1. Introduction2. Android

i. Historyii. WorldPhoneiii. Ecosystemiv. DesignConsiderationsv. EmergingUseCases

3. TDDwithRobolectrici. LabBackgroundii. Lab:RobolectricIntegrationiii. Lab:FirstTestiv. WhatToTestv. BestPracticesvi. Lab:UtilityFunctionsvii. OtherTesting

4. Architecturei. Androidii. ModelViewControlleriii. BuildingBlocksiv. MessagePassingv. ThreadingModel

5. Fundamentalsi. Activitiesii. Manifestiii. LayoutsandViewsiv. ViewGroupsv. Fragmentsvi. Lab:DesignChunking

i. Handout:DesignChunkingii. Solution:DesignChunking

vii. Lab:ConstructTheViewi. Lab:AddDisplayFragmentii. Lab:AddButtonFragmentiii. Lab:DisplayViewiv. Lab:AddButtons

viii. Applicationix. Lab:AddApplicationx. Lab:EventBus

6. ResourceSystemi. DesignPrinciplesii. Styles&Themesiii. Dimensions&Colorsiv. Lab:ViewStylesv. Qualifiersvi. Lab:FlexibleDimensionsvii. Lab:Internationalizationviii. Drawablesix. Lab:ButtonStatex. Lab:AppIcon

7. ManagingtheLifecyclei. ApplicationLifecycleii. ActivityLifecycle

TableofContents

iii. FragmentLifecycleiv. Lab:VisualizingtheLifecyclev. Backstackvi. FragmentManagervii. Lab:AddCalculatorFragmentviii. InstanceState

8. Lab:Calculatori. Lab:Requirements&Designii. Lab:UserInteractioniii. Lab:GettingOnTheBusiv. Lab:Testingv. Lab:RoutingEventsvi. Lab:MakeItWorkvii. Lab:DeviceRotation

9. Appendixi. Toolsii. Maveniii. Resourcesiv. IntelliJCommands

10. Epilogue11. AboutTheAuthor12. Bibliography

ThisworkbookwasoriginallycreatedbyCoreyLeighLatislawastrainingmaterialsforanin-personclass.

Thisisfreealphaversionofthisbook,Ihopeyouenjoyit!Jointhemailinglisttokeepupwiththeofficialrelease.

Aportionofthedaywillbededicatedtolecture,butit'simportanttogetyoucodingandexploringassoonaspossible!

Wewillbeworkingthroughaseriesoflabassignmentsasacomplementtothematerialyouwillbelearning.Ourfirstassignmentwillbecreatingacalculatorapplication.ThiswillcoverseveralfoundationalAndroidtopics.Thesecondassignmentwillbearegionalfoodrecommendationappwherewe'llcovernetworking,datamanagement,andservices.

We'llbepairprogrammingforthemajorityofthelabsessions.Youarewelcometoswitchuppairsasoftenasyoulike,butworkingsoloisn'tpermitted.Ifwehaveanoddnumberofparticipants,I'llpairwithsomeoneintheclass.

Therearemanypairingmethodologiesoutthere,butIgenerallyfavorpingponging.Inthismodelsomeonewritesafailingtest(red)andthenyouswitchwho'sinthedriver'sseat.Thenewdevelopermakesthetestpass(green)andrefactors(refactor)asnecessary.Thentheywriteafailingtestandthecyclestartsoveragain.

Ifyouhaven'tpairprogrammedbefore,Ithinkyou'lllikeit.Itcanbequitefunandit'sagreatwaytolearnfromothers.

WhatToExpect

HandsOn

PairProgramming

AccordingtoMeier,"mobile-phoneownershipeasilysurpassescomputerownership[and]2009markedtheyearthatmorepeopleaccessedtheInternetforthefirsttimefromamobilephoneratherthanaPC.Manypeoplebelievethatwithinthenext5yearsmorepeoplewillaccesstheInternetbymobilephoneratherthanusingpersonalcomputers."

Devices,suchasphonesandtablets,arequiteliterallychangingtheworldonepersonandoneappatatime.Smartphoneshavebecomeanindispensablepartofourlivesintheshorttimetheyhavebeenaround!

Thepotentialyouhavetocreateausefulappforpeopletheworldoverisarareandspecialgift.It'shardtothinkofsomethingmorerewardingtodointhisworldthantomakesuchapersonalconnectionandchangethecourseofpeople'slives.Youcanequippeoplewithknowledge,tools,andgamesthatwillmakethemcompetitiveintheyearstocomeastechnologyadvances.

It'sanexcitingtimetobecomeandAndroiddeveloper!Thereisahighdemandandlotsofopportunitytomakeanimpactlocallyandglobally.

KnowingthefoundationsofAndroidwillhelpyouonyourexplorationofthisfascinatingplatformtohelpyoumakeappsthatcanliterallychangetheworld!

Meier,Reto(2012-04-05).ProfessionalAndroid4ApplicationDevelopment(KindleLocations499-502).JohnWileyandSons.KindleEdition.

Chapter1:Android

Resources

AbriefhistoryoftheAndroidworld.

Globalshipmentshavebeenrisingatafastpace.AccordingtotheIDC,lastyearaloneitrose23%.By2018,therewillbeanadditional1.8billiondevicesinpeople'shands.

Ofthosephones,80.2%willbeAndroid!

History

SmartphoneMomentumStillEvidentwithShipmentsExpectedtoReach1.2Billionin2014andGrowing23.1%Over2013.May28,2014.Retrievedfromhttp://www.idc.com/getdoc.jsp?containerId=prUS24857114.

References

Androidissointriguingbecauseit'sasystemthat'saccessibletotheworldover,notjusttherichestinoursocieties.

WhatmakesAndroidsoaccessibleisit'sprice.AccordingtoSherman,it'sonaveragelessthanhalfthepriceofaniOSdevice.

AsofJanuarythisyear,we'vereachedatippingpointwitha$50phone,accordingtoOxford.Thisflingsthedoorswidetodevelopingnationsandopensanewworldofpossibilitiesforapps.Wecancreatemeaningfulexperiencesthatwilltransformtheworld.PhonesarenowhalfthepriceofanOneLaptopPerChildlaptopandarguablymorepowerfultoempowernewpeopletojointheglobalstage.

AtGoogleI/O,theyunveiledAndroidOne.ThissystemofpartnershipsbetweenOEMsandGooglewillrapidlyaccelerateadoptioninemergingmarketslikelysurpassingcurrentprojections.ThisprojectcoupledwithotherinitiativestobringfasterInternetconnectionstothe"dark"regionsoftheworldwillrapidlyacceleratetechnologyinthoselocations.

Emergingmarkets,suchasChina,Russia,andIndiaarethefastestgrowingsegment,whichprovidesplentyofnewusecasesandproblemstosolve.

"Shipmentswillmorethandoublebetweennowand2018withinkeyemergingmarkets,includingIndia,Indonesia,andRussia.Inaddition,Chinawillaccountfornearlyathirdofallsmartphoneshipmentsin2018."

AccordingtoOxford,"two-thirdsofSouthAfricanswillhaveamobiledatasubscriptionby2017,morethandoubling"thecurrentusage.Also,predictionsestimatethat"mobiledatasubscriptionsinNigeriaandKenyawillrisefromfourpercent"toapproximately25%.

Howcanyoubestimpactthosemarkets?

Sherman,J.February18,2014.Retrievedfromhttp://www.digitaltrends.com/mobile/android-way-cheaper-than-ios/.

WorldPhone

References

Oxford,A.January31,2014.Sub-$50AndroidsmartphonehitsSouthAfricaasMTNlaunchesSteppa.Retrievedfromhttp://www.zdnet.com/sub-50-android-smartphone-hits-south-africa-as-mtn-launches-steppa-7000025828/.Oxford,A.September19,2013.Two-thirdsofSouthAfricanswillbeonlineby2017asmobiledatabooms,Retrievedfromhttp://www.zdnet.com/two-thirds-of-south-africans-will-be-online-by-2017-as-mobile-data-booms-7000020901/.SmartphoneMomentumStillEvidentwithShipmentsExpectedtoReach1.2Billionin2014andGrowing23.1%Over2013.May28,2014.Retrievedfromhttp://www.idc.com/getdoc.jsp?containerId=prUS24857114.

Androidhasbeenevolvingforthelastseveralyearsandexpandingitsreachthroughvariousphonesandtablets.AtGoogleI/O2014,theyannouncedthattheyarestandardizingtheAndroidlandscapeacrossphones,tablets,inadditiontowearabletechnologysuchasGlassandWear,TVandevencars!AllofthesedevicesruntheAndroidOSandgiveyoumanyavenuestocreateinnovativenewsystems.

OneofthelatestadditionstotheunifiedplatformisAndroidinwatchform.

Thisexcitingnewplatformnotonlyprovidesnotifications(similartothestatusbaronyourphone),butalsoprovidesnewmodesofinteraction.Ifyouhaveanexistingapplicationwithnotifications,youalreadyhaveapresenceonWear.

Ifyou'reinterestedinWear,checkoutAndroid'swebsite:http://developer.android.com/training/building-wearables.html

GoogleGlassisanotificationengine,camera,videorecorder,andapplicationhostonyourface.Controversyaside,thereareplentyofinterestingtechnicalaspectstoexplore.

TherearetwobasicflavorsofGlassapps.FirstyoucanwriteapplicationswiththemirrorAPI,whichdeliverscontenttoyourGlassusingyourownbackend.YoudeliverHTML-basedcardsfordisplay.

TheotheroptionistowritenativeAndroidapplicationsusingtheGlassDevelopmentKit(GDK).Ifyou'reinterestedindevelopingGlassapps,checkoutthedeveloperwebsite:https://developers.google.com/glass/develop/gdk/

Google'slatestattemptatputtingAndroidonyourTVwasannouncedatGoogleI/Othisyear.InsteadofrunningaforkofAndroid,astheill-fatedGoogleTVdid,itnowrunsfull,nativeAndroid.Italsohascastingabilitiesbuiltin(integratedChromecast).

Ifyou'reinterestedindevelopingTVapps,here'smoreinfo:http://developer.android.com/preview/tv/start/index.html

Weknowrelativelylittleabouttheplatformsinceitwasrecentlyannounced,butit'llworkasaseconddisplayandaninputdevice.YourappswillrunontheintegratedAndroiddeviceinthedashboard(notonthecar).

DeviceEcosystem

AndroidWear

GoogleGlass

AndroidTV

AndroidAuto

DesigningamobileapplicationisverydifferentfromdesigningforaPC.OnaPC,youcanassumefastprocessors,sizablememory,lotsofstoragespace,andalargedisplay.Usersaregenerallyexpectingtospendalotoftimeinyourapplicationtoaccomplishalargergoal,suchaswritingabookordoingtheirfinances.

Amobilephoneisaverydifferentdevice!Usersinteractwithitinverydifferentwaysthantheydowithanormalcomputer.Theyareoftenaccomplishingshorttaskswhileonthego.

AccordingtoMeier,"comparedtodesktopornotebookcomputers,mobiledeviceshaverelatively:

LowprocessingpowerLimitedRAMLimitedpermanentstoragecapacitySmallscreenswithlowresolutionHighcostsassociatedwithdatatransferIntermittentconnectivity,slowdatatransferrates,andhighlatencyUnreliabledataconnectionsLimitedbatterylife"

Mobilephonebatteriesarenotoriousforquicklylosingachargeandpeoplegetveryfrustratedwhentheycan'tusetheirphoneforanentireday.Manypeoplecarryaboutbatteryboostersandchargerssothattheywillhaveaccesstotheirphonesafteradayofheavyusage.Youshouldwriteyourapplicationstobeabatteryfriendlyaspossible.

Thisisevenmoreimportantinthefurtherflungregionsoftheworld,whereKochisharesthat"rechargingyourphoneeverynightisnotanoptionifyouliveinaruralvillagewithoutelectricity.AtoneofUNICEF'sprojectsinruralSenegal,Iencounteredavillageentrepreneurwhostartedabusinesswherehewouldcollecteveryone'scellphonesandforasmallfee,biketoanelectrifiedvillageafewhoursaway,thenbikebackwithphonesatfullcharge."

Kochifurtherstatesthat,"peopleinthesecountriesspendalotofmoneytokeeptheirphonescharged.Developingaphonewhosebatterylastsforaweek,"andapplicationsthatdon'tneedlesslywastebatterypower,"wouldunlocksmartphonestoalargemarketsegment."

It'sexpensivetopurchasedata.We'refairlyluckyintheUnitedStatestohaveubiquitousaccesstonetworksonthegoandaffordableplans.That'snotalwaysthecase,eveninotherdevelopednations.

Tobeabetterdevicecitizen,limittheamountofdatayoudownloadwhileonmobilenetworksandmaximizetheamountyoudownloadanduploadwhenusershaveafasterconnection,suchasWi-Fi.

Youhavenoideawhatdevicewillberunningyourapplication,especiallysincetheAndroidOSiseverexpandingtonewdevicesandformfactors.Youmustdesignresponsiveappsthatscaletothemultitudeofdevicesonwhichyourapplicationcouldrun.

DesignConsiderations

Hardwareconsiderations

Batteryusage

Datausage

Unknownenvironments

Anotherthingtokeepinmindisthatyouruser'sattentionspanismuchshorterwhenusingaportabledevice.Usersareusuallyengagedinadifferentactivitywhenusingyourapp,e.g.attendingaparty.ShortburstsofactivitylikesharingapictureonInstagram,sendingatweetaboutthefestivities,orsendingatexttomeetupwiththeirfriendsisthenameofthegame.

Youalsocan'tassumethatyouhavetheirfullattentionspanforlong.Youwantyourdesignstobebeautifulandintuitivetohelpthemquicklyaccomplishtheirtask.

Youdon'twantyouruserstobesurprisedbyyourapplication.Youwanttomakesurethatyourdesignsareintuitiveandbehaveinwaysthatareeasytounderstand.Ageneralruleofthumbisifyouneedalengthytutorialtointroduceyourusertotheinterface,it'sprobablytoocomplicated!

Youalsodon'twantuserssurprisedbyabackgroundactionorlocation-basedactionthattheyhaven'texplicitlysignedupfor.Agreatexampleofwhatnottodoisregularlyannoyingthemwithnotificationsaboutratingyourapplicationorsendingadswhentheyhaven'trequestedthem.

Kochi,E.May27,2012.Retrievedfromhttp://techcrunch.com/2012/05/27/mobile-developing-world/.Meier,Reto(2012-04-05).ProfessionalAndroid4ApplicationDevelopment(KindleLocations1123-1128).JohnWileyandSons.KindleEdition.

Attentionspan

Principleofleastsurprise

References

Inseveralculturestabletsandevenphonesareviewedascommunaldevicesthataresharedforthebenefitofthecommunity.ThatisadifferentmodelthanwetypicallyassumeintheUnitedStates!

Herearesomeofthemostinterestingemergingusecasesindevelopingnations.

AccordingtoKochi,"airtimehasbecomeanotherformofcurrency.Imagineyouneedtogetasmallamountofmoneytoyoursisterwholivesinavillagethat'stenhoursdriveaway.Theeasiestwayforyoutodothatistobuysomeairtime,butinsteadoftoppingupyourownprepaidmobileserviceyoutopuphers.Forasmallfee,shecannowgoandcashoutthisairtimewithanagentthatsellsairtime."

Ogunlesialsosharesthatphonesareableto"abletotransformordinarycitizensdisenchantedbytheirgovernments,intoresistancefighters."Theabilitytosharepicturesandtextinrealtimeisapowerfulwaytofightbrutaland/orcorruptregimes.Ontheflipside,theycanmakecitizenseasiertotrack.

MobilephonescanspeedreconnectionwithlovedonesinrefugeecampsbyprovidingaSMSorotherregistryfordisplacedpersons(Ogunlesi).Theycouldalsobeusedtocoordinatevolunteereffortsontheground.

AccordingtoOgunlesi,"byservingasplatformsforsharingweatherinformation,marketprices,andmicro-insuranceschemes,mobilephonesareallowingAfrica'sfarmerstomakebetterdecisions,translatingintohigher-earningpotentials.Farmersareabletosendatextmessagetofindoutcroppricesinplacesthousandsofkilometersaway."

AccordingtoTsao,inUganda,"lessthan21%ofbirthsofchildrenlessthanfiveyearsoldareregistered."Amobileplatformwasdevelopedsothat"individualscanregisterbirthsanddeaths."

Also"malaria,adiseaseaffectingnearly3.5billionpeople,hastheopportunitytobethefirstdiseasebeatenentirelybymobile."Thereareseveraleffortsincludingamobileremindersforusingbednets,enabledonations,andincreaseaccesstotestingandtreatment(Tsao).

"Traffickers,throughtheuseofmobiles,areabletoorganize,advertise,andstreamlinetheirillicitactivitieswhileexpandingtheircriminalnetworks.Asaconsequence,morepeopleareenslavedthanattheheightoftheAtlantictrade,andpartlyduetoanadditiveabilitytocommunicate."MobileprovidesavarietyoftoolsthatcouldmakethisamuchriskierbusinessbyincreasingcommunicationcapabilitiesandphysicaltrackingthroughGPS(Tsao).

Ogunlesi,T.andBusari,S.September14,2012.Retrievedfromhttp://www.cnn.com/2012/09/13/world/africa/mobile-

EmergingUseCases

MobilePayments

Activism

DisasterManagement

Agriculture

Health

HumanTrafficking

References

phones-change-africa/.Kochi,E.May27,2012.Retrievedfromhttp://techcrunch.com/2012/05/27/mobile-developing-world/.Tsao,C.October,8,2013.Retrievedfromhttp://www.huffingtonpost.com/clara-tsao/6-ways-mobile-techology-h_b_4054076.html.

IcompletelyagreewithMartinFowler:

Tome,legacycodeissimplycodewithouttests....Codewithouttestsisbadcode.Itdoesn'tmatterhowwellwrittenitis;itdoesn'tmatterhowprettyorobject-orientedorwell-encapsulateditis.Withtests,wecanchangethebehaviorofourcodequicklyandverifiably.Withoutthem,wereallydon'tknowifourcodeisgettingbetterorworse.

Unittestingisafundamentalaspectofcomputersciencethatisoftenignored.WenevertalkedaboutitincollegeandIdidn'tstarthearingmuchaboutituntilafewyearsintomycodingcareer.

Iamafairlyrecentconverttounittesting.AtfirstIdidn'tseethevalue.Itfeltlikeextrawork.Afewyearsago,IspentthreemonthsofintensepairingwithanotherAndroiddeveloperanditchangedmywholeoutlook!Seeinghowmuchwewroteeachdayandhowmuchconfidenceweendedupwithinourdesignwasrefreshing.ItwasadeparturefromothergroupsIhadworkedwiththatonlyvaluedquickcode.Thismentalityencouragesgunslinging,cowboycoders.

Manylanguagesandframeworkshighlyvaluetesting,butit'sanareathatAndroidoverlooked.TherearesometestingcapabilitiesinAndroid,buttheyrelyontheemulatororanattacheddevicesandaretooslowtouseastheprimarymeansoftestingduringthedevelopmentphase.Thistypeoftestingisbettersuitedforfunctionaland/orintegration-basedtestingoffeaturesinyourapplication.

Whennotusingtesting,thealternativeistobuildtheapplicationandseewhathappens,lookatapptoverifyexpectedbehavior,andreadlogs.It'snotterriblyefficient!

Unittestingisabestpractice,buthasbeenparticularlydifficultinAndroid.OnelibrarythatmakesthisprocessmuchsimplerisRobolectric.

Robolectricallowsyoutofocuscloselyontheapplicationyouarebuildingasyoubuildoutpiecebypiece.Youwritejustenoughcodetopassthetests.Itallowsyoutodotargetedandbroadrefactoringwithoutworryingaboutbreakingtherestofthesystem.Ithelpsuswritebettercodeandhelpskeepusontrack.

RobolectricwascreatedtoruncoreAndroidcomponentsontheJVMandallowdeveloperstoverifyaspectsoftheircodeastheyaredevelopinginsteadofafterthefeaturehasbeendeployedtoanemulatorordevice.

RunningtestsonanAndroidemulatorordeviceisslow!Building,deploying,andlaunchingtheappoftentakesaminuteormore.That'snowaytodoTDD.Theremustbeabetterway.

Wouldn'titbenicetorunyourAndroidtestsdirectlyfrominsideyourIDE?Perhapsyou'vetried,andbeenthwartedbythedreadedjava.lang.RuntimeException:Stub!?

Robolectricisaunittestframeworkthatde-fangstheAndroidSDKjarsoyoucantest-drivethedevelopmentofyourAndroidapp.TestsruninsidetheJVMonyourworkstationinseconds.

Chapter2:TDDwithRobolectric

Android

Robolectric

ThislabwillwalkyouthroughusingIntelliJtogeneratetheprojectandmaventomakeintegrateRobolectric.

AftercreatinganAndroidprojectwiththewizard,youmovethesourcefilesintoamvn-likestructure.ThenyouconfiguremodulesettingsinIntelliJ.ToinstallRobolectric,youwilladdapomfile(mavendependencyfile)intotheproject.Finally,youwillwriteyourfirsttestandrunitinsidetheIDE.

Integrationcanbetricky,especiallywhencreatingaprojectfromscratch.I'mahugefanoflivinginIDE-landasmuchaspossible,sothisapproachminimizescommandlineworkandmanualprojectconfiguration.

AversionofthisCalculatorprojectcanbefoundhere:CalculatorLab.

Ithastagsforallthemajorstepstohelpyouasyouworkthroughthelabs.Ifyouwantedtofollowalongfromthebeginning,startwiththetag2.2-step1.Eachtagmatchesupwiththechapter'ssectionnumbers.

YouhaveinstalledIntelliJ(CEedition).YouhaveinstalledtheAndroidSDKandconfiguredIntelliJtouseit(tutorialhere).Youhavemaveninstalled.Youhaveinstalledmaven-android-sdk-deployeranddeployedatleastoneSDK,butpreferablyall,toyourlocal~/.m2/repository.

Adaptedfrom:Latislaw,C.August3,2012.IntegratingRobolectricwithIntelliJ.Retrievedfromhttp://chariotsolutions.com/blog/post/integrating-robolectric-with-intellij/.

LabBackground

github

Prerequisites

References

UsetheIntelliJAndroidwizardtocreateaHelloWorldproject.First,choosethestoragelocationandplatform.

Onthenextscreen:

NameyourapplicationCalculatorCreatea"Hello,World!activity"andnameitCalculatorActivitySetthepackagenametocom.mobiquity.calculatorChoose"USBdevice"asthe"TargetDevice"

RobolectricIntegration

Step1:CreateAndroidproject

UseIntelliJorthecommandlinetomovefilesintothefollowingstructure:

src/main/java/...src/test/java/...

Note:IntelliJmightnotlikeitwhenyouaddsubdirectoriestothefoldermarkedassource.Ifyouarehavingtroublesettingupthedirectorystructure,openthescreenshowninthenextstepandremovetheoldsourcefolderbeforeaddingnewsubfolders.

UpdatemodulesettingsinIntelliJtorecognizethesourceandtestdirectories(below:bluefolderissourceandtestfolderisgreen).

Step2:Setupdirectoriesformaven

Step3:ConfigureIntelliJsourceandtestfolders

Afteryouaredone,yourprojectshouldlooksomethinglikethis:

Copythissamplepom.xmlintoliveintherootofyourproject.ChangethegroupIdtosuityourproject(e.g.com.mobiquity.calculator).Ifdesired,alsoedittheartifactId,version,andnamevalues.

Check"MavenProjects"viewinIntelliJtoensurethatitlookssomethinglikethis:

Step4:IntegrateRobolectric

Step5:Maven

Ifyouseeerrors,youmayjustneedtorefreshandwaitforittofinishindexing/importingyourlibraries.ItmayhelptorunmvninstallonthecommandlineandrestartIntelliJ.

Ifyouarestillhavingissues,yourAndroidfacetmaybetheproblem.OpentheAndroidfacetforyourprojectandchangeto"GeneratebyIDE."

Adaptedfrom:Latislaw,C.August3,2012.IntegratingRobolectricwithIntelliJ.Retrievedfromhttp://chariotsolutions.com/blog/post/integrating-robolectric-with-intellij/.

References

Let'swriteourfirsttest!

IusetheIDEtogenerateatestinthecorrectfolder.OpenCalculatorActivity.javaandplaceyourcursoronthenameoftheclass.

UsetheMackeycombinationCommand+Shift+Ttocreatethetestforthisclass.

Lab:FirstTest

Step1:Createtestfile

WeneedRobolectric'shelptorunourtests.Addthislineabovethetestclassnameandimportassociatedclasses.

@RunWith(RobolectricTestRunner.class)

Step2:Testrunner

Addafieldfortheactivityundertestsothatwecanaccessitinallofthetestsinthisclass.

CalculatorActivityactivity;

ThenusesetUp()topopulateourfield.

@BeforepublicvoidsetUp()throwsException{activity=Robolectric.buildActivity(CalculatorActivity.class).create().start().resume().get();}

WeusetheRobolectriclifecyclemanagementfunctionstobuildandstartanactivity.Thelastfunctioncall,get(),returnsatestinstancethatyoucanusetoverifyvariousaspectsoftheactivity'sviewandbehavior.

Note:Thecallstocreate(),start(),andresume()referencethedifferentphasesofAndroid'sactivitylifecycle.ThiswillbecoveredindetailinChapter6:ManagingtheLifecycle.

Writeatestfortheactivity.

@TestpublicvoidshouldNotBeNull()throwsException{assertNotNull(activity);}

Youcouldruneachtestindividuallyasyouworkwithnewclasses,howeveritshouldbeacommontasktorunalltheunittests(e.g.priortocommit).Icreatearunconfigurationforthewholeproject.Let'screatearunconfigurationthatwillrunallthetestsatonce.

First,choose"EditConfigurations..."fromthe"Run"dropdownmenu.

Then,hitthe+buttonandchooseJUnit.

Step3:Setup

Step4:Test

Step5:Createarunconfigforalltests

Thenselect,"Allinpackage"andgiveyourconfigurationadescriptivename.

Usetherunconfigurationcreatedintheprevioussteptoensureourtestspass.

Ifyouforgotstep2,you'llseethiserrormessage:

java.lang.RuntimeException:Stub!atandroid.content.Context.(Context.java:4)atandroid.content.ContextWrapper.(ContextWrapper.java:5)atandroid.view.ContextThemeWrapper.(ContextThemeWrapper.java:5)atandroid.app.Activity.(Activity.java:6)...

Inthefuture,youcanrightclickonthetestfilenameoramethodnametorunatest,useakeyboardshortcut,orrunthemfromthecommandlinewithmvncleaninstall.

Ifyouarestillseeingissues,rebuildyourprojectafewtimestoconvinceIntelliJtogeneratetheR.javafile(whichlinkstoallyourapplicationsresources)and/orrunmvninstallfromthecommandline.

WecanuseIntelliJ'stoolsorthecommandlinetocommitourchangestoagitrepository.Thisstepshowsyoudetailsfor

Step6:Run

Step7:IntelliJgitintegration

theIDEroute.

FirstwewanttotellIntelliJthatwewillbeworkinginagitrepository.UsethedropdownmenuVCS->ImportintoVersionControl->CreateGitRepositorytocompletethisstep.

TODO:Insertimage

Afterwehaveintegratedgit,let'sviewourcurrentchangeset.UsethedropdownmenuVCS->ShowChangesViewtoseeourcurrentchangeset.

TODO:Insertimage

Beforewecommit,weneedtomakesurethatwe'rehappythefileslistedinourchangeset.Thereareseveralfilesweshouldignore,includingIntelliJ'sprojectfileslocatedinthe.idea/folder,the.imlfileforyourproject,andthegen/directory(usedbehindthescenesduringthebuildprocess).Let'suseIntelliJ'stoolstodothiswithintheIDE.

TODO:Insertimage

Note:TheIntelliJwizardaddsafewfileswewon'tneedsincewe'renotusingtheantbuildtool.WecansafelydeletethesefilesinsidetheIDEbyrightclickingonthefileandselectingdelete.Thesefilesareant.properties,build.xml,project.properties,local.propertiesandthebin/directory.

Note:Wealsoremoveproguard-project.txtforthetimebeing.Ifproguardisdesiredforyourproject,youcanconfigureitusingthisfile.

Oncewe'rehappywiththechangeset,let'scommit.Youshouldalwaysreviewthefilesandchangesyou'reabouttocommitafterpassingallprojecttests.

TODO:Insertimage

Nowlet'stalkaboutwhattotest!

Adaptedandexpanded:Latislaw,C.August3,2012.IntegratingRobolectricwithIntelliJ.Retrievedfromhttp://chariotsolutions.com/blog/post/integrating-robolectric-with-intellij/.

References

Inthissection,we'llcoversomeofthemostcommontypesoftestcasesandbestpracticestoconsiderwhendeterminingyourtestingstrategy.

Youshouldfocusyourunittestingonbusinesslogic,basicviewvalidation,andfunctionality.Youcanvalidatecertainrequirementsverywellwithunittesting(e.g."whenIclickthisbellimage,itwhistles"or"allactivitieshavealogoonthescreen").

Herearesomecommonexamples:

Ensuretheactivityandviewelementsarenotnull.Ensureexpectedfragmentandviewelementsarevisibleonthescreen.Ensurethattheproperresourcesareusedforviewelements.Ensureitemsarehiddenwhenexpected.Ensuretoastsareshown.Ensurethatyourintentstartsthecorrectthing.

Idon'trecommendinvestingmuchtimeinverifyinglessimportantstylingdetailsandXMLattributes.Youruserinterfaceislikelytochangemanytimesaweek,buttypicallythebasicviewelementsandtheirbehaviorremainthesame.Ifyouupdatedatesteachtimeabuttonhadnewpadding,thatwouldgetverytediousindeed!

Theapplogois250dphighwithaproportionalwidth,thefilenameismain_logo.png,ithasa20dpleftmarginand12dprightmargin,hasacontentdescriptionof"Text",andiscenteredverticallyoneveryscreen.

ReturnsstartdiminishingprettyquicklywhenyouverifyeverypossibleXMLattribute!Yourtimeisbestspentonitemsthatarerelevanttobusinessobjectives.Fromthisexample,likelythemostbangforyourbuckwillcomefromtestingthattheproperimageisusedandmakingsurethatitappearsonallexpectedscreens.

Rememberanyoftheattributesyoudon'ttestcanbecaughtbydesigners,qualityassurance,business,product,and/ortheengineers.Asolidstrategyistosweeptheappneardeploymentwithadesignertomakesuretheappappearsasexpectedonawiderangeofdevices.

SimpleAnimation

Latislaw,C.August7,2012.AndroidUnitTestingWithRobolectric.Retrievedfromhttp://chariotsolutions.com/blog/post/android-unit-testing-with-robolectric/.

TestingConsiderations

WhatToTest

WhatNotToTest

Example

AdditionalExamples

References

Aswithmostobjectorientedrealms,attempttosimplifythearchitectureasmuchaspossible.Dothisbycreatingabstractorbaseobjectsorinterfaces.Thiswayyoucantestsharedbehaviorinoneplaceinsteadofseveral,whichsimplifiestestsandreducescodeduplication.

Oftenwewanttoensurethatacertainactionwasperformedbutnotactuallyrunthecode.Todothis,youcreateatestclasswhichextendstheclassundertestandoverride/mockout/trackthataparticularfunctionwascalled.

Forexample,ifyouwantaparticularclicktomakeanAPIcall,thereisnoneedtomaketheactualcall(sincethiswouldbeanintegrationleveltestanyway).Youcanusethisstrategytotrackthatthefunctionthatinvokesthecallhasbeencalled,butavoidmakingtheactualcall.

Thisiscanalsobehelpfulwhenanoperationcrashestheunittestingframework(e.g.specialtylibrarythatcausesfunkysideeffects),doesn'tplaynice,orisotherwiseunnecessarytoinvokedirectly.

Icreateseveralutilityclassestoimprovethereadabilityofmycode.Theseliveinmyteststructureunderthepackagesupport.We'lladdthesefilesinthenextlab.

Androidstronglyencouragestheuseofabstractingstringresourcesintooneplaceoverusinghard-codedstringconstants.Iliketofollowasimilarpatternanduseatestconstantsclasswhenyouhavelotsoftestdata.ThiscanbereallyhelpfulwhencreatingauserwithlotsoffieldstomockoutaJSONresponse.

Ifyoufindyourselfwritingsomethingmorethanonce,that'sanexcellenttimetoreassess.LuckilysinceyouwillhavealargebaseofunittestsatyourdisposalaswellaspowerfulIDEtools,therefactoringwillhaveminimalimpactontherestofthesystem!

Finally,youshouldn'trelysolelyonunitteststoensuretheproperbehaviorofyourapp.Thesetests,thoughquiteuseful,onlygiveyouasmallwindowintoyourappandit'sbehavior.Atminimum,youshouldincludeintegrationleveltestsandhavesomelevelofmanualQAintheprocesstoensureyourappiseverythingthatyouwantittobe.

Latislaw,C.August7,2012.AndroidUnitTestingWithRobolectric.Retrievedfromhttp://chariotsolutions.com/blog/post/android-unit-testing-with-robolectric/.

BestPractices

SimplifyYourArchitecture

Mock/StubFunctionality

UtilityFunctions

CentralizeTestConstants

Don'tRepeatYourself(DRY)

RobustTestingStrategy

References

Let'saddutilityfunctionstooursupportpackage.It'llhelpreducethesomeoftheboilerplatewhenweworkthroughlaterlabs.

TechnicallywithTDDyou'dwaituntiltheexactmomentyouneedthecodetowriteit.Ipreferpracticalityoverbeingpedantic.

publicclassAssert{publicstaticvoidassertViewIsVisible(Viewview){assertNotNull(view);assertThat(view.getVisibility(),equalTo(View.VISIBLE));}}

publicclassResourceLocator{publicstaticStringgetString(intstringId){returnRobolectric.application.getString(stringId);}

publicstaticDrawablegetDrawable(intdrawableId){returnRobolectric.application.getResources().getDrawable(drawableId);}}

WiththeversionofRobolectricwe'reusing,weneedtomakeourownversionofafragmentstarter.

Robolectrichasoneforsupportfragments,butdoesn'thaveonefor"normal"platformfragments.Thisshouldbeinanupcomingrelease.We'vecopiedtheirframeworkversionhereandmodifiedtousenormalfragments.YoucanfindthelatestsourceforFragmentTestUtilongithub.

publicclassFragmentUtil{publicstaticvoidstartFragment(Fragmentfragment){Activityactivity=createActivity();

FragmentManagerfragmentManager=activity.getFragmentManager();fragmentManager.beginTransaction().add(fragment,null).commit();}

privatestaticActivitycreateActivity(){returnRobolectric.buildActivity(Activity.class)

Lab:UtilityFunctions

CreateAssert.java

CreateResourceLocator.java

CreateFragmentUtil.java

.create().start().resume().get();}}

Therearemanyotherformsoftestingthatyoucanincorporateintoyourdevelopmentlifecycle.Theseothertoolsareoutsidethescopeofthisbook,butarelistedhereforeasyreferenceandfutureexploration.

HerearetheAndroidsanctionedwaystotest.

YouuseJunitstyletestsandcreateatestapplicationthatrunswithyournormalapplication.Thetestapplicationexercisestheuserinterface.

Itcanbegreatforfunctionalorintegrationtesting,butsinceitreliesonanemulator,it'sjusttooslowforas-you-are-building-a-featuretesting.

http://developer.android.com/tools/testing/testing_android.html

Thistestingframeworkrunsonthedeviceandusesaccessibilityfeaturestoconductfunctionaltesting.

http://developer.android.com/tools/help/uiautomator/index.html

ThisframeworkallowsyoutoscripttestinPythonandrunsyourtestsonanemulator.http://developer.android.com/tools/help/monkeyrunner_concepts.html

Therearemanytoolsoutthere.Eachapplicationmayleadtoadifferentselection!

Calabash:http://calaba.sh/Robotium:https://code.google.com/p/robotium/Appium:http://appium.io/

OtherTesting

Android

InstrumentationTesting

uiautomator

monkeyrunner

OtherTools

NowthatyouknowwhyAndroidissuchacompellingsystem,let'slookathowthesystemisconstructed.AlotofpainandsufferingcanbesparedifwefollowAndroid'sconventionsandlooselycoupledmodel.Writingcodethiswaymakesiteasiertowriteandmaintain.Weshouldstrivenotonlytomakebeautifulcode,butalsoengagingpersonal,andfastexperiencesforourusers.

TherearemanylayersofdecouplingintheAndroidsystem.Theapplicationsareindependententitiesthatcansendmessages,butneverknowtoomuchabouteachother.

Themodelisabstractedawayfromthedisplayofthedataandaccessedbycontentprovidersandothermechanisms.

ViewsareabstractedfromthebusinesslogicandintoXMLfilesthatmakeiteasytochangetheappearanceoftheviewwithoutchangingthewaythattheviewworks.

Viewsarealsodecoupledfromtheresourcesthattheyuseandthelogicfromchoosingwhichviewisrightfortheparticulardeviceitisrunningon.

Assetsandothercontentareabstractedfromtheviewandbusinesslogicsothatthecontentcanchangewithoutrequiringanupdateinthecodetosupportsmallcopychanges.

Chapter3:Architecture

AndroidisanopensourcesoftwareandhardwaresystemthatsitsontopofaLinuxkernel.ItalsoincludesdevicesandthesetofapplicationsthatrunontheOS.

YoucanbrowsethesourceAndroidOpenSourceProject(AOSP)atsource.android.com.

Android'sarchitecturehasmanylayers.

Ifyou'dlikedetailedinformationaboutthestackandAndroid'ssecurityfeatures,youcanreadmorehere:http://source.android.com/devices/tech/security/index.html

Thetopofthestackiswhereallthebuiltinapplications,3rdpartyapplications,andyourapplicationslive.Allappsherearecreatedequalandhavethesameaccesstotherestofthestack.

Android

ArchitectureLayers

Thesecondlayerincludestheapplicationframework,whichgivesyouthetoolstowriteapplications,suchastheSDK,activitymanagers,locationmanagers,notificationmanagers,andtheviewsystem.

ThehardwareaccesslayeriswherelibrariesarelocatedforinteractingwithGPS,Wi-Fi,Bluetooth,NFC,andotherhardwarefeatures.Theruntimeisalsoatthislayer.

Eachapplicationrunsinit'sownvirtualmachine(VM)instance,whichmeansthatapplicationscannotdirectlyinvadeeachother'sprocessspace.ThesystemprovidesLinux-stylepermissioncontrolswhilemaintaininganopensystemthroughIntentsandotherinterprocesscommunicationcapabilities.

Atit'slowestlevel,theLinuxkernelhandlesdrivers,powermanagement,andotherlowlevelprocesses.

ThecompilationphasesincludeturningyourJavafilesinto.dexbytecodefiles,whichisAndroid'sversionofJavabytecode.AnR.javafileiscreatedsothatJavacanrefertotheXMLcomponentsandotherapplicationresources.

Theoutputofcompilationisan.apk,whichatit'sheartisbasicallya.zipfile.

Here'smoredetailhereaboutthestagesofcompilation:http://developer.android.com/tools/building/index.html

DEXbytecodeisrunonavirtualmachine(muchlikeJavarunsontheJVM),calledtheDVM,orDalvikVirtualMachine.TheDVMwaswrittentobeoptimizedformobiledevices.

Getallthelowleveldetailshere:https://source.android.com/devices/tech/dalvik/index.html

InthefuturetheDVMwillbereplacedwiththenewAndroidRunTime(ART).

Yourapplication'sresourcesareboundatruntimewhenAndroiddetermineswhichdeviceitisrunningonandchoosesthebestresourcesforthatparticulardevice.

Intentsarealsoaruntimebinding.Youissuearequestandanyappthatcanrespondtotherequestwill.Theuserchooseswhichactiontotakebasedonaparticulartypeofrequestorthesystemusesuser'sdefaults.

Applicationsaresignedwithakey.Thiscombinedwiththeuniquepackagenameiswhatidentifiesanapplicationonthesystem.

Bydefault,whenyoucreatedevelopmentbuilds,youareusingadefaultkeytosignyourapplication.Youwilluseadifferentkeywithapasswordwhenyouprepareforrelease.

Note:Onceyoudeployyourapplicationwiththisreleasekeyyouareforeverstuckwiththekeyandpackagename.That'swhyit'ssoimportanttodeterminewhatyou'dliketouseforyourpackagenameandtoalwayskeepyourreleasekeysafe!

Note:It'spossibletohavebothadebugandreleasesignedversionofthesameapplicationonyourdevicesincethepackagenameandsignatureareusedtogethertoidentifyanapplication.

Compilation

Runtime

Signing

Thereareabstractionsateveryleveltohelpyouseparateconcerns,maintaincodeeasier,andsupportthemultitudeofdevicesandformfactorsinthewild.Androidgivesyoutoolstotodecouplethepresentationlayerfromthebusinesslogic.

AlthoughsomearguethatAndroidisnotatrueMVCsystem,it'shelpfultoapproachitinthisway.

ModelViewController

Theviewandresourcesystemallowsustobreakoutvisualcomponents.Androidautomaticallyhandlesmostofthelogic

View

aboutchoosingwhichcomponenttouseforwhichformfactor.YouspecifythisinXMLandputinspecialfolders.Thisenablesscalingtodifferentformfactorsaswellasinternationalization.

TheJavalayeriswhereyoutiethevisualcomponentstothebusinesslogicofyourapplicationandwhereyouwouldaccessthemodelordataofyoursystem.Serviceswouldalsofallintothislayer.

Finally,themodellayeriswhereyouwouldstorethedatathatpowerstheapplication.ContentprovidersallowyoutoabstractSQLqueriesawayfromyourmodel'susersandsurfacedatathroughouttheapplicationandsystemwide,ifyoudesire.

Controller

Model

Anapplicationismadeupofaseriesofactivityscreens.Thesearestrungtogetherwithintentstostartupthenextactivity.Activitiesarebuildofviewsandfragments.Fragmentsarebuiltfromviews.

Activitiesarethemajorbuildingblocksofyourapplicationandareroughlythescreensthatyouseeinanapplication.Theyusefragmentsandviewstoconstructtheuserinterfacethatyousee.

Activitiesarethemajorbuildingblocksofyourapplicationandarethepresentationlayer,orscreensyouseeinanapplication.Activitiesarecomposedofviewsandfragmentsandseveralactivitiesarecombinedtomakeanapplication.

Fromtheactivityyouhaveaccesstoalltheviews,resources,systemstate,andthemodel.

Servicesareusedforlongrunningapplications,suchasnetworkoperations.

Thisisanapplicationwithtextviewsandbuttons.Whenweclickonthebuttonitlaunchesanactivity.

BuildingBlocks

Example:

We'llgooveralloftheseingreaterdetailinlaterchapters.

Intentsallowmessagepassingandlateruntimebindingbetweencomponents.Basicallyyoubroadcastadesire,suchasopeningawebbrowseroraspecificActivityyoucreated.Androidhandlestherest.

Agoodexampleiswhensharingapictureyousnappedwithasocialnetwork.Youhaveoptions,suchasTwitter,Instagram,etc.dependingonwhatyouhaveinstalled.Ifyouarewritingacameraapplication,youdon'thavetocareabouthowsomeoneplanstosharethepicture,justthattheyareabletodoitinthemannertheywish.

MessagePassing

Intents

Usingintentsfreesyoutofocusoncreatingthecontentthatisimportanttoyourapplication,notimplementingorforcingpeopletouseaparticularmethod.Itmakesyourappaparticipantinthesysteminsteadofaself-containedappthatmust

handleeverythingbyitself.You'repartofthecommunity!

Youhaveseveraloptionswithwheninvokinganintent:

Startoneofyourapplication'sowncomponents(e.g.byusingstartActivity()withaninternalclass).Thiskeepstheintentwithinthecurrentprocess'boundaries.Sendanintentforanactivityfromanotherapplicationthatcrossesprocessboundaries.Broadcastasystem-wideintent,suchasopeningawebbrowserorsharingapieceofcontent.Thisalsocrossesprocessboundaries.Thesystempresentstheuserwithanoptionofhowtoreacttotherequest.

Inthisexample,wearegettingareferencetoabuttonandsettingaclicklistenerthatstartsaninternalactivity.

findViewById(R.id.activity_button).setOnClickListener(newView.OnClickListener(){@OverridepublicvoidonClick(Viewv){startActivity(ViewSystemActivity.createIntent(LooselyCoupledActivity.this));}};)

Eventbusesareagreatwaytodecoupleourcomponentswithoutusingainterfaceorlistenerpatternthatcanproducealotofboilerplatecode.Youcanuseanapplication-widebus,suchasOtto,topassmessages.

CodeExample

EventBus

Androidisaneventdrivensystem.ThemainUIthreadloopsindefinitelywaitingforaneweventoruserinput.Whensomethingisreceived,itisprocessed.

Ifadditionalprocessingisrequiredforaparticulareventthatincludesalongrunningoperation,itshouldbedoneinanotherthread.Examplesoflongrunningprocessesarenetworkdownloads,databaselookups,orfileI/O.

Ifyouattempttodolongrunningprocessingonthemainthread,it'slikelyyouwilleithergetanexceptionoractivitynotrespondingdialog(ANR).Thisshouldbeavoidedatallcostssinceit'sawfuluserexperience!

Ourfirstapplicationdoesn'tdoanyofthissortofprocessing,sowewilllookatthosetopicsingreaterdetaillater.

Youcandoallthenormalthreadingthingsyou'reusedtowithJava.YouuseThreadandHandlerclassestopostinformationbacktothemaincallingthread.

Thesetasksareusedtodobackgroundprocessing,butshouldn'tbeusedforlongrunningtasks.TheyhaveconveniencemethodsthatallowyoutointeractwiththeUIthreadbefore,during,andafteryourprocessiscomplete.ThesetasksaretiedtotheActivity'slifecycle.

Thisiswhereyouconductlongrunningprocessesthateitherhandlenetworking,streaming,updatingwidgets,oravarietyofothertasks.ServiceslivewithinyourApplication'sprocessboundaries.

Youcanalsouseafragmentwithoutaviewasabackgroundworker.Whenyouinflatetheview,yousettheviewtonull.ThisistiedtothelifecycleoftheActivity.

ThreadingModel

UIThread

JavaThreads

AsyncTask

Service

BackgroundFragments

Inthischapter,we'llgooverthefoundationalbuildingblocksofAndroidandextendourfirstapplication!

Forthischapter,we'llbereferringthisexampleandstartingourownproject!

Chapter4:AndroidFundamentals

Calculator

ActivitiesarewritteninJavaandregisteredinthemanifest.Theyliveinthepackagestructurethatyoudefineinthemanifestfile.Youcancreatesubdirectoriestobetterorganizeyourfiles.

publicclassLooselyCoupledActivityextendsActivity{@OverridepublicvoidonCreate(BundlesavedInstanceState){super.onCreate(savedInstanceState);

setContentView(R.layout.activity_loosely_coupled);}}

Whereverpossible,youshouldstrivemakeyouractivitiesasdumbaspossible,essentiallyanemptyshellforyourfragments.You'dalsodoworklikeconfiguringtheactionbarandmenushere.

IdeallymostofthebusinesslogicwouldbemovedtoPlainOldJavaObjects(POJOs)forunittestingpurposes,butinpracticesomeofthatlogicendsupinthesubviewsorfragments.

OftenActivitiesareusedasanintermediarybetweencomponents(e.g.Fragments)becauseyoudon'twantthemtalkingdirectlytoeachother.Byusingthelistenerpatternorasystembus,suchasOtto,thecomponentscanpostamessageandtheActivitywillreaditandrespond.Thiskeepstheconcernsseparateandeasiertomaintaintheindividualcomponents.

Youcanstartanactivityinsideahostingactivityandgetresultsfromthatactivity.

YouusestartActivityForResult()tostarttheactivity.Intheactivitythatwasstarted,youusesetResult()tosettheresultthatwillbereturned.Whenbackinthecallingactivity,youchecktheresultcodeandrespondappropriately.

Agreatexampleofthisisinvokingthesystemcameraandthenprocessingwhetherthepicture-takingeventwassuccessful:http://developer.android.com/guide/topics/media/camera.html

Activities

CodeExample

Activity'sRole

ActivityResults

Thelooselycoupledcomponents(e.g.activitiesandservices)arestitchedtogetherbytheAndroidManifest.xmlfileatruntime.Thisfiledescribeseachofyourcomponentsandhowtheyworktogether.Youdon'tregisterfragmentsherebecausetheyaretransientandtiedtotheactivitythathoststhem.

Inthisfileyouspecifywhichactivity(oractivities)thatarelaunchable.Youcanspecifyhowthingsarelaunched,howtohandleorientations,testingapplicationinformation(whenusinginstrumentation),andhowtohandletheSDcard.Finally,youspecifymetadataabouttheapplicationlikethename,versionname,versioncode,icon,andtheme.

Thepackagespecifiesthepackagestructureforyourapplicationandisusedtouniquelyidentifyyourapplicationinthemarket.

Theapplicationlabelreferstoastringresourcethatwillbeshownonthelaunchgridofthedevice.Usingastringresourceallowsyoutocustomizeforinternationalization.We'llcoverresourcesmoreindepthlater.

TheversionNameisapublic-facingnamefortheversionoftheapplication.TheversionCodeisanintegervalue.Youshouldincreaseitforeachreleasetothemarketandgenerallywhendevelopingtheapplicationanddoinginternalreleases.TheversioncodecombinedwiththesignatureandpackagenameiswhattellsAndroiddeviceusersthatthereisanupdatefortheirphone.

Insidethetag,youspecifytheactivitiesandservicesthatyouwilluseintheapplication.

Ifyoucreateanactivityanddon'tregisteritinthemanifest,youwillgetacrashwithasurprisinglyhelpfulerrormessage.

ThisfileisalsousedasafilterbytheGooglePlaystore.Youcanspecifyapplicationpermissions,whathardwarefeaturesyourequire,andwhatOSversionsyousupport.

Iftheuser'sdevicedoesn'tsupportoneofyourrequirements,thenitwon'tbeshowninsearchresultswhentheysearchonthedevice.Iftheysearchontheweb,theywillfindyourapp,butwon'tbeabletoinstallondevicesthatdon'tsupportyourapplication'srequirements.

Youcanfindmoreaboutfilteringinthestorehere:http://developer.android.com/google/play/filters.html

AndroidManifest.xml

Example

ManifestFiltering

LayoutsarewhereyoudefinetheviewofyourapplicationusingbuiltinAndroidviews,viewgroups,and/oryourowncustomviewsbasedonthem.TheseXMLfilesliveinyourres/directory.Writinglayoutsthiswayallowsustodecouplethepresentationlayerfrombusinesslogic.

AlthoughyoucouldwriteallyourviewsinJava,thatmakesitalothardertoleveragethefullpowerofresourcesystem.Plusitoftenbecomesamaintenanceissue.

Thereisalwaysoneparentattherootofthelayoutandthelayoutmaycontainmanyviews.

...

Therearemanyprebuiltitemsthatyoucanuse,includingButton,TextView,ImageView,grids,andmore!

YougiveeachviewanidsothatyoucanwireuptologicintheJavaclassthatpointstothisview.ThesystemgeneratesanR.javafilebehindthescenesthatmapsyourresourcesandviewstoaJava-accessibleconstruct.Thisisgeneratedatcompiletime,butthedecisionofwhichviewtoshowisdeterminedatruntime.

Note:SometimestheR.javafilesgetsoutofsyncwithyourviewsandresources.Thisoftenhappensifyouchangealotinasmallamountoftime.Ifyoustartseeingweirdclasscastexceptions,thenthismaybeyourculprit.

Inthisexample,theviewactivity_buttonisdefinedinactivity_loosely_coupled.xmlwithanid:

Intheactivity,youusesetContentView()tospecifywhichlayouttouseandAndroidbringsittolife.Afterthat,youcanaccessitssubviewswiththeidyougaveitintheXMLfile.

findViewById(R.id.activity_button).setOnClickListener(newView.OnClickListener(){

Layouts

Example:activity_loosely_coupled.xml

XMLviews

Referencingintheactivity

@OverridepublicvoidonClick(Viewv){startActivity(createViewSystemIntent());}};}

InthisexamplelayoutwecanmaketheactivitybuttondosomethingbyreferencingitinonCreate().Hereweattachaclicklistenerthatwillopenanotheractivity.

Youcanchangeallmannerofinformationabouttheviews.Goodexamplesaresettingthetextorcolorstodisplay,animatingviews,and/orattachinguseractions.

TheXMLgetsturnedintoJavacomponentsatruntimewhentheAndroidsystem"inflates"theview.

Asshownabove,withanActivitytheinflationoccursinthelifecyclemethodonCreate()withthesetContentView()function.

It'salittledifferentinFragment'sbecausetheinflationoccursinthelifecyclemethodonCreateView()byusingtheinflate()function.

Whenviewsareinflated,theyareaddedtotheviewhierarchy.Anytimethatyouaddsubviewsorviewgroups,youaredeepeningthehierarchytreethatrepresentsyourviews.YoucanusetheHierarchyViewertooltooptimizeviewsthatareloadingslowly.

AlloftheviewcomponentsareJavaclasses,whichmeanstheycanbeextended!

Youcanaddcustombehaviorwhenabuiltincomponentsprovidesome,thoughnotallofthebehavioryou'dlike.Youcanalsocreatecustomviewsthatarecollectionsofthebasicviewtypes.

Forexample,sayyouwantedtocreateadateandtimeclock.YoucouldcreateaviewthatcombinesaTextViewforthedateandandimageorothercontroltoshowananalogversionofthetime).

Theseviewsareonlylimitedbyyourimagination!Wewon'tbecoveringthemindepthinthisclass,butthere'sanexcellentpresentationbyChiu-KiChan:CustomComponents.

Inflation

Customviews

AwaytoorganizeandsimplifyyourXMLlayoutsistouseviewgroups.Youcanusethemtoholdchildrenviewsandmakereusablecomponents.Youcanalsoextendthemtoaddyourownbehavior.

Herearesomeofthemostcommonlyusedoptions.

Thisisthesimplestoftheviewgroups.It'sdesignedtoholdonechildview.Thislayoutisoftenusedasaholderfordynamicfragments.

Asthenameimplies,withthisnameyoulayviewitemsoutinaline,eitherverticallyorhorizontally.

ViewGroups

FrameLayout

LinearLayout

Withthisviewgroup,youcanlayoutelementsinarelativefashion.Forexample,placethestartotherightofthecircleandtheheartbelowthecircle.

RelativeLayout

Withthisviewgroup,youcanlayoutsimilarelementsinagridfashion.ThisavailableinlaterOSversionsandhasbeenbackportedforolderOSversions.

GridLayout

ViewStubs

Whenyourviewsstarttogetcomplicated,youcanbreakitupusingviewstubs.Thiscanbeusedtolazilyinflateviewsatruntime.

Moreinformationhere:http://developer.android.com/reference/android/view/ViewStub.html

Anactivityisthestartingpointforascreen,butifweputalltheviewsandtheirlogictogetheritquicklydissolvesintoahugemess!Amuchbetterwaytoconstructyourviewsiswithfragmentstofurtherencapsulatetheviewlogicintoself-containedpieces.

Itbreaksthelogicoftheactivityupintoself-containedpiecesthathandleuserinput.Thisisgreatforalotofreasons.Itletsyoureusethesecomponentsinotherlayoutstosupportdifferentformfactorswithoutchangingcode,justconstructinganewlayoutwithadifferentarrangementoffragmentsandviews.

Activitiesholdfragments,whichcan'tliveoutsideahost.Theactivityreactstonotificationsfromthefragmentthattheviewshouldbealtered.ThefragmentholdsareferencetothehostingactivityandcanaccessitbycallinggetActivity().

Considertheexampleapplicationabove.Thetabletversionhasalistofarticlesontheleftsideofthescreenandadetailpaneontheright.Thephonesusestwoseparateactivitiestoshowtheseviews.

Whenauserselectsanewarticletoview,thefragmentontherightshouldupdate.Youwouldn'twantthearticledetail,suchasanarticleaboutDoctorWho,toberesponsibleforupdatingtheviewtoshowanarticleaboutcats.

Italsodoesn'tmakemuchsenseforthelisttoknowalotofinformationaboutthedetailit'sgoingtoshow.HereyouwouldusetheActivitytodeterminewhichdetailviewnext.Thisbecomesimportantwhenyoualsohaveaphoneimplementationthatwouldappearintotallydifferentactivities.

So,howdowedoit?Whentheusertapsanarticleinthelist,aneventistriggeredandtheActivityrespondstothisreceivedevent.Inthecaseofthetablet,itwillsimplyupdatetherightpane.Inthecaseofthephone,itwouldstartanewactivity.

Fragmentsweren'talwaysaround.TheyintroducedafewyearsagowiththefirsttabletsandHoneycomb(Android3.x).

Fragments

MasterDetailPattern

TheGreatSchism

Dashboard,July2014:https://developer.android.com/about/dashboards/index.html

ItmakesitcomplicatedtosupportthefullrangeofOSversions,butit'sbecomingmoreandmorecompellingtosunsettheolderversionsastheirpercentagecontinuestodrop.Asofthewritingofthisbook,thepercentageofOSesinthewildthatdon'tincludeFragment'sisonly14%(combinedpercentagesofFroyoandGingerbread).

However,ifyoudointendtosupportolderversions,theyhavebackporteditallthewaybackto1.6usingthesupportlibrary.

InthislabwewilllearnabouttheAndroidvisualparadigmsbyexploringthedesignsofexistingapplications.Thiswillhelpusdevelopaprocessforbreakingdownadesignintoimplementablepieces.Thiswillcomeinhandywhenstartingnewscreens.

Afterwefinishthislab,we'llbereadytostartbuildingourapplication.

Pleaserefertotheclasshandoutforparts1,2,&3.Asolutionhandoutdetailshowthedesignscouldbebrokendown.

Let'sgetfamiliarwiththeAndroiddesignsite:

http://developer.android.com/design/building-blocks/index.html

Thisexcellentresourceliststheitemsyoucanuseaswellasbestpracticesfortheplatform.Wewon'tbecoveringAndroiddesignindetail,butthisresourceisagreatstartingplaceforunderstandingthedesignlanguageoftheplatform.

MakesuretocheckoutMaterialDesignresourcestoseewhatiscomingwiththeLreleaselaterthisyear!CheckoutthisvideoformoreinformationontrainsitioningfromHolotoMaterial.

Note:Seetheappendixformoredesignresources.

Whatdoyoufindinterestingaboutthedesignlanguage?Howdoesitdifferfromotherplatforms?Canyouthinkofotherplatformfeaturesthatdon'tfeelathomeonAndroid?Doyoufindthenavigationparadigmsintuitive?WhatdoyouthinkoftheevolutionofAndroid'sdesignthroughtheages?WhatdoyouthinkofMaterialDesign?Hadyouheardanythingaboutitbeforetheclass?

We'llbreakdownthedesignoftheGoogleMusicappasaclass.

Pleasepairup,analyzetheview,andidentifyviewcomponentstheymayhaveusedtoconstructthisview.

Let'sstartourcalculator!

WorkwithyourpartnertoidentifyatleasttwodifferentwaystoyoucouldbreakdownthisviewintoXMLcomponents.We'llstartimplementingsoon!

Thenexttimeyou'rebreakingdownadesign,thinkabouthowyoucansegmentitintoviewsandfragmentstobestsupporttheuserexperienceyouaregoingfor.

Lab:DesignChunking

AndroidDesign

DiscussionQuestions

Part1:ClassDesign

Part2:PairDesign

Part3:ClassProject

We'llworkthroughthisexercisetogetherasaclass.

Handout:DesignChunking

Part1:GoogleMusic

Pleasepairup,analyzetheview,andidentifyviewcomponentstheymayhaveusedtoconstructthisview.

Part2:Twitter

WorkwithyourpartnertoidentifyatleasttwodifferentwaystoyoucouldbreakdownthisviewintoXMLcomponents.

Chooseyourfavoriteapplicationandbreakdownseveraloftheirscreensintodesignchunks.It'sagreatwaytolearnfromothers!

Part3:Calculator

ExtraCredit

TheyuseActionBar(transparent),withatitleofthealbumandoneicon(search).

Solution:DesignChunking

Part1:GoogleMusic

TheactionbaroverlaysanImageViewfortheartist.Belowthatisanimageofthealbumwe'reviewing.TotherightofthealbumisalbuminformationdisplayedinTextView'sandseveraloptionsavailablejusttotherightofthealbumcover(eitherButton'sorImageView's).ThisislikelyaRelativeLayoutsincethingsarelaidoutrelativetootheritemsonthescreen.

UnderthealbuminfoisthelistofsongsforthisalbuminaListView.EachlistviewitemisfairlysimplecollectionofTextView'sandanImageViewforalbumoptions.There'sanImageViewthatshowsonarowonlyifthesongiscurrentlyplaying.

Note:Whenscrollingdowninthelistofsongs,thealbumandartistinformationispushedoffthescreensothatyoucanfocusonthemostrelevantinformation.Thiswouldbeacustomimplementationtoaddthisbehavior.

Attheverybottomofthescreen,thereisacustomviewthatallowsyoutoplay/pausethecurrentsongoropenthefullsongviewthathasahostofotheroptions.

Note:Thisviewispersistentthroughouttheapplicationevenifyoubrowseotheralbums.

There'salotgoingoninthisdesign!

Twitteralsousesanactionbarwithicons,notitle,andanoverflowmenu.Theyuseatabcontrollerjustbelowtheactionbarforthedifferenttweetstreams,whichhasaindicatorforthecurrenttab.

Part2:Twitter

YourtweetstreamisdisplayedinaListView.Eachtweetishasseveralpiecesofdata,suchastextviewsandimagesthatrepresentretweets,authors,timesinceposting,etc.

Atthebottomofthescreen,theyhaveacustomviewthatcombinestwobuttonsforpostingimagesandanEditText(customimplementation)forenteringanewtweet.

Clickingonmostoptionstakesyoutoanotheractivity.

Therearemanyvalidwaystobreakdownadesign.Eachchoicehasconsequencesorbenefitswhenwebuildouttheapplication.

Inourclassimplementation,we'llbeusingtwoFragmentslaidoutinaLinearLayoutwithandroid:orientation="vertical".

Part3:Calculator

TheDisplayFragmentwillhandlethedisplay.We'lluseanEditTexttodisplaythenumbersenteredintothecalculatoraswellascalculations.

TheButtonFragmentwillcontainandcontrolthecalculatorbuttons.We'lluseaRelativeLayouttopositionmanyButton'sforoperationsandnumbers.

Whatwasyourdesign?Howdoesitdiffer?Howdoyouthinkthatwillimpactimplementation?

DiscussionQuestions

Ensuretheactivityandviewelementsarenotnull.Ensureexpectedfragmentandviewelementsarevisibleonthescreen.Ensurethattheproperresourcesareusedforviewelements.Ensureitemsarehiddenwhenexpected.Ensuretoastsareshown.Ensurethatyourintentstartsthecorrectthing.

Lab:ConstructTheView

TestingReminder

Let'sdothistogetherasaclass.

publicclassDisplayFragmentextendsFragment{@OverridepublicViewonCreateView(LayoutInflaterinflater,ViewGroupcontainer,BundlesavedInstanceState){Viewlayout=inflater.inflate(R.layout.display,container,false);returnlayout;}}

TheXMLviewdoesn'texist,sowe'llcreateafilecalleddisplay.xmlinthesrc/layout/folder.We'lladdthespecificsoftheviewlater.

@RunWith(RobolectricTestRunner.class)

publicclassDisplayFragmentTest{@TestpublicvoidshouldNotBeNull()throwsException{DisplayFragmentfragment=newDisplayFragment();startFragment(fragment);assertNotNull(fragment);}}

Atthispointweshouldbeabletorunthetestsuccessfully.

Let'saddourfragmenttomain.xml(layoutfilespecifiedinsetContentView()oftheCalculatorActivity).

android:name="com.mobiquity.calculator.DisplayFragment"android:layout_width="match_parent"android:layout_height="wrap_content"/>

@TestpublicvoidshouldHaveDisplayFragment()throwsException{assertNotNull(activity.getFragmentManager().findFragmentById(R.id.display_fragment));}

Makesuretorunthetestsandthencommityourworktoyourrepository.

Testpresenceintheactivity

Test&commit

Yourturn!Pleasecompletethistaskwithyourpartner.

publicclassButtonFragmentextendsFragment{@OverridepublicViewonCreateView(LayoutInflaterinflater,ViewGroupcontainer,BundlesavedInstanceState){Viewlayout=inflater.inflate(R.layout.buttons,container,false);returnlayout;}}

TheXMLviewdoesn'texist,sowe'llcreateafilecalledbuttons.xmlinthesrc/layout/folder.We'lladdthespecificsoftheviewlater.

@RunWith(RobolectricTestRunner.class)

publicclassButtonFragmentTest{@TestpublicvoidshouldNotBeNull()throwsException{ButtonFragmentfragment=newButtonFragment();startFragment(fragment);assertNotNull(fragment);}}

Let'saddourfragmenttomain.xmlbelowtheDisplayFragment.

Lab:AddButtonFragment

CreateButtonFragment.java

Createtheview

CreateButtonFragmentTest.java

Addtoview

@TestpublicvoidshouldHaveButtonsFragment()throwsException{assertNotNull(activity.getFragmentManager().findFragmentById(R.id.buttons_fragment));}

Makesuretorunthetestsandthencommityourworktoyourrepository.

Testpresenceintheactivity

Test&commit

ReplacetheLinearLayoutfrompreviousstepswiththisEditTextindisplay.xml.

Wecandothissinceeachviewexpectsonlyoneviewattheroot,butmayhavemore.Sinceourviewissosimple,thereisnoneedtohaveanenclosingviewgroup.

HereI'veaddedmanyXMLattributes!Theattributesaremostlyselfexplanatory,butI'dbehappytoansweranyquestionsonparticularattributes.

We'lllearnmoreaboutabstractingsomeofthehardcodedvaluesoutlaterintodimensionsandstyles.

ForthebackgroundcolorI'musingabuiltinAndroidresource:

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

ForthetextcolorIdefinedanewcolorinres/values/colors.xml:

#ff313131

Wegoingtorefactorabitheretomakeiteasiertotestnewitems.First,makeafield,fragment,forthefragmentundertest.Then,movethefragmentinitializationandfragmentstartingtothesetUp()function.

publicclassDisplayFragmentTest{privateDisplayFragmentfragment;

@BeforepublicvoidsetUp()throwsException{

Lab:DisplayView

Addtheview

Addcolors.xml

AddtesttoDisplayFragmentTest.java

fragment=newDisplayFragment();startFragment(fragment);}

@TestpublicvoidshouldNotBeNull()throwsException{assertNotNull(fragment);}}

Nowwe'rereadytoaddthenewtest:

@TestpublicvoidshouldHaveDefaultDisplay()throwsException{EditTextdisplay=(EditText)fragment.getView().findViewById(R.id.display);assertViewIsVisible(display);assertThat(display.getText().toString(),equalTo(""));}

Inthislabwe'lladdthebuttonstotheviewcompletewithtests.

Note:Theywon'tbeprettyandtheywon'tdoanything!

AsIbuildeachkey,Iwriteatest.ThenIaddthenextkey.Itypicallydon'tstartlayingouttheviewsormakingthemprettyuntiltheyareallpresentintheviewandthetestsarepassing.Icommitaftertheviewsarepresent.ThenIdoastylingcommitafterward(we'lldothatasaseparatestep).

Lastwesawthisfile,wehadalltheinitializationcodeinthethetestthatwewrote.Let'smakeafieldforthefragmentandmovetheinitializationtothesetUp()function:

privateButtonFragmentbuttonFragment;

@BeforepublicvoidsetUp()throwsException{buttonFragment=newButtonFragment();startFragment(buttonFragment);}

Nowwecanaddanewtest.

WeusegetView()togetareferencetotheviewandthenfindthespecificid.

@TestpublicvoidshouldHaveOneKey()throwsException{assertViewIsVisible(buttonFragment.getView().findViewById(R.id.key1));}

Nowweaddthebuttontotheview.

It'sbestpracticetomoveyourstringstothestrings.xmlfileinsteadofleavingthemhardcodedintheview.Italsomakesiteasiertotestthatthecorrectstringisconfiguredforaview.

1

Lab:AddButtons

Testing

Addatest

Addabutton

Addastring

Thelinttoolwillrecommendthisforyoubyshowingyellowbarsandalightbulbintheview.

Let'sextendourtesttoensurethatthecorrectstringisconfiguredfortheview.We'lluseourResourceLocatorclasstogettheresourcestringandcompareittoTextView'sgetText()returntoensuretheyareequal.

Ourfinaltestlookslikethis:

@TestpublicvoidshouldHaveOneKey()throwsException{TextViewkey1=(TextView)buttonFragment.getView().findViewById(R.id.key1);assertViewIsVisible(key1);assertThat(key1.getText().toString(),equalTo(ResourceLocator.getString(R.string.key1)));}

Addeachnumberandoperatorkeyinturnandmakesurethetestspassalongtheway.Afteryou'redonewiththebuttons,commit.

Let'sreplaceourparentLinearLayoutwithaRelativeLayoutsothatwecandefinethepositionofthebuttonsrelativetotheotherbuttons.

Pleaserefertothescreenshotoftheexampleprojecttodeterminewhereeachbuttonshouldbepositioned.

android:id="@+id/key4"android:layout_width="60dp"android:layout_height="60dp"android:layout_margin="5dp"android:layout_below="@id/key1"android:text="@string/key4"/>...

Note:Therearemanywaysthisviewcouldbelaidout.RelativeLayoutisn'tthemostintuitivechoice,butitisquiteusefulandmasteryofitearlyinyourAndroidcareerwillleadtogreatthings.

AccordingtoMeieratKindlelocations2459-2461,youdefineyourownapplicationimplementationwhenyouneedto:

RespondtoapplicationleveleventsbroadcastbytheAndroidruntimesuchaslowmemoryconditions.Transferobjectsbetweenapplicationcomponents.Manageandmaintainresourcesusedbyseveralapplicationcomponents.

Youdeclareyourapplicationinthemanifestandtheapplicationclasswillbeautomaticallyinstantiatedwhentheapplicationisrun.

It'sbestpracticetodeclareyourapplicationasasingleton.

Application

Declaration

Let'saddthefollowingattributetoourtagofourAndroidManifest.xml.

CreateafilecalledCalculatorApplication.javainthepackagestructure.YoucanusetheIDEtocreateitforyouordoitmanually.

It'sbestpracticetosetitupasasingleton.

publicclassCalculatorApplicationextendsApplication{privatestaticCalculatorApplicationinstance=newCalculatorApplication();

publicstaticCalculatorApplicationgetInstance(){returninstance;}}

CreateafilecalledCalculatorApplicationTest.javainyourtestpackagestructure.YoucanusetheIDEtocreateitforyouordoitmanually.

Let'saddthebasicnon-nulltest:

publicclassCalculatorApplicationTest{@TestpublicvoidshouldNotBeNull()throwsException{assertNotNull(CalculatorApplication.getInstance());}}

That'sit!Nowwecanaddmoreitemstothisclassasweneedthem.

Let'scommitourchanges.

Lab:AddApplication

Addtothemanifest

Createclass

WriteTest

Eventbusesareagreatwaytodecoupleourcomponentswithoutusingainterfaceorlistenerpatternthatcanproducealotofboilerplatecode.

Ottoisasystem-widenotificationsystem.Acomponent(e.g.anActivityorFragment)postsanevent,withanoptionalmessage,toOtto.Othercomponentsthathaveregisteredforeventswillreceivetheeventandreactasappropriate.

Let'saddanOttoBus!

Ifnotalreadypresent,addthemavendependencytoyourpom.xmlfilesothatwecanreferenceOttothroughoutourproject.

com.squareupotto1.3.4

NowaddtheselinestoourCalculatorApplication.javaclass.

privateBusbus;

publicBusgetBus(){returnbus;}

publicstaticvoidpostToBus(BaseEventevent){//Note:AutoGeneratingBaseEventnextgetInstance().getBus().post(event);}

@OverridepublicvoidonCreate(){super.onCreate();instance.bus=newBus();}

ThefunctionpostToBus()givesusaconvenientwayposttothebusfromanyactivityorfragmentinourapplication.IfwebuildallofoureventstoextendtheBaseEventthenwecanusethisforalleventsintheapplication.

CreateafilecalledBaseEvent.java.Isuggestcreatingapackagecalledeventstoholdeventsandcreatefurtherpackagesasneededtokeepyourcodeorganized.

Theeventcanbequitesimple,oryoucanincludedatawithyourevents.Inthiscase,wewillmakeitasbasicaspossible:

publicclassBaseEvent{}

Lab:EventBus

IntegrateOtto

Applicationbus

CreateBaseEvent

Let'smakesurethattheBusexistsforourapplication.Firstwe'llneedtomigrateourapplicationtoafieldandinitializeinsetUp().Thenwecanaddthistest:

@TestpublicvoidshouldHaveBus()throwsException{assertNotNull(application.getBus());}

Onceallthetestspass,committoyourrepository.

Addatest&commit

Meierputsitwell,"usinglayoutresourcesdecouplesyourpresentationlayerfromtheapplicationlogic,providingtheflexibilitytochangethepresentationwithoutchangingcode.Thismakesitpossibletospecifydifferentlayoutsoptimizedfordifferenthardwareconfigurations,evenchangingthematruntimebasedonhardwarechanges(suchasscreenorientationchanges)."

I'veseenatoomanyduplicatedlayouts,hardcodedvalues,andhardcodedJavaviewsclutteringAndroidapplications!Allofthesepracticesleadtodifficulttomaintainappsandmakesithardertoscaletonewerdevicesandformfactors.However,ifyouleverageAndroidsystemfromthestartandletitdotheheavingliftingforyou,youcanavoidalotofpaindowntheroad.

AlthoughIfindXMLapaintoreadandwrite,I'vegrowntolovetheresourcesystem.Itisoneofthemostpowerfultoolsyouhavewhenconstructingyourapplication,butisoftenmisunderstoodanddefinitelyunderratedandunderutilized.

Youplaceyourlayouts,drawables,andvalues(e.g.strings,colors,dimensions)inthisfolder.

Thebasicfolderstructurelookslikethis:

res/drawable/values/layout/

Oneannoyingthingaboutthesefoldersisthatyoucan'tcreatesubfolders.Thisisespeciallyannoyinginthelayoutfoldersinceyouendupwithlotsofviewsinyoursystem.Youcanhowever,makeupyourownfilenamesandgroupresourcesthatbelongtogether.

There'slotsofgreatinformationonAndroid'ssiteabouthowtosuportmutipleformfactors:http://developer.android.com/guide/practices/screens_support.html

Meier,Reto(2012).ProfessionalAndroid4ApplicationDevelopment(Loc.2816-2818).JohnWileyandSons.KindleEdition.

Chapter5:ResourceSystem

res/

Resources

InAndroid,youcreatestyles(whichisanalogoustoCSS),externalizeyourresources,andusewhatAndroidcallsresourcequalifierstoadaptyourdesigntodifferentformfactors.

Ifyouhaveawebprogrammingbackground,thiswillfeelfamiliar.Ifnot,theideaisthatyourviewautomaticallyscalestosuittheamountofspaceithasandyoudefinehowthatviewshouldadapttonewsizes.

Don'tbaseyoudesignsonspecificdevicesordevicecategories,ratherthinkaboutthenaturalseparationorbreakinglinesforyourviews.Thereisno"phone"or"tablet",theyarejustdevicesinacontinuum.

Responsivedesign,asopposedtopixel-perfectdesigns,fromthestartwillmakeitaloteasiertoscaleyourviews.

Androiddynamicallyselectsresourcesatruntimethatarebestsuitedtothedevicerunningtheapplication.Youcansetupalternativesforthingslikeorientations,hardware,languages,locations,viewsizes,andmore.ItfreesyoufromtheburdenoffiguringoutincodewhatresourceyoushouldbeshowingifyouuseAndroid'ssystemtodoitforyou.

Externalizingresources,suchasimages,strings,dimensions,styles,themes,andlayoutmakesitmucheasiertomaintainandscaleyourviews.

ThisistheheartoftheAndroid-therearenoguaranteesofwhatyourappwillrunon,soyouneedtocreatethemostflexibleappandviewspossibletoavoidheadachesfromhardcodedvalues.

TheActivityclassprovideshelpermethodstogettheseresourcessuchasgetString(R.string.name)andgetDrawable(R.drawable.name).There'salsoamethodgetResources().SomeoftheseareavailableintheFragmentclassandyoucanalwaysaskfortheactivity'sresourcesbycallinggetActivity().getResources().

Userelativepositioningwhenlayingoutyourviewssothattheyadaptwellwhenrunningondifferentscreensizes.RelativeLayoutandLinearLayoutaregreatchoices.

Usewrap_contentandmatch_parentwheneverpossiblewhendefiningthelayout_heightandlayout_widthofyourviews.wrap_contenttellsthesystemtomeasuretheviewatinflationandrenderthewidgetwithjustenoughspacetocontainit.Ontheotherhand,match_parentsaystakeupalltheavailablewidthandheightwhenrenderingthisview.

DesignPrinciples

Thinklikeawebprogrammer

LetAndroiddotheheavylifting

ExternalizeResources

ScalableLayouts

Stylesandthemesarespecifiedinres/styles.xml.Themesareusedfortheoverallappearanceoftheapplication,whilestylesareappliedtospecificviews.

Inmostcases,youwon'tneedmorethanonestylefile.Ifyouuseabstracteddimensionsandimageassetsinyourstyles(asopposedtohard-codedvalues)combinedwiththequalifiersystem(allofwhichwillbecoveredindepthinthischapter),itmakesyourviewsscalable.

Youcaninheritfromotherstylesandthemes.Youcanoverrideattributesandaddnewonesinderivedstylesorwhenspecifyingviewattributesinthelayoutfile.

Stylesallowyoutoabstractoutviewattributesintoacentralizedlocationtoenablereuse.

Inthisexample,I'vedefinedastylecalledSquareButtonthatconfiguresaheightandwidth.

50dp50dp

Note:Thesyntaxisabitdifferentfromhowyouspecifyviewattributesinyourlayouts,buttheybothusethesameXMLattributes.

Afteryoudefineastyle,youcanreferenceitintheXMLlayoutbyusingthestyleattribute:

Note:styledoesn'tusetheandroidnamespace.

ThemesprovideaconvenientwaytoapplystyletoanentireapplicationorjustanActivity.

Thisisusefulbecauseyoucanrapidlyreskinyourapplicationbychangingjustafewlinesofcode.

Touseathemeinyourapplication,youspecifyitintheAndroidManifest.xml.YoucaneitheruseAndroid'sbuiltinthemes(examplebelow)orcreateyourown.

Styles&Themes

Styles

Definingstyles

Usingstyles

Themes

Ifyouwanttocustomizeatheme,youcanextendanexistingAndroidthemeandaddingattributesoroverrideattributesasdesired.

AndroidManifest.xml

styles.xml

Athemeisjustastyle.Whatmakesitdifferentiswhereyouapplyit!

...

MyapproachtodimensionsandstyleshasevolvedovertimeasIgetexposedtonewteamsandnewdesigners.I'llshowyouwhatittookmeawhiletodiscoverformyselfinhopesofsavingyousomeheadachesdowntheroad.

WhenIstartedwithAndroid,theteamandIgleefullythrewhard-codedvaluesallovertheplace,oftenduplicatingvaluesinthesamefile!Notonlydidthislitterthecode,butitmadedebuggingviewissuesmoredifficult.

ThroughoutthischapterI'llshowyouascalablewaytomanagetheseresources.

It'sstraightforwardtocreateadimension.You'llneedadimens.xmlfileinres/values/:

25dp

Youcanreferencetheminstyles:

@dimen/my_dimen

OrinlineinyourXML:

OreveninJava:

floatdimen=getResources().getDimension(R.dimen.my_dimen);

Itmightnotbeimmediatelyapparent,butusingdimensionswithresourcequalifiers(coveredindepthlater)allowyoutocreateresponsivecomponents.You'llseethisinactioninthe"FlexibleDimensions"lab.

Abstractingcolorsgivesyouaconvenientplacetostoreandnameyourcolorsinsteadofusinghardcodedhexvaluesallovertheplace.Havingnamesassociatedwiththecolorsmakesiteasiertomaintainviewchanges.

Plusyouhaveanaddedbonusofpreviewsofyourcolorswatchesandacolorpicker(includingdropper!)whenyouareopencolors.xmlinIntelliJ.

Dimensions&Colors

Dimensions

Benefit

Colors

Youcanabstractmanytypesofvalues.Checkoutthisarticleformoreinformation:http://developer.android.com/guide/topics/resources/available-resources.html

Let'smakeourcalculatorlooknice!Bytheendofthislabwewillcreateandapplystylestoallofourbuttons.We'llalsocreateastyleforthedisplay.

ColorScheme

Numberbutton:#876D13(Brown)Operatorbutton:#668113(Green)Equalsbutton:#268474(Blue)Clearbutton:#B0281A(Red)

First,createafilecalledstyles.xmlinres/values/.Thisiswhereallofourstylesandthemesliveintheapplication.

Ifyouanalyzethedesign,you'llnoticethatthebuttonsarebasicallyvariationsonatheme.Theonlyvariantsinthestylearedifferentcolorsandsomebuttonsarewiderthanothers.Sincethesebuttonsaresosimilar,itmakessensetocreateabasicstylethateachbuttontypewillinherit.

Let'saddthisbasebuttonstyletostyles.xml.

@dimen/button_dimensions@dimen/button_dimensions@dimen/button_margin@dimen/key_text_size@android:color/white

Herewe'vespecifiedtheheightandwidthsoftheview,themarginbetweenthebuttons,thecolorofthetext,andthesizeofthefont.Allbutthelastuseabstracteddimen's.We'lladdtheseinthenextsection.Forthefinalitem(textcolor),weuseanAndroidsuppliedcolorinsteadofcreatingourown.

Nowit'stimetostartusingdimensions!

Lab:ViewStyles

Createstyles

Basebutton

Createdimensions

Startbycreatingthedimens.xmlfileinres/values/.Thenaddthebaselinevaluesfortheview.We'lladddifferentversionsofthisfileinalaterlabtoscaletodifferentscreensizes.

5dp60dp30sp

NowthatwehaveBaseButtonandallthedimensionsneededtomakeitareality,let'suseittocreateourNumberstyle.

Youcaninheritattributesfromparentstylesandaddyourownconfigurationsforthenewlyderivedstyle.

@color/brown

Fornowwe'llsetthebackgroundtoaflatcolor.Inalaterlabwe'llextendthisstyletoprovidevisualfeedbackuponuserinteraction.

Note:Youcanalsoinheritfrommultiplestyles:http://developer.android.com/guide/topics/ui/themes.html#Inheritance

Let'saddcolorstocolors.xmlforthenewbuttons.TheNumbercolorbrownisshownbelow:

#876D13

AnotherbenefitofcreatingstylesisthatitwillcleanupourXMLfiles.Removeanyattributethatiscoveredbythestyle.Here'stheupdated1key:

Muchcleaner!ImoveasmuchaspossibletostylestokeepmyXMLfileslean.IgenerallyleaveattributesthesourceXMLfilethatrelatetopositioningintheview(e.g.RelativeLayoutpositioning),textforabuttonortextview,andtheid.

Usingtheinformationabove,createandusestylesforeachofthesekeytypes.Whenyoufinish,theviewshouldlooklikethescreenshot.

Numberstyle

Createcolors

Removeextraattributes

Operators,Equals,andZero

Display

Finally,cleanupthedisplayviewindisplay.xmlusingastyle.

Tosetupalternativelayoutsandresourcestoberesolvedatruntime,youuseresourcequalifiers.

Qualifierscoverthingslikescreensize(widthandheight),languagesandregions,aspectration,orientation,andOSversionamongothers.

Checkoutthecompletelistingofqualifieroptionsaswellasdetaileddocumentationonhowresourcesareselected:http://developer.android.com/guide/topics/resources/providing-resources.html

Inthisexampleres/folder,wehaveanumberofdirectories.QualifiedfolderscanberecognizedbythedashintheirnameandtellsAndroidtousespecificresourcesforspecificinstances.

res/drawable/values-sw600dp/values-fr/layout/layout-land/

-frstandsforFrench,-sw600dpmeanssmallestwidthofthedeviceis600dpandhigher,and-landiswherethelandscapelayoutslive.Youcouldcombineseveralqualifiersintoonefolderbyusingadashbetweeneachqualifier.

There'sabitofAndroidmagicthatselectsthebestversionofyourvieworresourceforthecurrentdevice.Ifyousetuptheparallelfolderstructuretosupportdifferentconfigurations,Androidwillhandletherest.Androidchoosesthebestresourcesatruntimebasedonthedevicethatishostingtheapplication.

Androidtriestomatchwiththemostspecificresourcequalifiersfirstandthenfallsbacktomoregenericoptions.Ifnoneoftheresourcequalifiersinyourapplicationmatchthehostdevice,thebasicvaluesspecifiedinlayout/,values/,anddrawable/willbeused.

Makesuretohaveasanedefault!Ifyoudefinesomethinginaspecificqualifiedfolder,suchasanid,andthenruntheapponadevicewithdifferentspecifications,itwillcrashbecauseitwon'tbeabletofindthedefaultvalueatruntime.

Youmightnotcatchthisduringdevelopmentsinceyouarelikelyusingthesamedevice.It'sgoodpracticetovaryyourtestdevicesandtestingsituationstoexploreunhappypaths.

Inthecaseoflayouts,ifyouwanttooverridetheviewforaspecificconfiguration,youwillneedtocreateanotherversionoftheviewinaqualifiedfolder,butyouusethesamenameforbothfiles.That'showtheresourcequalificationsystemworks!

Inthecaseofstrings,dimens,drawables,andotherresources,makesuretousethesamenameinthedefaultandqualifiedpathstooverridethevalueforyournewconfiguration.

Invalues/strings.xmlIhavestringsforawelcomescreen.

Qualifiers

Folderstructure

Resolution

Naming

Example:Internationalization

HelloDutchMobileConference!ProgrammedbyCoreyLeighLatislaw

Invalues-nl/strings.xmlIdefinedthesamename,butputthefileinthequalifiedstructureandchangedthetext.

HalloDutchMobileConference!GeprogrammeerdedoorCoreyLeighLatislaw

Inthislab,we'llusethequalifiersystemanddimensionstoscaleourviewfordifferentformfactors.

Ifyoudon'thaveaccesstoaNexus5,pleasecreateaninstanceusingGenymotion.

TheActionBarinthiscasedoesn'thelpourapplicationsincewe'llonlybeshowingonescreenanddon'thaveanyconfigurationornavigationoptions.It'sjusttakingupvaluablescreenrealestate!

OnnewerOSesyougetitbydefaultunlessyouexplicitlyexcludeitinthemanifestfile:

Let'screateafoldercalledvalues-w350dpandadimens.xmlinthatfolder.Hereiswhereyou'dputyourvaluesyou'dliketouseonscreenswithatleast350dpinscreenwidth.

78dp4dp50sp

164dp

250dp

8dp40sp

Youdon'thavetocopyallthedimensionsoverfromvalues/dimens.xml-justtheonesthatyouareinterestedinoverwriting.

Iadjustedmydisplaymarginsafteradjustingallmybuttonstomaketheedgeslineupbetter.

Lab:FlexibleDimensions

RemoveActionBar

Alternatedimens.xml

Adjustdisplay&commit

Let'saddJapanesenumbers!

Createafoldervalues-jaandastringsfileunderthisdirectory.

Copythecharactersfromhereintoyourstrings.xmlfolderforkeys0-9:http://en.wikipedia.org/wiki/Japanese_numerals

Robolectricallowsyouconfigurethequalifiersforaspecifictest:

@Test@Config(qualifiers="ja")publicvoidshouldHaveJa0Key(){verifyKey(R.id.key0,R.string.key0,"");}

Ihaveahelperfunctiontoreducetheduplicatedcodeforeachkey.Youcouldrefactorthisevenfurtherintoanarraythatyouloopthroughtoverifyeachbutton.

Buttonkey=(Button)buttonFragment.getView().findViewById(id);assertViewIsVisible(key);

StringresourceString=getString(stringId);assertThat(key.getText().toString(),equalTo(resourceString));assertThat(expectedString,equalTo(resourceString));

Buildandchangeyourdevice'slanguagetoJapanesetovisuallyverifytheinternationalizationworked.

Lab:Internationalization

Addtests

Drawablesaretheimagesinyourapplication.Theseimagescanbein.png,.jpg,.gif,orspecifiedinXML.

YousavethefilesindrawableoraqualifiedversionofthedrawablefolderandthenreferenceinXMLwithouttheextension.

Insteadofincludinganimagewithdifferentdensities,youcouldspecifyresourcesinXMLandevenJava.

Forexample,todrawaredrectangle,youcouldcreateitusingXML.

You'dsavethefileinthedrawable/folderandgiveitadescriptivenamelikerectangle.xml.Torefertoitincode,youusethesamemethodofreferencing:

Thisisaspecialfilethatscalestofillaview.Youareabletospecifyhowcertainregionsstretchandwhatregionsshouldstaythesame.

Drawables

ColorDrawable,ShapeDrawable,GradientDawable

9-patch

Youcanfindmoreinformationaboutusingandcreatingthesefileshere:http://developer.android.com/tools/help/draw9patch.html

YoucanalsospecifyhowviewsappearindifferentstatesviaXML.Acommonusageissettingbuttoninteractionstates.Youcandefinewhatitlookslikenormally,whatitlookslikewhenyoupressthebutton,whatitlookslikewhenfocused(e.g.throughakeyboardormouseinteraction).We'llbedoingthisnextinthelab!

StateListDrawables

Startbycreatingthedrawable/folderunderres/.

Createnumber_key.xmlinres/drawable/.

Eachitemherecorrespondstoadifferent

You'refreetochooseyourowncolorsandcustomizethedesign!I'veaddedmycolorsforthedifferentstatestores/colors.xml:

#ffafb315#ff604613

Tomakethisallwork,youneedtoassociateitwiththenumberkeys.EdittheNumberstyletoincludethisnewdrawableasourbackgroundimage.

@drawable/number_key

Nowourbuttonsrespondtotouches!

Lab:ButtonState

Selector

Colors

Applyinstyle

Dothisforeachtypeofbuttonandcommit.

Let'screateaniconforourapplication!

OpenAndroidAssetStudioandchoose"Launchericons".

Createanimageofyourchoiceanddownloadthezipfile.Openingthefileyouwillseethatthere'sseveralimagesinsidequalifiedfolders.Moveeachoftheseimagesintothecorrectfoldersandaddqualifiedfoldersthatdon'tcurrentlyexit.Overridetheexistingiconswhenprompted.

Note:Thetooldoesn'tprovidearesourcefordrawable-ldpi.

Wealreadyhavethisfilenamespecifiedinthemanifest,sowewon'tneedtoupdatethefile.Ingeneral,Ifyouwanttoaddanicon,addittothetag:

Commit!

Lab:AppIcon

Anapplication'slifecyclecanbeinterruptedbymanyevents,suchasauseransweringaphonecall.Itisimperativetounderstandwhathappenswhenausernavigatesawayfromyourphoneandthencomesbacksincethiswilllikelyhappenoften.

It'srarethatauserwillspendsignificanttimeinyourapplicationandprogressthroughthescreensexactlythewayyouenvision.Auseristypicallyquicklyconsumingorsharingcontentandthenmovingontothenextthing.It'slikelythattheuserwillexitandcomebacktoyourapplicationmanytimesaday.Dependingonhowtheyleftyourapplicationandhowyoumanagethelifecycle,itcouldleadtosomesurprisingresultswhentheylaunchyourapplicationthenexttime!

Weoftenoverlookthisfactwhenwearewritingapplicationsbecausewestareatitforalongtimeandworkthroughtheapplicationinaparticularway(asitwasdesigned).Weenduponlythinkingaboutthehappypathandmissmanybugsthatarisefromimproperlifecyclemanagement.Onlybyinteractingwithyourapplicationasanormaluserwouldwillyoustarttoseethesequirks.

Anapplicationhasalifecycle.It'sactivitieshavealifecycle.Theactivitymayhostoneormorefragmentsthatalsohavetheirownlifecycles.

We'llgothelifecyclesofthesecomponentsinfurtherdetailinthischapterandendwithalabtosolidifytheseconcepts.

Chapter6:ManagingtheLifecycle

Calledwhentheapplicationisstarting,beforeanyactivity,service,orreceiverobjects(excludingcontentproviders)havebeencreated.Makeitfast,thisaffectsstartupperformance.

Whentheoverallsystemisrunninglowonmemory,youusethistotrimmemoryusage.Releaseanycachesorotherunnecessaryresourcesyoumaybeholdingonto.Thesystemwillperformagarbagecollectionforyouafterreturningfromthismethod.

Calledwhentheoperatingsystemhasdeterminedthatitisagoodtimeforaprocesstoclearupunneededmemory.Thiscanhappenwhentheapplicationgoesinthebackgroundandthereisnotenoughmemorytokeepasmanybackgroundprocessesrunningasdesired.

Calledbythesystemwhenthedeviceconfigurationchangeswhileyourcomponentisrunning.

Atthetimethatthisfunctionhasbeencalled,yourResourcesobjectwillhavebeenupdatedtoreturnresourcevaluesmatchingthenewconfiguration.

ApplicationLifecycle

onCreate()

onLowMemory()

onTrimMemory()

onConfigurationChanged()

Therearemanystates,butinpracticeyouuseonCreate(),onResume(),onPause(),andonDestroy()mostoften.Theactivitygoesthroughthecreationflowwhenstartingupandthenfollowsasimilar(butreverse)teardownflowwhenmovingtothebackground.

WhenonCreate()iscalled,theactivityisbeingcreated,butnotyetvisibletotheuser.Youcangetreferencestoviewelementsandconfigurelongrunningprocesses.

WhenonStart()iscalled,theactivityisbeingcreatedandmaybevisibletotheuser,buttheuserwon'tbeabletointeract.

WhenonResume()iscalled,theactivityisvisibletotheuserandreadyforuserinput.

WhenonPause()iscalled,theactivityisstillpartiallyvisible.TheusermayhavebeenshownadialogorotheritemthatbrieflytakesthefocusawayfromtheactiveActivity.It'spossiblethattheymayresumetheactivityshortly,butyoushouldstartpreparingfortheteardown.

WhenonStop()iscalled,theactivityishiddenandmaybecleanedupifresourcesareneededforthenew(andcurrentlydisplayed)activitythatauserisinteractingwith.

ActivityLifecycle

ActiveStates

Created

Started

Resumed

Inactive

Stopped

Destroyed

onDestroy()iscalledrightbeforeyouractivityisdestroyed.

Thiscanhappeneitherbecausetheactivityisfinishing(someonecalledfinish()onit,orbecausethesystemistemporarilydestroyingthisinstanceoftheactivitytosavespace.YoucandistinguishbetweenthesetwoscenarioswiththeisFinishing()method.

AFragment'slifecycleistiedtoitshostingactivity,buthasindependentmethodsaswell.

ManyoftheselifecyclemethodsaresimilartotheActivity'smethodsandareintertwinedwiththeActivity'sstate.

Ifyou'dlikemoreindepthinformationaboutthefragmentlifceycle,checkoutAndroid'sdocumentation:FragmentLifecycleandCoordinatingwiththeactivity.

Fragment

Thisiswhereyouconfigureviewcomponents.

Afterthisphase,youhaveaccesstotheActivity.

onCreateView()

onActivityCreated()

Let'saddloggingtothelifecyclemethodstoseewhat'shappeningbehindthescenesinCalculatorActivity,CalculatorApplication,ButtonFragment,andDisplayFragment.

Sothatwecaneasilyidentifyourlogmessages,addaconstantfieldtoeachclass:

privatestaticfinalStringTAG="Lifecycle"+[ClassName].class.getSimpleName();

Makesuretoreplace[ClassName]withthenameoftheclass(e.g.CalculatorApplication).

UseOtooverridethelifecyclefunctions.

Addalogcallineachmethod.Forexample,youronCreate()shouldlooklikethis:

@OverridepublicvoidonCreate(BundlesavedInstanceState){super.onCreate(savedInstanceState);Log.d(TAG,"onCreate()");...}

YoucanfiltertheIntelliJlogstoshowonlyaspecifictag(thefirststringprovidedtoLog.d()):

Lab:VisualizingtheLifecycle

Tagging

Instrumenting

Run

Youcannavigateforwardsandbackwardsinanapplication.

Thebackstackkeepstrackofallnewactivitiesandfragmentsthatwereeitherimplicitlyorexplictlyadded.

WhenyouusestartActivity()withanintent,itisautomaticallyaddedtothebackstackforyou.Withfragments,youcanexplicitlyaddthefragmenttothebackstackwhencommittingaFragmentTransaction.

YoucaninterceptbackclicksinanActivity,thoughbecarefulbecauseyoushouldn'tviolateauser'sexpectations.

@OverridepublicvoidonBackPressed(){...}

Backstack

Backbutton

WhenFragment'sareaddedtotheviewinanXMLfile,theyarestaticandalwaysvisibletotheuser.Youcan'tmanagethestatedirectly,itistiedtothestateoftheactivity.

WhenyoucreateFragment'sincode,youcandynamicallymanagethemwiththeFragmentManager.Youmanuallyshow,hide,andreplacefragments.

TypicallyyoudeclareanXMLplaceholdertohouseyourfragment.ApopularchoiceisFrameLayoutwithanid.IfyouplantouseaFragmentwithoutaview(discussedlaterinthischapter),youdon'tneedaplaceholderlocation.

FragmenttransactionsoperateonFragments.YoucanbeginonebygettingareferencetotheFragmentManagerandthechangeswilltakeeffectwhenyouusecommit().

Usingadd(),yousupplytheidofyourfragmentholderandareferencetothefragmentyou'dlikecreated.

getSupportFragmentManager().beginTransaction().add(R.id.holder,newMyFrag()).commit();

Insteadofusingfragmentstoencapsulateviewfragments,youcancouldusethemtohandlebackgroundprocessing.

Todothis,youreturnnullfromonCreate()andaddthefragmentmanually(notinXML)inthehostingactivityusingtheFragmentManager.It'sessentialtouseastringtagtoidentifythefragmentsinceyoudon'thaveanidassociatedwithit.

Note:YounormallyusethiswithsetRetainInstance(true)toensurethattheFragmentisnotdestroyedonconfigurationchanges.

Backgroundfragmentsdon'tprovideaviewandarenotattachedaaholderinyourlayout.Whenaddingabackgroundfragmenttothebackstack,youmustgiveita"tag"soyoucanrefertoitagain.Otherwiseyouhavenowaytoretrievethefragmentoncethetransactioniscomplete.

getFragmentManager().beginTransaction().add(newMyFrag(),"tag").commit();

Youcanaddfragmentstothebackstack.Todoso,justaddacalltoaddToBackStack(true)beforethecommit()inyourtransaction.

FragmentManager

FragmentTransaction

Addingfragment

Backgroundfragments

Backstack

CreateCalculatorStateFragment.java.Thisfragmentwillbeabackgroundframentthatwillmanagethestateofourcalculator.Noticethatwearereturninganullviewwhencreatingtheview.

publicclassCalculatorStateFragmentextendsFragment{@OverridepublicViewonCreateView(LayoutInflaterinflater,ViewGroupcontainer,BundlesavedInstanceState){returnnull;}}

Addthenormalfirsttesttoourfragmentfile:

@RunWith(RobolectricTestRunner.class)

publicclassCalculatorStateFragmentTest{@TestpublicvoidshouldNotBeNull()throwsException{assertNotNull(newCalculatorStateFragment());}}

NowaddatesttoCalculatorActivitytoensurethatthefragmentispresent.Itshouldfail!

@TestpublicvoidshouldHaveCalculatorStateFragment()throwsException{assertNotNull(activity.getFragmentManager().findFragmentByTag("calculatorstate"));}

We'reusingfindFragmentByTag()sincethisisabackgroundfragment.Whenweaddthefragmenttotheactivity,we'lluseatagsothatwecanreferencethefragment.

Nowwehaveareasontowritecodeintheactivity.FirsttimethisisstartingtofeellikerealTDD!

AddanewinstanceofthefragmenttoourActivity'sFragmentManagerviaaFragmentTransactioninonCreate().

getFragmentManager().beginTransaction().add(newCalculatorStateFragment(),

Lab:AddCalculatorStateFragment

Createfragment

Testfragment

Testactivity

AddCalculatorStateFragmenttoCalculatorActivity

CALCULATOR_STATE_FRAGMENT_TAG).commit();

Auto-generateaTAGforthecalculatorstatefragmentusingtheIDE.

Nowretest-everythingshouldpass.

Yay,timeforacommit!

Commit

Whenyouwanttosavethestateofviewcomponentsorotherthingsthatarenotstoredinmorepermanentstorage,youwouldusethesaveandrestoreinstancestate.

Let'ssayyou'rebuildinganapplicationthatsearchesforyourfavoritecity'scuisineandyouhaveanEditTextthatallowsthemtoenterasearchterm.Ifyourotatethedevice,theactivityisdestroyedandrecreatedtherebyusingthetermthattheyhave