Android Chapter03 Life Cycle

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Part3

AndroidApplicationsLifeCycle

VictorMatosClevelandStateUniversity

Notesarebasedon:U l ki A d idUnlockingAndroidbyFrankAbleson,CharlieCollins,andRobi Sen.ISBN9781933988672ManningPublications,2009.AndroidDevelopershttp://developer.android.com/index.html

3.Android Application'sLifeCycle

AndroidApplicationsAnapplicationconsistsofoneormorecomponents thataredefined in the application's manifest file. A component can be onedefinedintheapplication smanifestfile.Acomponentcanbeoneofthefollowing:

1. AnActivity2. AService3. Abroadcastreceiver4. Acontentprovider

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AndroidApplications1.ActivityAnactivity usuallypresentsasinglevisualuserinterfacefromwhichanumberofactionscouldbeperformed.Altoughactivitiesworktogethertoformacohesiveuserinterface,eachactivityisindependentoftheothers.Typically,oneoftheactivitiesismarkedasthefirst onethatshouldbepresented

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totheuserwhentheapplicationislaunched.Movingfromoneactivitytoanotherisaccomplishedbyhavingthecurrentactivitystartthenextonethroughsocalledintents.

3Reference:FriedgerMffke([email protected])


AndroidApplications2.ServiceAservicedoesn'thaveavisualuserinterface,butratherrunsinthebackgroundforanindefiniteperiodoftime.It'spossibletoconnectto(bindto)anongoingservice(andstarttheserviceifit'snotalreadyrunning).

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Whileconnected,youcancommunicatewiththeservicethroughaninterfacethattheserviceexposes.


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AndroidApplications3.BroadcastreceiverAbroadcastreceiver isacomponentthatdoesnothingbutreceiveandreacttobroadcastannouncements.Manybroadcastsoriginateinsystemcode(eg.yougotmail)butanyotherapplicationscanalsoinitiatebroadcasts.Broadcastreceiversdonotdisplayauserinterface.However,theymaystartan

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p y f , y yactivityinresponsetotheinformationtheyreceive,or asservicesdo theymayusethenotificationmanagertoalerttheuser.



AndroidApplications4.ContentproviderAcontentprovidermakesaspecificsetoftheapplication'sdataavailabletootherapplications.Thedatausuallyisstoredinthefilesystem,orinanSQLitedatabase.Thecontentproviderimplementsastandardsetofmethodsthatenableotherapplicationstoretrieveandstoredataofthetypeitcontrols.

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However,applicationsdonotcallthesemethodsdirectly.Rathertheyuseacontentresolverobjectandcallitsmethodsinstead.Acontentresolvercantalktoanycontentprovider;itcooperateswiththeprovidertomanageanyinterprocesscommunicationthat'sinvolved.


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AndroidApplicationsEveryAndroidapplicationrunsinitsownprocess(with its own instance of the Dalvik virtual machine).(withitsowninstanceoftheDalvikvirtualmachine).Wheneverthere'sarequestthatshouldbehandledbyaparticularcomponent,

Androidmakessurethattheapplicationprocessofthecomponentisrunning,

startingitifnecessary,and thatanappropriateinstanceofthecomponentisavailable,creatingthe

instanceifnecessary.

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ApplicationsLifeCycleALinuxprocessencapsulatinganAndroidapplicationiscreatedforthep p g ppapplicationwhensomeofitscodeneedstoberun,andwillremainrunninguntil

1. itisnolongerneeded,OR2. thesystemneedstoreclaimitsmemoryforusebyother

applications.

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ApplicationsLifeCycleAnunusualandfundamentalfeatureofAndroidisthat anapplicationppprocess'slifetimeis not directlycontrolledbytheapplicationitself.Instead,itisdeterminedbythesystemthroughacombinationof

1. thepartsoftheapplicationthatthesystemknowsarerunning,2. howimportantthesethingsaretotheuser,and3. how much overall memory is available in the system.

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3. howmuchoverallmemoryisavailableinthesystem.

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ComponentLifecyclesApplicationcomponentshavea lifecycle1. Abeginning whenAndroidinstantiatesthemtorespondto

intents2. Anend whentheinstancesaredestroyed.3. Inbetween,theymaysometimesbeactive orinactive,orinthe

caseofactivities visible totheuserorinvisible.

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LifeasanAndroidApplication:Active/InactiveVisible/Invisible

Start End

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Activty Stack

Activitiesinthesystemaremanagedasanactivitystack.y g y Whenanewactivityisstarted,itisplacedonthetop ofthe

stackandbecomestherunningactivity thepreviousactivityalwaysremainsbelowitinthestack,andwillnotcometotheforegroundagainuntilthenewactivityexits.

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IftheuserpressestheBackButtonthenextactivityonthestackmovesupandbecomesactive.


ActivityStackNewActivity RunningActivity

LastRunningActivity

Activityn1. . .

NewActivitystarted

Backbuttonpushedorrunningactivityclosed

Activity Stack

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Activity1Activity2Activity3...ActivityStack

PreviousActivities Removedto

freeresources

Figure1.

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3.Android Application'sLifeCycleLifeCycleStates

Anactivityhasessentiallythreestates:1. Itisactive orrunning2. Itispaused or3. Itisstopped .

1313Figure2.


LifeCycleStatesAnactivityhasessentiallythreestates:

1. Itisactive orrunningwhenitisintheforeground ofthescreen(atthetopoftheactivitystackforthecurrenttask).Thisistheactivitythatisthefocusfortheuser'sactions.

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LifeCycleStatesAn activityhasessentiallythreestates(cont.):

2. Itispaused ifithaslostfocusbutisstillvisibletotheuser.Thatis,anotheractivityliesontopofitandthatnewactivityeitheristransparent ordoesn'tcoverthefullscreen.Apausedactivityiscompletelyalive (itmaintainsallstateandmemberinformationandremainsattachedtothewindowmanager),butcanbe

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g ),killedbythesysteminextremelowmemorysituations.


LifeCycleStatesAnactivityhasessentiallythreestates(cont.):

3. Itisstopped ifitiscompletelyobscured byanotheractivity.Itstillretainsallstateandmemberinformation.However,itisnolongervisibletotheusersoitswindowishiddenanditwilloftenbekilledbythesystemwhenmemoryisneededelsewhere.

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ApplicationsLifeCycle

1717Figure3.


ApplicationsLifeCycleYourturn!EXPERIMENT1. Teachingnotes1. WriteanAndroidapp.(PuraVida)toshowthedifferentcyclesfollowedbyan

application.2. Themain.xmllayoutshouldincludeaButton(text:Finish,id:btnFinish)and

anEditText container(txt:andidtxtMsg).3. UsetheonCreate methodtoconnectthebuttonandtextboxtotheprogram.

Addthefollowinglineofcode:Toast.makeText(this, "onCreate", 1).show();

4. Theclickmethodhasonlyonecommand:finish(); calledtoterminatethe

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application.AddaToastcommand(astheoneabove)toeachoftheremainingsixmainevents.TosimplifyyourjobusetheEclipsestopmenu:Source>Override/ImplementMethods

5. Ontheoptionwindowcheckmarkeachofthefollowingevents:onStart,onResume,onPause,onStop,onDestry,onRestart(noticehowmanyonEventmethodsarethere!!!)

6. Saveyourcode.

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ApplicationsLifeCycleYourturn!EXPERIMENT1(cont.) Teachingnotes7. Compileandexecuteapplication.8. WritedownthesequenceofmessagesdisplayedbytheToastcommands.9. PresstheFINISHbutton.Observethesequenceofstates.10. Reexecutetheapplication11. PressemulatorsHOMEbutton.Whathappens?12. Clickonlaunchpad,lookforiconandreturntothePuraVidaapp.What

sequenceofmessagesisdisplayed?13. ClickontheemulatorsCALL(Greenphone).Istheapppausedorstopped?

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( p ) pp p pp14. ClickontheBACKbuttontoreturntotheapplication.15. LongtapontheemulatorsHANGUPbutton.Whathappens?


ApplicationsLifeCycleYourturn!EXPERIMENT2 Teachingnotes7. Runasecondemulator.

1. Makeavoicecalltothefirstemulatorthatisstillshowingourapp.Whathappensonthiscase?(realtimesynchronousrequest)

2. Sendatextmessagetofirstemulator(asynchronousattentionrequest)8. WriteaphraseintheEditText box(thesearethebestmomentsofmylife.).9. Reexecutetheapp.Whathappenedtothetext?

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pp pp

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ApplicationsLifeCycleYourturn!EXPERIMENT3 TeachingnotesProvidedatapersistency.18. UsetheonPausemethodtoaddthefollowingfragment

SharedPreferences myFile1 = getSharedPreferences("myFile1", Activity.MODE_PRIVATE);

SharedPreferences.Editor myEditor = myFile1.edit();String temp = txtMsg.getText().toString();myEditor.putString("mydata", temp);myEditor.commit();

18 Use the onResumemethod to add the following frament

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18. UsetheonResumemethodtoaddthefollowingframentSharedPreferences myFile = getSharedPreferences("myFile1",

Activity.MODE_PRIVATE);if ( (myFile != null) && (myFile.contains("mydata")) ) {

String temp = myFile.getString("mydata", "***");txtMsg.setText(temp);

}

19. Whathappensnowwiththedatapreviouslyenteredinthetextbox?


LifeCycleEventsSummary:APPMILESTONESIfanactivityispausedorstopped,thesystemcandropitfrommemoryeitherbyaskingittofinish(callingitsfinish() method),orsimplykillingitsprocess.Whenitisdisplayedagaintotheuser,itmustbecompletelyrestartedandrestoredtoitspreviousstate.Asanactivitytransitionsfromstatetostate,itisnotifiedofthechangebycallstothefollowingprotectedtransitionmethods:

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voidonCreate(BundlesavedInstanceState)voidonStart()voidonRestart()voidonResume()

voidonPause()voidonStop()voidonDestroy()

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LifeCycleEventsAllofthesemethodsarehooks thatyoucanoverridetodoappropriateworkwhenthestatechanges.

(MUST)AllactivitiesmustimplementonCreate() todotheinitialsetupwhentheobjectisfirstinstantiated.(HighlyRecommended)Many activities will also implement onPause() to commit data

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ManyactivitieswillalsoimplementonPause() tocommitdatachangesandotherwisepreparetostopinteractingwiththeuser.


ApplicationsLifetimeEntireLifetimet e et eTheseventransitionmethods(Figure3)definetheentirelifecycleofanactivity.

Theentirelifetime ofanactivityhappensbetweenthefirstcalltoonCreate() throughtoasinglefinalcalltoonDestroy().

Anactivitydoesallitsinitialsetupof"global"stateinonCreate(),

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andreleasesallremainingresourcesinonDestroy().

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VisibleLifetimeVisibleLifetimes b e et eThevisiblelifetime ofanactivityhappensbetweenacalltoonStart() untilacorrespondingcalltoonStop().

Duringthistime,theusercanseetheactivityonscreen,thoughitmaynotbeintheforegroundandinteractingwiththeuser.

TheonStart()andonStop()methodscanbecalledmultipletimes,

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astheactivityalternatesbetweenbeingvisibleandhiddentotheuser.

Betweenthesetwomethods,youcanmaintainresourcesthatareneededtoshowtheactivitytotheuser.


ForegroundLifetimeForegroundLifetimeo eg ou d et eTheforegroundlifetime ofanactivityhappensbetweenacalltoonResume() untilacorrespondingcallto onPause().

Duringthistime,theactivityisinfrontofallotheractivitiesonscreenandisinteractingwiththeuser.

Anactivitycanfrequentlytransitionbetweentheresumed andpaused

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states forexample, onPause()iscalledwhenthedevicegoestosleeporwhenanew

activityisstarted, onResume()iscalledwhenanactivityresultoranewintentis

delivered.

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LifeCycleMethodsMethod: onCreate()

Calledwhentheactivityisfirstcreated. Thisiswhereyoushoulddoallofyournormalstaticsetup

createviews,binddatatolists,andsoon. ThismethodispassedaBundle objectcontainingtheactivity's

previousstate,ifthatstatewascaptured. AlwaysfollowedbyonStart()

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y y ()


LifeCycleMethodsMethod: onRestart()

Calledaftertheactivityhasbeenstopped,justpriortoitbeingstartedagain.

AlwaysfollowedbyonStart()

Method: onStart()

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Calledjustbeforetheactivitybecomesvisibletotheuser. FollowedbyonResume()iftheactivitycomestotheforeground,

oronStop()ifitbecomeshidden.

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LifeCycleMethodsMethod: onResume()

1. Calledjustbeforetheactivitystartsinteractingwiththeuser.2. Atthispointtheactivityisatthetopoftheactivitystack,with

userinputgoingtoit.3. AlwaysfollowedbyonPause().

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LifeCycleMethodsMethod: onPause()

1. Calledwhenthesystemisabouttostartresuminganotheractivity.

2. Thismethodistypicallyusedtocommit unsavedchangestopersistentdata,stopanimationsandotherthingsthatmaybeconsumingCPU,andsoon.

3. Itshoulddowhateveritdoesveryquickly,becausethenext

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y q y,activitywillnotberesumeduntilitreturns.

4. FollowedeitherbyonResume()iftheactivityreturnsbacktothefront,orbyonStop()ifitbecomesinvisibletotheuser.

5. Theactivityinthisstateiskillable bythesystem.

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LifeCycleMethodsMethod: onStop()

1. Calledwhentheactivityisnolongervisibletotheuser.2. Thismayhappenbecauseitisbeingdestroyed,orbecause

anotheractivity(eitheranexistingoneoranewone)hasbeenresumedandiscoveringit.

3. FollowedeitherbyonRestart()iftheactivityiscomingbacktointeractwiththeuser,orbyonDestroy()ifthisactivityisgoing

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, y y() y g gaway.



LifeCycleMethodsMethod: onDestroy()

1. Calledbeforetheactivityisdestroyed.2. Thisisthefinalcallthattheactivitywillreceive.3. Itcouldbecalledeitherbecausetheactivityisfinishing(someone

calledfinish() onit),orbecausethesystemistemporarilydestroyingthisinstanceoftheactivitytosavespace.

4. Youcandistinguishbetweenthesetwoscenarioswiththe

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gisFinishing()method.


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LifeCycleMethodsKillableStates Activitiesonkillablestatescanbeterminatedbythesystematany

timeafterthemethodreturns,withoutexecutinganotherlineoftheactivity'scode.

Threemethods(onPause(),onStop(),andonDestroy())arekillable.() h l h d b ll d b f h

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onPause()istheonlyonethatisguaranteedtobecalledbeforetheprocessiskilled onStop()andonDestroy()maynotbe.

Therefore,youshoulduseonPause()towriteanypersistentdata(suchasuseredits)tostorage.

AsanasideAndroidPreferences


LifeCycleMethods

Preferencesisalightweightmechanismtostoreandretrievekeyvalue pairsofprimitivedatatypes.Itistypicallyusedtostoreapplicationpreferences,suchasadefaultgreetingoratextfonttobeloadedwhenevertheapplicationisstarted.CallContext.getSharedPreferences() toreadandwritevalues.Assignanametoyoursetofpreferencesifyouwanttosharethemwithothercomponentsinthesameapplication,oruse Activity.getPreferences()withnonametokeepthemprivatetothecallingactivity.Youcannotsharepreferencesacrossapplications(exceptbyusingacontentprovider). 3434

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ExampleLifeCycleExample

LAYOUT

/T Vi

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Example:LifeCycleCode:LifeCycleDemo.Part1Package cis493.lifecycleimport android.app.Activity;import android.content.SharedPreferences;import android.os.Bundle;import android.view.View;import android.widget.*;//GOAL: show the following life-cycle events in action //protected void onCreate(Bundle savedInstanceState);// t t d id St t()

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//protected void onStart();//protected void onRestart();//protected void onResume();//protected void onPause();//protected void onStop();//protected void onDestroy();

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Example:LifeCycleCode:LifeCycleDemo.Part1

public class GoodLife extends Activity {publicclassGoodLife extendsActivity{//classvariablesandconstantspublicstaticfinalStringMYPREFSID ="MyPrefs001";publicstaticfinalint actMode =Activity.MODE_PRIVATE;LinearLayout myScreen;EditText txtColorSelect;TextView txtToDo;

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Button btnFinish;



@Overridepublic void onCreate(Bundle savedInstanceState) {

super.onCreate(savedInstanceState);setContentView(R.layout.main);myScreen = (LinearLayout) findViewById(R.id.myScreen);

txtToDo = (TextView) findViewById(R.id.txtToDo);String msg = "Instructions: \n "

+ "0. New instance (onCreate, onStart, onResume) \n "+ "1. Back Arrow (onPause, onStop, onDestroy) \n "+ "2. Finish (onPause, onStop, onDestroy) \n "+ "3. Home (onPause, onStop) \n "+ "4. After 3 > App Tab > re-execute current app \n "

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pp pp+ " (onRestart, onStart, onResume) \n "+ "5. Run DDMS > Receive a phone call or SMS \n "+ " (onRestart, onStart, onResume) \n "+ "6. Enter some data - repeat steps 1-5 \n ";

txtToDo.setText(msg);

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Code:LifeCycleDemo.Part2txtColorSelect = (EditText) findViewById(R.id.txtColorSelect);// you may want to skip discussing the listener until later

l l dd h d i ( t t h (){


Example:LifeCycletxtColorSelect.addTextChangedListener(new TextWatcher(){ public void onTextChanged(CharSequence s, int start, int before, int count) {// TODO Auto-generated method stub

}public void beforeTextChanged(CharSequence s, int start, int count,int after) {// TODO Auto-generated method stub

}public void afterTextChanged(Editable s) {changeBackgroundColor(s.toString());

}});

btnFinish = (Button) findViewById(R.id.btnFinish);btnFinish.setOnClickListener(new OnClickListener() {

public void onClick(View arg0) {finish();

} }); Toast.makeText(getApplicationContext(), "onCreate", 1).show();}

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@Overrideprotected void onPause() {

super.onPause();saveDataFromCurrentState();Toast.makeText(this, "onPause", 1).show();

}

@Overrideprotected void onRestart() {

super.onRestart();Toast.makeText(this, "onRestart", 1).show();

}

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}

@Overrideprotected void onResume() {

super.onResume();Toast.makeText(this, "onResume", 1).show();

}

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Example:LifeCycleCode:LifeCycleDemo.Part4@Overrideprotected void onStart() {

// TODO Auto-generated method stubsuper.onStart();updateFromSavedState();Toast.makeText(this, "onStart", 1).show();

}

@Overrideprotected void onDestroy() {

// TODO Auto-generated method stubsuper.onDestroy();

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Toast.makeText(this, "onDestroy", 1).show();}

@Overrideprotected void onStop() {// TODO Auto-generated method stubsuper.onStop();Toast.makeText(this, "onStop", 1).show();

}


Example:LifeCycleCode:LifeCycleDemo.Part5protected void saveDataFromCurrentState() {

SharedPreferences myPrefs = getSharedPreferences(MYPREFSID, actMode);h d f di di f di ()SharedPreferences.Editor myEditor = myPrefs.edit();myEditor.putString("myBkColor", txtColorSelect.getText().toString());myEditor.commit();

}// saveDataFromCurrentState

protected void updateFromSavedState() {SharedPreferences myPrefs = getSharedPreferences(MYPREFSID, actMode);

if ((myPrefs != null) && (myPrefs.contains("myBkColor"))) {String theChosenColor = myPrefs.getString("myBkColor", "");txtColorSelect.setText(theChosenColor);

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changeBackgroundColor(theChosenColor);}

}// UpdateFromSavedState

protected void clearMyPreferences() {SharedPreferences myPrefs = getSharedPreferences(MYPREFSID, actMode);SharedPreferences.Editor myEditor = myPrefs.edit();myEditor.clear();myEditor.commit();

}

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Example:LifeCycleCode:LifeCycleDemo.Part6private void changeBackgroundColor (String theChosenColor){

// h b k d l// change background colorif (theChosenColor.contains("red"))

myScreen.setBackgroundColor(0xffff0000);else if (theChosenColor.contains("green"))

myScreen.setBackgroundColor(0xff00ff00);else if (theChosenColor.contains("blue"))

myScreen.setBackgroundColor(0xff0000ff);else {

//reseting user preferencesclearMyPreferences();myScreen.setBackgroundColor(0xff000000);

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}}



/*protectedvoidonRestoreInstanceState(BundlesavedInstanceState)ThismethodiscalledafteronStart()whentheactivityisbeingreinitializedfromapreviouslysavedstate.ThedefaultimplementationofthismethodperformsarestoreofanyviewstatethathadpreviouslybeenfrozenbyonSaveInstanceState(Bundle).*/@Overrideprotected void onRestoreInstanceState(Bundle savedInstanceState) {super.onRestoreInstanceState(savedInstanceState);Toast.makeText(getBaseContext(),

"onRestoreInstanceState ...BUNDLING",

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,Toast.LENGTH_LONG).show();

}

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Example:LifeCycleCode:LifeCycleDemo.Part9/*

d id ( dl )protectedvoidonSaveInstanceState(BundleoutState)Calledtoretrieveperinstancestatefromanactivitybeforebeingkilledsothatthestatecanberestoredin

onCreate(Bundle)oronRestoreInstanceState(Bundle)(theBundlepopulatedbythismethod

willbepassedtoboth).Thismethodiscalledbeforeanactivitymaybekilledsothatwhenitcomesbacksometimeinthefutureitcanrestoreitsstate.Forexample,ifactivityBislaunchedinfrontofactivityA,andatsomepointactivityAiskilledtoreclaimresources,activityAwillhaveachancetosavethecurrentstateof

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y fitsuserinterfaceviathismethodsothatwhentheuserreturnstoactivityA,thestateoftheuserinterfacecanberestoredvia:onCreate(Bundle)oronRestoreInstanceState(Bundle).*/



@Overrideprotected void onSaveInstanceState(Bundle outState) {

super.onSaveInstanceState(outState);Toast.makeText(getBaseContext(),

"onSaveInstanceState ...BUNDLING",Toast.LENGTH_LONG).show();

} // onSaveInstanceState

}//LyfeCicleDemo

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Example:LifeCycleonCreate onStart onResume

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Example:LifeCycleonPause onStop onDestroy

4848AfterpressingBackArrow

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Example:LifeCycleAfterpressingHome

AfterreexecutingAndLife2

AfterBackArroworFinish

onSavedInstanceState >onPause >onStop >

onRestart >onStart >onResume >

onPause >onStop >onDestroy >

PreservingStateInformation1 Enter data: Hasta la vista!

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EndofExample

1. Enter data: Hasta lavista!2. ClickHomebutton3. onSavedInstance >onPause >onStop4. Readyour SMS5. Executeaninstanceoftheapplication6. onRestart >onStart >onResume7. Youseethedataenteredinstep1

ApplicationsLifeCycleQuestions ?Questions?

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ApplicationsLifeCycleAppendixAppendixSavingState

@OverridepublicvoidonCreate(BundlesavedInstanceState){

...somevalue =savedInstanceState.getString(SOME_KEY);

...

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}...@OverrideprotectedvoidonSaveInstanceState(BundleoutState){

super.onSaveInstanceState(outState);outState.putString(SOME_KEY,"blahblah blah");

}

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Android Chapter03 Life Cycle