActivityName=".MainActivity">

<meta-data

android:name="android.support.PARENT_ACTIVITY"

android:value=".MainActivity"/>

</activity>

4. Runtheapp.Taptheoverflowiconfortheoptionsmenu(asshownontheleftsideofthefigurebelow),andtapSettingstoseethesettingsactivity(asshowninthecenterofthefigurebelow).TaptheUpbuttonintheappbarofthesettingsactivity,shownontherightsideofthefigurebelow,toreturntothemainactivity.

1.5Savethedefaultvaluesinsharedpreferences

Althoughthedefaultvalueforthetoggleswitchsettinghasalreadybeensetintheandroid:defaultValueattribute(inStep1.2ofthistask),theappmustsavethedefaultvalueintheSharedPreferencesfileforeachsettingwhentheuserfirstopenstheapp.Followthesestepstosetthedefaultvalueforthetoggleswitch:

1. InMainActivity,addthefollowingtotheendoftheexistingonCreate()method:

protectedvoidonCreate(BundlesavedInstanceState){

...

PreferenceManager.setDefaultValues(this,R.xml.preferences,false);

}

Theabovecodeensuresthatthesettingsareproperlyinitializedwiththeirdefaultvalues.ThesetDefaultValues()methodtakesthreearguments:

2. Theappcontext,suchasthis.3. TheresourceID(preferences)fortheXMLresourcefilewithoneormoresettings.4. Abooleanindicatingwhetherthedefaultvaluesshouldbesetmorethanonce.Whenfalse,thesystemsetsthe

defaultvaluesonlyifthismethodhasneverbeencalledinthepast.Aslongasyousetthisthirdargumenttofalse,youcansafelycallthismethodeverytimethemainactivitystartswithoutoverridingtheuser'ssavedsettingsvalues.However,ifyousetittotrue,themethodwilloverrideanypreviousvalueswiththedefaults.

1.6Readthechangedsettingsvaluefromsharedpreferences

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Whentheappstarts,theMainActivity'sonCreate()methodcanreadsettingvaluesthathavechanged,andusethechangedvaluesratherthanthedefaultvalues.

Eachsettingisidentifiedusingakey-valuepair.TheAndroidsystemusesthiskey-valuepairwhensavingorretrievingsettingsfromaSharedPreferencesfileforyourapp.Whentheuserchangesasetting,thesystemupdatesthecorrespondingvalueintheSharedPreferencesfile.Tousethevalueofthesetting,theappcanusethekeytogetthesettingfromtheSharedPreferencesfile.

Followthesestepstoaddthatcode:

1. Beforeaddingcodetoreadthesettingvalue,createastaticstringvariableinSettingsActivitytoholdthekeyforthevalue:

publicclassSettingsActivityextendsAppCompatActivity{

publicstaticfinalString

KEY_PREF_EXAMPLE_SWITCH="example_switch";

...

}

2. IntheonCreate()methodinMainActivity,andaddthefollowingatendofthemethod:

protectedvoidonCreate(BundlesavedInstanceState){

...

SharedPreferencessharedPref=

PreferenceManager.getDefaultSharedPreferences(this);

BooleanswitchPref=sharedPref.getBoolean

(SettingsActivity.KEY_PREF_EXAMPLE_SWITCH,false);

}

Theabovecodesnippetuses

PreferenceManager.getDefaultSharedPreferences(this)togetthesettingasaSharedPreferencesobject(sharedPref).getBoolean()togettheBooleanvalueofthesettingthatusesthekey(KEY_PREF_EXAMPLE_SWITCHdefinedinSettingsActivity)andassignittoswitchPref.Ifthereisnovalueforthekey,thegetBoolean()methodsetsthesettingvalue(switchPref)tofalse.Forothervaluessuchasstrings,integers,orfloatingpointnumbers,youcanusethegetString(),getInt(),orgetFloat()methodsrespectively.

3. AddaToast.makeText()methodtoonCreate()thatdisplaysthevalueoftheswitchPrefsettinginatoast:

Toast.makeText(this,switchPref.toString(),Toast.LENGTH_SHORT).show();

4. Runtheappandthenfollowthesesteps:i. TapSettingstoseethesettingsactivity.ii. Tapthesettingtochangethetogglefromontooff,asshownontheleftsideofthefigurebelow.iii. TaptheUpbuttoninthesettingsactivitytoreturntothemainactivity.Thetoastmessageshouldappearinthe

mainactivitywiththevalueofthesetting,asshownontherightsideofthefigurebelow.iv. Repeatthesestepstoseethetoastmessagechangeasyouchangethesetting.

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WhenevertheMainActivitystartsorrestarts,theonCreate()methodshouldreadthesettingvaluesinordertousethemintheapp.TheToast.makeText()methodwouldbereplacedwithamethodthatinitializesthesettings.

Younowhaveaworkingsettingsactivityinyourapp.

Solutioncode:

AndroidStudioproject:AppWithSettings

Task2:UsingtheSettingsActivitytemplateIfyouneedtobuildseveralsub-screensofsettingsandyouwanttotakeadvantageoftablet-sizedscreensaswellasmaintaincompatibilitywitholderversionsofAndroidfortablets,AndroidStudioprovidesashortcut:theSettingsActivitytemplate.

Intheprevioustaskyoulearnedhowtouseanemptysettingsactivityandablankfragmentinordertoaddasettingtoanapp.Task2willnowshowyouhowtousetheSettingsActivitytemplatesuppliedwithAndroidStudioto:

Dividemultiplesettingsintogroups.Customizethesettingsandtheirvalues.DisplayamainSettingsscreenwithaheaderlinkforeachgroupofsettings,suchasGeneralforgeneralsettings,asshowninthefigurebelow.

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Displayamaster/detailscreenlayoutwithaheaderlinkforeachgroupontheleft(master)side,andthegroupofsettingsontheright(detail)side,asshowninthefigurebelow.

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InapreviouspracticalyoucreatedanappcalledDroidCafeusingtheBasicActivitytemplate,whichprovidesanoptionsmenuintheappbarasshownbelow.

Intheabovefigure:

1. Appbar.2. Optionsmenuactionicons.3. Overflowbutton.4. Optionsoverflowmenu.

AndroidStudioproject:Tostarttheprojectfromwhereyouleftoffinthepreviouspractical,downloadtheAndroidStudioprojectDroidCafe.

2.1ExploretheSettingsActivitytemplate

ToincludetheSettingsActivitytemplateinyourappprojectinAndroidStudio,followthesesteps:

1. CopytheDroidCafeprojectfolder,renameittoDroidCafeWithSettings,andrefactorit.(SeetheAppendixforinstructionsoncopyingaproject.)Runtheapptomakesureitrunsproperly.

2. SelectappatthetopoftheProject:Androidview,andchooseNew>Activity>SettingsActivity.3. Inthedialogthatappears,accepttheActivityName(SettingsActivityisthesuggestedname)andtheTitle(Settings).4. ClickthethreedotsattheendoftheHierarchicalParentfieldandchooseMainActivityastheparentactivity,sothat

theUpbuttonintheSettingsActivityreturnstheusertotheMainActivity.ChoosingtheparentactivityautomaticallyupdatestheAndroidManifest.xmlfiletosupportUpbuttonnavigation.

5. ClickFinish.

TheSettingsActivitytemplatenotonlyprovideslayoutsforsmartphone-sizedandtablet-sizedscreens,butalsoprovidesthefunctionoflisteningtoasettingschange,andchangingthesummarytoreflectthesettingschange.Forexample,ifyouchangethe"Addfriendstomessages"setting(thechoicesareAlways,Whenpossible,orNever),thechoiceyoumake

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appearsinthesummaryunderneaththesetting:

Ingeneral,youneednotchangetheSettingsActivitytemplatecodeinordertocustomizetheactivityforthesettingsyouwantinyourapp.Youcancustomizethesettingstitles,summaries,possiblevalues,anddefaultvalueswithoutchangingthetemplatecode,andevenaddmoresettingstothegroupsthatareprovided.

YouusetheSettingsActivitytemplatecodeas-is.Tomakeitworkforyourapp,addcodetotheMainActivitytosetthedefaultsettingsvalues,andtoreadandusethesettingsvalues,asshownlaterinthistask.

TheSettingsActivitytemplatecreatesthefollowingforyou:

XMLfilesintheres>xmldirectory,whichyoucanaddtoorcustomizeforthesettingsyouwant.

pref_data_sync.xml:PreferenceScreenlayoutfor"Data&sync"settings.pref_general.xml:PreferenceScreenlayoutfor"General"settings.pref_headers.xml:LayoutofheadersfortheSettingsmainscreen.pref_notification.xml:PreferenceScreenlayoutfor"Notifications"settings.

TheaboveXMLlayoutsusevarioussubclassesofthePreferenceclassratherthanViewobjects,anddirectsubclassesprovidecontainersforlayoutsinvolvingmultiplesettings.Forexample,PreferenceScreenrepresentsatop-levelPreferencethatistherootofaPreferencehierarchy.TheabovefilesusePreferenceScreenatthetopofeachscreenofsettings.OtherPreferencesubclassesforsettingsprovidetheappropriateUIforuserstochangethesetting.Forexample:

CheckBoxPreference:Acheckboxforasettingthatiseitherenabledordisabled.ListPreference:Adialogwithalistofradiobuttons.SwitchPreference:Atwo-statetoggleableoption(suchason/offortrue/false).EditTextPreference:AdialogwithanEditTextwidget.RingtonePreference:Adialogwithringtonesonthedevice.

Tip:YoucanedittheXMLfilestochangethedefaultsettingstosettingsyouneedforyourapp.

Stringresourcesinthestrings.xmlfileintheres>valuesdirectory,whichyoucancustomizeforthesettingsyouwant.

AllstringsusedintheSettingsActivity,suchasthetitlesforsettings,stringarraysforlists,anddescriptionsforsettings,aredefinedasstringresourcesattheendofthisfile.Theyaremarkedbycommentssuchas<!--StringsrelatedtoSettings-->and<!--ExampleGeneralsettings-->.

Tip:Youcaneditthesestringstocustomizethesettingsyouneedforyourapp.

SettingsActivityinthejava>com.example.android.projectnamedirectory,whichyoucanuseasis.

Thisistheactivitythatdisplaysthesettings.SettingsActivityextendsAppCompatPreferenceActivityformaintainingcompatibilitywitholderversionsofAndroid.

AppCompatPreferenceActivityinthejava>com.example.android.projectnamedirectory,whichyouuseasis.

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ThisactivityisahelperclassthatSettingsActivityusestomaintainbackwardscompatibilitywithpreviousversionsofAndroid.

2.2AddtheSettingsmenuitemandconnectittotheactivity

Asyoulearnedinapreviouspractical,youcaneditthemenu_main.xmlfileintheres>menudirectoryfortheoptionsmenutoaddorremovemenuitems.

1. Editthemenu_main.xmlfiletoaddanothermenuitemcalledSettingswiththenewresourceidaction_settings:

<item

android:id="@+id/action_settings"

android:orderInCategory="50"

android:title="Settings"

app:showAsAction="never"/>

Specify"never"fortheapp:showAsActionattributesothatSettingsappearsonlyintheoverflowoptionsmenuandnotintheappbaritself,sinceitshouldnotbeusedoften.

Specify"50"fortheandroid:orderInCategoryattributesothatSettingsappearsbelowFavorites(setto"40")but

aboveContact(setto"100").

2. Extractthestringresourcefor"Settings"intheandroid:titleattributetotheresourcenamesettings.3. InMainActivity,findtheswitch-caseblockintheonOptionsItemSelected()methodwhichhandlesthetaponitemsin

theoptionsmenu:

publicbooleanonOptionsItemSelected(MenuItemitem){

switch(item.getItemId()){

caseR.id.action_order:

displayToast(getString(R.string.action_order_message));

returntrue;

caseR.id.action_status:

displayToast(getString(R.string.action_status_message));

returntrue;

caseR.id.action_favorites:

displayToast(getString(R.string.action_favorites_message));

returntrue;

caseR.id.action_contact:

displayToast(getString(R.string.action_contact_message));

returntrue;

}

returnsuper.onOptionsItemSelected(item);

}

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4. UseanintenttolaunchtheSettingsActivityfromtheMainActivity.Addtheintenttotheendoftheswitchcaseblock:

...

caseR.id.action_settings:

Intentintent=newIntent(this,SettingsActivity.class);

startActivity(intent);

returntrue;

}

returnsuper.onOptionsItemSelected(item);

}

5. RuntheappusingasmartphoneorsmartphoneemulatorsothatyoucanseehowtheSettingsActivitytemplatehandlesthesmartphonescreensize,andfollowthesesteps:

i. Taptheoverflowiconfortheoptionsmenu,andtapSettingstoseethesettingsactivity,asshownontheleftsideofthefigurebelow.

ii. Tapeachsettingheader(General,Notifications,andData&sync),asshowninthecenterofthefigurebelow,toseethegroupofsettingsoneachchildscreenoftheSettingsscreen,shownontherightsideofthefigurebelow.

iii. TaptheUpbuttoninthesettingsactivitytoreturntothemainactivity.

2.3CustomizethesettingsprovidedbythetemplateTocustomizethesettingsprovidedbytheSettingsActivitytemplate,editthestringandstringarrayresourcesinthestrings.xmlfileandthelayoutattributesforeachsettinginthefilesinthexmldirectory.Inthisstepyouwillchangethe"Data&sync"settings.

1. Openthestrings.xmlfileintheres>valuesdirectory,andscrollthecontentstothe<!--ExamplesettingsforData&Sync-->comment:

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<!--ExamplesettingsforData&Sync-->

<stringname="pref_header_data_sync">Data&amp;sync</string>

<stringname="pref_title_sync_frequency">Syncfrequency</string>

<string-arrayname="pref_sync_frequency_titles">

<item>15minutes</item>

<item>30minutes</item>

<item>1hour</item>

<item>3hours</item>

<item>6hours</item>

<item>Never</item>

</string-array>

<string-arrayname="pref_sync_frequency_values">

<item>15</item>

<item>30</item>

<item>60</item>

<item>180</item>

<item>360</item>

<item>-1</item>

</string-array>

...

2. Editthepref_header_data_syncstringresource,whichissettoData&amp;sync(the&amp;isHTMLcodeforanampersand).ChangethevaluetoAccount(withoutquotationmarks).

3. Refactortheresourcenamebyfollowingthesesteps(theappwillstillworkwithoutrefactoringthenames,butrefactoringmakesthecodeeasiertounderstand):

i. Control-click(orright-click)thepref_header_data_syncresourcenameandchooseRefactor>Rename.ii. Changethenametopref_header_account,clicktheoptiontosearchincommentsandstrings,andclick

Refactor.4. Editthepref_title_sync_frequencystringresource(whichissettoSyncfrequency)toMarket.

5. Refactor>Renametheresourcenametopref_title_accountasyoudidpreviously.6. Refactor>Renamethestringarrayresourcenamepref_sync_frequency_titlestopref_market_titles.7. Changeeachvalueinthepref_market_titlesstringarray(15minutes,30minutes,1hour,etc.)tobethetitlesof

markets,suchasUnitedStates,Canada,etc.,ratherthanfrequencies:

<string-arrayname="pref_market_titles">

<item>UnitedStates</item>

<item>Canada</item>

<item>UnitedKingdom</item>

<item>India</item>

<item>Japan</item>

<item>Other</item>

</string-array>

8. Refactor>Renamethestringarrayresourcenamepref_sync_frequency_valuestopref_market_values.9. Changeeachvalueinthepref_market_valuesstringarray(15,30,60,etc.)tobevaluesforthemarkets—

abbreviationssuchasUS,CA,etc.:

<string-arrayname="pref_market_values">

<item>US</item>

<item>CA</item>

<item>UK</item>

<item>IN</item>

<item>JA</item>

<item>-1</item>

</string-array>

10. Scrolldowntothepref_title_system_sync_settingsstringresource,andedittheresource(whichissettoSystemsyncsettings)toAccountsettings.

11. Refactor>Renamethestringarrayresourcenamepref_title_system_sync_settingstopref_title_account_settings.

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12. Openthepref_data_sync.xmlfile.TheListPreferenceinthislayoutdefinesthesettingyoujustchanged.Notethatthestringresourcesfortheandroid:entries,android:entryValuesandandroid:titleattributesarenowchangedtothevaluesyousuppliedintheprevioussteps:

<ListPreference

android:defaultValue="180"

android:entries="@array/pref_market_titles"

android:entryValues="@array/pref_market_values"

android:key="sync_frequency"

android:negativeButtonText="@null"

android:positiveButtonText="@null"

android:title="@string/pref_title_account"/>

13. Changetheandroid:defaultValueattribute:

android:defaultValue="US"

Sincethekeyforthissettingpreference("sync_frequency")ishard-codedelsewhereintheJavacode,don'tchangetheandroid:keyattribute—keepusing"sync_frequency"asthekeyforthissettinginthisexample.Ifyouarethoroughlycustomizingthesettingsforareal-worldapp,youwouldspendthetimechangingthehard-codedkeysthroughoutthecode.

Note:Whynotuseastringresourceforthekey?Becausestringresourcescanbelocalizedfordifferentlanguagesusingmultiple-languageXMLfiles,andthekeystringmightbeinadvertentlytranslatedalongwiththeotherstrings,whichwouldcausetheapptocrash.

2.4AddcodetosetthedefaultvaluesforthesettingsFindtheonCreate()methodinMainActivity,andaddthefollowingPreferenceManager.setDefaultValuesstatementsattheendofthemethod:

@Override

protectedvoidonCreate(BundlesavedInstanceState){

...

PreferenceManager.setDefaultValues(this,R.xml.pref_general,false);

PreferenceManager.setDefaultValues(this,R.xml.pref_notification,false);

PreferenceManager.setDefaultValues(this,R.xml.pref_data_sync,false);

}

ThedefaultvaluesarealreadyspecifiedintheXMLfilewiththeandroid:defaultValueattribute,buttheabovestatementsensurethattheSharedPreferencesfileisproperlyinitializedwiththedefaultvalues.ThesetDefaultValues()methodtakesthreearguments:

Theappcontext,suchasthis.TheresourceIDforthesettingslayoutXMLfilewhichincludesthedefaultvaluessetbytheandroid:defaultValueattribute.Abooleanindicatingwhetherthedefaultvaluesshouldbesetmorethanonce.Whenfalse,thesystemsetsthedefaultvaluesonlyifthismethodhasneverbeencalledinthepast.Aslongasyousetthisthirdargumenttofalse,youcansafelycallthismethodeverytimeyouractivitystartswithoutoverridingtheuser'ssavedsettingsvaluesbyresettingthemtothedefaultvalues.However,ifyousetittotrue,themethodwilloverrideanypreviousvalueswiththedefaults.

2.5Addcodetoreadvaluesforthesettings

1. AddthefollowingcodeattheendoftheMainActivityonCreate()method.Youcanadditimmediatelyafterthecodeyouaddedintheprevioussteptosetthedefaultsforthesettings:

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...

SharedPreferencessharedPref=

PreferenceManager.getDefaultSharedPreferences(this);

StringmarketPref=sharedPref.getString("sync_frequency","-1");

Toast.makeText(this,marketPref,Toast.LENGTH_SHORT).show();

}

Asyoulearnedintheprevioustask,youusePreferenceManager.getDefaultSharedPreferences(this)togetthesettingasaSharedPreferencesobject(marketPref).YouthenusegetString()togetthestringvalueofthesettingthatusesthekey(sync_frequency)andassignittomarketPref.Ifthereisnovalueforthekey,thegetString()methodsetsthesettingvalueofmarketPrefto-1,whichisthevalueofOtherinthepref_market_valuesarray.

2. Runtheapp,againusingasmartphoneorsmartphoneemulator.Whentheapp'smainscreenfirstappears,youseeatoastmessageatthebottomofthescreen.Thefirsttimeyouruntheapplication,youshouldsee"-1"displayedinthetoastbecauseyouhaven'tchangedthesettingyet.

3. TapSettingsintheoptionsmenu,andtapAccountintheSettingsscreen.ChooseCanadaunder"Market"asshownbelow:

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4. TaptheUpbuttonintheappbartoreturntotheSettingsscreen,andtapitagaintoreturntothemainscreen.Youshouldseeatoastmessagewith"CA"(forCanada):

YouhavesuccessfullyintegratedtheSettingsActivitywiththeDroidCafeapp.

5. Nowruntheapponatabletortabletemulator.Becauseatablethasaphysicallylargerscreen,theAndroidruntimetakesadvantageoftheextraspace.Onatablet,thesettingsanddetailsaredisplayedonthesamescreenmakingiteasierforuserstomanagetheirsettings.

SolutioncodeAndroidStudioproject:DroidCafeWithSettings(Includescodingchallenge#1.)

AndroidStudioproject:DroidCafeWithSettingsChallenge(Includescodingchallenge#2.)

Codingchallenges

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Note:Allcodingchallengesareoptionalandnotprerequisiteforthematerialinthenextchapter.

Challenge1:AddcodetoDroidCafeWithSettingsthatreadsthevalueofthetoggleswitch"Enablesocialrecommendations"ontheGeneralchildscreenofSettings,anddisplaysitsvaluealongwiththe"Market"settinginthesametoastmessageonthemainscreen.

Hint:UseaBooleanvariablewithshared.Pref.getBooleanandthekey"example_switch".

Challenge2:TheDroidCafeWithSettingsappdisplaysthesettingsonatablet-sizedscreenproperly,buttheUpbuttonintheappbardoesn'treturntheusertotheMainActivityasitdoesonasmartphone-sizedscreen.ThisisduetotheonOptionsItemSelected()methodineachfragmentinSettingsActivity.ItusesthefollowingtorestarttheSettingsActivitywhentheusertapstheUpbutton:

startActivity(newIntent(getActivity(),SettingsActivity.class));

TheaboveistheappropriateactiononsmartphonescreensinwhichSettingsheaders(General,Notifications,andAccount)appearinaseparatescreen.Afterchangingasetting,youwanttheuser'stapontheUpbuttontotakethembacktotheSettingsheaders.

However,onatablet,theheadersarealwaysvisibleintheleftpane(whilethesettingsareintherightpane).Asaresult,tappingtheUpbuttondoesn'ttaketheusertoMainActivity.

FindawaytomaketheUpbuttonworkproperlyinSettingsActivityontablet-sizedscreens.

Hint:Thereareseveralwaystofixthisproblem.Considerthefollowing:

Youcanusemultipledimens.xmlfilesinyourapptoaccommodatedifferentscreensizes.Whentheapprunsonaspecificdevice,theappropriatedimens.xmlfileischosenbasedonthequalifiersforthedimens.xmlfiles.Forexample,theappalreadyhasadimens.xml(w820dp)fileintheres>valuesdirectory,usingthe(w820dp)qualifiertospecifyadevicewithan820dpscreenwidthorlarger.Youcanaddanotherdimens.xmlfilewiththeLargequalifiertospecifyanydevicewithalargescreen,suchasatablet.Theappalsoincludesadimens.xmlfileintheres>valuesdirectoryforallotherdevices,suchassmartphones.Youcanaddthefollowingboolresourcebetweenthe<resources>and</resources>tagsinthedimens.xml(large)file,whichisautomaticallychosenfortablets:

<resources>

<boolname="isTablet">true</bool>

</resources>

Youcanaddthefollowingboolresourcetothedimens.xmlfile,whichischosenwhentheapprunsonanydevicethatisnotlarge:

<boolname="isTablet">false</bool>

Nowyoucanaddanif-elseblocktotheonOptionsItemSelected()methodineachfragmentinSettingsActivitythatcheckstoseeifisTabletistrue.Ifitis,yourcodecanredirecttheUpbuttonactiontoMainActivity.

SummaryInthispracticalyoulearnedto:

Addatoggleswitchsetting(SwitchPreference)withattributesinapreferenceXMLfile,andsetitsattributes:android:defaultValue:Thesettingdefaultvalue.android:title:Thesettingtitle.android:key:Thesettingkey.android:summary:Thesettingsummary.

Addasettingsactivitytoviewsettings,andafragmentthatextendsPreferenceFragmentforeachspecificsetting.

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UsegetFragmentManager()toaddthefragmenttothesettingsactivityUseaddPreferencesFromResource()ineachfragmenttoloadtheappropriatepreferencesXMLfileforthatfragment.

UseanintenttoconnecttheSettingsitemintheoptionsmenutothesettingsactivity.SetthedefaultvaluesforsettingsusingPreferenceManager.setDefaultValues().ReadthesettingsvaluesfromSharedPreferencesusingPreferenceManager.getDefaultSharedPreferences(),andobtaineachsettingvalueusing.getString,.getBoolean,etc.

RelatedconceptsTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

AppSettings

LearnmoreAndroidStudiodocumentation:

AndroidStudioUserGuideAndroidAPIGuide,"Develop"section:

Settings(coding)PreferenceclassPreferenceFragmentFragmentSharedPreferencesSavingKey-ValueSetsSupportingDifferentScreenSizes

MaterialDesignSpecification:Settings(design)

Other:StackOverflow:Howdoesonegetdimens.xmlintoAndroidStudio?StackOverflow:Determineifthedeviceisasmartphoneortablet?

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10.1A:SQLiteDatabaseContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask0.DownloadandrunthebasecodeTask1.CreateadatamodelforwordlistdataTask2:ExtendSQLiteOpenHelpertocreateandpopulatethedatabaseTask3:DisplaythedataintheRecyclerViewTask4:EditwordsintheUIandstorechangesinthedatabaseTask5:CreateUIElementsTask6:HandleClicksCodingchallengesSummaryRelatedConceptLearnMore

ASQLitedatabaseisagoodstoragesolutionwhenyouhavestructureddatathatyouneedtostorepersistentlyandaccess,search,andchangefrequently.

WhenyouuseaSQLitedatabase,allinteractionswiththedatabasearethroughaninstanceoftheSQLiteOpenHelperclasswhichexecutesyourrequestsandmanagesyourdatabaseforyou.

Inthispractical,youwillcreateaSQLitedatabaseforasetofdata,displayretrieveddatainaRecyclerView,addfunctionalitytoadd,delete,andeditthedataintheRecyclerViewandstoreitinthedatabase.

Note:AdatabasethatpersistentlystoresyourdataandabstractsyourdataintoadatamodelissufficientforsmallAndroidappswithminimalcomplexity.Inlaterchapters,youwilllearntoarchitectyourappusingloadersandcontentproviderstofurtherseparatedatafromtheuserinterface.TheseclasseswillhelptomoveworkofftheUIthreadtoassistinmakingtheuser'sexperienceassmoothandnaturalaspossible.Inadditiontoimprovingtheuserexperiencebyremovingapotentialperformanceissue,theyimproveyourabilitytoextendandmaintainyourapp.Important:Inthispractical,theSQLiteOpenHelperexecutesdatabaseoperationsinthemainthread.Inaproductionapp,wheredatabaseoperationsmighttakequitesometime,youwouldperformtheseoperationsonabackgroundthread,forexample,usingaloadersuchasAsyncTaskLoaderandCursorLoader.

WhatyoushouldalreadyKNOWForthispracticalyoushouldbefamiliarwith:

Creating,building,andrunningappsinAndroidStudio.DisplayingdatainaRecyclerView.Usingadaptersasintermediariesbetweendataandviews.AddingonClickeventhandlerstoviewsanddynamicallycreatingonClickhandlers.Startingasecondactivityandreturningdatafromait.Passingdatabetweenactivitiesusingintentextras.UsinganEditTextviewtogetdataenteredbytheuser.

YoualsoneedabasicunderstandingofSQLdatabases,howtheyareorganizedintotablesofrowsandcolumns,andtheSQLlanguage.SeetheSQLitePrimer

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WhatyouwillLEARNInthispracticalyouwilllearnto:

CreateandmanageaSQLitedatabasewithanSQLiteOpenHelper.Implementinsert,delete,update,andqueryfunctionalitythroughyouropenhelper.Useanadapterandcustomclickhandlertoletusersinteractwiththedatabasefromtheuserinterface.

WhatyouwillDOYoustartwithanappthatisthesameastheRecyclerViewwordlistappyoucreatedpreviously,withadditionaluserinterfaceelementsalreadyaddedforyou,sothatyoucanfocusonthedatabasecode.

Youwillextendandmodifythebaseappto:

Implementacustomclasstomodelyourdata.CreateasubclassofSQLiteOpenHelperthatcreatesandmanagesyourapp'sdatabase.DisplaydatafromthedatabaseintheRecyclerView.Implementfunctionalitytoadd,modify,anddeletedataintheUI,andstorethechangesinthedatabase.

AppOverviewStartingfromaskeletonapp,youwilladdfunctionalityto:

DisplaywordsfromaSQLitedatabaseinaRecyclerView.Eachwordcanbeeditedordeleted.Youcanaddnewwordsandstoretheminthedatabase.

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MinimumSDKVersionisAPI15:Android4.0.3IceCreamSandwichand*target*SDKisthecurrentversionofAndroid(version23asofthewritingofthisbook).

Task0.DownloadandrunthestartercodeInordertosaveyousomework,inparticularwritingdatabase-unrelatedactivitiesanduserinterfacecode,youneedtogetthestartercodeforthispractical.

1. DownloadtheWordListSqlStarterCodestartercode.

2. OpentheappinAndroidStudio.

3. Runtheapp.YoushouldseetheUIasshowninthepreviousscreenshot.Allthedisplayedwordsshouldbe"placeholder".Clickingthebuttonsdoesnothing.

Task1.ExtendSQLiteOpenHelpertocreateandpopulateadatabaseAndroidappscanusestandardSQLitedatabasestostoredata.ThispracticaldoesnotteachSQLite,butshowshowtouseitinanAndroidapp.ForinfoonlearningaboutSQLite,seetheSQLPrimerinthepreviouschapter.

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SQLOpenHelperisautilityclassintheAndroidSDKforinteractingwithaSQLitedatabaseobject.ItincludesonCreate()andonUpdate()methodsthatyoumustimplement,andinsert,delete,update,andqueryconveniencemethodsforallyourdatabaseinteractions.

TheSQLOpenHelperclasstakescareofopeningthedatabaseifitexists,creatingitifitdoesnot,andupgradingitasnecessary.

Note:Youcanhavemorethanonedatabaseperapp,andmorethanoneopenhelpermanagingthem.Howeverconsidercreatingmultipletablesinthesamedatabaseinsteadofusingmultipledatabasesforperformanceandarchitecturalsimplicity

1.1CreateaskeletonWordListOpenHelperclassThefirststepinaddingadatabasetoyourcodeisalwaystocreateasubclassofSQLiteOpenHelperandimplementitsmethods.

1. CreateanewJavaclassWordListOpenHelperwiththefollowingsignature.

publicclassWordListOpenHelperextendsSQLiteOpenHelper{}

2. Inthecodeeditor,hoverovertheerror,thenclickthelightbulbimageandselectImplementmethods.MakesurebothmethodsarehighlightedandclickOK.

3. AddthemissingconstructorforWordListOpenHelper.(Youwilldefinetheundefinedconstantsnext.)

publicWordListOpenHelper(Contextcontext){

super(context,DATABASE_NAME,null,DATABASE_VERSION);

}

1.2.AdddatabaseconstantstoWordListOpenHelper

1. AtthetopoftheWordListOpenHelperclass,definetheconstantsforthetables,rows,andcolumnsasshowninthecodebelow.Thisshouldgetridofalltheerrors.

//It'sagoodideatoalwaysdefinealogtaglikethis.

privatestaticfinalStringTAG=WordListOpenHelper.class.getSimpleName();

//hastobe1firsttimeorappwillcrash

privatestaticfinalintDATABASE_VERSION=1;

privatestaticfinalStringWORD_LIST_TABLE="word_entries";

privatestaticfinalStringDATABASE_NAME="wordlist";

//Columnnames...

publicstaticfinalStringKEY_ID="_id";

publicstaticfinalStringKEY_WORD="word";

//...andastringarrayofcolumns.

privatestaticfinalString[]COLUMNS={KEY_ID,KEY_WORD};

2. Runyourcodetomakesureithasnomoreerrors.

1.3.BuildtheSQLqueryandcodetocreatethedatabaseSQLqueriescanbecomequitecomplex.Itisabestpracticetoconstructthequeriesseparatelyfromthecodethatusesthem.Thisincreasescodereadabilityandhelpswithdebugging.

ContinueaddingcodetoWordListOpenHelper.java:

1. Belowtheconstants,addthefollowingcodetoconstructthequery.RefertotheSQLitePrimerifyouneedhelpunderstandingthisquery.

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//BuildtheSQLquerythatcreatesthetable.

privatestaticfinalStringWORD_LIST_TABLE_CREATE=

"CREATETABLE"+WORD_LIST_TABLE+"("+

KEY_ID+"INTEGERPRIMARYKEY,"+

//idwillauto-incrementifnovaluepassed

KEY_WORD+"TEXT);";

2. Addinstancevariablesforthereferencestowritableandreadabledatabases.Storingthesereferencessavesyoutoworkofgettingadatabasereferenceeverytimeyouneedtoreadorwrite.

privateSQLiteDatabasemWritableDB;

privateSQLiteDatabasemReadableDB;

3. IntheonCreatemethod,addcodetocreateadatabaseandthetable(Thehelperclassdoesnotcreateanotherdatabase,ifonealreadyexists.)

@Override

publicvoidonCreate(SQLiteDatabasedb){

db.execSQL(WORD_LIST_TABLE_CREATE);

}

4. FixtheerrorbyrenamingthemethodargumentfromSQLiteDatabasetodb.

1.4CreatethedatabaseinonCreateoftheMainActivityTocreatethedatabase,createaninstanceoftheWordListOpenHelperclassyoujustwrote.

1. OpenMainActivity.javaandaddaninstancevariablefortheopenhelper:

privateWordListOpenHelpermDB;

2. InonCreate,initializemDBwithaninstanceofWordListOpenHelper.ThiscallsonCreateoftheWordListOpenHelper,whichcreatesthedatabase.

mDB=newWordListOpenHelper(this);

3. Addabreakpoint,runtheappwiththedebugger,andcheckthatmDBisaninstanceforWordListOpenHelper.

1.5AdddatatothedatabaseThelistofwordsforyourappcouldcomefrommanysources.Itcouldbecompletelyusercreated,ordownloadedfromtheinternet,orgeneratedfromafilethat'spartofyourAPK.Forthispractical,youwillseedyourdatabasewithasmallamountofhard-codeddata.

Notethatacquiring,creating,andformattingdataisawholeseparatetopicthatisnotcoveredinthiscourse.

1. OpenWordListOpenHelper.java.2. InonCreate,aftercreatingthedatabase,addafunctioncallto

fillDatabaseWithData(db);

Next,implementthefillDatabaseWithData()methodinWordListOpenHelper.

3. Implementthemethodstub.

privatevoidfillDatabaseWithData(SQLiteDatabasedb){}

4. Insidethemethod,declareastringofwordsasyourmockdata.

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String[]words={"Android","Adapter","ListView","AsyncTask",

"AndroidStudio","SQLiteDatabase","SQLOpenHelper",

"Datamodel","ViewHolder","AndroidPerformance",

"OnClickListener"};

5. Createacontainerforthedata.TheinsertmethodthatyouwillcallnextrequiresthevaluestofillarowasaninstanceofContentValues.AContentValuesstoresthedataforonerowaskey-valuepairs,wherethekeyisthenameofthecolumnandthevalueisthevaluetoset.

//Createacontainerforthedata.

ContentValuesvalues=newContentValues();

6. Addkey/valueforthefirstrowtovalues,theninsertthatrowintothedatabase.Repeatforallthewordsinyourarrayofwords.

db.insertisaSQLiteDatabaseconveniencemethodtoinsertonerowintothedatabase.(It'saconveniencemethod,becauseyoudonothavetowritetheSQLqueryyourself.)Thefirstargumenttodb.insertisthetablename,WORD_LIST_TABLE.ThesecondargumentisaStringnullColumnHack.It'saSQLworkaroundthatallowsyoutoinsertemptyrows.Seethedocumentationforinsert().Usenullforthisargument.ThethirdargumentmustbeaContentValuescontainerwithvaluestofilltherow.Thissampleonlyhasonecolumn"words"asrepresentedbytheconstantKEY_WORDsetearlier;fortableswithmultiplecolumns,addthevaluesforeachcolumntothiscontainer.

for(inti=0;i<words.length;i++){

//Putcolumn/valuepairsintothecontainer.

//put()overridesexistingvalues.

values.put(KEY_WORD,words[i]);

db.insert(WORD_LIST_TABLE,null,values);

}

7. Beforeyourunandtestyourapp,youshouldclearthedatafromyourSQLitedatabaseanddeletethedatabase.Thenwecanrunourappandrecreateitsothatthedatabaseisinitializedwiththeseeddata.Youcanuninstalltheappfromyourdevice,oryoucanclearallthedataintheappfromSettings>Apps>WordList>Storage>ClearDataonyourAndroidemulatororphysicaldevice

8. Runyourapp.Youwillnotseeanychangesintheuserinterface.Checkthelogsandmakesuretherearenoerrorsbeforeyoucontinue.Ifyouencountererrors,readthelogcatmessagescarefullyanduseresources,suchasStackOverflow,ifyougetstuck.Youcanalsocheckinsettings,thattheappusersstorage.

Task2.CreateadatamodelforasinglewordAdatamodelisaclassthatencapsulatesacomplexdatastructureandprovidesanAPIforaccessingandmanipulatingthedatainthatstructure.YouneedadatamodeltopassdataretrievedfromthedatabasetotheUI.

Forthispractical,thedatamodelonlycontainsthewordanditsid.Whiletheuniqueidwillbegeneratedbythedatabase,youneedawayofpassingtheidtotheuserinterface.Thiswillidentifythewordtheuserischanging.

2.1.Createadatamodelforyourworddata

1. CreateanewclassandcallitWordItem.2. Addthefollowingclassvariables.

privateintmId;

privateStringmWord;

3. Addanemptyconstructor.

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4. Addgettersandsettersfortheidandword.5. Runyourapp.YouwillnotseeanyvisibleUIchanges,butthereshouldbenoerrors.

Solution:

publicclassWordItem{

privateintmId;

privateStringmWord;

publicWordItem(){}

publicintgetId(){returnthis.mId;}

publicStringgetWord(){returnthis.mWord;}

publicvoidsetId(intid){this.mId=id;}

publicvoidsetWord(Stringword){this.mWord=word;}

}

Task3.Implementthequery()methodinWordListOpenHelperThequery()methodretrievesrowsfromthedatabaseasselectedbyaSQLquery.

Forthissample,inordertodisplaywordsintheRecyclerView,weneedtogetthemfromthedatabase,oneatatime,asneeded.Thewordneededisidentifiedbyitspositionintheview.

Assuch,thequerymethodhasaparameterfortherequestedpositionandreturnsaWordItem.

3.1.Implementthequery()method

1. CreateaquerymethodthattakesanintegerpositionargumentandreturnsaWordItem.

publicWordItemquery(intposition){

}

2. Constructaquerythatreturnsonlythenthrowoftheresult.UseLIMITwithpositionastherow,and1asthenumberofrows.

Stringquery="SELECT*FROM"+WORD_LIST_TABLE+

"ORDERBY"+KEY_WORD+"ASC"+

"LIMIT"+position+",1";

3. InstantiateaCursorvariabletonulltoholdtheresultfromthedatabase.

Cursorcursor=null;

TheSQLiteDatabasealwayspresentstheresultsasaCursorinatableformatthatresemblesofaSQLdatabase.

Acursorisapointerintoarowofstructureddata.Youcanthinkofitasanarrayofrows.TheCursorclassprovidesmethodsformovingthecursorthroughthatstructure,andmethodstogetthedatafromthecolumnsofeachrow.

4. InstantiateaWordItementry.

WordItementry=newWordItem();

5. Addatry/catch/finallyblock.

try{}catch(Exceptione){}finally{}

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6. Insidethetryblock,

i. getareadabledatabaseifitdoesn'texist.

if(mReadableDB==null){

mReadableDB=getReadableDatabase();

}

ii. sendarawquerytothedatabaseandstoretheresultinacursor.

cursor=mReadableDB.rawQuery(query,null);

TheopenhelperquerymethodcanconstructaSQLquerystringandsenditasarawQuerytothedatabasewhichreturnsacursor.Ifyourdataissuppliedbyyourapp,andunderyourfullcontrol,youcanuserawquery().

i. Movethecursortothefirstitem.

cursor.moveToFirst();

ii. SetthetheidandwordoftheWordItementrytothevaluesreturnedbythecursor.

entry.setId(cursor.getInt(cursor.getColumnIndex(KEY_ID)));

entry.setWord(cursor.getString(cursor.getColumnIndex(KEY_WORD)));

7. Inthecatchblock,logtheexception.

Log.d(TAG,"EXCEPTION!"+e);

8. Inthefinallyblock,closethecursorandreturntheWordItementry.

cursor.close();

returnentry;

Solution:

publicWordItemquery(intposition){

Stringquery="SELECT*FROM"+WORD_LIST_TABLE+

"ORDERBY"+KEY_WORD+"ASC"+

"LIMIT"+position+",1";

Cursorcursor=null;

WordItementry=newWordItem();

try{

if(mReadableDB==null){

mReadableDB=getReadableDatabase();

}

cursor=mReadableDB.rawQuery(query,null);

cursor.moveToFirst();

entry.setId(cursor.getInt(cursor.getColumnIndex(KEY_ID)));

entry.setWord(cursor.getString(cursor.getColumnIndex(KEY_WORD)));

}catch(Exceptione){

Log.d(TAG,"QUERYEXCEPTION!"+e.getMessage());

}finally{

cursor.close();

returnentry;

}

}

3.2.TheonUpgrademethod

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EverySQLiteOpenHelpermustimplementtheonUpgrade()method,whichdetermineswhathappensifthedatabaseversionnumberchanges.Thismayhappenifyouhaveexistingusersofyourappthatuseanolderversionofthedatabase.Thismethodistriggeredwhenadatabaseisfirstopened.Thecustomarydefaultactionistodeletethecurrentdatabaseandrecreateit.

Important:Whileit'sOKtodropthetableinasampleapp,Inaproductionappyouneedtocarefullymigratetheuser'svaluabledata.YoucanusethecodebelowtoimplementtheonUpgrade()methodforthissample.

BoilerplatecodeforonUpgrade():

@Override

publicvoidonUpgrade(SQLiteDatabasedb,intoldVersion,intnewVersion){

Log.w(WordListOpenHelper.class.getName(),

"Upgradingdatabasefromversion"+oldVersion+"to"

+newVersion+",whichwilldestroyallolddata");

db.execSQL("DROPTABLEIFEXISTS"+WORD_LIST_TABLE);

onCreate(db);

}

Task4.DisplaydataintheRecyclerViewYounowhaveadatabase,withdata.Next,youwillupdatetheWordListAdapterandMainActivitytofetchanddisplaythisdata.

4.1.UpdateWordListAdaptertodisplayWordItems1. OpenWordListAdapter.2. InonBindViewHolderreplacethecodethatdisplaysmockdatawithcodetogetanitemfromthedatabaseanddisplay

it.YouwillnoticeanerroronmDB.

WordItemcurrent=mDB.query(position);

holder.wordItemView.setText(current.getWord());

3. DeclaremDBasaninstancevariable.

WordListOpenHelpermDB;

4. TogetthevalueformDB,changetheconstructorforWordListAdapterandaddasecondparameterfortheWordListOpenHelper.

5. AssignthevalueoftheparametertomDB.Yourconstructorshouldlooklikethis:

publicWordListAdapter(Contextcontext,WordListOpenHelperdb){

mInflater=LayoutInflater.from(context);

mContext=context;

mDB=db;

}

ThisgeneratesanerrorinMainActivity,becauseyouaddedanargumenttotheWordListAdapterconstructor.

6. OpenMainActivityandaddthemissingmDBargument.

mAdapter=newWordListAdapter(this,mDB);

7. Runyourapp.Youshouldseeallthewordsfromthedatabase.

Task5.Addnewwordstothedatabase

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WhentheuserclickstheFAB,anactivityopensthatletsthementerawordthatgetsaddedtothedatabasewhentheyclicksave.

ThestartercodeprovidesyouwiththeclicklistenerandtheEditWordActivitystartedbyclickingtheFAB.Youwilladdthedatabasespecificcodeandtiethepiecestogether,fromthebottomup,likeyoujustdidwiththequerymethod.

5.1.Writetheinsert()method

InWordListOpenHelper:

1. Createtheinsert()methodwiththefollowingsignature.Theusersuppliesaword,andthemethodreturnstheidforthenewentry.Generatedid'scanbebig,soinsertreturnsanumberoftypelong.

publiclonginsert(Stringword){}

2. Declareavariablefortheid.Iftheinsertoperationfails,themethodreturns0.

longnewId=0;

3. Asbefore,createaContentValuesvaluefortherowdata.

ContentValuesvalues=newContentValues();

values.put(KEY_WORD,word);

4. Putyourdatabaseoperationintoatry/catchblock.

try{}catch(Exceptione){}

5. Getawritabledatabaseifonedoesn'talreadyexist.

if(mWritableDB==null){

mWritableDB=getWritableDatabase();

}

6. Inserttherow.

newId=mWritableDB.insert(WORD_LIST_TABLE,null,values);

7. Logtheexception.

Log.d(TAG,"INSERTEXCEPTION!"+e.getMessage());

8. Returntheid.

returnnewId;

Solution:

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publiclonginsert(Stringword){

longnewId=0;

ContentValuesvalues=newContentValues();

values.put(KEY_WORD,word);

try{

if(mWritableDB==null){

mWritableDB=getWritableDatabase();

}

newId=mWritableDB.insert(WORD_LIST_TABLE,null,values);

}catch(Exceptione){

Log.d(TAG,"INSERTEXCEPTION!"+e.getMessage());

}

returnnewId;

}

5.2.GetthewordtoinsertfromtheuserandupdatethedatabaseThestartercodecomeswithanEditWordActivitythatgetsawordfromtheuserandreturnsittothemainactivity.InMainActivity,youjusthavetofillintheonActivityResult()method.

1. Checktoensuretheresultisfromthecorrectactivityandgetthewordthattheuserenteredfromtheextras.

if(requestCode==WORD_EDIT){

if(resultCode==RESULT_OK){

Stringword=data.getStringExtra(EditWordActivity.EXTRA_REPLY);

2. Ifthewordisnotempty,checkwhetherwehavebeenpassedanidwiththeextras.Ifthereisnoid,insertanewword.Inthenexttask,youwillupdatetheexistingwordifanidispassed.

if(!TextUtils.isEmpty(word)){

intid=data.getIntExtra(WordListAdapter.EXTRA_ID,-99);

if(id==WORD_ADD){

mDB.insert(word);

}

3. ToupdatetheUI,notifytheadapterthattheunderlyingdatahaschanged.

mAdapter.notifyDataSetChanged();

4. Ifthewordisemptybecausetheuserdidn'tenteranything,showatoastlettingthemknow.Anddon'tforgettoclosealltheparentheses.

}else{

Toast.makeText(

getApplicationContext(),

R.string.empty_not_saved,

Toast.LENGTH_LONG).show();

}

}

}

Solution:

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if(requestCode==WORD_EDIT){

if(resultCode==RESULT_OK){

Stringword=data.getStringExtra(EditWordActivity.EXTRA_REPLY);

//Updatethedatabase

if(!TextUtils.isEmpty(word)){

intid=data.getIntExtra(WordListAdapter.EXTRA_ID,-99);

if(id==WORD_ADD){

mDB.insert(word);

}

//UpdatetheUI

mAdapter.notifyDataSetChanged();

}else{

Toast.makeText(

getApplicationContext(),

R.string.empty_not_saved,

Toast.LENGTH_LONG).show();

}

}

}

5.3.ImplementgetItemCount()Inorderforthenewitemstobedisplayedproperly,getItemCountinWordListAdapterhastoreturntheactualnumberofentriesinthedatabaseinsteadofthenumberofwordsinthestarterlistofwords.

1. ChangegetItemCounttothecodebelow,whichwilltriggeranerror.

return(int)mDB.count();

2. OpenWordListOpenHelperandimplementcount()toreturnthenumberofentriesinthedatabase.

publiclongcount(){

if(mReadableDB==null){

mReadableDB=getReadableDatabase();

}

returnDatabaseUtils.queryNumEntries(mReadableDB,WORD_LIST_TABLE);

}

3. Runyourappandaddsomewords.

Task6.DeletewordsfromthedatabaseToimplementthedeletefunctionalityyouneedto:

Implementthedelete()methodinWordListOpenHelperAddaclickhandlertotheDELETEbuttoninWordListAdapter

6.1.Writethedelete()method

Youusethedelete()methodonSQLiteDatabasetodeleteanentryinthedatabase.

AddamethoddeletetotheWordListOpenHelperthat:

1. Createthemethodstubfordelete(),whichtakesanintargumentfortheidoftheitemtodelete,andreturnsthenumberofrowsdeleted.

publicintdelete(intid){}

2. Declareavariabletoholdtheresult.

intdeleted=0;

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3. Asforinsert,addatryblock.

try{}catch(Exceptione){}

4. Getawritabledatabase,ifnecessary.

if(mWritableDB==null){

mWritableDB=getWritableDatabase();

}

5. CalldeleteontheWORD_LIST_TABLE,selectingbyKEY_IDandpassingthevalueoftheidastheargument.The"?"isaplaceholderthatgetsfilledwiththestring.Thisisamoresecurewayofbuildingqueries.

deleted=mWritableDB.delete(WORD_LIST_TABLE,

KEY_ID+"=?",newString[]{String.valueOf(id)});

6. Printalogmessageforexceptions.

Log.d(TAG,"DELETEEXCEPTION!"+e.getMessage());

7. Returnthenumberofrowsdeleted.

returndeleted;

Solution:

publicintdelete(intid){

intdeleted=0;

try{

if(mWritableDB==null){

mWritableDB=getWritableDatabase();

}

deleted=mWritableDB.delete(WORD_LIST_TABLE,//tablename

KEY_ID+"=?",newString[]{String.valueOf(id)});

}catch(Exceptione){

Log.d(TAG,"DELETEEXCEPTION!"+e.getMessage());

}

returndeleted;

}

6.2.AddaclickhandlertoDELETEbutton

YoucannowaddaclickhandlertotheDELETEbuttonthatcallsthedelete()methodyoujustwrote.

TakealookattheMyButtonOnClickListenerclassinyourstartercode.TheMyButtonOnClickListenerclassimplementsaclicklistenerthatstorestheid,andthewordthatyouneedtomakechangestothedatabase.

Eachviewholder,whenattached(bound)totheRecyclerViewintheonBindViewHoldermethodofWordListAdapter,needstoalsoattachaclicklistenertotheDELETEbutton,passingtheid,andwordtotheMyButtonOnClickListenerconstructor.ThesevaluesarethenusedbytheonClickhandlertodeletethecorrectitemandnotifytheadapter,whichitemhasbeenremoved.

NotethatyoucannotusethepositionargumentpassedintoonBindViewHolder,becauseitmaybestalebythetimetheclickhandleriscalled.YouhavetokeepareferencetotheviewholderandgetthepositionwithgetAdapterPosition().

Solution:

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//Keepareferencetotheviewholderfortheclicklistener

finalWordViewHolderh=holder;//needstobefinalforuseincallback

//AttachaclicklistenertotheDELETEbutton.

holder.delete_button.setOnClickListener(

newMyButtonOnClickListener(current.getId(),null){

@Override

publicvoidonClick(Viewv){

intdeleted=mDB.delete(id);

if(deleted>=0)

notifyItemRemoved(h.getAdapterPosition());

}

});

Task7.UpdatewordsinthedatabaseToupdateexistingwordsyouhaveto:

Addanupdate()methodtoWordListOpenHelper.AddaclickhandlertotheEDITbuttonofyourview.

7.1.Writetheupdate()method

Youusetheupdate()methodonSQLiteDatabasetoupdateanexistingentryinthedatabase.

1. AddamethodtotheWordListOpenHelperthat:TakesanintegeridandaStringwordforitsargumentsandreturnsaninteger.

publicintupdate(intid,Stringword)

InitializesintmNumberOfRowsUpdatedto-1.

intmNumberOfRowsUpdated=-1;

2. Insideatryblock,dothefollowingsteps:3. GetawritableSQLiteDatabasedbifthereisn'tonealready.

if(mWritableDB==null){

mWritableDB=getWritableDatabase();

}

4. CreateanewinstanceofContentValuesandattheKEY_WORDwordtoit.

ContentValuesvalues=newContentValues();

values.put(KEY_WORD,word);

5. Calldb.updateusingthefollowingarguments:

mNumberOfRowsUpdated=db.update(WORD_LIST_TABLE,

values,//newvaluestoinsert

//selectioncriteriaforrow(the_idcolumn)

KEY_ID+"=?",

//selectionargs;valueofid

newString[]{String.valueOf(id)});

6. Inthecatchblock,printalogmessageifanyexceptionsareencountered.

Log.d(TAG,"UPDATEEXCEPTION:"+e.getMessage());

7. Returnthenumberofrowsupdated,whichshouldbe-1(fail),0(nothingupdated),or1(success).

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returnmNumberOfRowsUpdated;

Solution:

publicintupdate(intid,Stringword){

intmNumberOfRowsUpdated=-1;

try{

if(mWritableDB==null){

mWritableDB=getWritableDatabase();

}

ContentValuesvalues=newContentValues();

values.put(KEY_WORD,word);

mNumberOfRowsUpdated=mWritableDB.update(WORD_LIST_TABLE,

values,

KEY_ID+"=?",

newString[]{String.valueOf(id)});

}catch(Exceptione){

Log.d(TAG,"UPDATEEXCEPTION!"+e.getMessage());

}

returnmNumberOfRowsUpdated;

}

7.2.AddaclicklistenertotheEDITbutton

AndhereisthecodefortheEditclicklistenerwhenwebindtheViewintheonBindViewHoldermethodofWordListAdapter.Thislistenerhasnothingdatabasespecific.ItstartstheEditWordActivityActivityusinganIntentandpassesitthecurrentid,position,andwordintheExtras.

IfyougetanerrorontheEXTRA_POSITIONconstant,additwithavalueof"POSITION",

Solution:

//AttachaclicklistenertotheEDITbutton.

holder.edit_button.setOnClickListener(newMyButtonOnClickListener(

current.getId(),current.getWord()){

@Override

publicvoidonClick(Viewv){

Intentintent=newIntent(mContext,EditWordActivity.class);

intent.putExtra(EXTRA_ID,id);

intent.putExtra(EXTRA_POSITION,h.getAdapterPosition());

intent.putExtra(EXTRA_WORD,word);

//Startanemptyeditactivity.

((Activity)mContext).startActivityForResult(

intent,MainActivity.WORD_EDIT);

}

});

7.3.AddupdatingtoonActivityResult

Asimplemented,clickingeditstartsanactivitythatshowstheuserthecurrentword,andtheycaneditit.Tomaketheupdatehappen,

1. AddonelineofcodetotheonActivityResultmethodinyourMainActivity.

elseif(id>=0){

mDB.update(id,word);

}

2. Runyourappandplaywithit!

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7.4.Designanderrorconsiderations

Themethodsyouwrotetoadd,updateanddeleteentriesinthedatabaseallassumethattheirinputisvalid.ThisisacceptableforsamplecodebecausethepurposeofthissamplecodeistoteachyouthebasicfunctionalityofaSQLitedatabase,andsonoteveryedgecaseisconsidered,noteveryvalueistested,andeverybodyisassumedtobewellbehaved.Ifthiswereaproductionapp,youwouldhavegreatersecurityconsiderations,andcontentwouldneedtobetestedforvalidityuntilyouknowitisnotmalicious.Inaproductionapp,youmustcatchspecificexceptionsandhandlethemappropriately.Youtestedthecorrectfunctioningoftheappbyrunningit.Foraproductionappwithrealdata,youwillneedmorethoroughtesting,forexample,usingunitandinterfacetesting.Forthispractical,youcreatedthethedatabaseschema/tablesfromtheSQLiteOpenHelperclass.Thisissufficientforasimpleexample,likethisone.Foramorecomplexapp,itisabetterpracticetoseparatetheschemadefinitionsfromtherestofthecodeinahelperclassthatcannotbeinstantiated.Youwilllearnhowtodothatinthechapteroncontentproviders.Asmentionedabove,somedatabaseoperationscanbelengthyandshouldbedoneonabackgroundthread.UseAsyncTaskforoperationsthattakealongtime.Useloaderstoloadlargeamountsofdata.

SolutioncodeAndroidStudioproject:WordListSqlfinished

CodingchallengesNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Challenge1:Extendtheapptohaveaneditabledefinitionforeachwordinthedatabase.

Challenge2:Addaconfirmationdialogtothedeletefunctionality.

SummaryInthischapter,youlearnedhowto

UseaSQLiteDatabasetostoreuserdatapersistently.WorkwithaSQLiteOpenHelpertomanageyourdatabase.RetrieveanddisplaydatafromthedatabaseEditdataintheuserinterfaceandreflectthosechangesinthedatabase

RelatedconceptsTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

SQLiteDatabase

LearnmoreDeveloperDocumentation:

StorageOptionsSavingDatainSQLDatabases

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10.1B:SearchingaSQLiteDatabaseContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask0.DownloadandrunthebasecodeTask1.AddaSearchMenuItemCodingchallengeSummaryRelatedConceptLearnMore

WhatyoushouldalreadyKNOWForthispracticalyoushouldbefamiliarwith:

SQLitedatabasesWritingbasicSQLitequeries

WhatyouwillLEARNYouwilllearnto:

AddsearchfunctionalitytoyourappviatheoptionsmenuBuildsearchqueriesfortheSQLitedatabasefromuserinput.

WhatyouwillDOInthispracticalyouwilladdanitemtotheoptionsmenuforsearchingthedatabase,andanactivitythatallowsuserstoenterasearchstringanddisplaystheresultofthesearchinatextview.

Why:Usersshouldalwaysbeabletosearchthedataontheirownterms.

Note:ThefocusofthispracticalisnotoptimizingtheUXofthesearchrequest,butshowingyouhowtoquerythedatabase.

AppOverviewYouwillmakeacopyofthefinishedWordListSQLInteractiveapp(orWordListSqlStarterCodeifyoudidn'trenameit;fromapreviouspractical),callitWordListSQLInteractiveWithSearch,andaddanactivitythatletsuserssearchforpartialandfullwordsinthedatabase.Forexample,entering"Android"willreturnallentriesthatcontainthesubstring"Android".

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Task0.DownloadandrunthebasecodeInordertosaveyousomework,thispracticalwillbuildonanappyouhavealreadybuilt.Inaproductionenvironment,buildingonexistingapplicationcodeisacommondevelopertasktoaddfeaturesorfixproblems.

1.Createyourproject

1. DownloadtheWordListSQLfinishedapp.

Youcanuseyourownapp,ordownloadthebaseapp.AslongastheappusesaSQLitedatabase,youcanusetheseinstructionstoextendit.

2. LoadacopyoftheappintoAndroidStudio.RefertotheAppendixforinformationoncopyingaproject.3. RenamethepackageusingRefactor>Rename.4. Changethepackagenameinyourbuild.gradlefile.5. Runtheapptoensureitbuildsandfunctionscorrectly.

Task1.AddSearch

1.1.AddanOptionsMenuwithSearchitem

UsetheOptionsMenuSamplecodefromyourpreviouspracticalsifyouneedanexampleofhowtodothis.

1. Inyourproject,createanAndroidResourcedirectoryandcallitmenuwith"menu"astheresourcetype(res>menu).2. Addamain_menu.xmlmenuresourcefiletores>menu.3. CreateamenuwithoneitemSearch.Referencethecodesnippetforvalues.

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<menu

xmlns:android="http://schemas.android.com/apk/res/android"

xmlns:app="http://schemas.android.com/apk/res-auto"

xmlns:tools="http://schemas.android.com/tools"

tools:context="com.android.example.wordlistsqlsearchable.MainActivity">

<item

android:id="@+id/action_search"

android:title="Search..."

android:orderInCategory="1"

app:showAsAction="never"/>

</menu>

4. InMainAcvitiy,inflatethemenubyoverridingonCreateOptionsMenu.

@Override

publicbooleanonCreateOptionsMenu(Menumenu){

getMenuInflater().inflate(R.menu.menu_main,menu);

returntrue;

}

5. OverrideonOptionsItemSelectedmethod.Switchonaction_search,andjustreturntrue.

@Override

publicbooleanonOptionsItemSelected(MenuItemitem){

switch(item.getItemId()){

caseR.id.action_search:

returntrue;

}

returnsuper.onOptionsItemSelected(item);

}

6. Runyourapp.Youshouldseethedotsfortheoptionsmenu.Whenyouclickit,youshouldseeonemenuitemforsearchthatdoesnothing.

1.2.CreatethelayoutforthesearchactivityThislayoutissimilartoactivity_edit_word,soyoucantakeadvantageofexistingcodeandcopyit.

1. Createacopyofactivity_editwordandcallitactivity_search.xml.2. Inactivity_search.xml,changetheid'sandstringstoberepresentativeofsearching.3. ChangetheonClickmethodforthebuttontoshowResult.4. AddaTextViewwithanidofsearch_result,atleast300dpheight,and18spfontsize.5. Runyourapp.Youshouldnoticenodifference.

1.3.AddanActivityforsearching

1. Createanewactivity,SearchActivity.IfyourcreateitbyNew>Android>ActivitythenDON'Tgeneratethelayoutfilebecausewecreateditintheprevioustask.

2. AddaprivateTextViewclassvariablemTextView.3. AddaprivateEditTextclassvariablemEditWordView.4. AddaprivateWordListOpenHelpervariablemDB.5. InonCreate,initializemDBwithanewWordListOpenHelper(this).6. InonCreate,initializemTextViewandmEditWordViewtotheirrespectiveviews.

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publicclassSearchActivityextendsAppCompatActivity{

privatestaticfinalStringTAG=EditWordActivity.class.getSimpleName();

privateTextViewmTextView;

privateEditTextmEditWordView;

privateWordListOpenHelpermDB;

@Override

publicvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_search);

mEditWordView=((EditText)findViewById(R.id.search_word));

mTextView=((TextView)findViewById(R.id.search_result));

mDB=newWordListOpenHelper(this);

}

}

7. AddtheactivitytotheAndroidManifest.

<activity

android:name="com.android.example.wordlistsqlsearchable.SearchActivity">

</activity>

1.4.TriggerSearchActivityfromthemenu1. TostartSearchActivitywhenthemenuitemisselected,insertcodetostartSearchActivityintotheswitchstatementin

theonOptionSelected()methodinMainActivity.

Intentintent=newIntent(getBaseContext(),SearchActivity.class);

startActivity(intent);

2. BuildandrunyourapptomakesureSearchActivityislaunchedwhenthe"Search"menuitemisselectedfromtheOptionsMenu.

3. Enterasearchstringandpress"Search".Yourappcrashes.4. Findoutwhytheapphascrashed,thenmovetothenexttask.

1.5.ImplementtheonClickhandlerfortheSearchbuttonintheSearchActivity

Yourappcrashed,becausetheonClickhandlersetfortheSearchbuttonintheXMLcodedoesn'texistyet.SoyouwillbuildshowResultnext.

WhentheSearchbuttonispressed,severalthingsneedtohappen:

TheeventhandlercallspublicvoidshowResult(Viewview)inSearchActivity.YourapphastogetthecurrentvaluefromthemEditWordView,whichisyoursearchstring.Youprintthe"Resultfor"andthewordinmTextView.Youcallthe(notyetwritten)searchfunctiononmDB(mDB.search(word)andgetbackaSQlitedatabasecursor.Youwillimplementthesearchfunctioninthenexttask.YouprocessthecursorandaddtheresulttomTextView.

1. InSearchActivity,createtheshowResultfunction.Itispublic,takesaViewargument,andreturnsnothing.2. CreateaStringvariablecalledwordandinitializeitwiththecontentsoftheinputedittextview,mEditWordView.3. ShowthesearchterminthesearchresultsTextView;somethinglike

"Searchterm:"+word

4. Searchthedatabaseandgetthecursor.

Cursorcursor=mDB.search(word);

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5. Toprocessthecursor,youneedtododothefollowing:

i. Makesurethecursorisnotnull.

ii. Movethecursortothefirstentry.

iii. Iterateoverthecursorprocessingthecurrententry,thenadvancingthecursor.

iv. Extracttheword.

v. Displaythewordinthetextview.

6. Closethecursor.7. Ifnoresultsarefound,theuserseesablankscreenwithnoresults.Youwouldwantthistobehandledinaproduction

app.8. Checktheannotatedcodeforadditionaldetails.

publicvoidshowResult(Viewview){

Stringword=mEditWordView.getText().toString();

mTextView.setText("Resultfor"+word+":\n\n");

//Searchforthewordinthedatabase.

Cursorcursor=mDB.search(word);

//Onlyprocessanon-nullcursorwithrows.

if(cursor!=null&cursor.getCount()>0){

//Youmustmovethecursortothefirstitem.

cursor.moveToFirst();

intindex;

Stringresult;

//Iterateoverthecursor,whilethereareentries.

do{

//Don'tguessatthecolumnindex.

//Gettheindexforthenamedcolumn.

index=cursor.getColumnIndex(WordListOpenHelper.KEY_WORD);

//Getthevaluefromthecolumnforthecurrentcursor.

result=cursor.getString(index);

//Addresulttowhat'salreadyinthetextview.

mTextView.append(result+"\n");

}while(cursor.moveToNext());//Returnstrueorfalse

cursor.close();

}//Youshouldaddsomehandlingofnullcase.Rightnow,nothinghappens.

}

Yourappwillnotrunwithoutatleastastubforsearch()implemented.AndroidStudiowillcreatethestubforyou.Inthelightbulb,choosecreatemethod.

9. OpenWordListOpenHelper.10. Implementastubforsearch,withaStringparameter,thatreturnsanullcursor.11. Runyourappandfixanyerrorsyoumayhave.NotethatmostofthecodeinshowResult()isnotexercisedyet.

1.6.ImplementthesearchmethodinWordListOpenHelper

Thefinalstepistoimplementtheactualsearchingofthedatabase.

Insidethesearch()method,youneedtobuildaquerywiththesearchstringandsendthequerytothedatabase.

Amoresecurewaytodothisisbyusingparametersforeachpartofthequery.

WHY:Inthepreviouspractical,forthequeryinWordListOpenHelper,youcouldbuildthequerystringdirectlyandsubmititasarawQuery(),becauseyouhadfullcontroloverthecontentsofthequery.Assoonasyouarehandlinguserinput,youmustassumethatitcouldbemalicious.

Important:Forsecurityreasons,youshouldalwaysvalidateuserinputbeforeyoubuildyourquery!YouwilllearnmoreaboutsecurityintheSecuritychapterandSecurityTips.

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TheSQLqueryforsearchingforallentriesinthewordlistmatchingasubstringhasthisform:

SELECT*FROMWORD_LIST_TABLEWHEREKEY_WORDLIKE%searchString%;

Theparametrizedformofthequerymethodyouwillcalllookslikethis:

Cursorquery(Stringtable,//Thetabletoquery

String[]columns,//Thecolumnstoreturn

Stringselection,//WHEREstatement

String[]selectionArgs,//ArgumentstoWHERE

StringgroupBy,//Groupingfilter.Notused.

Stringhaving,//Additionalconditionfilter.Notused.

StringorderBy)//Ordering.Settingtonullusesdefault.

SeetheSQLiteDatabaseAndroidandthedocumentationforvariousquery())methods.

Forthequeryinthesearch()method,youneedtoassignonlythefirstfourarguments.

1. ThetableisalreadydefinedastheWORD_LIST_TABLEconstant.2. Insearch(),createavariableforthecolumns.YouneedonlythevaluefromtheKEY_WORDcolumn.

String[]columns=newString[]{KEY_WORD};

3. Addthe%tothesearchStringparameter.

searchString="%"+searchString+"%";

4. Createthewhereclause.Omit"WHERE"asit'simplied.UseaquestionmarkfortheargumenttoLIKE.Makesureyouhavethecorrectspacing.

Stringwhere=KEY_WORD+"LIKE?";

5. Specifytheargumenttothewhereclause,whichisthesearchString.

String[]whereArgs=newString[]{searchString};

6. AddaCursorcursorvariableandinitializeittonull.7. Inatry/catchblock.

i. GetareadabledatabaseifmReadableisnotsetyet.

ii. Querythedatabaseusingtheaboveformofthequery.Passnullfortheunusedparameters.

iii. Handletheexception.Youcanjustlogit.

8. Returnthecursor.9. Runyourappandsearchforsomestrings.

Hereisthesolutionforthecompletemethod:

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publicCursorsearch(StringsearchString){

String[]columns=newString[]{KEY_WORD};

searchString="%"+searchString+"%";

Stringwhere=KEY_WORD+"LIKE?";

String[]whereArgs=newString[]{searchString};

Cursorcursor=null;

try{

if(mReadableDB==null){mReadableDB=getReadableDatabase();}

cursor=mReadableDB.query(WORD_LIST_TABLE,columns,where,whereArgs,null,null,null);

}catch(Exceptione){

Log.d(TAG,"SEARCHEXCEPTION!"+e);

}

returncursor;

}

SolutioncodeAndroidStudioproject:WordListSqlSearchable

CodingchallengesNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Handlethecasewherenoresultsarefoundinamoreuser-friendlyway.MostofthecodesamplesusethedefaultAppBarthatcomeswiththeEmptyTemplate.Insomeofthepreviouschapters,youlearnedabouttheToolbar,forexample,whenusingtheBasicTemplate.

ChangetheapptousetheToolbarandSearchViewandshowthesearchicononthetoolbar.

https://developer.android.com/training/search/setup.html

https://developer.android.com/training/appbar/setting-up.html

Aswritten,thisappisnotverysecure.Considerhowtoaddbasicinputvalidationforthesearchstring.SeeSecurityTips.

SummaryAnoptionsmenucanbeaneffectiveUIforsearchingaSQlitedatabaseAseparateactivitytohandletheUXforsearchcanhelpfocustheuserInaproductionapplication,SQlitequeriesshouldbemanagedcarefullytoavoiddatacorruptionorsecurityissuesSQLitesearchqueriescanbeconstructeddynamicallyusinguserinputforthequeryparameters.Thequery()methodsearchesadatabaseformatchingwords.Thequery()methodreturnsadatabasecursorwhichcantraversetheresultsetefficientlyThecursorcanbeusedtodisplaytheresultstotheuser.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

SQLiteDatabase

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LearnmoreDeveloperDocumentation:

StorageOptionsSavingDatainSQLDatabases

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11.1A:ImplementaMinimalistContentProviderContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1:CreatetheMinimalistContentProviderprojectTask2:CreateaContractclass,aURIscheme,andmockdataTask3:ImplementtheMiniContentProviderclassTask4:UseaContentResolvertogetdataCodingchallengesSummaryRelatedconceptLearnmore

Acontentproviderisacomponentthatsecurelymanagesaccesstoasharedrepositoryofdata.Itprovidesaconsistentinterfaceforapplicationstoaccesstheshareddata.Applicationsdonotaccesstheproviderdirectlybutuseacontentresolverobjectthatprovidesaninterfacetoandmanagestheconnectionwiththecontentprovider.

Contentprovidersareusefulbecause:

AppscannotsharedatainAndroid—exceptthroughcontentproviders.Contentprovidersallowmultipleappstosecurelyaccess,use,andmodifyasingledatasource.Examples:Contacts,gamescores,spell-checkingdictionary.Youcanspecifylevelsofaccesscontrol(permissions)foryourcontentprovider.Youcanstoredataindependentlyfromtheapp.Havingacontentproviderallowsyoutochangehowthedataisstoredwithoutneedingtochangetheuserinterface.Forexample,youcanbuildaprototypeusingmockdata,thenuseanSQLdatabasefortherealapp.Youcouldevenstoresomeofyourdatainthecloudandsomedatalocally,andtheuserinterfacewouldremainthesametoyourapplication.Thisarchitectureseparatesdatafromtheuserinterfacesodevelopmentteamscanworkindependentlyontheclient-facingapplicationandserver-sidecomponentsofyourapp.Forlarger,complexappsitisverycommonthattheuserinterfaceandthedataservicesaredevelopedbydifferentteams.Theycanevenbeseparateapps.Itisnotevenrequiredthatanappwithacontentproviderhasauserinterface.YoucanuseCursorLoaderandotherclassesthatexpecttointeractwithacontentprovider.Note:Ifyourappdoesnotsharedatawithotherapps,thenyourappdoesnotrequireacontentprovider.However,becausethecontentprovidercleanlyseparatestheimplementationofyourbackendfromtheuserinterface,itcanalsobeusefulforarchitectingmorecomplexapplications.

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Thefollowingdiagramsummarizesthepartsofthecontentproviderarchitecture.

Data:Theappthatcreatesthecontentproviderownsthedataandspecifieswhatpermissionsotherappshavetoworkwiththedata.

ThedataisoftenstoredinaSQLitedatabase,butthisisnotmandatory.Typically,thedataismadeavailabletothecontentproviderastables,similartodatabasetables,whereeachrowrepresentsoneentry,andeachcolumnrepresentsanattributeforthatentry.Forexample,eachrowinacontactdatabasecontainsoneentryandthatentrymayhavecolumnsforemailaddressesandphonenumbers.

ContentProvider:Thecontentproviderprovidesapublicandsecureinterfacetothedata,sothatotherappscanaccessthedatawiththeappropriatepermissions.

ContentResolver:UsedbytheActivitytoquerythecontentprovider.ThecontentresolverreturnsdataasaCursorobjectwhichcanthenbeused,forexample,byanadapter,todisplaythedata.

Contractclass(notshown):Thecontractisapublicclassthatexposesimportantinformationaboutthecontentprovidertootherapps.ThisusuallyincludestheURIstoaccessthedata,importantconstants,andthestructureofthedatathatwillbereturned.

AppssendrequeststothecontentproviderusingcontentUniformResourceIdentifiersorURIs.AcontentURIforcontentprovidershasthisgeneralform:

scheme://authority/path-to-data/dataset-name

scheme(forcontentURI,thisisalwayscontent://)authority(representsthedomain,andforcontentproviderscustomarilyendsin.provider)path(thisrepresentsthepathtothedata)ID(uniquelyidentifiesthedatasettosearch;suchasafilenameortablename)

ThefollowingURIcouldbeusedtorequestalltheentriesinthe"words"table:

content://com.android.example.wordcontentprovider.provider/words

DesigningURIschemesisatopicinandofitselfandisnotcoveredinthiscourse.

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ContentResolver:TheContentResolverobjectprovidesquery(),insert(),update(),anddelete()methodsforaccessingdatafromacontentproviderandmanagesallinteractionwiththecontentproviderforyou.Inmostsituations,youcanjustusethedefaultcontentresolverprovidedbytheAndroidsystem.

Inthispractical,youwillbuildabasiccontentproviderfromscratch.Youwillcreateandprocessmockdatasothatyoucanfocusonunderstandingcontentproviderarchitecture.Likewise,theuserinterfacetodisplaythedataisminimal.Inthenextpractical,youwilladdacontentprovidertotheWordListapp,usingthisminimalistappasyourtemplate.

WhatyoushouldalreadyKNOWForthispracticalyoushouldunderstandhowto:

Create,buildandruninteractiveappsinAndroidStudio.DisplaydatainaRecyclerViewusinganadapter.Abstractandencapsulatedatawithdatamodels.Create,manage,andinteractwithaSQLitedatabaseusingaSQLiteOpenHelper.

WhatyouwillLEARNYouwilllearn:

Thearchitectureandanatomyofacontentprovider.Whatyouneedtodotobuildaminimalcontentproviderthatyoucanuseasatemplateforcreatingothercontentproviders.

WhatyouwillDOYouwillbuildastand-aloneapptolearnthemechanicsofbuildingacontentprovider.

AppOverviewThisappgeneratesmockdataandstoresitinalinkedlistcalled"words".Theapprequestsdatathroughacontentresolveranddisplaysit.TheUIconsistsofoneactivitywithaTextViewandtwoButtons.The"Listallwords"buttondisplaysallthewords,andthe"Listfirstword"buttondisplaysthefirstwordinthetextview.Thecontentproviderabstractsandmanagestheinteractionbetweenthedatasourceandtheuserinterface.TheContractdefinesURIsandpublicconstants.

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Note:MinimumSDKVersionisAPI15:Android4.0.3IceCreamSandwichandtargetSDKisthecurrentversionofAndroid(version23asofthewritingofthisbook).

Task1.CreatetheMinimalistContentProviderproject

1.1.Createaprojectwithinthegivenconstraints

Createanappwithoneactivitythatshowsonetextviewandtwobuttons.Onebuttonshowsthefirstwordinourdata(thelist),andtheotherbuttonwilllistallwords.BothbuttonscallonClickDisplayEntries()whentheyareclicked.Fornow,thismethodwilluseaswitchstatementtojustdisplayastatementthataparticularbuttonwasclicked.Usethetablebelowasaguidelineforsettingupyourproject.

Appname MinimalistContentProvider

OneActivity

EmptyActivitytemplate

Name:MainActivity

privatestaticfinalStringTAG=MainActivity.class.getSimpleName();

publicvoidonClickDisplayEntries(Viewview){Log.d(TAG,"Yay,Iwasclicked!");}

TextView@+id/textview

android:text="response"

Button

@+id/button_display_all

android:text="Listallwords"

android:onClick="onClickDisplayEntries"

Button

@+id/button_display_first

android:text="Listfirstword"

android:onClick="onClickDisplayEntries"

1.2.Completethebasicsetup

Completethebasicsetupoftheuserinterface:

1. IntheMainActivity,createamembervariableforthetextviewandinitializeitinonCreate().2. InonClickDisplayEntries(),useaswitchstatementtocheckwhichbuttonwaspressed.Usetheviewidtodistinguish

thebuttons.Printalogstatementforeachcase.3. InonClickDisplayEntries(),attheendappendsometexttothetextview.4. Asalways,extractthestringresources.5. Runtheapp.

YourMainActivityshouldbesimilartothissolution.

Solution:

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packageandroid.example.com.minimalistcontentprovider;

[...imports]

publicclassMainActivityextendsAppCompatActivity{

privatestaticfinalStringTAG=MainActivity.class.getSimpleName();

TextViewmTextView;

@Override

protectedvoidonCreate(BundlesavedInstanceState){

super.onCreate(savedInstanceState);

setContentView(R.layout.activity_main);

mTextView=(TextView)findViewById(R.id.textview);

}

publicvoidonClickDisplayEntries(Viewview){

Log.d(TAG,"Yay,Iwasclicked!");

switch(view.getId()){

caseR.id.button_display_all:

Log.d(TAG,"Yay,"+R.id.button_display_all+"wasclicked!");

break;

caseR.id.button_display_first:

Log.d(TAG,"Yay,"+R.id.button_display_first+"wasclicked!");

break;

default:

Log.d(TAG,"Error.Thisshouldneverhappen.");

}

mTextView.append("Thuswego!\n");

}

}

Task2.CreateaContractclass,aURI,andmockdataThecontractcontainsinformationaboutthedatathatappsneedtobuildqueries.

Contractisapublicclassandincludesimportantinformationforotherappsthatwanttoconnecttothiscontentproviderandaccessyourdata.TheURIshowshowtobuildURIstoaccessthedata.TheURIschemebehavesasanAPItoaccessthedata.It'sverysimilartodesigningRESTcallsforCRUD.OtherapplicationswillusetheseContentURIs.

2.1.CreatetheContractclass

1. CreateanewpublicJavaclassContractwiththefollowingsignature.Itmustbefinal.

publicfinalclassContract{}

2. TopreventsomeonefromaccidentallyinstantiatingtheContractclass,giveitanemptyprivateconstructor.

privateContract(){}

2.2.CreatetheURI

AcontentURIforcontentprovidershasthisgeneralform:

scheme://authority/path/id

schemeisalwayscontent://forcontentURIs.authorityrepresentsthedomain,andforcontentproviderscustomarilyendsin.provider

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pathisthepathtothedataiduniquelyidentifiesthedatasettosearch

ThefollowingURIcouldbeusedtorequestalltheentriesinthe"words"table:

content://com.android.example.wordcontentprovider.provider/words

TheURIforaccessingthecontentproviderisdefinedintheContractsothatitisavailabletoanyappthatwantstoquerythiscontentprovider.Customarily,thisisdonebydefiningconstantsforAUTHORITY,CONTENT_PATH,andCONTENT_URI.

1. IntheContractclass,createaconstantforAUTHORITY.TomakeAuthorityunique,usethepackagenameextendedwith"provider."publicstaticfinalStringAUTHORITY="com.android.example.minimalistcontentprovider.provider";

2. CreateaconstantfortheCONTENT_PATH.Thecontentpathidentifiesthedata.Youshouldusesomethingdescriptive,forexample,thenameofatableorfile,orthekindofdata,suchas"words".publicstaticfinalStringCONTENT_PATH="words";

3. CreateaconstantfortheCONTENT_URI.Thisisacontent://styleURIthatpointstoonesetofdata.Ifyouhavemultiple"datacontainers"inthebackend,youwouldcreateacontentURIforeach.

UriisahelperclassforbuildingandmanipulatingURIs.SinceitisaneverchangingstringforallinstancesoftheContractclass,youcaninitializeitstatically.publicstaticfinalUriCONTENT_URI=Uri.parse("content://"+AUTHORITY+"/"+CONTENT_PATH);

4. CreateaconvenienceconstantforALL_ITEMS.Thisisthedatasetnameyouwillusewhenretrievingallthewords.Thevalueis-2becausethat'sthefirstlowestvaluenotreturnedbyamethodcall.staticfinalintALL_ITEMS=-2;

5. CreateaconvenienceconstantforWORD_ID.Thisistheidyouwillusewhenretrievingasingleword.staticfinalStringWORD_ID="id";

2.3.AddtheMIMEType

Contentprovidersprovidecontent,andyouneedtospecifywhattypeofcontenttheyprovide.Appsneedtoknowthestructureandformatofthereturneddata,sothattheycanproperlyhandleit.

MIMEtypesareoftheformtype/subtype,suchastext/htmlforHTMLpages.Foryourcontentprovider,youneedtodefineavendor-specificMIMEtypeforthekindofdatayourcontentproviderreturns.Thetypeofvendor-specificAndroidMIMEtypesisalways:

vnd.android.cursor.itemforonedataitem(arecord)vnd.android.cursor.dirforssetofdata(multiplerecords).

Thesubtypecanbeanything,butitisagoodpracticetomakeitinformative.Forexample:

vnd—avendorMIMEtypecom.example—thedomainprovider—it'sforacontentproviderwords—thenameofthetable

ReadImplementingContentProviderMIMEtypesfordetails.

1. DeclaretheMIMEtimeforonedataitem.

staticfinalStringSINGLE_RECORD_MIME_TYPE="vnd.android.cursor.item/vnd.com.example.provider.words";

2. DeclaretheMIMEtypeformultiplerecords.

staticfinalStringMULTIPLE_RECORD_MIME_TYPE="vnd.android.cursor.dir/vnd.com.example.provider.words";

2.4.Createthemockdata

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ThecontentprovideralwayspresentstheresultsasaCursorinatableformatthatresemblesaSQLdatabase.Thisisindependentofhowthedataisactuallystored.Thisappusesastringarrayofwords.

Instrings.xml,addashortlistofwords:

<string-arrayname="words">

<item>Android</item>

<item>Activity</item>

<item>ContentProvider</item>

<item>ContentResolver</item>

</string-array>

Task3.ImplementtheMiniContentProviderclass

3.1.CreatetheMiniContentProviderclass

1. CreateaJavaclassMiniContentProviderextendingContentProvider.(Forthispractical,tonotusetheCreateClass>Other>ContentProvidermenuoption.)

2. Implementthemethods(Code>Implementmethods).3. Addalogtag.4. Addamembervariableforthemockdata.

publicString[]mData;

5. InonCreate(),initializemDatafromthearrayofwords,andreturntrue.

@Override

publicbooleanonCreate(){

Contextcontext=getContext();

mData=context.getResources().getStringArray(R.array.words);

returntrue;

}

6. Addanappropriateloggingmessagetotheinsert,delete,andupdatemethods.Youwillnotimplementthesemethodsforthispractical.

Log.e(TAG,"Notimplemented:updateuri:"+uri.toString());

3.2.PublishthecontentproviderbyaddingittotheAndroidmanifest

Inordertoaccessthecontentprovider,yourappandotherappsneedtoknowthatitexists.AddadeclarationforthecontentprovidertotheAndroidmanifestinsidea<provider>tag.

Thedeclarationcontainsthenameofthecontentproviderandtheauthorities(itsuniqueidentifier).

1. IntheAndroidManifest,insidetheapplicationtag,aftertheactivityclosingtag,add:

<provider

android:name=".MiniContentProvider"

android:authorities="com.android.example.minimalistcontentprovider.provider"/>

2. Runyourcodetomakesureitcompiles.

3.3.SetupURImatching

AContentProviderneedstorespondtodatarequestsfromappsusinganumberofdifferentURIs.TotakeappropriateactiondependingonaparticularrequestURI,thecontentproviderneedstoanalyzetheURItoseeifitmatches.UriMatcherisahelperclassthatyoucanuseforprocessingtheacceptedURIschemesforagivencontentprovider.

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BasicstepstouseUriMatcher:

CreateaninstanceofUriMatcher.AddeachURIthatyourcontentproviderrecognizestotheUriMatcher.AssigneachURIanumericconstant.HavinganumericconstantforeachURIisconvenientwhenyouareprocessingincomingURIsbecauseyoucanuseaswitch/casestatementonthenumericvaluestoworkthroughtheURIs.

MakethefollowingchangesintheMiniContentProviderclass.

1. IntheMiniContentProviderclass,createaprivatestaticvariableforanewUriMatcher.

Theargumenttotheconstructorspecifiesthevaluetoreturnifthereisnomatch.Asabestpractice,useUriMatcher.NO_MATCH.

privatestaticUriMatchersUriMatcher=newUriMatcher(UriMatcher.NO_MATCH);

2. CreateyourownmethodforinitializingtheURImatcher.

privatevoidinitializeUriMatching(){}

3. CallinitializeUriMatchinginonCreate()oftheMiniContentProviderclass.4. IntheinitializeUriMatching()method,addtheURIsthatyourcontentprovideracceptstothematcherandassignthem

anintegercode.ThesearetheURIsbasedontheauthorityandcontentpathsspecifiedinthecontract.

The#symbolmatchesastringofnumericcharactersofanylength.Inthisapp,itreferstotheindexofthewordinthestringarray.Inaproductionapp,thiscouldbetheidofanentryinadatabase.AssignthisURIanumericvalueof1.

sUriMatcher.addURI(Contract.AUTHORITY,Contract.CONTENT_PATH+"/#",1);

5. ThesecondURIistheoneyouspecifiedinthecontractforreturningallitems.Assignitanumericvalueof0.sUriMatcher.addURI(Contract.AUTHORITY,Contract.CONTENT_PATH,0);

NotethatifyourappismorecomplexandusesmoreURIs,usenamedconstantsforthecodes,asshownintheUriMatcherdocumentation.

Solution:

privatevoidinitializeUriMatching(){

sUriMatcher.addURI(Contract.AUTHORITY,Contract.CONTENT_PATH+"/#",1);

sUriMatcher.addURI(Contract.AUTHORITY,Contract.CONTENT_PATH,0);

}

3.4.ImplementthegetType()method

ThegetType()methodofthecontentproviderreturnstheMIMEtypeforeachofthespecifiedURIs.

Unlessyouaredoingsomethingspecialinyourcode,thismethodimplementationisgoingtobeverysimilarforanycontentprovider.Itdoesthefollowing:

1. MatchtheURI.2. Switchonthereturnedcode.3. ReturntheappropriateMIMEtype.

LearnmoreintheUriMatcherdocumentation.

Solution:

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publicStringgetType(Uriuri){

switch(sUriMatcher.match(uri)){

case0:

returnContract.MULTIPLE_RECORD_MIME_TYPE;

case1:

returnContract.SINGLE_RECORD_MIME_TYPE;

default:

//Alternatively,throwanexception.

returnnull;

}

}

3.5Implementthequery()methodThepurposeofthequery()methodistomatchtheURI,convertittoayourinternaldataaccessmechanism(forexampleaSQlitequery),executeyourinternaldataaccesscode,andreturntheresultinaCursorobject.

Thequery()methodThequerymethodhasthefollowingsignature:

publicCursorquery(Uriuri,String[]projection,Stringselection,String[]selectionArgs,StringsortOrder){}

TheargumentstothismethodrepresentthepartsofaSQLquery.Evenifyouareusinganotherkindofdatastoragemechanism,youmuststillacceptaqueryinthisstyleandhandletheargumentsappropriately.(InthenexttaskyouwillbuildaqueryintheMainActivitytoseehowtheargumentsareused.)ThemethodreturnsaCursorofanykind.

uri ThecompleteURI.Thiscannotbenull.

projection Indicateswhichcolumns/attributestoaccess.

selection Indicateswhichrows/recordsoftheobjectstoaccess.

selectionArgsThebindingparameterstothepreviousselectionargument.

Forsecurityreasons,theargumentsareprocessedseparately.

sortOrderWhethertosort,andifso,whetherascending,descendingorby.

Ifthisisnull,thedefaultsortornosortisapplied.

Analyzethequery()method1. Identifythefollowingprocessingstepsinthequery()methodcodeshownbelowinthesolutionssection.

Queryprocessingalwaysconsistsofthesesteps:

i. MatchtheURI.

ii. Switchonthereturnedcode.

iii. Processtheargumentsandbuildaqueryappropriateforthebackend.

iv. Getthedataand(ifnecessary)dropitintoaCursor.

v. Returnthecursor.

2. Identifyportionsofthecodethatneedtobedifferentinareal-worldapplication.

Thequeryimplementationforthisbasicapptakessomeshortcuts.

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Errorhandlingisminimal.Becausetheappisusingmockdata,theCursorcanbedirectlypopulated.BecausetheURIschemeissimple,thismethodisrathershort.

3. Identifyatleastonedesigndecisionthatmakesiteasiertounderstandandmaintainthecode.Analyzingthequeryandexecutingittopopulateacursorareseparatedintotwomethods.Thecodecontainsmorecommentsthanexecutablecode.

4. Addthecodetoyourapp.

Note:YouwillgetanerrorforthepopulateCursor()method,andwilladdressthisinthenextstep.

AnnotatedSolutionCodeforthequery()methodinMiniContentProvider.java

@Nullable

@Override

publicCursorquery(Uriuri,String[]projection,Stringselection,String[]selectionArgs,StringsortOrder){

intid=-1;

switch(sUriMatcher.match(uri)){

case0:

//MatchesURItogetalloftheentries.

id=Contract.ALL_ITEMS;

//Lookattheremainingarguments

//toseewhetherthereareconstraints.

//Inthisexample,weonlysupportgetting

//aspecificentrybyid.Notfullsearch.

//Forareal-lifeapp,youneederror-catchingcode;

//hereweassumethatthe

//valueweneedisactuallyinselectionArgsandvalid.

if(selection!=null){

id=parseInt(selectionArgs[0]);

}

break;

case1:

//TheURIendsinanumericvalue,whichrepresentsanid.

//ParsetheURItoextractthevalueofthelast,

//numericpartofthepath,

//andsettheidtothatvalue.

id=parseInt(uri.getLastPathSegment());

//Withadatabase,youwouldthenusethisvalueand

//thepathtobuildaquery.

break;

caseUriMatcher.NO_MATCH:

//Youshoulddosomeerrorhandlinghere.

Log.d(TAG,"NOMATCHFORTHISURIINSCHEME.");

id=-1;

break;

default:

//Youshoulddosomeerrorhandlinghere.

Log.d(TAG,"INVALIDURI-URINOTRECOGNIZED.");

id=-1;

}

Log.d(TAG,"query:"+id);

returnpopulateCursor(id);

}

3.6.ImplementthepopulateCursor()methodOncethequery()methodhasidentifiedtheURI,itcallsyourpopulateCursor()withthelastsegmentofthepath,whichistheid(index)ofthewordtoretrieve.ThepopulateCursor()methodseparatesthequerymatchingfromgettingthedataandcreatingtheresultcursor.Thisisagoodpracticeasinarealapp,thequery()methodcanbecomeverylarge.

ThequerymethodmustreturnaCursortype,sothepopulateCursor()methodhastocreate,fillin,andreturnacursor.

IfyourdatawerestoredinaSQLitedatabase,executingthequerywouldreturnaCursor.Ifyouarenotusingadatastoragemethodthatreturnsacursor,suchasfilesorthemockdata,youcanusea

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MatrixCursortoholdthedatatoreturn.AMatrixCursorisageneralpurposecursorintoanarrayofobjectsthatgrowsasneeded.TocreateaMatrixCursor,yousupplyitwithastringarrayofcolumnnames.

ThepopulateCursor()methoddoesthefollowing:

1. ReceivestheidextractedfromtheURI.2. CreatesaMatrixCursortostorereceiveddata(becausethemockdatareceivedisnotacursor).3. Createsandexecutesaquery.Forthisapp,thisgetsthestringattheindexidfromthestringarray.Inamore

realisticapp,thiscouldexecuteaquerytoadatabase.4. Addstheresulttothecursor.5. Returnsthecursor.

privateCursorpopulateCursor(intid){

MatrixCursorcursor=newMatrixCursor(newString[]{Contract.CONTENT_PATH});

//Ifthereisavalidquery,executeitandaddtheresulttothecursor.

if(id==Contract.ALL_ITEMS){

for(inti=0;i<mData.length;i++){

Stringword=mData[i];

cursor.addRow(newObject[]{word});

}

}elseif(id>=0){

//Executethequerytogettherequestedword.

Stringword=mData[id];

//Addtheresulttothecursor.

cursor.addRow(newObject[]{word});

}

returncursor;

}

Task4.UseaContentResolvertogetdataWiththecontentproviderinplace,theonClickDisplayEntries()methodintheMainActivitycanbeexpandedtoqueryanddisplaydatatotheUI.Thisrequiresthefollowingsteps:

1. CreatetheSQL-stylequery,dependingonwhichbuttonwaspressed.2. UseacontentresolvertointeractwiththecontentprovidertoexecutethequeryandreturnaCursor.3. ProcesstheresultsintheCursor.

4.1.GetthecontentresolverThecontentresolverinteractswiththecontentprovideronyourbehalf.

ThecontentresolverexpectsaparsedContentURIalongwithqueryparametersthatassistinretrievingthedata.

Youdon'thavetocreateyourowncontentresolver.YoucanusetheoneprovidedinyourapplicationcontextbytheAndroidframeworkbycallinggetContentResolver().

1. InMainActivity,removeallcodefrominsideonClickDisplayEntries().2. AddthiscodetoonClickDisplayEntries()inMainActivity.

Cursorcursor=getContentResolver().query(Uri.parse(queryUri),projection,selectionClause,selectionArgs,sort

Order);

Note:theargumentstogetContentResolver.query()areidenticaltotheparametersofContentProvider.query().

NextyoumustdefinetheargumentstogetContentResolver.query().

4.2.DefinethequeryargumentsInorderforgetContentResolver.query()towork,youneedtodeclareandassignvaluestoallitsarguments.

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1. URI:DeclaretheContentURIthatidentifiesthecontentproviderandthetable.GettheinformationforthecorrectURIfromthecontract.

StringqueryUri=Contract.CONTENT_URI.toString();

2. Projection:Astringarraywiththenamesofthecolumnstoreturn.Settingthistonullreturnsallcolumns.Whenthereisonlyonecolumn,asinthecaseofthisexample,settingthisexplicitlyisoptional,butcanbehelpfulfordocumentationpurposes.//Onlygetwords.String[]projection=newString[]{Contract.CONTENT_PATH};

3. selectionClause:Argumentclausefortheselectioncriteria,thatis,whichrowstoreturn.FormattedasanSQLWHEREclause(excludingthe"WHERE"keyword).PassingnullreturnsallrowsforthegivenURI.Sincethiswillvarydependingonwhichbuttonwaspressed,declareitnowandsetitlater.

StringselectionClause;

4. selectionArgs:Argumentvaluesfortheselectioncriteria.Ifyouinclude?sintheselectionString,theyarereplacedbyvaluesfromselectionArgs,intheorderthattheyappear.IMPORTANT:ItissecuritybestpracticestoalwaysseparateselectionandselectionArgs.StringselectionArgs[];

5. sortOrder:Theorderinwhichtosorttheresults.FormattedasaSQLORDERBYclause(excludingtheORDERBYkeyword).UsuallyASCorDESC;nullrequeststhedefaultsortorder,whichcouldbeunordered.

//Forthisexample,accepttheorderreturnedbytheresponse.

StringsortOrder=null;

4.3.Decideonselectioncriteria

TheselectionClauseandselectionArgsvaluesdependonwhichbuttonwaspressedinourUI.

Todisplayallthewords,setbothargumentstonull.Togetthefirstword,queryforthewordwiththeIDof0.(ThisassumesthatwordIDsstartat0andarecreatedinorder.Youknowthis,becausetheinformationisexposedinthecontract.Foradifferentcontentprovider,youmaynotknowtheids,andmayhavetosearchinadifferentway.)

1. ReplacetheexistingswitchblockwiththefollowingcodeinonClickDisplayEntries,beforeyougetthecontentresolver.

switch(view.getId()){

caseR.id.button_display_all:

selectionClause=null;

selectionArgs=null;

break;

caseR.id.button_display_first:

selectionClause=Contract.WORD_ID+"=?";

selectionArgs=newString[]{"0"};

break;

default:

selectionClause=null;

selectionArgs=null;

}

4.4.ProcesstheCursorAftergettingthecontentresolver,youhavetoprocesstheresultfromtheCursor.

Ifthereisdata,displayitinthetextview.Ifthereisnodata,reporterrors.

1. Examinethefollowingcodeandmakesureyouunderstandeverything.

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if(cursor!=null){

if(cursor.getCount()>0){

cursor.moveToFirst();

intcolumnIndex=cursor.getColumnIndex(projection[0]);

do{

Stringword=cursor.getString(columnIndex);

mTextView.append(word+"\n");

}while(cursor.moveToNext());

}else{

Log.d(TAG,"onClickDisplayEntries"+"Nodatareturned.");

mTextView.append("Nodatareturned."+"\n");

}

cursor.close();

}else{

Log.d(TAG,"onClickDisplayEntries"+"Cursorisnull.");

mTextView.append("Cursorisnull."+"\n");

}

2. InsertthiscodeattheendofonClickDisplayEntry().3. Runyourapp.4. Clickthebuttonstoseetheretrieveddatainthetextview.

SolutioncodeAndroidStudioproject:MinimalistContentProvider

CodingchallengesNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Implementmissingmethods

CodingChallenge1:Implementtheinsert,delete,andupdatemethodsfortheMinimalistContentProviderapp.Providetheuserwithawaytoinsert,delete,andupdatedata.

Hint:Ifyoudon'twanttobuildouttheuserinterface,createabuttonforeachactionandhardwirethedatathatisinserted,updated,anddeleted.Thepointofthisexerciseistoworkonthecontentprovider,nottheuserinterface.

Why:YouwillimplementthefullyfunctioningcontentproviderwithUIinthenextpractical,whenyouwilladdacontentprovidertotheWordListSQLapp.

AddUnitTestsforthecontentprovider

CodingChallenge2:Afteryouimplementedthecontentprovider,therewasnowayforyoutoknowwhetherornotthecodewouldwork.Inthissample,youbuiltoutthefront-endandbywatchingitwork,assumedtheappworkedcorrectly.Inareal-lifeapp,thisisnotsufficient,andyoumaynotevenhaveaccesstoafront-end.Theappropriatewayfordeterminingthateachmethodactsasexpected,writeasetofunittestsforMiniContentProvider.

SummaryInthischapter,youlearned

Contentprovidersarehigh-leveldataabstractionsthatmanagesaccesstoasharedrepositoryContentprovidersareprimarilyintendedtobeusedbyappsotherthanyourown.Contentproviders(server-side)areaccessedbyContentresolvers(app-side)

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AContractisapublicclassthatexposesimportantinformationaboutacontentprovider.contractscanbeusefulbeyondcontentproviders,AcontentproviderneedstodefineasetofcontentURIssoappscanaccessdatathroughyourcontentprovider.ThecontentURIconsistsofseveralcomponents:"content://",auniquecontentauthoriity(typicallyafully-qualifiedpackagename)andthecontent-path.Useacontentresolvertorequestdatafromacontentprovideranddisplayittotheuser.Ifyourappdoesnotsharedatawithotherapps,thenyourappdoesnotrequireacontentprovider.ContentprovidersmustimplementthegetType()methodwhichreturnstheMIMEtypeforeachcontenttype.ContentProvidersneedtobe"published"intheAndroidmanifestusingtheelementwithintheelementContentProvidersneedtoinspecttheincomingURItodetermineURIpatternmatchesinordertoaccessanydataYoumustaddtargetURIpatternstoyourcontentprovider.TheUriMatcherclassisahelpfulclassforthispurpose.Theessenceofacontentproviderisimplementedinitsquery()method.Themethodsignatureofthequery()methodinacontentresolver(datarequester)matchesthemethodsignatureofthequery()methodinacontentprovider(datasource).Thequery()methodreturnsadatabase-stylecursorobjectregardlessifthedataisrelationalornot.

RelatedconceptsTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

ContentProviders

LearnmoreDeveloperDocumentation:

UniformResourceIdentifiersorURIsMIMEtypeMatrixCursorandCursorsContentProviders

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11.1B:AddacontentprovidertoyourdatabaseContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppOverviewTask1.DownloadandrunthebasecodeTask2:AddaContractclasstoWordListSQLInteractiveTask3:CreateaContentProviderTask4:ImplementContentProvidermethodsCodingchallengeSummaryRelatedconceptLearnmore

Contentprovidersinrealappsaremorecomplexthanthebasicversionyoubuiltinthepreviouspractical.

Intherealworld:

Thebackendisadatabase,filesystem,orotherpersistentstorageoption.Thefront-enddisplaysthedatainapleasingUIandallowsuserstomanipulatethedata.

Youwillrarelybuildanappfromscratch.Moreoften,youwilldebug,refactor,orextendanexistingapplication.

Inthispractical,youwilltaketheWordListSQLappandrefactorandextendittouseacontentproviderasalayerbetweentheSQLdatabaseandtheRecyclerView.

Youcangoaboutthisintwoways.

RefactorandextendtheWordListSQLapp.Thisinvolveschangingtheapparchitectureandrefactoringcode.Startfromscratchandre-usecodefromWordListSQLandMinimalistContentProvider.

ThepracticalwilldemonstratehowtorefactortheexistingWordListSQLapp,becauseit'swhatyouaremorelikelytoencounteronthejob.

WhatyoushouldalreadyKNOWForthispracticalyoushouldbefamiliarwithhowto:

DisplaydatainaRecyclerView.StartandreturnfromanActivity.Create,change,andinteractwithaSQLitedatabaseusingaSQLiteOpenHelper.Understandthearchitecturetheminimalcontentprovideryoubuiltinthepreviouspractical.

WhatyouwillLEARNYouwilllearnhowto:

Createafullydevelopedcontentproviderforanexistingapplication.Refactoranapplicationtoaccommodateacontentprovider.

WhatyouwillDO

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Thispracticalrequiressetupthatismoretypicalforreal-wordappdevelopment.

YoustartwiththeWordListSQLInteractiveappyoucreatedinapreviouspractical,whichdisplayswordsfromaSQLitedatabaseinaRecyclerView,anduserscancreate,edit,anddeletewords.

Youwillextendandmodifythisapp:

ImplementaContractclasstoexposeyourapp'sinterfacetootherapps.ImplementaContentProviderandqueryitusingaContentResolver.RefactortheMainActivity,WordListAdapter,andWordListOpenHelperclassestoworkwiththecontentprovider.

AppOverviewThecompletedWordListSQLWithContentProviderappwillhavethefollowingfeatures:

Acontentproviderthatcaninsert,delete,update,andquerythedatabase.Acontractandpermissionssetthatallowotherappstoaccessthiscontentprovider.Acontentresolverthatinteractswiththecontentprovidertoinsert,delete,update,andquerydata.Unchangeduserinterfaceandfunctionality.

Yourappwilllookthatsameasattheendofthedatastoragepractical.

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Appcomponentoverview

ThefollowingdiagramshowsanoverviewofthecomponentsofanappthatusesaSQLiteDatabasewithacontentprovider.Theonlydifferencefromtheminimalcontentproviderappisthatthecontentproviderfetchesthedatafromadatabasethroughanopenhelper.

ThediagrambelowshowsthearchitectureoftheWorldListSQLInteractiveappwithacontentprovideradded;thisistheWordListSQLWithContentProviderappthatyouwillbuildinthispractical.

Seetheconceptschapterforadetailedexplanationofallthecomponentsandhowtheyinteract.

ChangesoverviewThisisasummaryofthechangesyouwillmaketoWordListInteractivetoaddacontentprovider.

NewClasses:Contract,ContentProvider,ContentResolverClassesthatchange:WordListOpenHelper,MainActivity,WordListAdapterClassesthatshouldnotchange:WordItem,MyButtonOnClickListener,ViewHolder

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Task1.DownloadandrunthebasecodeThispracticalbuildsontheWordListSQLInteractiveandMinimalistContentProviderappsthatyoubuiltpreviously.YouwillextendacopyofWordListSQLInteractive.Youcanstartfromyourowncode,ordownloadtheapps.

WordListSQLInteractiveMinimalistContentProvider

MakeacopyofWordListSQLInteractiveandloaditintoAndroidStudio.

Changethepackagenametowordlistsqlwithcontentprovider.

Task2.AddaContractclasstoWordListSQLInteractiveYouwillstartbycreatingacontractclassthatdefinespublicdatabaseconstants,URIconstants,andtheMIMEtypes.Youwillusetheseconstantsinalltheotherclasses.

2.1AddaContractclass1. StudytheDefineaSchemaandContractdocumentation.2. AddanewpublicfinalclasstoyourprojectandcallitContract.

ThisContractclasscontainsalltheinformationthatanotherappneedstouseyourapp'scontentprovider.Youcouldnametheclassanything,butitiscustomarilycalled"Contract".

publicfinalclassContract{}

3. TopreventtheContractclassfrombeinginstantiated,addaprivate,emptyconstructor.

Thisisastandardpatternforclassesthatareusedtoholdmetainformationandconstantsforanapp.

privateContract(){}

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2.2MovedatabaseconstantsintoContract

MovetheconstantsforthedatabasethatanotherappwouldneedtoknowoutofWordListOpenHelperintothecontractandmakethempublic.

1. MoveDATABASE_NAMEandmakeitpublic.

publicstaticfinalStringDATABASE_NAME="wordlist";

Createastaticabstractinnerclassforeachtablewiththecolumnnames.ThisinnerclasscommonlyimplementstheBaseColumnsinterface.ByimplementingtheBaseColumnsinterface,yourclasscaninheritaprimarykeyfieldcalled_IDthatsomeAndroidclasses,suchascursoradapters,expecttoexist.Theseinnerclassesarenotrequired,butcanhelpyourdatabaseworkwellwiththeAndroidframework.

2. CreateaninnerclassWordListthatimplementsBaseColumns.

publicstaticabstractclassWordListimplementsBaseColumns{

}

3. MoveWORD_LIST_TABLEname,aswellasKEY_IDandKEY_WORDcolumnnamesfromWordListOpenHelperintotheWordListclassinContract,andmakethempublic.

4. GobacktoWorldListOpenHelperandwaitforAndroidStudiotoimporttheconstantsfromtheContract;orimportthemmanually,ifyouarenotsetupforauto-imports.

UseFile>Settings>Editor>General>AutoImportonWindows/LinuxorAndroidStudio>Preferences>Editor>General>AutoImportonMactoconfigureautomatedimports.)

2.3DefineURIConstants1. DeclaretheURIschemeforyourcontentprovider.

UsingtheContractinMinimalistContentProviderasanexample,declareAUTHORITY,CONTENT_PATH.AddCONTENT_PATH_URItoreturnallitems,andROW_COUNT_URIthatreturnsthenumberofentries.IntheAUTHORITY,useyourapp'sname.

publicstaticfinalintALL_ITEMS=-2;

publicstaticfinalStringCOUNT="count";

publicstaticfinalStringAUTHORITY=

"com.android.example.wordlistsqlwithcontentprovider.provider";

publicstaticfinalStringCONTENT_PATH="words";

publicstaticfinalUriCONTENT_URI=

Uri.parse("content://"+AUTHORITY+"/"+CONTENT_PATH);

publicstaticfinalUriROW_COUNT_URI=

Uri.parse("content://"+AUTHORITY+"/"+CONTENT_PATH+"/"+COUNT);

2.4DeclaretheMIMEtypes

TheMIMEtypedescribesthetypeandformatofdata.TheMIMEtypesisusedtoprocessthedataappropriately.CommonMIMEtypesincludetext/htmlforwebpages,andapplication/json.ReadmoreaboutMIMEtypesforcontentprovidersintheAndroiddocumentation.

1. DeclareMIMEtypesforsingleandmultiplerecordresponses:

staticfinalStringSINGLE_RECORD_MIME_TYPE=

"vnd.android.cursor.item/vnd.com.example.provider.words";

staticfinalStringMULTIPLE_RECORDS_MIME_TYPE=

"vnd.android.cursor.item/vnd.com.example.provider.words";

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2. Runyourapp.Itshouldrunandlookandactexactlyasbeforeyouchangedit.

Task3.CreateaContentProvider

Inthistaskyouwillcreateacontentprovider,implementitsquerymethod,andhookitupwiththeWordListAdapterandtheWordListOpenHelper.InsteadofqueryingtheWordListOpenHelper,theWordListAdapterwilluseacontentresolvertoquerythecontentprovider,whichinturnwillqueryWordListOpenHelperwhichwillquerythedatabase.

3.1CreateaWordListContentProviderclass

1. CreateanewclassthatextendsContentProviderandcallitWordListContentProvider.2. InAndroidStudio,clickontheredlightbulb,select"Implementmethods",andclickOKtoimplementalllistedmethods.3. SpecifyalogTAG.4. DeclareaUriMatcher.

ThiscontentproviderusesanUriMatcher,autilityclassthatmapsURIstonumbers,soyoucanswitchonthem.

privatestaticUriMatchersUriMatcher=newUriMatcher(UriMatcher.NO_MATCH);

5. DeclareaWordListOpenHelperclassvariable,mDB.

privateWordListOpenHelpermDB;

6. DeclarethecodesfortheURImatcherasconstants.

Thisputsthecodesinoneplaceandmakesthemeasytochange.Usetens,sothatinsertingadditionalcodesisstraightforward.

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privatestaticfinalintURI_ALL_ITEMS_CODE=10;

privatestaticfinalintURI_ONE_ITEM_CODE=20;

privatestaticfinalintURI_COUNT_CODE=30;

7. ChangetheonCreate()methodtoinitializemDBwithaWordListOpenHelper,calltheinitializeUriMatching()methodthatyouwillcreatenext,andreturntrue.

@Override

publicbooleanonCreate(){

mDB=newWordListOpenHelper(getContext());

initializeUriMatching();

returntrue;

}

8. CreateaprivatevoidmethodinitializeUriMatching().9. IninitializeUriMatching(),addURIstothematcherforgettingallitems,oneitem,andthecount.

RefertotheContractandusetheinitializeUriMatching()methodintheMinimalistContentProverappasatemplate.

Solution:

privatevoidinitializeUriMatching(){

sUriMatcher.addURI(Contract.AUTHORITY,Contract.CONTENT_PATH,URI_ALL_ITEMS_CODE);

sUriMatcher.addURI(Contract.AUTHORITY,Contract.CONTENT_PATH+"/#",URI_ONE_ITEM_CODE);

sUriMatcher.addURI(Contract.AUTHORITY,Contract.CONTENT_PATH+"/"+Contract.COUNT,URI_COUNT_CODE);

}

3.2ImplementWordListContentProvider.query()

UsetheMiniContentProviderasatemplatetoimplementthequery()method.

1. ModifyWordListContentProvider.query().2. UseaSwitchstatementforthecodesreturnedbysUriMatcher.3. ForURI_ALL_ITEMS_CODE,URI_ONE_ITEM_CODE,URI_COUNT_CODE,callthecorrespondingin

WordListOpenHelper(mDB).

NoticehowassigningtheresultsfrommDB.query()toacursor,generatesanerror,becauseWordListOpenHelper.query()returnsaWordItem.

NoticehowassigningtheresultsfrommDB.count()toacursorgeneratesanerror,becauseWordListOpenHelper.count()returnsalong.

Youwillfixboththeseerrorsnext.

Solution:

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@Nullable

@Override

publicCursorquery(Uriuri,String[]projection,Stringselection,

String[]selectionArgs,StringsortOrder){

Cursorcursor=null;

switch(sUriMatcher.match(uri)){

caseURI_ALL_ITEMS_CODE:

cursor=mDB.query(ALL_ITEMS);

break;

caseURI_ONE_ITEM_CODE:

cursor=mDB.query(parseInt(uri.getLastPathSegment()));

break;

caseURI_COUNT_CODE:

cursor=mDB.count();

break;

caseUriMatcher.NO_MATCH:

//Youshoulddosomeerrorhandlinghere.

Log.d(TAG,"NOMATCHFORTHISURIINSCHEME:"+uri);

break;

default:

//Youshoulddosomeerrorhandlinghere.

Log.d(TAG,"INVALIDURI-URINOTRECOGNIZED:"+uri);

}

returncursor;

}

3.3FixWordListOpenHelper.query()toreturnaCursorandhandlereturningallitems

Sincethecontentproviderworkswithcursors,youcansimplifytheWordListOpenHelper.query()methodtoreturnacursor.

1. Addcodewithaquerytoreturnallitemsfromthedatabasetohandlethecursor=mDB.query(ALL_ITEMS)casefromtheaboveswitchstatement.

2. SimplifyWordListOpenHelper.query()toreturnacursor.

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ThisfixestheerrorinWordListContentProvider.query().

However,thisbreaksWordListAdapter.OnBindViewHolder(),whichexpectsaWordItemfromWordListOpenHelper.

Toresolvethis,WordListAdapter.onBindViewHolder()needstouseacontentresolverinsteadofcallingthedatabasedirectly,whichyouwilldoafterfixingWordListContentProvider.count().

Note:Thiskindofcascadingerrorsandfixesistypicalforworkingwithreal-lifeapplications.Ifanappyouareworkingwithiswellarchitected,youcanfixtheerrorsonebyone.Solution:

/**

*Queriesthedatabaseforanentryatagivenposition.

*

*@parampositionTheNthrowinthetable.

*@returnaWordItemwiththerequesteddatabaseentry.

*/

publicCursorquery(intposition){

Stringquery;

if(position!=ALL_ITEMS){

position++;//Becausedatabasestartscountingat1.

query="SELECT"+KEY_ID+","+KEY_WORD+"FROM"

+WORD_LIST_TABLE

+"WHERE"+KEY_ID+"="+position+";";

}else{

query="SELECT*FROM"+WORD_LIST_TABLE

+"ORDERBY"+KEY_WORD+"ASC";

}

Cursorcursor=null;

try{

if(mReadableDB==null){

mReadableDB=this.getReadableDatabase();

}

cursor=mReadableDB.rawQuery(query,null);

}catch(Exceptione){

Log.d(TAG,"QUERYEXCEPTION!"+e);

}finally{

returncursor;

}

}

3.4FixWordListOpenHelper.count()toreturnaCursor

Sincethecontentproviderworkswithcursors,youmustalsochangetheWordListOpenHelper.count()methodtoreturnacursor.

UseaMatrixCursor,whichisacursorofchangeablerowsandcolumns.

1. CreateaMatrixCursorusingContract.CONTENT_PATH.2. Insideatryblock,getthecountandadditasarowtothecursor.3. Returnthecursor.

Solution:

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publicCursorcount(){

MatrixCursorcursor=newMatrixCursor(newString[]{Contract.CONTENT_PATH});

try{

if(mReadableDB==null){

mReadableDB=getReadableDatabase();

}

intcount=(int)DatabaseUtils.queryNumEntries(mReadableDB,WORD_LIST_TABLE);

cursor.addRow(newObject[]{count});

}catch(Exceptione){

Log.d(TAG,"EXCEPTION"+e);

}

returncursor;

}

ThisfixestheerrorinWordListContentProvider.count(),butbreaksWordListAdapter.getItemCount(),whichexpectsalongfromWordListOpenHelper.

InWordListAdapter.onBindViewHolder(),insteadofcallingthedatabasedirectly,youwillhavetousecontentresolvers,whichyouwilldonext.

3.5FixWordListAdapter.onBindViewHolder()touseacontentresolverNext,youwillfixWordListAdapter.onBindViewHolder()touseacontentresolverinsteadofcallingtheWordListOpenHelperdirectly.

1. InWordListAdapter,deletethemDBvariable,sinceyouarenotdirectlyreferencingthedatabaseanymore.ThisshowserrorsinAndroidStudiothatwillguideyoursubsequentchanges.

2. Intheconstructor,deletetheassignmenttomDB.3. Refactor>Changethesignatureoftheconstructorandremovethedbparameter.4. Addinstancevariablesforthequeryparameterssincetheywillbeusedmorethanonce.

Thecontentresolvertakesaqueryparameter,whichyoumustbuild.ThequeryissimilarlystructuredtoaSQLquery,butinsteadofaselectionstatement,itusesaURI.QueryparametersareverysimilartoSQLqueries.

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privateStringqueryUri=Contract.CONTENT_URI.toString();//baseuri

privatestaticfinalString[]projection=newString[]{Contract.CONTENT_PATH};//table

privateStringselectionClause=null;

privateStringselectionArgs[]=null;

privateStringsortOrder="ASC";

5. InonBindViewholder(),deletethefirsttwolinesofcode.WordItemcurrent-mDB.query(position);holder.wordItemView.setText(current.getWord());

6. DefineanemptyStringvariablenamedword.7. Defineanintegervariablecalledidandsetitto-1.8. CreateacontentresolverwiththespecifiedqueryparametersandstoretheresultsinaCursorcalledcursor.(See

MainActivityofMinimalistContentProviderappforanexample.)

Stringword="";

intid=-1;

Cursorcursor=mContext.getContentResolver().query(Uri.parse(

queryUri),null,null,null,sortOrder);

9. InsteadofjustgettingaWordItemdelivered,WordListAdapter.onBindViewHolder()hastodotheextraworkofextractingthewordfromthecursorreturnedbythecontentresolver.

Ifthereturnedcursorcontainsdata,extractthewordandsetthetextoftheviewholder.Extracttheid,becauseyou'llneeditfortheclicklisteners.Closethecursor.RememberthatyoudidnotclosethecursorinWordListOpenHelper.query(),becauseyoureturnedit.Handlethecaseofnodatainthecursor.Implementanyreferencedstringresources.

if(cursor!=null){

if(cursor.moveToPosition(position)){

intindexWord=cursor.getColumnIndex(Contract.WordList.KEY_WORD);

word=cursor.getString(indexWord);

holder.wordItemView.setText(word);

intindexId=cursor.getColumnIndex(Contract.WordList.KEY_ID);

id=cursor.getInt(indexId);

}else{

holder.wordItemView.setText(R.string.error_no_word);

}

cursor.close();

}else{

Log.e(TAG,"onBindViewHolder:Cursorisnull.");

}

1. Fixtheparametersfortheclicklistenersforthetwobuttons:

current.getId()⇒idcurrent.getWord()⇒word

TheupdatedclicklistenerfortheDELETEbuttonlookslikethis:

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@Override

publicvoidonClick(Viewv){

selectionArgs=newString[]{Integer.toString(id)};

intdeleted=mContext.getContentResolver().delete(

Contract.CONTENT_URI,Contract.CONTENT_PATH,selectionArgs);

if(deleted>0){

//Needbothcalls

notifyItemRemoved(h.getAdapterPosition());

notifyItemRangeChanged(

h.getAdapterPosition(),getItemCount());

}else{

Log.d(TAG,mContext.getString(R.string.not_deleted)+deleted);

}

}

2. ReplacethecalltomDB.delete(id)intheDELETEbuttoncallbackwithacontentresolvercalltodelete.

selectionArgs=newString[]{Integer.toString(id)};

intdeleted=mContext.getContentResolver().delete(

Contract.CONTENT_URI,Contract.CONTENT_PATH,selectionArgs);

3.6ChangeWordListAdapter.getItemCount()touseacontentresolverInsteadofrequestingthecountfromthedatabase,getItemCount()hastoconnecttothecontentresolverandrequestthecount.IntheContract,youdefinedaURIforgettingthatcount:

publicstaticfinalStringCOUNT="count";

publicstaticfinalUriROW_COUNT_URI=

Uri.parse("content://"+AUTHORITY+"/"+CONTENT_PATH+"/"+COUNT

ChangeWordListAdaptergetItemCount()to:

UseacontentresolverquerytogettheitemcountUsetheROW_COUNT_URIinyourqueryThecountisanintegertypeandisthefirstelementofthereturnedCursorExtractcountfromthecursorandreturnitReturn-1otherwiseClosethecursor

UsethecodeyoujustwroteforonBindViewHolderasaguideline.

Solution:

@Override

publicintgetItemCount(){

Cursorcursor=mContext.getContentResolver().query(

Contract.ROW_COUNT_URI,newString[]{"count(*)AScount"},

selectionClause,selectionArgs,sortOrder);

try{

cursor.moveToFirst();

intcount=cursor.getInt(0);

cursor.close();

returncount;

}catch(Exceptione){

Log.d(TAG,"EXCEPTIONgetItemCount:"+e);

return-1;

}

}

3.7AddthecontentprovidertotheAndroidManifest1. Runyourapp.

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2. Examinelogcatforthe(verycommon)causeoftheerror.3. AddthecontentprovidertotheAndroidManifestinsidethe<application>tag.

<provider

android:name=".WordListContentProvider"android:authorities="com.android.example.wordlistsqlwithcontentprovi

der.provider">

</provider>

4. Runyourapp.

Yourappshouldrunandbefullyfunctional.Ifitisnot,compareyourcodetothesuppliedsolutioncode,andusethedebuggerandloggingtofindtheproblem.

3.8What'snext?Youhaveimplementedacontentprovideranditsquery()method.

YoufollowedtheerrorstoupdatemethodsintheWordListOpenHelperandWordListAdapterclassestoworkwiththecontentprovider.

Whenyourunyourapp,forqueries,themethodcallsgothroughthecontentprovider.

Fortheinsert,delete,andupdateoperations,yourappisstillcallingWordListOpenHelper.

Withtheinfrastructureyouhavebuilt,implementingtheremainingmethodswillbealotlesswork.

Task4.ImplementContentProvidermethods

4.1getType()ThegetType()methodiscalledbyotherappsthatwanttousethiscontentprovider,todiscoverwhatkindofdatayourappreturns.

UseaswitchstatementtoreturntheappropriateMIMEtypes.

TheMIMEtypesarelistedinthecontract.SINGLE_RECORD_MIME_TYPEisforURI_ALL_ITEMS_CODEMULTIPLE_RECORDS_MIME_TYPEisforURI_ONE_ITEM_CODE

Solution:

@Nullable

@Override

publicStringgetType(Uriuri){

switch(sUriMatcher.match(uri)){

caseURI_ALL_ITEMS_CODE:

returnMULTIPLE_RECORDS_MIME_TYPE;

caseURI_ONE_ITEM_CODE:

returnSINGLE_RECORD_MIME_TYPE;

default:

returnnull;

}

}

Challenge:Howcanyoutestthismethod,asitisnotcalledbyyourapp.Canyouthinkofthreedifferentwaysoftestingthatthismethodworkscorrectly?

4.2CallthecontentprovidertoinsertandupdatewordsinMainActivityTofixinsertoperationsMainActivity().onActivityResultneedstocallthecontentproviderinsteadofthedatabaseforinsertingandupdatingwords.

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1. InMainActivity,deletethedeclarationofmDBanditsinstantiation.

InOnActivityResult()

Inserting:

1. Ifthewordlengthisnotzero,createaContentValuesvariablenamed"values"andaddtheuser-inputtedwordtoitusingthestring"word"asakey.

2. ReplacemDB.insert(word);withaninsertrequesttoatoacontentresolver.

Updating:

1. ReplacemDB.update(id,word);withanupdaterequesttoatoacontentresolver.

Solutionsnippet:

//Updatethedatabase

if(word.length()!=0){

ContentValuesvalues=newContentValues();

values.put(Contract.WordList.KEY_WORD,word);

intid=data.getIntExtra(WordListAdapter.EXTRA_ID,-99);

if(id==WORD_ADD){

getContentResolver().insert(Contract.CONTENT_URI,values);

}elseif(id>=0){

String[]selectionArgs={Integer.toString(id)};

getContentResolver().update(Contract.CONTENT_URI,values,Contract.WordList.KEY_ID,selectionArgs

);

}

//UpdatetheUI

mAdapter.notifyDataSetChanged();

4.3Implementinsert()inthecontentprovider

Theinsert()methodinthecontentproviderisapass-through.Soyou

1. calltheOpenHelperinsert()method,2. convertthereturnedlongidtoacontentURItotheinserteditem,3. andreturnthatURI.

AndroidStudioreportsanerrorforthevaluesparameter,whichyouwillfixinthenextsteps.

Solution:

publicUriinsert(Uriuri,ContentValuesvalues){

longid=mDB.insert(values);

returnUri.parse(CONTENT_URI+"/"+id);

}

4.4Fixinsert()inWordListOpenHelperAndroidStudioreportsanerrorforthevaluesparameter.

1. OpenWordListOpenHelper.Theinsert()methodiswrittentotakeaStringparameter.2. ChangetheparametertobeoftypeContentValues.3. Deletethedeclarationandassignmentofvaluesinthebodyofthemethod.

4.5Implementupdate()inthecontentprovider

Fixtheupdatemethodsinthesamewayasyoufixedtheinsertmethods.

1. InWordListContentProvider,Implementupdate(),whichisonelineofcodethatpassestheidandthewordasarguments.

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returnmDB.update(parseInt(selectionArgs[0]),

values.getAsString(Contract.WordList.KEY_WORD));

2. Youdon'tneedtomakeanychangestoupdateinWordListOpenHelper.

4.6Implementdelete()inthecontentprovider

InWordListContentProvider,Implementthedelete()methodbycallingthedelete()methodinWordListOpenHelperwiththeidofthewordtodelete.

returnmDB.delete(parseInt(selectionArgs[0]));

4.7Runyourapp

Yup.That'sit.Runyourappandmakesureeverythingworks.

Andifyourappstilldoesn'twork,youshouldcorrectanyissues.Youwillneedtheworkingcodeinalaterpractical.Inthatlessonyouwillwriteanappthatusesthiscontentprovidertoloadwordlistdataintoitsuserinterface.

SolutioncodeAndroidStudioproject:word_list_sql_with_content_provider

CodingchallengeNote:Allcodingchallengesareoptionalandarenotprerequisitesforlaterlessons.

Thewordlistisjustalistofsinglewords,whichisn'tterriblyuseful.Extenttheapptodisplaydefinitions,aswellasalinktousefulinformation,suchasdeveloper.android.com,stackoverflow,orwikipedia.Addanactivitythatallowsuserstosearchforwords.AddbasictestsforallthefunctionsinWordListContentProvider.

SummaryInproduction,mostapplicationdeveloperswilltypicallyrefactorappstoaccommodateacontentprovider.Duringrefactoring,developerswilltypicallyexperiencecascadingchangesanderrorsYouneedtoseparatetheUIfromthedatabaseusingacontentproviderandacontentresolverTheUIshouldnotchangeduringtherefactorfromanembeddeddatabasetoanexternaldatasource.TheContractclassdefinesthecommonconstantsforallthecomponentsintherefactoredapplication.TheContractclasslocalizesallthecommonconstantsforeaseofmaintenance.Whenrefactoring,itisveryusefultohavediagramsofthedatabaseaccessclassesCarefulthoughtshouldbegiventodesigningthedatabaseaccessURIsthatotherapplicationsneedtoaccessthedata.AllaccesstoyourdatabasemustbechangedtouseaContentResolverinsteadofdirectlyaccessingahelperclass(forexample:WordListOpenHelper)Iftheunderlyingdatahaschanged,itisimportanttosignaltheUItorefreshusingnotifyDataSetChanged().

RelatedconceptsTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

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ContentProviders

LearnmoreDeveloperDocumentation:

UniformResourceIdentifiersorURIsMIMEtypeMatrixCursorandCursorsContentProviders

Videos:

AndroidApplicationArchitectureAndroidApplicationArchitecture:TheNextBillionUsers

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11.1C:SharingcontentwithotherappsContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.MakeyourcontentprovideravailabletootherappsSummaryRelatedconceptLearnmore

Toprotectappanduserdata,appscannotsharedatawithotherappsdirectly.However,appscanmakedataavailabletootherappsbyusingacontentprovider.Clientappscanthenuseacontentresolvertoaccessthedataviathecontentprovider'spublicinterface.

Thefollowingdiagramshowshowahatwholesalermightuseacontentprovidertoshareinformationaboutitsinventorytoappsthatsellhats.

InthispracticalyouwillmodifyWordListSQLWithContentProvidertoallowotherappstoaccessthedatainitscontentprovider.Thenyouwillcreateasecondapp,WordListClient,thathasnodataofitsown,butinstead,fetchesdatafromWordListSQLWithContentProvider'scontentprovider.

WhatyoushouldalreadyKNOWForthispracticalyoushouldbefamiliarwith:

ContentprovidersandresolversHowtorenamepackagesTheWordListSQLWithContentProviderappfromthepreviouspractical

WhatyouwillLEARNYouwilllearnhowto:

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Setpermissions,sootherappscanuseyourapp'scontentprovider.Buildaclientappthatfetchesdatafromyourapp'scontentprovider.

WhatyouwillDOYouwill:

EnableWordListSQLWithContentProvidertoshareitsdata.CreateaclientappthatgetsdatafromthecontentproviderofWordListSQLWithContentProvider.

AppsOverviewYouwillusetwoappsinthispractical.

TheexistingWordListSQLWithContentProviderappthatyoubuiltinthepreviouspractical.AnewWordListClientappthatwillquerythecontentproviderofWordListSQLWithContentProvider.TheUIforthisappisthesameasWordListInteractive.

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Task1.MakeyourcontentprovideravailabletootherappsBydefault,appscannotaccessthedataofotherapps.

Tomakeyourcontentprovideravailabletootherapps,youmustspecifypermissionsintheAndroidManifestofyourapp.Thisistrueforanyappthathasacontentprovider.EachcontentproviderneedspermissionsspecifiedinitsAndroidManifest.

Permissionsarenotcoveredindetailinthesepracticals.YoucanlearnmoreinImplementingContentProviderPermissions.

1.1.ModifyWordListWithContentProvidertoallowappsaccess1. OpenWordListSQLWithContentProviderinAndroidStudio.2. OpentheAndroidManifest.xmlfile.3. Addanexportstatementinsidethe<provider>.

android:exported="true"

4. Atthetoplevel,insidethe<manifest>tagaddapermissionforthecontentprovider.

Itisgoodpracticetouseyouruniquepackagenameinordertokeepthepermissionunique.

<permission

android:name="com.android.example.wordlistsqlwithcontentprovider.PERMISSION"/>

5. Runtheapptomakesuretherearenoerrors,andleaveitinstalledonthedevice.

InorderforanotherapptoaccessWordListWithContentProvider'scontentprovider,theappwiththecontentproviderhastobeinstalledonthedevice.Itisnotnecessaryforittoberunning.

Younowhaveacontentprovideronyourdevicethatanotherappcanaccess.Next,youaregoingtobuildanapp,WordListClient,thatgetswordsfromthecontentprovideranddisplaysthem.

1.2.CreatetheWordListClientapp

Insteadofbuildingaclientappfromscratch,youwillcreateWordListClientfromacopyofWordListSQLWithContentProvider.Youwillkeeptheuserinterfaceandtheadaptertodisplaythedata.Youwillremovethecontentproviderandthedatabase,andinsteadgetdatafromthecontentproviderofWordListSQLWithContentProvider.

1. CreateacopyoftheWordListSQLWithContentProviderfolderandcallitWordListClient.2. OpenthecopiedappintheWordListClientfolderinAndroidStudio.3. Renamethepackage(Refactor>Rename)towordlistclient.4. Openbuild.gradle(Module:app)andchangetheappidtowordlistclient.5. Instrings.xml,changetheappnametoWordListClient.6. IntheAndroidManifestofWordListClient,removethe<provider>declarationastherewon'tbeaproviderin

WordListClient.7. Atthetoplevel,insidethe<manifest>tag,adda<uses-permission>permissiontousethecontentproviderof

WordListSQLWithContentProvider.

<uses-permissionandroid:name="com.android.example.wordlistsqlwithcontentprovider.PERMISSION"/>

8. DeletetheWordListContentProviderclass,becausetheappwillaccessthecontentproviderofWordListSQLWithContentProvider.

9. DeletetheWordListOpenHelperclass,becauseyourappdoesnotneedadatabaseoranopenhelperofitsown.10. LookatMainActivityandWordListAdapter.Notethatthecodeforinserting,deleting,andupdatingwordsremains

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unchanged,callingthecontentproviderofWordListSQLWithContentProviderusingtheURIsspecifiedintheContractclass.

11. RunWordListClient.Inspiteofnothavingdataofitsown,WordListClientdisplaysdata,whichisthedataitfetchesfromtheWordListSQLWithContentProviderapp'scontentprovider.

12. InsertafewwordsonWordListClient.13. StartWordListSQLWithContentProvider.

NoticethatthewordyouinsertedwithWordListClient,displaysalsoinWordListSQLWithContentProvider,becausetheyshareonedatasource.DeletethewordinWordListSQLWithContentProviderandnoticethewordalsobeingdeletedfromthedisplayofWordListClient.(Youmayneedtoscrolltomakethechangeappear.)

14. Asyouinteractwithothertheotherapp,changesmadebyoneapparereflectedintheotherapp.

Intheprevioushatstoreexample,thewarehouseownercanupdatethehatinventorywithnewredorfancyhats,andthestoreappswillimmediatelybeabletoshowthesenewhatstotheircustomers.Andiftheredhatstoresellsalltheredfancyhats,thefancyhatstorewillknowthattheinventoryoffancyredhatsissoldout.

SolutioncodeAndroidStudioproject:WordListClient

SummaryYourappcanpermitotherappstointeractwithitscontentproviderandgetoreditdata.Youcanbuildaclientappthatinsteadofprovidingit'sowndata,fetchesdatafromanotherapp'scontentprovider.Youcanseparatemanagementofthedatafromdisplayingthedata.Thatis,youcanhaveoneappthatmanagesthecontentprovider,andmanyclientappsthatusethedataprovidedbythecontentprovider.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

ContentProviders

LearnmoreDeveloperDocumentation:

WorkingwithSystemPermissionsImplementingContentProviderPermissions

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12.1:LoadanddisplaydatafetchedfromacontentproviderContents:

WhatyoushouldalreadyKNOWWhatyouwillLEARNWhatyouwillDOAppoverviewTask1.CreatethebaseappforWordListLoaderTask2:MainActivity:AddingaLoaderManagerandLoaderCallbacksTask3:WordListAdapter:ImplementsetData(),getItemCount(),andonBindViewHolder()SummaryRelatedconceptLearnmore

Inthispracticalyouwilllearnhowtoloaddataprovidedbyanotherapp'scontentproviderinthebackgroundanddisplayittotheuser,whenitisready.

AskingaContentProviderfordatayouwanttodisplaymaytaketime.IfyourequestdatafromthecontentproviderfromanActivity(andrunitontheUIthread),theappmaygetblockedlongenoughtocauseavisibledelayfortheuser,andthesystemmayevenissuean"ApplicationNotResponding"message.Therefore,youshouldloaddataonaseparatethread,inthebackground,anddisplaytheresultsafterloadingisfinished.

Torunaqueryonaseparatethread,youuseloaderthatrunsasynchronouslyinthebackgroundandreconnectstotheActivitywhenfinished.Specifically,CursorLoaderrunsaqueryinthebackground,andautomaticallyre-runsitwhendataassociatedwiththequerychanges.

YouhaveusedanAsyncTaskLoaderinapreviouspractical.CursorLoaderextendsAsyncTaskLoadertoworkwithcontentproviders.

Atahighlevel,youneedthefollowingpiecestousealoadertodisplaydatafromacontentprovider:

AnActivityorfragment.AninstanceoftheLoaderManagerintheActivity.ACursorLoadertoloaddatabackedbyaContentProvider.AnimplementationforLoaderManager.LoaderCallbacks,anabstractcallbackinterfacefortheclienttointeractwiththeLoaderManager.Awayofdisplayingtheloader'sdata,commonlyusinganadapter.Forexample,youcoulddisplaythedatainaRecyclerView.

Thefollowingdiagramshowsacompleteapparchitecturewithaloader.

Theloaderperformsqueryingforitemsinthebackground.Ifthedatachanges,itautomaticallygetsanewsetofdatafortheadapter.Theinsert,delete,andupdateoperationsdonotusetheloader.However,afterthedatachangesbecauseofaninsert,delete,orupdateoperation,theloaderfetchestheupdateddataandnotifiestheadapter.

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WhatyoushouldalreadyKNOWForthispracticalyoushouldbeableto:

DisplaydatainaRecyclerView.WorkwithsimpleAdapters.UnderstandCursors(seepreviouspracticalandconcepts).WorkwithAsyncTaskLoader.UnderstandhowtoworkwithaContentProviders.

WhatyouwillLEARNYouwilllearnto:

LoaddatafromacontentproviderusingaCursorLoader.Usecodefromafinishedapptoquicklybuildanewappwithrelatedfunctionality.

WhatyouwillDOYouwillcreateabasicappthatusesaCursorLoadertoquerythecontentproviderofWordListSQLWithContentProvideranddisplaythedatainaRecyclerView.UseWordListClientasareferenceforsomeofthecode.Inparticular,youcanreusetheContractandWordItemClasses,aswellaspartsoftheMainActivityandWordListAdapterclasses.TheappyouwillcreatewillhaveaverybasicUI.UnlikeWordListClient,itwillnothaveinsert,delete,orupdatefunctionality.

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AppOverviewUsingWordListClientfromthepreviouspracticalasasourceforsomeofthecode,youwillcreateanewapp,WordListLoaderthatloadsanddisplaysdatafromthecontentproviderforWordListSQLWithContentProvider.Thefollowingscreenshotshowshowthefinishedappwilldisplaythewords.

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IMPORTANT:YoumustinstallaWordListWithContentProviderappthatsharesitscontentprovidersothatthereisacontentprovideravailableforWordListLoader.UsetheWordListClientappthatyoubuiltinthepreviouspracticalasareferenceandtoreusecode.

Task1.CreatethebaseappforWordListLoaderInthistaskyouwillcreateaprojectandpartsoftheappthatarenotspecifictoloaders.YouneedtheWordListClientapploadedinAndroidStudio,soyoucancopycodefromit.

1.1CreateaprojectwithContractandWordListItemclassesandlayoutfiles

1. StartAndroidStudioandloadthefinishedWordListClientappfromthepreviouspractical.2. CreateanewprojectwiththeEmptyActivitytemplateandcallitWordListLoader.3. AddthepermissionforWordListSQLWithContentProvider'scontentprovidertotheAndroidManifest.

<uses-permissionandroid:name=

"com.android.example.wordlistsqlwithcontentprovider.PERMISSION"/>

4. CreateanewJavaclassandcallitContract.5. CopytheContractclassfromWordListClientintothenewContractclassofWordListLoader.Makesurenottocopythe

packagename.6. InWordListLoader,createanewJavaclassandcallitWordListItem.7. CopytheWordItemclassfromWordListClientintothenewWordItemclassofWordListLoader.8. Copythelayoutfortherecyclerviewfromactity_main.xmlfromWordListClienttoWordListLoader.Removethefloating

actionbutton.9. CreateanewlayoutforWordListItem,wordlist_item.xml.10. Usingwordlist_item.xmlfromWordListClientasyourreference,createaLinearLayoutwithasingleTextView.

TheidoftheTextViewmustbeandroid:id="@+id/word".Resolvestrings,dimensions,andstylesthatyouarereusing.Notethatyoucancopy/pastefilesbetweenprojects.OverwritetheexistingXMLfilesinWordListLoader.Changetheapp_nametoWordListLoaderinstrings.xml.

11. Atthispoint,youshouldseenoerrorsinAndroidStudio.

1.2AddaRecyclerViewtoMainActivityTodisplaythedata,addaRecyclerViewtoyourMainActivity.Youcandothisonyourown,orreusecodefromWordListClient.

1. AddtheRecyclerViewandCoordinatorLayoutfromthesupportlibrarytoyourbuild.gradlefile.

compile'com.android.support:recyclerview-v7:24.1.1'

compile'com.android.support:design:24.1.1'

2. ImportthesupportlibraryversionsofRecyclerViewandLinearLayoutManagerintoyourMainActivity.

importandroid.support.v7.widget.LinearLayoutManager;

importandroid.support.v7.widget.RecyclerView;

3. CreateaTAGforMainActivity.4. CreateaprivatevariablemRecyclerViewfortheRecyclerView.5. CreateaprivatevariablemWordListAdapterfortheadapter.Thiswillremainred,untilyoucreatetheadapterclass.6. InonCreate()ofMainActivity,createaRecyclerView,createaWordListAdapter,settheadapterontheRecyclerview,

andattachaLinearLayoutManger.SeeWordListClientforsamplecode.

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//Createrecyclerview.

mRecyclerView=(RecyclerView)findViewById(R.id.recyclerview);

//Createanadapterandsupplythedatatobedisplayed.

mAdapter=newWordListAdapter(this);

//Connecttheadapterwiththerecyclerview.

mRecyclerView.setAdapter(mAdapter);

//Givetherecyclerviewadefaultlayoutmanager.

mRecyclerView.setLayoutManager(newLinearLayoutManager(this));

7. Ifyoubuildyourappnow,onlyWordListAdaptershouldbered.Theappdoesnotrunyet.

1.3CreateWordListAdapter

UseWorldListAdapterfromWordListClientandthesnippetsbelowasareferenceforcreatingthisadapter.Ifyouneedarefresher,revisittheRecyclerViewchapterofthiscourse.

1. CreateanewJavaclassWordListAdapterthatextendsRecyclerview.Adapter.

publicclassWordListAdapter

extendsRecyclerView.Adapter<WordListAdapter.WordViewHolder>{}

UsingWordListAdapterasareference,addthefollowing:

2. AddaninnerViewHolderclasswithoneTextView,calledwordItemViewandinflateitfromthetextviewwiththeid"word".

classWordViewHolderextendsRecyclerView.ViewHolder{

publicfinalTextViewwordItemView;

publicWordViewHolder(ViewitemView){

super(itemView);

wordItemView=(TextView)itemView.findViewById(word);

}

}

3. AddaTAGforlogmessages.

privatestaticfinalStringTAG=WordListAdapter.class.getSimpleName();

4. AddmembervariablesfortheLayoutInflatorandthecontext.

privatefinalLayoutInflatermInflater;

privateContextmContext;

5. ImplementtheconstructorforWordListAdapter.

publicWordListAdapter(Contextcontext){

mInflater=LayoutInflater.from(context);

this.mContext=context;

}

6. Implement(orcopy)theonCreateViewHoldermethodtoinflateawordlist_itemview.

@Override

publicWordViewHolderonCreateViewHolder(

ViewGroupparent,intviewType){

ViewmItemView=mInflater.inflate(

R.layout.wordlist_item,parent,false);

returnnewWordViewHolder(mItemView);

}

7. PressAlt-Enterontheadapter'sclassheaderand"chooseimplementmethods"tocreatemethodstubsforthe

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getItemCount()andonBindViewHolder()methods.8. Atthispoint,thereshouldbenoredunderlinesorwordsinyourcode.9. Runyourapp,anditshouldshowablankactivityasshowninthefollowingscreenshot,sinceyouhaven'tloadedany

datayet.Youwilladddatainthenexttask.

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Task2.MainActivity:AddingaLoaderManagerandLoaderCallbacksWhenyouusealoadertoloadyourdataforyou,youusealoadermanagertotakecareofthedetailsofrunningtheloader.

TheLoaderManagerisaconvenienceclassthatmanagesallyourloaders.Youonlyneedoneloadermanagerperactivity.Forexample,theloadermanagertakescareofregisteringanobserverwiththecontentprovider,whichreceivescallbackswhendatainthecontentproviderchanges.

2.1AddtheLoaderManager

1. OpenMainActivity.java2. ExtendtheclasssignaturetoimplementLoaderManager.LoaderCallbacks.Importthesupportlibraryversion.

publicclassMainActivityextendsAppCompatActivityimplementsLoaderManager.LoaderCallbacks<Cursor>

3. ImplementmethodstubsforonCreateLoader(),onLoadFinished(),andonLoaderReset().4. InonCreate(),createaLoaderManagerfromthesupportlibraryandregisteraloaderwithit.

Thefirstargumentisanumerictag;sinceyouonlyhaveoneloader,itdoesn'tmatterwhatnumberyouchoose.Youarenotpassinginanydata,sothesecondargumentisnull.AndyoubindtheloadertothecurrentMainActivity(this).

getSupportLoaderManager().initLoader(0,null,this);

2.2ImplementonCreateLoader()

TheLoaderManagercallstheonCreateLoader()methodtocreatetheloader,ifitdoesnotalreadyexist.

Youcreatealoaderbysupplyingitwithacontext,andtheURIfromwhichtoloaddata—inthiscase,forcontentproviderofWordListSQLWithContentProvider,theURIspecifiedintheContract.

1. InonCreateLoader(),createaqueryUriandprojection.UsethesameURIthatthecontentresolverisusingtoquerythecontentprovider.YoucanfinditintheContractanditisusedinWordListClient.

2. CreateandreturnanewCursorLoaderfromthesearguments.ImporttheCursorLoaderfromthesupportlibrary.

@Override

publicLoader<Cursor>onCreateLoader(intid,Bundleargs){

StringqueryUri=Contract.CONTENT_URI.toString();

String[]projection=newString[]{Contract.CONTENT_PATH};

returnnewCursorLoader(this,Uri.parse(queryUri),projection,null,null,null);

}

2.3ImplementonLoadFinished()Whenloadinghasfinished,youneedtosendthedatatotheadapter.

1. CallsetData()inonLoadFinished().Thecodewillturnred,andyouwillimplementitinthenexttask.TheargumentforsetData()isthecursorwith"data"returnedbytheloaderwhenitisfinishedloading.

@Override

publicvoidonLoadFinished(Loader<Cursor>loader,Cursordata){

mAdapter.setData(data);

}

2.4ImplementonLoaderReset()

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Onresettingtheloader,lettheadapterknowthatthedatahasbecomeunavailablebypassingnulltosetData().

@Override

publicvoidonLoaderReset(Loader<Cursor>loader){

mAdapter.setData(null);

}

Task3.WordListAdapter:ImplementsetData(),getItemCount(),andonBindViewHolder()Asyourfinaltasks,youneedtoimplementthesetData()methodreferencedabove,andimplementonBindViewHolder()toworkwiththeloadertodisplaythedata.Hereishowthishappens:

Whentheloaderfinishesloadingneworchangeddatainthebackground,theonLoadFinished()methodthatyouimplementedintheMainActivityisexecuted.onLoadFinished()callsWordListAdapter.setData(),whichupdatesthemCursorvariableintheadapterwiththeloader'slatestdataandnotifiestheadapterthatthedatahaschanged.TheadapterupdatestheUIwiththenewdata,bybindingviewstothedatainonBindViewHolder().

3.1.ImplementsetData()

Youneedawaytosetandstorethelatestloadedversionofthedatawiththeadapter.Forthisapp,theloaderreturnsdataasacursor,soyouneedtocreateaCursormembervariablemCursorthatwillalwaysholdthelatestdataset.

ThesetData()methodiscalledbytheloaderwhenitfinishedloadingorisreset,anditneedstoupdatemCursor.

1. CreateaprivatemembervariableoftypeCursor.Callit"mCursor"andinitializeittonull.2. ImplementthepublicmethodsetData().IttakesaCursorargumentandreturnsnothing.3. Inthebody,setmCursortothepassedinCursorargumentandcallnotifyDataSetChanged(),sothattheadapter

updatesthedisplay.

publicvoidsetData(Cursorcursor){

mCursor=cursor;

notifyDataSetChanged();

}

3.2.ImplementgetItemCount()

Insteadof0,getItemCount()needstoreturnthenumberofitemsinmCursor.IfmCursorisnull,return-1.

@Override

publicintgetItemCount(){

if(mCursor!=null){

returnmCursor.getCount();

}else{

return-1;

}

}

3.3ImplementonBindViewHolder()

InWordListClient,theonBindViewHolder()methodusesacontentresolvertofetchdatafromWordListSQLWithContentProvider'scontentprovider.Inthisapp,onBindViewHolder()usesthedataprovidedbytheloaderandstoredinmCursor.

InonBindViewHolder,handlethefollowingsituations.

1. IfmCursorisnull,donothing,butdisplayalogmessage.Inarealapplication,youwouldneedtoalsonotifytheuserin

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ameaningfulway.2. IfmCursorisnotnullbutcontainsnoword,setthetextoftheTextViewtoERROR:NOWORD.Again,inareal

application,youwouldhandlethisdependingonthetypeofappyouhave.3. Otherwise,getthecolumnindexforthe"word"column(youcannotassumethecolumnisinafixedlocationinthe

cursor'srow),andusingtheindex,retrievetheword.Setthetextofthetextviewtotheword.

@Override

publicvoidonBindViewHolder(WordViewHolderholder,intposition){

Stringword="";

if(mCursor!=null){

if(mCursor.moveToPosition(position)){

intindexWord=mCursor.getColumnIndex(Contract.WordList.KEY_WORD);

word=mCursor.getString(indexWord);

holder.wordItemView.setText(word);

}else{

holder.wordItemView.setText(R.string.error_no_word);

}

}else{

Log.e(TAG,"onBindViewHolder:Cursorisnull.");

}

}

3.4Runandtestyourapp

YourWordListLoaderappshouldexactlyworkthesameastheWordListClientappfordisplayingalistofwords.Totestyourapp,dothefollowing.

1. MakesureWordListSQLWithContentProvderisinstalledonthedevice,sothatyourapphasacontentprovidertoloadfrom.Otherwise,yourappwilldisplayablanktextview.

2. RunWordListLoader.YoushouldseethesamelistofwordsasinWordListSQLWithContentProvider.

SolutioncodeAndroidStudioproject:WordListLoader

SummaryInthischapter,youlearnedhowtousealoadertoloaddatafromacontentproviderthatisnotpartofyourapp.

RelatedconceptTherelatedconceptdocumentationisinAndroidDeveloperFundamentals:Concepts.

Loaders

LearnmoreLoadersRunningaquerywithaCursorLoaderCursorLoader

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Appendix:HomeworkAssignmentsThisappendixlistspossiblehomeworkassignmentsthatstudentscancompleteattheendofeachpractical.Itistheinstructor'sresponsibilityto:

assignhomeworkifrequiredcommunicatetostudentshowtosubmitthehomeworkassignmentsgradethehomeworkassignments

Instructorscanusethesesuggestionsaslittleorasmuchastheywant,andshouldfeelfreetoassignanyotherhomeworktheyfeelisappropriate.

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HomeworkAssignments:Lesson1Contents:

1.1:InstallAndroidStudioandRunHelloWorld1.2A,B:MakeYourFirstInteractiveUI/UsingLayouts1.3:TextandScrollingViews1.4:Resources

1.1:InstallAndroidStudioandRunHelloWorld

Buildandrunanapp

1. CreateanewAndroidprojectfromtheEmptyTemplate.2. AddloggingstatementsforvariousloglevelsinonCreate()inthemainactivity.3. Createanemulatorforadevice,targetinganyversionofAndroidyoulike,andruntheapp.4. Usefilteringinlogcattofindtheyourlogstatementsandadjustthelevelstoonlydisplaydebugorerrorlogging

statements.

Answerthesequestions

Question1Whatisthenameofthelayoutfileforthemainactivity?

Question2Whatisthenameofthestringresourcethatspecifiestheapplication'sname?

Question3Whichtooldoyouusetocreateanewemulator?

AndroidDeviceMonitorAVDManagerSDKManagerThemeEditor

Question4

Whichdeviceshavethefollowingspecifications?Youcanseethedifferentdevicespecificationswhilecreatinganewdeviceemulator.

Whatisdevice1?

Size=4.7inchesResolution=768x1280

Whatisdevice2?

Size=8.86inchesResolution=2048x1536

Question5

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Assumethatyourappincludesthisloggingstatement:

Log.i("MainActivity","MainActivitylayoutiscomplete");

Youseethestatement"MainActivitylayoutiscomplete"inthelogcatconsoleiftheLoglevelmenuissettowhichofthefollowing?(Hint:multipleanswersareOK.)

VerboseDebugInfoWarnErrorAssert

Question6

Ifyourapplogsthemessage"XXActivitylayoutiscomplete"eachtimeanewactivityisdisplayed,howcanyoumakethelogcatconsoledisplayONLYstatementsthatinclude"layoutiscomplete?"

Submityourappforgrading

Noapptosubmitforthishomeworkassignment.

1.2A,B:MakeYourFirstInteractiveUI/UsingLayouts

BuildandrunanappOpentheHelloConstraintappthatyoucreatedintheUsingLayoutslesson.

1. Modifytheactivity_main.xmllayouttoincludeathirdbuttoncalledZerothatappearsbetweenthe"Toast"and"Count"buttons.

2. InitiallytheZerobuttonhasagraybackground.3. Displayallthreebuttonsontheleftoftheshow_countTextView.Distributethebuttonsverticallybetweenthetopand

bottomoftheshow_countTextView.4. MakesurethatyouincludetheZerobuttonforthelandscapeorientationinactivity_main.xml(land),andalsofora

tablet-sizedscreeninactivity_main(xlarge).5. MaketheZerobuttonchangethevalueintheshow_countTextViewto0.6. UpdatetheclickhandlerfortheCountbuttonsothatitchangesitsownbackgroundcolor,dependingonwhetherthe

newcountisoddoreven.Hint:Don'tusefindViewByIdtofindtheCountbutton.Istheresomethingelseyoucanuse?FeelfreetotouseconstantsontheColorclassforthetwodifferentbackgroundcolors.

7. AlsoupdatetheclickhandlerfortheCountbuttontosetthebackgroundcolorfortheZerobuttontosomethingother

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thangraytoshowitisnowactive.Hint:YoucanusefindViewByIdinthiscase.8. UpdatetheclickhandlerfortheZerobuttontoresetthecolortogray(sothatitisgraywhenthecountiszero).

Answerthesequestions

Question1WhatarethelayoutconstraintattributesontheZerobuttontopositionitverticallyequaldistancebetweentheothertwobuttons?

Question2WhatisthelayoutconstraintattributeontheZerobuttontopositionithorizontallyinalignmentwiththeothertwobuttons?

Question3WhichofthefollowingoperationscanyouperformtoincludetheZerobuttoninthexlarge(tablet)andland(landscape)layoutsthathavealreadybeencreated?

Repeattheprocedureusedinthefirstlayout:Openthesecondlayout,clicktheDesigntab,dragthebuttonfromthePalettepane,setitsconstraintsinthedesignpane,andsetitsID,width,height,color,andtextinthePropertiespane.InthefirstlayoutclicktheTexttab,selectandCopytheXMLcodefortheZerobutton,openthesecondlayout,andPastetheXMLcodeforthebutton.Eitheroperationworks.

Question4

Whatisthecorrectsignatureforamethodusedasthevalueoftheandroid:onClickXMLattribute?

publicvoidcallMethod()

publicvoidcallMethod(Viewview)

privatevoidcallMethod(Viewview)

publicbooleancallMethod(Viewview)

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Question5

TheclickhandlerfortheCountbuttonstartswiththefollowingmethodsignature:

publicvoidcountUp(Viewview)

Whichofthefollowingtechniquesismoreefficienttousewithinthishandlertochangethebutton'sbackgroundcolor?Chooseone:

UsefindViewByIdtofindtheCountbuttonview.AssigntheresulttoaViewvariable,andthenusesetBackgroundColor().UsetheviewparameterthatispassedtotheclickhandlerwithsetBackgroundColor().

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Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

ItdisplaystheZerobutton.TheZerobuttonuseslayoutconstraintstopositionitselfbetweentheToastandCountbuttons.Itincludesanimplementationofactivity_main.xml,activity_main.xml(land),andactivity_main.xml(xlarge),includinganadjustmenttothetoastbuttoninactivity_main.xml(land).ItincludesanimplementationoftheclickhandlermethodfortheZerobuttontoresetthecountto0.Themethodmustshowthezerocountintheshow_countview.TheclickhandlermustalsoresettheZerobutton'sownbackgroundcolortogray.TheclickhandlermethodfortheCountbuttonhasbeenupdatedtochangeitsownbackgroundcolordependingonwhetherthenewcountisoddoreven.Thismethodmustusetheviewparametertoaccessthebutton.ThismethodmustalsochangethebackgroundoftheZerobuttontoacolorotherthangray.

1.3:TextandScrollingViews

Buildandrunanapp

OpentheScrollingText2appthatyoucreatedintheWorkingwithTextViewElementslesson.

1. Changethesubheadingsothatitwrapswithinacolumnontheleftthatis100dpwide,asshownbelow.2. Placethetextofthearticletotherightofthesubheadingasshownbelow.

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Answerthesequestions

Question1HowmanyViewscanaScrollViewcontain?Chooseone:

OneViewonlyOneVieworoneViewGroupAsmanyasyouneed

Question2

WhichXMLattributedoyouuseinaLinearLayouttoshowviewsside-by-side?Chooseone:

android:orientation="horizontal"

android:orientation="vertical"

android:layout_width="wrap_content"

Question3

WhichXMLattributedoyouusetodefinethewidthoftheLinearLayoutinsidethescrollingview?Chooseone:

android:layout_width="wrap_content"

android:layout_width="match_parent"

android:layout_width="200dp"

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Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

Thelayoutshowsthesubheadingintheleftcolumnandthearticletextintherightcolumn,asshownintheabovefigure.TheScrollViewincludesaLinearLayoutwithtwoTextViews.TheLinearLayoutorientationissettohorizontal.

1.4:Resources

Loadandrunanexistingapp,exploreresources

1. LoadoneofthesampleappsintoAndroidStudio.2. OpenoneoftheJavaactivityfilesintheapp.Lookforaclass,type,orprocedurethatyou'renotfamiliarwithandlook

itupintheAndroidDeveloperdocumentation.3. GotoStackoverflowandsearchforquestionsandanswerstothesametopic.4. FindtheGoogleDeveloperschannelonYouTube.FindaplaylistorvideoaboutAndroidStudioandwatchoneofthe

videos.

Answerthesequestions

Question1

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InAndroidStudio,whatismenucommandtoopenthelistofsampleapps?

Question2

Whatdidyoulookup,andwhataretheURLstothedocumentationyoufound?

Question3

Whatare2differencesbetweenthekindofinformationyoufindintheAndroidDeveloperdocumentationandonStackoverflow?WhenwouldyouusetheAndroidDeveloperdocumentation?WhenwouldyouuseStackoverflow?

Question4

WhatistheURLtotheAndroidStudioPlaylistorvideothatyouwatched?Whatdidyoulearn?

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GuidanceforgradersNoapptosubmitforthishomeworkassignment.

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513

HomeworkAssignments:Lesson2Contents:

2.1:CreateandStartActivities2.2:TheActivityLifecycleandManagingState2.3:StartActivitieswithImplicitIntents

2.1:CreateandStartActivities

Buildandrunanapp

OpentheHelloToastappthatyoucreatedintheMakeYourFirstInteractiveUIlesson.

1. Modifythetoastbuttonsothatitlaunchesanewactivitytodisplaytheword"Hello!"andthecurrentcount,asshownbelow.

2. Changethetextonthetoastbutton.

Answerthesequestions

Question1

HomeworkLesson2

514

Whatmenucommanddoyouusetoaddanewactivitytoyourapp?

Question2

WhatfilesareaddedwhenyouaddanewactivitycalledHelloActivitytoyourapp?Whatchangesaremadetoexistingfiles?

Question3

Whichconstructormethoddoyouusetocreateanewexplicitintent?

newIntent()

newIntent(Contextcontext,Class<?>class)

newIntent(Stringaction,Uriuri)

newIntent(Stringaction)

Question4

Howdoyouaddthecurrentvalueofthecounttotheintent?

AstheintentdataAsanintentactionAsanintentextra

Question5HowdoyouupdatethecountinHelloActivitytodisplaythecurrentcount?

Gettheintenttheactivitywaslaunchedwith.Getthecurrentcountvalueoutoftheintent.Updatethetextviewforthecount.Alloftheabove.

Submityourappforgrading

GuidanceforgradersCheckthattheapphasthefollowingfeatures:

ItdisplaystheHellobuttoninsteadoftheHelloToastbutton.TheHelloActivitystartswhentheHellobuttonispressed,andthenewactivitydisplaysthemessage"Hello!"andthecurrentcountfromthemainactivity.TheHelloActivity.javaandactivity_hello.xmlfileshavebeenaddedtotheproject.Theactivity_hello.xmlfilecontainstwotextviewobjects,onewiththestringHello!andthesecondwiththecount.ItincludesanimplementationofaclickhandlermethodfortheHellobutton(inMainActivity).ItincludesanimplementationoftheonCreate()methodfortheHelloActivityandupdatesthecountTextViewwiththecountfromMainActivity.

2.2:TheActivityLifecycleandManagingState

Buildandrunanapp1. Createanappwithalayoutthatholdsacounter,abuttontoincrementthecounter,andanedittext.Seethe

screenshotbelowasasample.Youdon'thavetopreciselyduplicatethelayout.

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2. Addaclickhandlerforthebuttonthatincrementsthecounter.3. Runtheappandincrementthecounter.Entersometextintotheedittext.4. Rotatethedevice.Notethatthecounterisreset,butthecontentsoftheedittextisnot.5. ImplementonSaveInstanceState()tosavethecurrentstateoftheapp.6. UpdateonCreate()torestorethestateoftheapp.7. Rotatethedeviceandensurethattheappstateispreserved.

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HomeworkLesson2

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Answerthesequestions

Question1Whenyourotatethedevice(beforeyouimplementonSaveInstanceState()),thecounterisresetto0butthecontentsoftheedittextispreserved.Why?

Question2WhatActivitylifecyclemethodsarecalledwhenadevice-configurationchange(suchasrotation)occurs?

Question3WhenintheActivitylifecycleisonSaveInstanceState()called?

Question4WhichisthecorrectmethodsignatureforonSaveInstanceState():

voidonSaveInstanceState(BundleoutState)

voidonSaveInstanceState()

voidonSaveInstanceState(BundleoutState,PersistableBundleoutPersistentState)

Question5

WhatisthedifferencebetweenrestoringyouractivitystateinonCreate()versusinonRestoreInstanceState()?

Question6

Ifyouquitandrestartyourapp,whathappenstotheActivitystate?

Submityourappforgrading

GuidanceforgradersCheckthattheapphasthefollowingfeatures:

Itdisplaysacounter,abuttontoincrementthatcounter,andanedittext.Clickingthebuttonincrementsthecounterby1.Whenthedeviceisrotated,boththecounterandedittextstateareretained.TheimplementationofMainActivity.javausestheonSaveInstanceState()methodtostorethecountervalue.TheimplementationofonCreate()testsfortheexistenceoftheoutStatebundle.Ifthatbundleexists,thecountervalueisrestoredandsavedtothetextview.

2.3:StartActivitieswithImplicitIntents

BuildandrunanappOpentheImplicitIntentsappthatyoucreatedintheStartActivitieswithImplicitIntentslesson.

1. Addanotherbuttonatthebottomofthescreen.2. Whenthebuttonisclicked,launchacameraapptotakeapicture.(Youdon'tneedtoreturnthepicturetotheoriginal

HomeworkLesson2

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app.)Note:IfyouusetheAndroidemulatortotestthecamera,opentheemulatorconfigurationintheAndroidAVDmanager,chooseAdvancedSettings,andthenchoose"Emulated"forbothfrontandbackcameras.Restartyouremulatorifnecessary.

HomeworkLesson2

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HomeworkLesson2

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Answerthesequestions

Question1Whichconstructormethoddoyouusetocreateanimplicitintenttolaunchacameraapp?

newIntent()

newIntent(Contextcontext,Class<?>class)

newIntent(Stringaction,Uriuri)

newIntent(Stringaction)

Question2

Whichintentactiondoyouusetorequestacameraapp?

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GuidanceforgradersCheckthattheapphasthefollowingfeatures:

Itdisplaysa"TakeaPicture"buttonatthebottomoftheapp.Whenclicked,thebuttonlaunchesacameraapponthedevice.TheonclickmethodfortheTakeaPicturebuttonensuresthereisanavailableapponthedevice(withtheresolveActivity()andgetPackageManager()methods)beforesendingtheintent.

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HomeworkAssignments:Lesson3&4Contents:

3.1:Debugging3.2:Testing3.3:SupportLibrariesandBackwardsCompatibility4.1:UserInputControls4.2:Menus4.3:ScreenNavigation4.4:RecyclerView

3.1:Debugging

Buildandrunanapp

OpentheSimpleCalcappfromtheUsingtheDebuggerlesson.

1. InMainActivity,placeabreakpointonthefirstlineoftheonAdd()method.2. Runtheappinthedebugger.Performanaddoperationintheapp.Theexecutionstopsatthebreakpoint.3. UsetheStepIntobuttontofollowtheexecutionoftheappstepbystep.NotethatStepIntoopensandexecutesfiles

fromtheAndroidframework,enablingyoutoseehowAndroiditselfoperatesonyourcode.4. Examinehowthedebuggerwindowschangeasyoustepthroughthecodeforthecurrentstackframeandlocal

variables.5. Examinehowthecodeitselfintheeditorwindowsisannotatedaseachlineisexecuted.6. UsetheStepOutbuttontoreturnbacktoyourappiftheexecutionstackgetstoodeeptounderstand.

Answerthesequestions

Question1

WhatisthedifferencebetweenStepOverandStepInto?

Question2

Howdoeseachpartofthedebuggerviewchangewhenyoustepintoanewmethod?

Submityourappforgrading

GuidanceforgradersNoapptosubmitforthishomeworkassignment.

3.2:Testing

Buildandrunanapp

OpentheSimpleCalcTestappthatyoucreatedintheTestingAppswithUnitTestslesson.You'regoingtoaddanPOWbuttontothelayout.Thisbuttoncalculatesthefirstoperandraisedtothepowerofthesecondoperand.Forexample,givenoperandsof5and4,theappcalculates5raisedtothepowerof4,or625.

HomeworkLessons3,4

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BEFOREyouwritetheimplementationofyourpowerbutton,considerthekindoftestsyoumightwanttoperformwiththiscalculation.Whatunusualvaluesmayoccurinthiscalculation?

1. UpdatetheCalculatorclassintheapptoincludeapow()method.(Hint:Consultthedocumentationforthejava.lang.Mathclass.)

2. UpdatetheMainActivityclasstoconnectthePOWbuttontothecalculation.3. Writeeachofthefollowingtestsforyourpow()method.Runyourtestsuiteeachtimeyouwriteatest,andfixthe

originalcalculationinyourappifnecessary.Atestwithpositiveintegeroperands.Atestwithanegativeintegerasthefirstoperand.Atestwithanegativeintegerasthesecondoperand.Atestwith0asthefirstoperandandapositiveintegerasthesecondoperand.Atestwith0asthesecondoperand.Atestwith0asthefirstoperandand-1asthesecondoperand.(Hint:consultthedocumentationforDouble.POSITIVE_INFINITY.)Atestwith-0asthefirstoperandandanynegativenumberasthesecondoperand.

Answerthesequestions

Noquestions.

Submityourappforgrading

Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

ItdisplaysaPOWbuttonthatprovidesanexponential("powerof")calculation.TheimplementationofMainActivityincludesanonclickmethodforthePOWbutton.TheimplementationofCalculatorincludesapow()methodthatperformsthecalculation.TheCalculatorTestmethodincludesseparatetestmethodsforthepow()methodintheCalculatorclassthatperformtestsfornegativeand0operands,andforthecaseof0and-1astheoperands.

3.3:SupportLibrariesandBackwardsCompatibility

RunanappOpentheHelloCompatappcreatedintheUsingtheAndroidSupportLibrarieslesson.

1. SetadebuggerbreakpointonthelineinthechangeColor()methodthatactuallychangesthecolor:

intcolorRes=ContextCompat.getColor(this,colorResourceName);

2. Runtheappindebugmodeonadeviceoremulatorthat'srunninganAPIversion23orhigher.StepintothegetColor()method,followingthemethodcallsdeeperintothestack.ExaminehowtheContextCompatclassdetermineshowtogetthecolorfromtheresources,andwhichotherframeworkclassesituses.

Note:Someclassesmayproduceawarningthatthe"sourcecodedoesnotmatchthebytecode."ClickStepOuttoreturntoaknownsourcefile,orkeepclickingStepIntountilthedebuggerreturnsonitsown.

3. RepeatthepreviousstepforadeviceoremulatorrunninganAPIversionlowerthan23.Notethedifferentpathsthattheframeworktakestoaccomplishgettingthecolor.

Answerthesequestions

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523

Question1

Basedonyourexplorationinthedebugger,howdoestheAndroidplatformdecidewhichimplementationtouseintheCompatclasses?

Question2

Besidesthedifferencesinthemethodsignatures,whatisthedifferencebetweentheimplementations?Whyisacompatibilityclassrequiredatall?

Submityourappforgrading

Guidanceforgraders

Noapptosubmitforthishomeworkassignment.

4.1:UserInputControls

Buildandrunanapp

1. Createanappwith5checkboxesandaShowToastbutton,asshownbelow.2. WhentheuserclicksasinglecheckboxandthenShowToast,displayatoastmessageshowingthecheckbox

selected.3. IftheuserselectsmorethanonecheckboxandthenShowToast,showatoastthatincludesthemessagesforall

selectedcheckboxes,asshowninthefigurebelow.

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Answerthesequestions

Question1What'sthemostimportantdifferencebetweencheckboxesandaRadioGroupofradiobuttons?Chooseone:

Theonlydifferencesishowtheyappear:checkboxesshowacheckmarkwhenselected,whilecircular"radio"buttonsappearfilledwhenselected.CheckBoxelementsinthelayoutcanusetheandroid:onClickattributetocallahandlerwhenselected.Themajordifferenceisthatcheckboxesenablemultipleselections,whileaRadioGroupallowsonlyoneselection.

Question2

WhichlayoutgroupisthepreferredwaytoalignasetofCheckBoxelementsvertically?Chooseone:

RelativeLayoutLinearLayoutScrollView

Question3

WhatmethodoftheCheckableinterfacedoyouusetocheckthestateofacheckbox(thatis,whetherithasbeencheckedornot)?

Submityourappforgrading

Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

ThelayoutincludesfiveCheckBoxviewsverticallyalignedonthescreen,andaShowToastbutton.TheonSubmit()methoddetermineswhichcheckboxischeckedbyusingfindViewById()withisChecked().Thestringsdescribingtoppingsareconcatenatedintoatoastmessage.

4.2:Menus

Buildandrunanapp

OpentheScrollingTextappthatyoucreatedintheWorkingwithTextViewElementslesson.

1. Addafloatingcontextmenutoshowthreemenuoptions:Edit,Share,andDelete,asshowninthefigurebelow.ThemenuappearswhentheuserperformsalongclickontheTextView.

2. Addlogmessagestoshowwhichmenuitemwasclicked.

HomeworkLessons3,4

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HomeworkLessons3,4

527

Answerthesequestions

Question1Whatisthenameandlocationofthefileinwhichyoucreatecontextmenuitems?

Question2Whathappenswhenalongtap(alsoknownasalongclick)occurs?Chooseone:

Whenaviewreceivesalong-clickevent,thesystemcallstheonCreateContextMenu()method,whichyoucan'tchange.Whenaregisteredviewreceivesalong-clickevent,thesystemcallstheonCreateContextMenu()method,whichyoucanoverrideinyouractivityorfragment.Whenaregisteredviewreceivesalong-clickevent,thesystemcallstheonContextItemSelected()method,whichyoucanoverrideinyouractivityorfragment.

Question3

Wheredoyouregisteracontextmenuforaview?Chooseone:

UseregisterForContextMenu()intheonCreate()method.UseregisterForContextMenu()intheonCreateContextMenu()method.UsegetMenuInflater()intheonCreateContextMenu()method.

Question4

WheredoyouinflatethecontextmenuusingMenuInflater?Chooseone:

IntheonCreate()method.IntheonCreateContextMenu()method.IntheonContextItemSelected()method.

Submityourappforgrading

GuidanceforgradersCheckthattheapphasthefollowingfeatures:

TheonCreateContextMenu()methodisimplementedintheMainActivityclassandusesaMenuInflatertoinflatethecontextmenu.Themenu_context.xmlfilecontainsthreeoptions:Edit,Share,andDelete.TheonContextItemSelected()methodisimplementedandusesgetItemId()todeterminewhichmenuitemisselected.

4.3:ScreenNavigation

Buildandrunanapp

Createanappwithamainactivityandatleastthreeotheractivities.AllactivitieshaveabasicOptionsmenuandusethev7appcompatsupportlibraryToolbarastheappbar,asshownbelow.

1. Inthemainactivity,buildagridlayoutwithimagesofyourownchoosing(orusetheimagesin

HomeworkLessons3,4

528

4_1_P_starter_images.zip).Resizetheimagessothatthreeofthemfithorizontallyonthescreeninthegridlayout.2. Enableeachimagetoprovidenavigationtoanotheractivity.

Whentheusertapstheimage,itstartstheotheractivity.Fromanyoftheotheractivities,theusercantaptheUpbuttonintheappbar(highlightedinthefigurebelow)to

returntothemainactivity.

Answerthesequestions

Question1Whichtemplateprovidesanactivitywithanoptionsmenu,theUpbutton,andthev7appcompatsupportlibraryToolbarastheappbar?

Question2WhywouldyouuseaGridLayoutcomparedtoaLinearLayoutoraRelativeLayouttoprovidenavigationusingimages?

Question3WheredoyouputtheGridLayoutofimages?Chooseone:

Inactivity_main.xmlfortheMainActivity.Incontent_main.xmlfortheMainActivity.Inthe"main"XMLlayoutfilesforeachotheractivity.Inthe"content"XMLlayoutfilesforeachotheractivity.

Question4

Wheredoyoudefinetheapp'sactivitiesandparentactivitytoprovideUpnavigation?Chooseone:

ToprovidetheUpbuttonforachildscreenactivity,declarethechildactivity'sparentintheactivity_main.xmlfile.ToprovidetheUpbuttonforachildscreenactivity,declaretheactivity'sparentintheAndroidManifest.xmlfile.ToprovidetheUpbuttonforachildscreenactivity,declarethechildactivity'sparentinthe"main"XMLlayoutfileforthechildscreenactivity.

Question5

Whichtechniquedoyouusetolaunchanotheractivityfromanavigationimage?Chooseone:

Usetheandroid:onClickattributewiththeImageViewintheXMLlayouttocallapublicmethodintheactivityassociatedwiththelayout.Usethefollowingcodeinapublicmethod(assumingtheotheractivityiscalledOtherActivity):Intentintent=newIntent(this,OtherActivity.class);startActivity(intent);

Bothoftheabove.

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Guidanceforgraders

HomeworkLessons3,4

529

Checkthattheapphasthefollowingfeatures:

AGridLayoutinthecontent_main.xmlfile.AnewIntentandstartActivity()methodforeachnavigationelementinthegrid.Aseparateactivityclassforeachnavigationelementinthegrid.

4.4:RecyclerView

Buildandrunanapp1. CreateanappthatusesaRecyclerViewtodisplayalistofrecipes.

Eachlistitemshowsthenameoftherecipewithashortdescription.UseseparateTextViewviewsandstylingfortherecipenameanddescription.

2. Whentheusertapsarecipe(aniteminthelist),startanactivitythatshowsthefullrecipetext.Youmayuseplaceholdertextforthefullrecipes.Optionally,addanimageforthefinisheddishtoeachrecipe.Clickingtheupbuttontakestheuserbacktothelistofrecipes.

Thescreenshotbelowshowsanexampleforasimpleimplementation.Yourappcanlookverydifferent,aslongasithastherequiredfunctionality.

Answerthesequestions

HomeworkLessons3,4

530

Question1

Whataretheprimarycomponentsyouneedtodisplaytherecipeslist?Checkallthatapply.

RecyclerView

RecyclerView.Adapter

RecyclerView.ViewHolder

AppCompatActivity

Question2Whatclassdoyouneedtoimplementinordertolistenandrespondtouserclicks?

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Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

ImplementsaRecyclerViewthatshowsascrollablelistofrecipetitlesandshortdescriptions.ThecodeextendsorimplementsRecyclerView,RecyclerView.Adapter,RecyclerView.ViewHolder,andView.OnClickListener.Clickingonalistitemstartsanactivitythatshowsthefullrecipe.ThemanifestfiledefinesaparentrelationshipsothatclickingtheUpbuttoninarecipeviewgoesbacktothelistofrecipes.ViewHoldercontainsalayoutwithtwoTextViews;forexample,aLinearLayoutwithtwoTextViews.

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HomeworkAssignments:Lesson5&6Contents:

5.1:Drawables,Themes,Styles5.2:MaterialDesign5.3:ProvidingResourcesforAdaptiveLayouts6.1:TestingtheUserInterface

5.1:Drawables,Themes,Styles

Buildandrunanapp

CreateanappthatdisplaysanImageViewandplusandminusbuttons,asshownbelow.TheImageViewcontainsalevellistdrawablethatisabatterylevelindicator.Pressingtheplusorminusbuttonchangestheleveloftheindicator.UsethebatteryiconsfromtheVectorAssetStudiotorepresent7differentvaluesforthebatterylevel.

Theapphasthefollowingproperties:

Theplusbuttonincrementsthelevel,causingthebatteryindicatortoappearmorefull.Theminusbuttondecrementsthelevel,causingtheindicatortoemptyonelevel.

HomeworkLessons5,6

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HomeworkLessons5,6

533

Answerthesequestions

Question1Whattwotypesofdrawablesdoyouusetocreateabuttonthatdisplaystext,wherethebuttonhasonebackgroundwhenitisactiveandadifferentbackgroundwhenitisdisabled,andbothbackgroundsarestretchedwhenthesizeofthebuttonislargerthanthetextitcontains?

LevelListDrawable

TransitionDrawable

StateListDrawable

NinePatchDrawable

Question2

Supposeyoucreateanappthathasadarkbackgroundandlighttext,andtheappdoesn'tneedanActionBar.Whichbasestyledoesyourapplicationstyleinheritfrom?

Theme.AppCompat.Light

Theme.AppCompat.Dark.NoActionBar

Theme.AppCompat.NoActionBar

Theme.NoActionBar

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Guidanceforgraders

ThebuttonsincrementacountvariablewhichisusedtosetthelevelontheImageViewusingthesetImageLevel()method.ThelevelsintheLevelListdrawablegofrom0to6.Thebuttons'onClickmethodschecktoseeifthecountvariableiswithintherangeofthelevellistdrawable(0-6)beforeincrementingordecrementingtheimagelevel,sothatyoucan'tsetalevelthatdoesn'texist.

5.2:MaterialDesign

BuildandrunanappOpentheMaterialMeappthatyoucreatedintheLessonSupportingLandscape,MultipleScreenSizesandLocalizationlesson.

1. CreateasharedelementtransitionbetweentheMainActivityandtheDetailActivity,withthebannerimageforthesportasthesharedelement.

2. ClickingonalistitemintheMaterialMeapptriggersthetransition.ThebannerimagefromthecardmovestothetopofthescreenintheDetailview.

Answerthesequestions

Question1Whichcolorattributeinyourstyledefinesthecolorofthestatusbar?

colorPrimary

HomeworkLessons5,6

534

colorPrimaryDark

colorAccent

colorAccentDark

Question2

WhichsupportlibrarydoestheFloatingActionButtonbelongto?

v4SupportLibrary

v7SupportLibrary

DesignSupportLibrary

CustomButtonSupportLibrary

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Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

Window-contenttransitionsareenabledintheapptheme.Asharedelementtransitionisspecifiedintheappstyle.ThetransitionisdefinedasanXMLresource.Acommonnameisassignedtothesharedelementsinbothlayoutswiththeandroid:transitionNameattribute.ThecodeusestheActivityOptions.makeSceneTransitionAnimation()method.

5.3:ProvidingResourcesforAdaptiveLayouts

BuildandrunanappOpentheRecyclerViewappthatyoucreatedintheCreateaRecyclerViewlesson.ModifytheapptouseaGridLayoutManagerwiththefollowingcolumncounts:

1. Foraphone:

i. 1columninportrait

ii. 2columnsinlandscape

2. Foratablet:

i. 2columnsinportrait

ii. 3columnsinlandscape

HomeworkLessons5,6

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HomeworkLessons5,6

536

Answerthesequestions

Question1Whatresourcequalifierisusedtospecifyresourcestobeusedwhenyourappisinnightmode?

Submityourappforgrading

Guidanceforgraders

HomeworkLessons5,6

537

Checkthattheapphasthefollowingfeatures:

Forphonesandtabletsinbothlandscapeandportraitmodes,thecodeincludesresource-qualifiedvaluesfilesthatcontaintheintegerforthecolumncount.TheappusesusesgetResources().getInteger()toretrieveavaluefromaresourcefile,thenusesthevalueasthecolumncountforgridlayout.

6.1:TestingtheUserInterfaceWriteanEspressotestfortheDroidCafeapp(createdinChapter4.3P)thatteststheimagesinthemainactivitytomakesurethattheytaketheusertothesecondactivity.

Buildandrunanapp

OpentheDroidCafeappthatyoucreatedinpreviouslessons.

1. CreateanEspressotestasaJavaclassinthecom.example.android.droidcafe(androidTest)folder(showninProject:Androidviewinthejavafolder).

2. CreateatestforeachimageintheMainActivitythat:

i. Clickstheimage.

ii. CheckstoseeiftheOrderActivityappears.

Answerthesequestions

Question1

Whichstepsdoyouperformtotestaninteraction,andinwhatorder?Enteranumberforeachstep,from1to3,tospecifytheorder:

Matchaview:Findaviewtorunthetest.Assertandverifytheresult:Checktheview'sstatetoseeifitreflectstheexpectedstateorbehaviordefinedbytheassertion.Performanaction:Performaclickorotheractionthattriggersaneventwiththeview.

Question2WhichofthefollowingannotationsenablesaninstrumentedJUnit4testclass?Chooseone:

@RunWith

@Rule

@Test

Question3

Whichofthefollowingannotationsestablishesthecontextforthetestingcode?Chooseone:

@RunWith

@Rule

@Test

Question4

HomeworkLessons5,6

538

Inthisassignment,youneedtotesteachimageviewusedfornavigationontheDroidCafeappmainscreenbyclickingit.WouldyouuseonView()tofindeachimageview,oronData(),andwhy?Chooseone:

IwoulduseonData()becausetheviewIwanttofindisanimageview.IwoulduseonView()becausetheviewIwanttofindisinthecurrentviewhierarchyandappearsonthescreen.TheonData()methodisforfindingachildviewinanAdapterViewbyfirstloadingtheview'sadapterandthenenablingthechildviewtoappearonthescreen.Iwoulduseneitherbecausetheviewisalreadyinthecurrentviewhierarchy.

Submityourappforgrading

Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

Includesatestclassinthecom.example.android.droidcafe(androidTest)folderwiththe@RunWith(AndroidJUnit4.class)annotation.Includesaseparatetest(annotatedwith@Test)foreachimage.UsestheonView(),check(),andperform()methods.Passesalltests.

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HomeworkAssignments:Lesson7&8Contents:

7.1:CreateanAsyncTask7.2:ConnecttotheInternet7.3:BroadcastReceivers8.1:Notifications8.2:AlarmManager8.3:JobScheduler

7.1:CreateanAsyncTask

Buildandrunanapp

OpentheSimpleAsyncTaskappthatyoucreatedintheCreateanAsyncTasklesson.AddaProgressBarthatdisplaysthepercentageofsleeptimecompleted.TheprogressbarfillsupastheAsyncTaskthreadsleepsfromavalueof0to100(percent).

Hint:Breakupthesleeptimeintochunks.

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AsyncTaskreference:developer.android.com/reference/android/os/AsyncTask.html

Answerthesequestions

Question1ForaProgressBar:

1. HowdoyoudeterminetherangeofvaluesthataProgressBarcanshow?2. Howdoyouchangehowmuchoftheprogressbarisfilledin?

Question2

IfanAsyncTaskisdefinedasfollows:

privateclassDownloadFilesTaskextendsAsyncTask<URL,Integer,Long>

1. WhatisthetypeofthevaluethatispassedtodoInBackground()intheAsyncTask?2. Whatisthetypeofthevaluethatispassedtothecallbackthatreportstheprogressofthetask?3. Whatisthetypeofthevaluethatispassedtothecallbackthatisexecutedwhenthetaskcompletes?

Question3

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ToreportprogressoftheworkexecutedbyanAsyncTask,whatcallbackmethoddoyouimplement,andwhatmethoddoyoucallinyourAsyncTasksubclass?

ImplementpublishProgress().CallpublishProgress().ImplementpublishProgress().CallonProgressUpdate().ImplementonProgressUpdate().CallpublishProgress().ImplementonProgressUpdate().CallonProgressUpdate().

Submityourappforgrading

Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

ThelayoutincludesaProgressBarthatsetstheappropriateattributestodeterminetherangeofvalues.TheAsyncTaskbreaksthetotalsleeptimeintochunksandupdatestheprogressbaraftereachchunk.TheAsyncTaskcallstheappropriatemethodandimplementstheappropriatecallbacktoupdatetheprogressbar.TheAsyncTaskneedstoknowwhichviewstoupdate.DependingonwhethertheAsyncTaskisimplementedasaninnerclassornot,theviewscaneitherbepassedtotheconstructoroftheAsyncTaskordefinedasmembervariablesontheActivity.

7.2:ConnecttotheInternet

BuildandrunanappCreateanappthatretrievesanddisplaysthecontentsofawebpageataURL.Theappdisplays:

AfieldwheretheuserentersaURLAfieldsuchasamenuorspinnerthatallowstheusertochoosetheprotocol(HTTPorHTTPS)AbuttonthatexecutesthetaskwhenclickedAscrollingdisplayofthesourcecodeofthewebpageattheURL

UseanAsyncTaskLoadertoretrievethesourcecodeofthewebpageattheURL.YouneedtoimplementasubclassofAsyncTaskLoader.

IfconnectiontotheInternetisnotavailablewhentheuserclicksthebutton,theappmustshowtheuseranappropriateresponse.Forexample,itmightdisplayamessagesuchas"CheckyourInternetconnectionandtryagain."

ThedisplaymustcontainaTextViewinaScrollViewthatdisplaysthesourcecode,buttheexactappearanceoftheinterfaceisuptoyou.Yourscreencanlookdifferentfromthescreenshotsbelow.Youcanuseapop-upmenu,spinner,orcheckboxestoallowtheusertoselectHTTPorHTTPS.

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Theimageontheleftshowsthestartingscreen,withapop-upmenufortheprotocol.TheimageontherightshowsanexampleoftheresultsofretrievingthepagesourceforgivenURL.

Answerthesequestions

Question1WhatpermissionsdoesyourappneedtoconnecttotheInternet?

android.permission.CONNECTIVITY

android.permission.INTERNET

Itdoesn'tneedanyspecialpermissions;allappsareallowedtoconnecttotheInternet.

Question2

HowdoesyourappcheckthatInternetconnectivityisavailable?

Inthemanifest:

requestACCESS_NETWORK_STATEpermissionrequestALL_NETWORK_STATEpermissionrequestNETWORK_CONNECTpermission

Inthecode:

WrapthecodetoconnecttotheInternetinatry/catchblock,andcatchNO_NETWORKerrors.

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UseConnectivityManagertocheckforanactivenetworkbeforeconnectingtothenetwork.PresentadialogtotheuserremindingthemtomakesurethatInternetconnectivityisavailablebeforeattemptingtoconnecttotheInternet.

Question3

Wheredoyouimplementtheloadercallbackmethodthat'striggeredwhentheloaderfinishesexecutingitstask?

IntheAsyncTaskLoadersubclass.TheAsyncTaskLoadermustimplementLoaderManager.LoaderCallbacks.IntheActivitythatdisplaystheresultsofthetask.TheActivitymustimplementLoaderManager.LoaderCallbacks.InaUtilityclassthatextendsObjectandimplementsLoaderManager.LoaderCallbacks.

Question4

Whentheuserrotatesthedevice,howdoAsyncTaskandAsyncTaskLoaderbehavedifferentlyiftheyareintheprocessofrunningataskinthebackground?

Option1ArunningAsyncTaskbecomesdisconnectedfromtheActivityeventhoughitkeepsexecuting.ArunningAsyncTaskLoaderbecomesdisconnectedfromtheActivitybutstopsrunning,preservingsystemresources.

Option2ArunningAsyncTaskbecomesdisconnectedfromtheActivitybutstopsrunning,preservingsystemresources.ArunningAsyncTaskLoaderautomaticallyrestartsexecutionofitstaskfromthebeginning.TheActivitydisplaystheresults.

Option3ArunningAsyncTaskbecomesdisconnectedfromtheActivityeventhoughitkeepsexecuting.ArunningAsyncTaskLoaderautomaticallyreconnectstotheActivityafterthedevicerotation.TheActivitydisplaystheresults.

Question5HowdoyouinitializeanAsyncTaskLoadertoperformthesteps,suchasinitializingvariables,thatmustbedonebeforetheloaderstartsperformingitsbackgroundtask?

InonCreateLoader()intheActivity,createaninstanceoftheAsyncTaskLoadersubclass.Intheloader'sconstructorperforminitializationtasks.InonCreateLoader()intheActivity,createaninstanceoftheAsyncTaskLoadersubclass.Intheloader'sinit()method,performinitializationtasks.IntheActivity,implementinitLoader()toinitializetheloader.PerforminitializationtasksfortheloaderatthestartofloadInBackgroud()intheLoader.

Question6

WhatmethodsmustanAsyncTaskLoaderimplement?

Submityourappforgrading

GuidanceforgradersCheckthattheapphasthefollowingfeatures:

Themanifestincludesrequestsfortheappropriatepermissions.UsesasubclassofAsyncTaskLoader.Respondsappropriatelyifthedevicecan'tconnecttotheInternet.CombinestheprotocolandthewebpagetocreateavalidURLthattheappusestoconnecttotheInternet.

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ImplementstherequiredLoadercallbackmethods.DisplaystheresultsofretrievingthesourceofthewebpageinTextViewinaScrollView.(It'sOKtodoitinthesameActivity,ortostartanewActivity.)

7.3:BroadcastReceivers

Buildandrunanapp

1. CreateanappcalledBroadcastCounterusingtheEmptyActivitytemplate.2. UseaBroadcastReceivertocounthowmanytimestheACTION_POWER_CONNECTEDbroadcastwasreceived.Hint:Define

yourBroadcastReceiverasaninnerclassandregisteritdynamically.3. DisplaythecountinaTextViewview.

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Answerthesequestions

Question1Whatarethedifferencesbetweenregisteringabroadcastreceiverstaticallyordynamically?

Registeringabroadcastreceiverdynamicallytiesitsoperationtothelifecycleofyouractivity.Ifyouregisteryourreceivertoreceiveonlylocalbroadcasts,youmustregisteritdynamically;staticregistrationisn'tanoption.Registeringabroadcastreceiverstaticallycreatesanewprocesstorunyourbroadcastreceiverifnoprocessesassociatedwithyourapplicationarerunning.Alloftheabove.

Question2

Trueorfalse?Ifabroadcastreceiverisregisteredstatically,itrespondstobroadcasteventsevenifyourappisnotrunning.

Question3

WhichclassisusedtomitigatethesecurityrisksofBroadcastReceiverswhenthebroadcastsarenotcross-application(thatis,theyaresentandreceivedbythesameapp)?

SecureBroadcastLocalBroadcastManagerOrderedBroadcastSecureBroadcastManager

Submityourappforgrading

Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

Thebroadcastreceiverregistersandunregistersdynamicallyinoneofthefollowinglifecyclemethodpairs:OnResume/OnPause,OnCreate/OnDestroy,orOnStart/OnStop.Thecounterisdisplayedandisincrementedwhenthephoneispluggedin.

8.1:Notifications

Buildandrunanapp

OpentheNotifyMeappthatyoucreatedintheNotificationslesson.ChangetheupdatednotificationintheapptousetheInboxStyleexpandedlayoutinsteadofBigPictureStyle.Usefakestringdataforeachlineandsummarytext.

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Note:Thenotificationmightlookalittledifferent,dependingontheAPIlevelofthedevice.

Answerthesequestions

Question1

Supposeyoucreateanapplicationthatdownloadsaworkofarteveryday.Oncetheartworkisavailable,theappshowsanotificationtotheuser,andtheusercaneitherdownloadorskiptheday'sworkofart.WhatPendingIntentmethodwouldyouusetostartaservicetodownloadtheimage?

Activity.startService()

PendingIntent.getBroadcast()

PendingIntent.getActivity()

PendingIntent.getService()

Submityourappforgrading

Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

Whentheusertapstheupdatebutton,thenotificationbecomesanInboxStylenotificationwithseveralrowsoftextrepresentinglineitems.Thescreenhasasummaryandtitletextline,whichchangesitspositiondependingontheAPIlevel.(SeeNotificationsinthematerialdesignguidelines.)UsestheNotificationCompat.InboxStyleclasssothatit'sbackwardscompatible.

8.2:AlarmManager

BuildandrunanappMakeanappthatdeliversanotificationwhenthetimeis11:11(AM).Thescreendisplaysatoggleswitchthatturnsthealarmonandoff.

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HomeworkLessons7,8

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Note:Thenotificationmightlookalittledifferent,dependingontheAPIlevelofthedevice.

Answerthesequestions

Question1

InwhichAPIleveldidinexacttimingbecomethedefaultforAlarmManager?(Allset()methodsuseinexacttiming,unlessexplicitlystated.)

APIlevel16APIlevel18APIlevel19APIlevel17

Submityourappforgrading

Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

Thealarmusesexacttiming.ThismeansthatthecodeincludesastatementcheckingthatthedevicesAPIlevelis>19,andusingthesetExact()methodifitis.Appshowsanotificationwhenthetimeis11:11AM.

8.3:JobScheduler

BuildandrunanappCreateanappthatsimulatesalargedownloadscheduledwithbatteryanddataconsumptioninmind.Itcontainsabuttonthatsays"DownloadNow"andhasthefollowingfeatures:

Itdeliversanotificationinplaceofperforminganactualdownload.The"download"isperformedonceaday,whenthephoneisidlebutconnectedtopowerandtoWiFi,orwhenthebuttonispressed.WhentheusertapstheDownloadNowbutton,ittriggersa"downloading"notification.Hint:DefinetheJobServiceclassasaninnerclass.Thatway,theDownloadNowbuttonandtheJobServicecancallthesamemethodtodeliverthenotification.

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Note:Thenotificationmightlookalittledifferent,dependingontheAPIlevelofthedevice.

Answerthesequestions

Question1

WhatclassdoyouuseifyouwantfeaturesliketheonesprovidedbyJobScheduler,butyouwantthefeaturestoworkfordevicesrunningAPIlevel20andbelow?

JobSchedulerCompatFirebaseJobDispatcherAlarmManager

Submityourappforgrading

Guidanceforgraders

Checkthattheapphasthefollowingfeatures:

TheJobInfoobjecthas4criteriaset:setRequiresCharging(),setPeriodic(),setRequiresDeviceIdle(),setRequiredNetworkType()

TheappcrashesiftheJobServiceclassdoesnothaveanemptyconstructor.

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HomeworkAssignments:Lesson9&10&11Contents:

9.1:SharedPreferences9.2:AppSetting10.1:SQLiteDatabase11.1:ContentProviders11.2:Loaders

9.1:SharedPreferences

Buildandrunanapp

OpentheScoreKeeperappthatyoucreatedintheDrawables,Styles,andThemeslesson.

1. Replacethesavedinstancestatewithsharedpreferencesforeachofthescores.2. Testtheapp:

Rotatethedevicetoensurethatconfigurationchangesreadthesavedpreferencesandupdatetheuserinterface.Stoptheappandrestartittoensurethatthepreferencesaresaved.

3. AddaResetbuttonthatresetsthescorevaluesto0andclearsthesharedpreferences.

Answerthesequestions

Question1

Inwhichlifecyclemethoddoyousavetheappstatetosharedpreferences?

Question2

Inwhichlifecyclemethoddoyourestoretheappstate?

Question3

Canyouthinkofacasewhereitmakessensetohavebothsharedpreferencesandinstancestate?

Submityourappforgrading

GuidanceforgradersCheckthattheapphasthefollowingfeatures:

Theappretainsthescoresonrotation.Theappretainsthecurrentscoresafterbeingstoppedandrestarted.TheappsavesthecurrentscorestothesharedpreferencesintheonPause()method.TheapprestoressharedpreferencesintheonCreate()method.TheappdisplaysaResetbuttonthatresetsthescoresto0.Theimplementationoftheonclickhandlermethodfortheresetbutton:

Resetsbothscorevariablesto0.UpdatesbothtextviewsClearsthesharedpreferences.

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9.2:AppSettings

Buildandrunanapp

OpentheDroidCafeWithSettingsappthatyoucreatedintheAddingSettingstoanApplesson.

1. AddaListPreference(adialogwithradiobuttons)tothe"General"groupofsettings.Putitinthe"Generalsettings"screenlayout,belowthe"Addfriendstoordermessages"ListPreference.

2. EditthestringarraysusedfortheListPreferencetoincludetheListPreferencetitle"Chooseadeliverymethod."UsethesamedeliverychoicesthatareusedintheradiobuttonsintheOrderActivity.

3. Maketheuser'schosenDeliverysettingappearinthesametoastmessageasthechosenMarketandRecommendationssettings.

4. Extracredit:ShowtheselecteddeliverymethodasthesettingsummarytextthatappearsunderneaththeListPreferencetitle.Enablethistexttochangewitheachupdate.

Answerthesequestions

Question1

InwhichfiledoyoudefinethearrayofentriesandthearrayofvaluesfortheListPreference?Chooseone:

pref_general.xmlstrings.xmlmenu_main.xmlcontent_main.xml

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Question2

InwhichfiledoyouusethearrayofentriesandthearrayofvaluesinsettinguptheListPreference,andalsosettheListPreferencekeyanddefaultvalue?Chooseone:

pref_general.xmlstrings.xmlmenu_main.xmlSettingsActivity.java

Question3Howdoyousetthedefaultvaluesforsettingsthefirsttimeanactivityruns?

Assignthedefaultvalueusingtheandroid:defaultValueattributeforeachsettingpreferenceinthepreferencesXMLfile.SetthedefaultvalueintheonCreate()methodfortheactivityusingPreferenceManager.setDefaultValues().Bothoftheabove.

Question4

ForanappthatsupportsAndroid3.0andnewerversions,thebestpracticeforsettingsistouseaSettingsActivitythatextendsActivity,andafragmentforeachpreferenceXMLfilethatextendsPreferenceFragment.Buthowdoyouremaincompatiblewiththev7appcompatlibrarywhenextendinganActivitywithAppCompatActivity?

Question5

WhenusingtheSharedPreferencesinterfaceforaccessingandmodifyingpreferencedatasuchassettings,thefollowingstatementreadsthesettingpreferencedefinedbythedeliverykey:

StringdeliveryPref=sharedPref.getString("delivery","1");

Trueorfalse?The"1"stringargumentisthevaluetoreturnifthesettingpreferencedoesnotexist.Itisusuallyastringforthedefaultvalueofthesetting,whichforthisexampleis"1".

Submityourappforgrading

GuidanceforgradersCheckthattheapphasthefollowingfeatures:

TheonCreate()methodreadsthedeliveryPrefsettingusingsharedPref.getString().Thepref_general.xmlfileincludesaListPreferencethatusesforitsentriesanarrayofdeliverychoices.Extracredit:ThestatementbindPreferenceSummaryToValue(findPreference("delivery"))hasbeenaddedtotheonCreate()methodoftheGeneralPreferenceFragmentclassintheSettingsActivityinordertoshowthedeliverychoiceinthepreferencesummary.

10.1:SQLiteDatabaseREADME:Inthenextgroupofhomeworkassignments(10.1,11.1,11.2),youbuild2apps.Theyrelatetoeachotherinthesamewayastheappsyoubuiltinthecorrespondingpracticals,asfollows:

1. Thefirstapp,in10.1,isaTODOlistthatusesaSQLitedatabasetostoreitems.Theappalsoincludesawaytoadd,display,andedititems.

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2. In11.1,youextendtheTODOlistapptouseacontentprovidertoservedatafromtheSQLitedatabasetotheuserinterface.

3. In11.2,youbuildanappcalledShowToDoItemsthataccessestheTODOlist'scontentproviderandloadsto-doitemsusingaloader.

BuildandrunanappthatusesaSQLitedatabase

CreateanappcalledTODOwithaSQLitedatabasewheretheusercancreateandeditto-dolistitemsthatarestoredinthedatabase.

1. ExtendtheSQLiteOpenHelperclasswithquery(),insert(),andupdate()methodsimplemented.2. Includetheappfeaturesdescribedbelow.

Features:

Theusercanaddnewitemstothelist.Eachiteminthedatabaseincludesatasktodo,creationandcompletiondates,andwhetherornotthetaskhasbeencompleted.Whentheappstarts,thescreenshowsalistofincompleteto-doitemssortedbycreationdate.TheUIincludesanOptionsmenuitemtostartanactivitythatshowsthecompletedtasks.Theusercanchangeanitem'scompletionstatus.Whentheusermarksataskascompleted,itismarkedcompleteandthecreationdateisreplacedwiththecompletiondate.Whentheusertapsanincompleteitem,editmodeistriggered,andtheusercanedittheitem.Whentheappisrestarted,thelateststateofitemsisvisible,whichdemonstratesthatthedatawassavedandreloaded.

Tips:

OnewaytoimplementtheUIistouseaRecyclerViewthatstartsaneditactivitywhenanitemisclicked.YouwillnotbegradedonthewayinwhichyouimplementtheUI,orhowtheUIlooks,aslongastheUIdemonstratesthefunctionality.AppsthatuseRecyclerViewandtheSQLitedatabasefollowapattern.ExamineandreusecodethatyouwrotefortheSQLiteDatabaselessonandtheSearchingaSQLiteDatabaselesson.Makesureyoucleanlyseparatedatafromtheuserinterface.Youwillextendthisto-doapptocompletefuturehomeworkassignmentsaboutcontentprovidersandloaders.

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Answerthesequestions

Question1Howmuchcodewereyouabletoreusefromotherapps?Howmuchtimedoyouthinkthatsavedyou?Howmuchdidusinganotherappasanexamplehelpyoustructureyourapp?Therearenorightorwronganswers.

Question2WhataresomeofthebenefitsofusingaSQLiteOpenHelperclass?Checkallthatapply.

Providesutilitiestosimplifythetasksofcreatingandinitializingthedatabase.ProvidestheonUpgrade()method.Mostimportantly,iftheupgradefails,itdoestherollbackforyou.Usingarecommendedpatternmakesiteasiertounderstand,maintain,andextendtheapp.

Question3

WhichofthefollowingarebenefitsofusingaSQLitedatabasetostoreyourdata?Checkallthatapply.

UsesSQLqueriestoretrievedata,allowingyoutomatchgivenconstraintsandconditions.Dataisstoredpersistentlyandsecurely,andcanberetrievedefficiently.Otherappscanuseyourdata.

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Submityourappforgrading

Guidanceforgraders

TherearenorightorwronganswerstoQuestion1.It'simportantthatstudentsreflectandrealizethebenefitsofbuildingontheirownandothers'work.

TheUIthatthestudentchoosesisn'tafactorforgrading,aslongastheappdemonstratesdatabasefunctionality.Studentshavealotoffreedominhowtoimplementthisfunctionality.

Checkthattheapphasthefollowingfeatures:

IncludesaSQLiteOpenHelperclasswithquery(),insert(),andupdate()methodsimplementedtosupporttherequiredfunctionality.Whentheappsstarts,thescreenshowsalistofto-doitemssortedbycreationdate.Whentheuserinteractswithanitem,editmodeistriggered,andtheusercanedittheitem.Theusercanchangeanitem'scompletionstatus.IncludesanOptionsmenuitemthatletstheuserseecompleteditems.Whenanitemischanged,theUIreflectsthechange.Whentheappisrestarted,thelateststateoftheitemsisvisible,whichdemonstratesthatthedatawassavedandreloaded.

11.1:ContentProvidersExtendtheTODOlistappfromhomework10.1touseacontentprovider.

1. AddaContractclassforthecommonandpublicconstants,URIs,andthedatabaseschema.2. AddaContentProviderclassthathandlesURIsandimplementsquery(),insert(),andupdate()methods.3. AddthecontentprovidertotheAndroidManifest.xmlfile.

Features:

Fromtheuser'sperspective,theappshouldhaveexactlythesamefunctionalityastheTODOappthatyoubuiltforthe10.1homeworkassignment.Allqueriesgothroughthecontentprovider,andfromtheretotheSQLitedatabase.

Tips:

Ifyouneedhelp,seetheword_list_sql_with_content_providerappfromtheSharingContentwithOtherAppslesson.

Answerthesequestions

Question1Whataretheprimarypurposesofacontentprovider?

Separatedatafromtheuserinterface.Makedataavailabletootherapps.Separatethebackendfromtheuserinterface.

Question2

WhataresomeofthebenefitsofusingaContractclass?

Contractcanbepublicsootherappscanfindouthowtoaccessacontentprovider.Youonlyneedtodefinecommonconstantsonce.

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Itdefinespartsofanappthatcannotbechanged.Forlargerandmorecomplexapps,itcollectsconstantsintooneplaceforeasiermaintenance.

Question3

WhydoesthecontentproviderneedtobedeclaredintheAndroidManifest?

TotelltheAndroidFrameworkwhattheuniqueIDofthecontentprovideris.Tomakesurethereisonlyonecontentproviderforeachapp.TotelltheAndroidFrameworktheproperties,suchaspermissionsforthiscontentprovider.

Submityourappforgrading

Guidanceforgraders

TheUIthatthestudentchoosesisnotafactorforgrading,aslongasitdemonstratesappfunctionality.

Checkthattheappimplementsthefollowing:

UsestheContractclassfortheURIsandotherconstants.IncludesaContentProviderclassthathandlesURIsandimplementsquery(),insert(),andupdate()methodsthatinteractwiththedatabase.Appisarchitectedsothatactivitiesusethecontentprovider'squery(),insert(),andupdate()methodstointeractwiththedatabase.Whentheappisrestarted,thelateststateoftheitemsisvisible,whichdemonstratesthatthedatawassavedandreloaded.

11.2:LoadersBuildandrunanappcalledShowToDoItemsthatusesaloadertofetchanddisplaydatafromthecontentproviderthatyouusedintheTODOappfromhomework11.1.

1. CreateabasicUItodisplayincompleteTODOlistitems.2. ImplementaContractclassforconstantsfortheTODOapp'scontentprovider.3. ImplementLoaderManager.LoaderCallbacks<>toloaddatafromthecontentprovider.4. Addaloadermanagertomanageyourloader.

Features:

Whentheappsstarts,thescreenshowsalistofto-doitemsfetchedfromtherunningcontentprovideroftheTODOapp.WhenthedataintheTODOapp'sdatabasechanges,italsoupdatesintheShowToDoItemsapp.

Tips:

Re-useUIelementsfrompreviousapps.Don'tforgettoaddpermissionstothemanifestfile.Ifyouneedhelp,seetheWordListClientandWordListLoaderappsonGitHub.

Answerthesequestions

Question1

Whichofthefollowingarebenefitsofusingloaders?

Loadersarefast.

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LoadersrunonseparatethreadstopreventjankyorunresponsiveUI.Loaderssimplifythreadmanagementbyprovidingcallbackmethodswheneventsoccur.Loaderspersistandcacheresultsacrossconfigurationchangestopreventduplicatequeries.Loaderscanimplementanobservertomonitorforchangesintheunderlyingdatasource.

Question2

InbuildingtheShowToDoItemsapp,whydon'tyouhavetoimplementacontentobserver?

Theloadermanagerhandlesdataobservationforyou.CursorLoaderautomaticallyregistersaContentObservertotriggerareloadwhendatachanges.TheTODOlistappsendsnewdatatotheShowToDoItemsappiftheitemsinthedatabasechange.

Submityourappforgrading

Guidanceforgraders

TheUIthatthestudentchoosesisnotafactorforgrading,aslongasitdemonstratesappfunctionality.

Checkthattheapphasthefollowingfeatures:

UsestheContractclass.ImplementsLoaderManager.LoaderCallbacks<>andusesaloadermanager.Whentheappsstarts,thescreenshowsalistofto-doitemsfetchedfromtherunningcontentprovideroftheTODOapp.WhenthedataintheTODOapp'sdatabasechanges,italsoupdatesintheShowToDoItemsapp.

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Appendix:Utilities

TableofContents:CopyandrenameaprojectDeleteaprojectExtractResourcesAddsupportlibrariesCreateimagesinAssetStudioComparecustomobjectsSavestateofcustomobjects

Thisappendixisacollectionoftasksyoumayneedtododuringdevelopmentoftheappsinthepracticals.Theyarenotspecifictoonepractical.

CopyandrenameaprojectForsomelessons,youwillneedtomakeacopyofaprojectbeforemakingnewchanges.Youmayalsowanttocopyaprojecttousesomeofitscodeinanewproject.Ineithercaseyoucancopytheexistingproject(ExistingProject),andthenrenameandrefactorthenewproject's(NewProject)componentstousethenewproject'sname.(Intheinstructionsbelow,substituteyouractualprojectnamesforExistingProjectandNewProject.

1.Copytheproject1. Onyourcomputer'sfilesystem(notinAndroidStudio),makeacopyoftheExistingProjectdirectory.2. RenamethecopieddirectorytoNewProject.

2.RenameandrefactortheprojectcomponentsTheoldnameoftheproject,ExistingProject,stillappearsthroughoutthepackagesandfilesinthenewcopyofyourproject.Changethefileandthepackagereferencesinyourapptothenewname,asfollows:

1. StartAndroidStudio2. ClickOpenanexistingAndroidStudioproject.3. NavigatetotheNewProjectdirectory,selectit,andclickOK.4. SelectBuild>CleanProjecttoremovetheauto-generatedfiles.5. Clickthe1:Projectside-tabandchooseAndroidfromthedrop-downmenutoseeyourfilesintheProjectview.6. Expandapp>java.7. Right-clickcom.example.android.existingprojectandchooseRefactor>Rename.ThisopenstheRenamedialog.8. Changeexistingprojecttonewproject.9. CheckSearchincommentsandstringsandSearchfortextoccurrencesandclickRefactor.10. TheFindRefactoringPreviewpaneappears,showingthecodetoberefactored.11. ClickDoRefactor.12. Expandres>valuesanddouble-clickthestrings.xmlfile.13. Changethename="app_name"stringtoNewProject.

3.Updatethebuild.gradleandAndroidManifest.xmlfiles

EachappyoucreatemusthaveauniqueapplicationID,asdefinedintheapp'sbuild.gradlefile.Eventhoughtheabovestepsshouldhavechangedthebuild.gradlefile,youshouldcheckittomakesure,andalsosynctheprojectwiththegradlefile:

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1. ExpandGradleScriptsanddouble-clickbuild.gradle(Module:app).2. UnderdefaultConfig,checktomakesurethatthevalueoftheapplicationIDkeyhasbeenchangedto

"com.example.android.newproject".Ifithasnotchanged,changeitmanuallnow.3. ClickSyncNowinthetoprightcorneroftheAndroidStudiowindow.

Tip:YoucanalsochooseTools>Android>SyncProjectwithGradleFiletosyncyourgradlefiles.

Inaddition,someappsincludetheappnameinreadableform(suchas"NewProject"ratherthannewproject)asalabelintheAndroidManifest.xmlfile.

1. Expandapp>manifestsanddouble-clickAndroidManifest.xml.2. Findthestatementbelow,andifnecessary,changethelabeliftothestringresourceforthenewappname:

android:label="@string/app_name"

DeleteaprojectAllthefilesforanAndroidprojectarecontainedintheproject'sfolderonthecomputer'sfilesystem.Todeleteaproject,deleteitsfolder.

AndroidStudioalsokeepsalistofrecentprojectsthatyouhaveopened.YoucandeleteaprojectfromthelistofrecentprojectsinAndroidStudio.(Deletingaprojectfromtherecentprojectslistdoesnotaffecttheactualprojectfiles.)

Toremoveaprojectfromtherecentprojectslist,dooneofthefollowing:

OntheAndroidStudiosstartupscreenscreen,clickthenameoftheprojectandpressthedeletekey.SelectFile>OpenRecent>ManageProjects,clickthenameoftheprojectandpressthedeletekey.

ExtractStringsandDimensions

ExtractingStringsInorderforyourapptobetranslatableintomultiplelanguagesyoumustkeepallofyourstringresourcesintheres/values/strings.xmlfile.

CreatingstringresourcesThereareseveralwaystocreatestringresources:

Addthemmanuallyinthestrings.xmlfileusingthefollowingsyntax:

<stringname="string_name">StringValue</string>

Whereverthestringwillbeused,suchasthetextattributeofaTextView:

1. Typeinthedesirednameforastringresourceinthefollowingformat:@string/string_name.Itwillbehighlightedinredsincetheresourcedoesnotyetexist.

2. Makesureyourcursorisinthehighlightedtext.

3. PressAlt+EnterandselectCreatestringvalueresource.

4. EnteryourdesiredstringandpressOKandhestringgetsaddedtoyourstrings.xmlfile.

Youcanselectanyexisting,hard-codedstringineitherXMLorJava,pressAlt+Enter,andselectExtractstringresource.

Accessingstringresources:

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InXML,referencesstringresourceusingthefollowingsyntax:@string/string_nameInJava,referencestringresourcesusingthefollowingsyntax:getString(R.string.string_name)

2.ExtractDimensions

Dimensionsshouldingeneralnotbehard-codedbutkeptinthedimens.xmlfile.Thisallowsforyoutospecifydifferentdimensionsusingresourcequalifiers.

Extractdimensionsinthesamewayasstrings(Alt-Enter),andtheywillbestoredinthedimens.xml.

3.ExtractStyles

Ifyouhaveseveralelementsthatshareattributes,youcancreateastyleinthestyle.xmlfile.Tolearnmoreaboutstyles,seetheStylesandThemeslesson.

Toextractexistingattributesintoastyle,dothefollowing:

1. Placeyourcursorintheviewwhoseattributesyouwanttoturnintoastyle.2. RightclickandselectRefactor>Extract>Style.3. Namethestyleandselectattributes.IfLaunch'UseStyleWherePossible'refactoringafterthestyleisextracted

ischecked,AndroidStudiowillsearchtherestofthefilefortheselectedattributesandapplythestyletoviewswheretheattributesmatch.

4. ClickOK.

AddAndroidsupportlibrariestothebuildfileAndroidSupportLibrariesprovidebackward-compatibleversionsofAndroidframeworkAPIs,additionalUIcomponentsandasetofusefulutilities.

Forexample,tousetheRecyclerViewclass,whichislocatedintheAndroidSupportpackage,youmustincludetwodependenciesinyourproject'sbuild.gradlefile.Theprocessisthesameforothersupportlibrarycomponents.

Followthesestepsandrefertothescreenshotbelow:

1. InAndroidStudio,inyourproject,makesureyouareintheProjectpane(1)andintheAndroidview(2).2. Inthehierarchyoffiles,findtheGradleScriptsfolder(3).3. ExpandGradleScripts,ifnecessary,andopenthebuild.gradle(Module:app)file(4).

4. Towardstheendofthebuild.gradle(Module:app)file,findthedependenciessection.5. Addthesetwolibrarydependenciesasthelasttwolines(insidethecurlybraces):

compile'com.android.support:recyclerview-v7:23.1.1'

compile'com.android.support:design:23.1.1'

Thereisprobablyanexistinglinesimilartothisone:

compile'com.android.support:appcompat-v7:23.1.1'

Addyourlinesbelowthatline.Matchtheversionnumberofyourlinestotheversionnumberofthatexistingline.MakesuretheversionnumbersofallthelibrariesarethesameandmatchupwiththecompiledSdkVersionatthetopofthefile.(Ifthesedon'tmatch,youwillgetabuildtimeerror.)

6. Ifprompted,syncyourappnow.7. Buildandrunyourapp.

Thefollowingisanexampleofthedependenciessectionofthebuild.gradlefilewithsupportlibrariesadded.

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dependencies{

compilefileTree(dir:'libs',include:['*.jar'])

testCompile'junit:junit:4.12'

compile'com.android.support:appcompat-v7:23.1.1'

compile'com.android.support:recyclerview-v7:23.1.1'

compile'com.android.support:design:23.1.1'

}

CreateimagesinAssetStudioUseImageAssetStudiotocreateandaddalaunchericon.

1. OpenyourappinAndroidStudio.2. Right-clicktheresfolderofyourprojectandselectNew>ImageAssetfrommenu.

ThisopenstheImageAssetStudiowindow,whereyoucancreateatexticon,choosefromavailableclipart,oraddyourowncustomicon.

Notethatthepanelonthetop-leftisscrollable;scrolltoseeadditionalcustomizations.

Toaddacustomtexticon:

1. ChangetheNameoftheicontoic_launcher_text,ifyoudon'twanttooverwritethedefaultAndroidic_launchericonthatcomeswithyourproject.

2. IntheAssetTyperow,selectText.3. Type"HelloWorld!"intothetextbox.4. Experimentwithadjustingthefont.5. Scrolldownandchangefontandbackgroundcolors.6. ClickNext.7. TheConfirmIconPathwindowshowshowaniconwithyourspecifiedtextwillbecreatedforeachresolution,aswell

asthedefaultstoragelocationandpathinyourapp.8. ClickFinish.9. Gotthetheres/mipmapfolder.Ifnowcontainsyournewicon,withadefaultversionatthetoplevel,andsize-adjusted

versionsfordifferentresolutions.10. Tousethenewicon,opentheAndroidmanifest.Changetheandroidiconlinefromreferencingic_launcherto

ic_launcher_text.

android:icon="@mipmap/ic_launcher_text"

11. Runyourapp.12. Aftertheapphaslaunched,gotothehomescreenandopenthelistofapps.13. Scrollandyoushouldseeyouriconlistedalongwiththeotherinstalledapps.

Toaddacliparticon:

Followthepreviousstepsexcept:

1. ChangetheNametoic_launcher_clipart.2. ChooseClipArtastheAssetType.3. IntheClipArtrow,clickthebuttonshowingthecurrenticon,thedefaultAndroid.4. Chooseaniconfromthepopupwindowofclipart.

Toaddacustomicon:

Followthepreviousstepsexcept:

1. ChangetheNametoic_launcher_image.2. ChooseImageastheAssetType.3. InthePathrow,chooseanimage.Thiscanbeanimagethatyou'veaddedtoyourprojectoranimageonyour

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computer.

ComparecustomobjectsWheneveryourdatamodelcallsforobjectstobesorted,itbecomesnecessarytodefinehowtheseobjectscanbecomparedtoeachother.

TheComparableinterfaceallowsyoutospecifyhowtocomparetwoobjectsanddeterminewhetheroneisbiggers,smaller,orthesameastheother.

TheComparableinterfacerequiresthatyouimplementasinglemethod:compareTo(<T>another)whereistheparameterizedtypeyouimplementedComparablewith,andthetypeofobjectyouarecomparingto(i.eifyouwanttocompareyourFoobarinstancetootherFoobarinstances,youwouldimplementComparable<Foobar>andyourcompareTomethodwouldtakeFoobarasaparameter).

Thecomparemethodshoulddothefollowing:

Returnanegativeintegeriftheobjectislessthantheparameter.Returnapositiveintegeriftheobjectisgreaterthantheparameter.Returnzeroiftheobjectsareequal.

Forexample,tocomparealistofbooksbypublicationdate:

@Override

publicintcompareTo(Bookbook){

if(this.publication==book.publication){return0;}

else{returnthis.publication>book.publication?1:-1;}

}

SavestateofcustomobjectsInAndroid,youwillfrequentlycreatecustomobjectstorepresentyourparticulardatamodel.Inordertopreservethestateoftheseobjects,youmustbeabletopassthemintothesavedInstanceStatebundle.Inordertodoso,yourcustomclassmustimplementtheParcelableinterface.Thisallowsforprimitivetypes(int,string,byte,etc)tobesavedinthesavedInstanceStatecallback.

Dothefollowing:

1. Aftersettingupthedatainyourcustomclass(onlytheprimitivedatatypeswillbesaved),addtheParcelableimplementationtoyourclassdeclaration.

2. Thedeclarationwillbeunderlinedinred,sinceyouhavetoimplementtheinterfacemethods.Withyourcursorontheunderlinedtext,pressAlt+EnterandselectImplementmethods.

3. ChoosebothdescribeContents()andwriteToParcel(Parceldest,intflags).ClickOK.4. Theclassnamewillstillbeunderlined,indicatingthattheinterfaceisnotfullyimplementedyet.Selecttheclassname,

andagainpressAlt+EnterandchooseAddParcelableimplementation.Androidstudiowillautomaticallyaddtherequiredcode.Notethevariablesforwhichyouwanttopreservethestate(primitivetypes)arewrittentotheParcelinthewriteToParcelmethod.

5. YoucannowsavethestateoftheseobjectsusingthesavedInstanceStatebundlesmethods:putParcelable,putParcelableArray,andputParcelableArrayListandtherespectivegetters.

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