CS4720

AndroidActivity

CS4720– MobileApplicationDevelopment

Source:developer.android.com

CS4720

Activity• Conceptually,anActivityisasinglescreenofyourapplication

• Inotherwords,anAppreallyisacollectionofrelatedActivities

• ConsidereachActivitybothascreenandafeature

• AppscanactivateActivitiesinotherApps

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TheAppLifecycle

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TheActivity

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TheLifecycle• AnActivitycanbe:

– Resumed– activeandintheforegroundwithuserfocus

– Paused– active,butis“coveredup”byanotheractivitythatcurrentlyhastheuserfocus

– Stopped– currentlyresidinginthebackgroundandisnotattachedtothewindowmanagerandisnotvisible;canbekilledbysystemifmemoryisneeded

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LifecycleCallbacks

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LifecycleCallbacks• Makesuretomakethecorrectcallsinthecorrectmethods!

• IfyoudoeverythinginonCreate(),thenproblemscouldoccurwhenyouswitch

• Onadevicerotation,onDestroy()/onCreate()iscalled

• ConsidersavingstateusingonSaveInstanceState()toretainAppstatebetweenswitching

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onCreate()• CalledwhenAppisstartingfresh• ThisiswheresetContentView()(settingtheUI)iscalled

• ThisiswhyonCreate()iscalledonarotation–youmaybeusingadifferentlayout

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NextSteps• onStart()- CalledrightbeforeActivityisshowntouser

• onResume()– CalledjustbeforeActivitywillstartacceptinguserinput

• onPause()– CalledwhenanotherActivitywillcallonResume()– usedtosaveremainingchanges

• onStop()– CalledwhenActivityisnolongervisible

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UI• UIcomponentscomefromtheViewclass• AViewcontrolsasetofrectangularspaceandcanrespondtouserinteraction

• Canbethewholescreen,orjustasmallportion

• Technically,a“widget”(likeabutton)isaverysmallView

• ALayout(andit’sxml)isagroupofViewswithlocationinstructions

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AddingtotheManifest• AllActivitiesmustbedefinedintheandroidmanifest.xml file

• IntentsthatthisActivitycanrespondtoarealsodefinedhere

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LaunchinganewActivity• TolaunchanewActivity,createanIntentforthatActivityandsenditout

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Fragments• ConsideraFragmentasortof“sub-Activity”• AnActivitycanbemadeupofnumerousFragments,eachwiththeirownfeatures

• Thisisusefulwhenyouwanttomove/reordercomponentsfordifferentdisplaysizes/rotations

• AFragmentobeystheActivity’slifecyclestate

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Fragments

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Fragments• AFragmenthas:

– Itsownlifecyclecalls– Itsownlayouts– Itsownviews

• Infact,aFragmentlooksalmostexactlylikeanActivity!

• ToaddaFragment,instantiateitinthelayoutoftheActivity

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FragmentManager• ThemainbenefitsFragmentsarereusabilityandaddressability

• FragmentscanbeaccessedthroughtheFragmentManager andcanbeswappedontheflywhiletheAppisrunning

• FragmentscanaddresstheActivitythatcontainsthem,allowingforsharingofdatabetweenFragments

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