Android chapter03 life cycle

9/12/2011
1
Part3
Android
Application’sLifeCycle
VictorMatos
ClevelandStateUniversity
Notesarebasedon:
Ul ki Ad id
U
n
l
oc
ki
ng
A
n
d
ro
id

byFrankAbleson,CharlieCollins,andRobi Sen.
ISBN978‐1‐933988‐67‐2
ManningPublications,2009.
AndroidDevelopers
/>3.Android– Application'sLifeCycle
AndroidApplications
Anapplicationconsistsofoneormorecomponents thatare
defined in the application
'
s manifest file. A component can be one

defined

in

the

application s

manifest

file.

A

component

can

be

one

ofthefollowing:
1. AnActivity
2. AService
3. Abroadcastreceiver
4.
A
contentprovide
r

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2
3.Android– Application'sLifeCycle
AndroidApplications
1.Activity
Anactivity usuallypresentsasinglevisualuserinterfacefromwhichanumberof
actionscouldbeperformed.
Altoughactivitiesworktogethertoformacohesiveuserinterface,eachactivity
isindependentoftheothers.
Typically,oneoftheactivitiesismarkedasthefirst onethatshouldbepresented
3
totheuserwhentheapplicationislaunched.
Movingfromoneactivitytoanotherisaccomplishedbyhavingthecurrent
activitystartthenextonethroughsocalledintents.
3
Reference:FriedgerMüffke()
3.Android– Application'sLifeCycle
AndroidApplications
2.Service
Aservicedoesn'thaveavisualuserinterface,butratherrunsinthebackground
foranindefiniteperiodoftime.
It'spossibletoconnectto(bindto)anongoingservice(andstarttheserviceifit's
notalreadyrunning).
4
Whileconnected,youcancommunicatewiththeservicethroughaninterface
thattheserviceexposes.
4
Reference:FriedgerMüffke()
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3
3.Android– Application'sLifeCycle
AndroidApplications
3.Broadcastreceiver
Abroadcastreceiver isacomponentthatdoesnothingbutreceiveandreactto
broadcastannouncements.
Manybroadcastsoriginateinsystemcode(eg.“yougotmail“)butanyother
applicationscanalsoinitiatebroadcasts.
Broadcastreceiversdonotdis
p
la
y
auserinter
f
ace.However
,
the
y
ma
y
startan
5
py f
, y y
activityinresponsetotheinformationtheyreceive,or‐ asservicesdo‐ they
mayusethenotificationmanagertoalerttheuser.
5
Reference:FriedgerMüffke()
3.Android– Application'sLifeCycle
AndroidApplications

4.Contentprovider
Acontentprovider makesaspecificsetoftheapplication'sdataavailableto
otherapplications.
Thedatausuallyisstoredinthefilesystem,orinanSQLitedatabase.
Thecontentproviderimplementsastandardsetofmethodsthatenableother
applicationstoretrieveandstoredataofthetypeit
controls.
6
However,applicationsdonotcallthesemethodsdirectly.Rathertheyusea
contentresolverobjectandcallitsmethodsinstead.Acontentresolvercantalk
toanycontentprovider;itcooperateswiththeprovidertomanageany
interprocesscommunicationthat'sinvolved.
6
Reference:FriedgerMüffke()
9/12/2011
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3.Android– Application'sLifeCycle
AndroidApplications
EveryAndroidapplicationrunsinitsownprocess
(
with its own instance of the Dalvik virtual machine
).
(
with

its

own

instance


of

the

Dalvik

virtual

machine
).

Wheneverthere'sarequestthatshouldbehandledbyaparticularcomponent,
• Androidmakessurethattheapplicationprocessofthecomponentis
running,
• startingitifnecessary,and
• thatanappropriateinstanceofthecomponentisavailable,creatingthe
instanceifnecessary.
77
3.Android– Application'sLifeCycle
Application’sLifeCycle
ALinux
p
rocessenca
p
sulatin
g
anAndroida
pp
licationiscreatedforthe

p pg pp
applicationwhensomeofitscodeneedstoberun,andwillremain
runninguntil
1. itisnolongerneeded,OR
2. thesystemneedstoreclaimitsmemoryforusebyother
applications.
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3.Android– Application'sLifeCycle
Application’sLifeCycle
AnunusualandfundamentalfeatureofAndroidisthat ana
pp
lication
pp
process'slifetimeis not directlycontrolledbytheapplicationitself.
Instead,itisdeterminedbythesystemthroughacombinationof
1. thepartsoftheapplicationthatthesystemknowsarerunning,
2. howimportantthesethingsaretotheuser,and
3.
how much overall memory is available in the sys tem.
9
3.
how

much

overall

memory


is

available

in

the

system.
9
3.Android– Application'sLifeCycle
ComponentLifecycles
Applicationcomponentshavea lifecycle
1. Abeginning whenAndroidinstantiatesthemtorespondto
intents
2. Anend whentheinstancesaredestroyed.
3. Inbetween,theymaysometimesbeactive orinactive,or‐inthe
caseofactivities‐ visible totheuserorinvisible.
1010
LifeasanAndroidApplication:
Active/Inactive
Visible/Invisible
Start
End
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3.Android– Application'sLifeCycle
Activty Stack
• Activitiesinthes

y
stemaremana
g
edasanactivit
y
stack.
y g
y
• Whenanewactivityisst arted,itisplacedonthetop ofthe
stackandbecomestherunningactivity‐‐ the previous
activityalwaysremainsbelowitinthestack,andwillnot
cometotheforegroundagainuntilthenewactivityexits.
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• IftheuserpressestheBackButtonthenextactivityonthe
stackmovesupandbecomesactive.
3.Android– Application'sLifeCycle
ActivityStack
NewActivity RunningActivity
LastRunning
Activity
Activityn‐1
. . .
NewActivity
started
Backbuttonpushedor
runningactivityclosed
Activity Stack
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Activity1
Activity2

Activity3
.

.

.
Activity

Stack
Previous
Activities
Removedto
freeresources
Figure1.
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3.Android– Application'sLifeCycle
LifeCycleStates
Anactivityhasessentially
threestates:
1. Itisactive orrunning
2. Itispaused or
3. Itisstopped .
1313
Figure2.
3.Android– Application'sLifeCycle
LifeCycleStates
Anactivityhasessentiallythreestates:
1. Itisactive orrunning whenitisintheforeground ofthescreen
(atthetopoftheactivitystackforthecurrenttask).

Thisistheactivitythatisthefocusfortheuser'sactions.
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3.Android– Application'sLifeCycle
LifeCycleStates
An activityhasessentiallythreestates(cont.):
2. Itispaused ifithaslostfocusbutisstillvisibletotheuser.
Thatis,anotheractivityliesontopofitandthatnewactivityeitheris
transparent ordoesn'tcoverthefullscreen.
Apausedactivityiscompletelyalive (itmaintainsallstateandmember
informationandremains
attachedtothewindowmana
g
er
),
butcanbe
151515
g),
killedbythesysteminextremelowmemorysituations.
3.Android– Application'sLifeCycle
LifeCycleStates
Anactivityhasessentiallythreestates(cont.):
3. Itisstopped ifitiscompletelyobscured byanotheractivity.
Itstillretainsallstateandmemberinformation.However,itisnolonger
visibletotheusersoitswindowishiddenanditwilloftenbekilledby
thesystemwhenmemoryisneededelsewhere.
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9

3.Android– Application'sLifeCycle
Application’s
LifeCycle
1717
Figure3.
3.Android– Application'sLifeCycle
Application’sLifeCycle
Yourturn!
EXPERIMENT1.
Teachingnotes
1. W r iteanAndroidapp.(“PuraVida”)toshowthedifferentcyclesfollowedbyan
application.
2. Themain.xmllayoutshouldincludeaButton(text:“Finish”,id:btnFinish)and
anEditTe xt container(txt:“”andidtxtMsg).
3. UsetheonCreate methodtoconnectthebuttonandtextboxtotheprogram.
Addthefollowinglineofcode:
Toast.makeText(this, "onCreate", 1).show();
4. Theclickmethodhasonlyonecommand:finish(); calledtoterminatethe
1818
application.AddaToast‐command(astheoneabove)toeachofthe remaining
sixmainevents.Tosimplifyyourjob usetheEclipse’stopmenu:Source>
Override/ImplementMethods…
5. Ontheoptionwindowcheckmarkeachofthefollowingevents:onStart,
onResume,onPause,onStop,onDestry,onRestart
(noticehowmanyonEvent… methods
arethere!!!)
6. Saveyourcode.
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3.Android– Application'sLifeCycle

Application’sLifeCycle
Yourturn!
EXPERIMENT1(cont.)
Teachingnotes
7. Compileandexecuteapplication.
8. W r itedownthesequenceofmessagesdisplayedbytheToast‐commands.
9. PresstheFINISHbutton.Observethesequenceofstates.
10. Re‐executetheapplication
11. Pressemulator’sHOMEbutton.Whathappens?
12. Clickonlaunchpad,lookforiconandreturntothe“PuraVida”app.What
sequenceofmessagesisdisplayed?
13. Click
ontheemulator’sCALL
(
Green
p
hone
)
.Isthea
pp

p
ausedorsto
pp
ed?
1919
( p) pp p pp
14. ClickontheBACKbuttontoreturntotheapplication.
15. Long‐tapontheemulator’sHANG‐UPbutton.Whathappens?
3.Android– Application'sLifeCycle

Application’sLifeCycle
Yourturn!
EXPERIMENT2
Teachingnotes
7. Runasecondemulator.
1. Makeavoice‐calltothefirstemulatorthatisstillshowingourapp.What
happensonthiscase?(real‐timesynchronousrequest)
2. Sendatext‐messagetofirstemulator(asynchronousattentionrequest)
8. W r iteaphraseintheEditText box(“thesearethebestmomentsofmylife….”).
9. Re‐ex ecutethea
pp
.Whatha
pp
enedtothetext?
2020
pp pp
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3.Android– Application'sLifeCycle
Application’sLifeCycle
Yourturn!
EXPERIMENT3
Teachingnotes
Providedatapersistency.
18. UsetheonPause methodtoaddthefollowingfragment
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
onResume
method to add the following
frament
2121
18
.
Use

the

onResume
method

to

add

the

following

frament
SharedPreferences myFile = getSharedPreferences("myFile1",
Activity.MODE_PRIVATE);
if ( (myFile != null) && (myFile.contains("mydata")) ) {
String temp = myFile.getString("mydata", "***");
txtMsg.setText(temp);

}
19. Whathappensnowwiththedatapreviouslyenteredinthetextbox?
3.Android– Application'sLifeCycle
LifeCycleEvents
Summary:APPMILESTONES
Ifanactivityispausedorstopped,thesystemcandropitfrommemoryeitherby
askingittofinish(callingitsfinish() method),orsimplykillingitsprocess.
Whenitisdisplayedagaintotheuser,itmustbecompletelyrestartedandrestored
toitspreviousstate.
Asanactivitytransitionsfromstatetostate,itisnotifiedofthechangebycallsto
thefollowingprotectedtransition methods:
2222
voidonCreate(BundlesavedInstanceState)
voidonStart()
voidonRestart()
voidonResume()
voidonPause()
voidonStop()
voidonDestroy()
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3.Android– Application'sLifeCycle
LifeCycleEvents
Allofthesemethodsarehooks thatyoucanoverridetodoappropriate
workwhenthestatechanges.
(MUST)
AllactivitiesmustimplementonCreate() todotheinitialsetup
whentheobjectisfirstinstantiated.
(HighlyRecommended)
Many activities will also implement

onPause
()
to commit data
2323
Many

activities

will

also

implement

onPause
()
to

commit

data

changesandotherwisepreparetostopinteractingwiththeuser.
3.Android– Application'sLifeCycle
Application’sLifetime
En
t
ir
e
Lif

et
im
e
te et e
Theseventransitionmethods(Figure3)definetheentirelifecycleofan
activity.
• Theentirelifetime ofanactivityhappensbetweenthefirstcallto
onCreate() throughtoasinglefinalcalltoonDestroy().
• Anactivitydoesallitsinitialsetupof"global"stateinonCreate(),
2424
andreleasesallremainingresourcesinonDestroy().
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3.Android– Application'sLifeCycle
VisibleLifetime
Vi
s
i
b
l
e
Lif
et
im
e
sbe et e
Thevisiblelifetime ofanactivityhappensbetweenacalltoonStart() untila
correspondingcalltoonStop().
Duringthistime,theusercanseetheactivityon‐screen,thoughit
maynotbeintheforegroundandinteractingwiththeuser.

• TheonStart()andonStop()methodscanbecalled
multipletimes,
2525
astheactivityalternatesbetweenbeingvisibleandhiddentothe
user.
• Betweenthesetwomethods,youcanmaintainresourcesthatare
neededtoshowtheactivitytotheuser.
3.Android– Application'sLifeCycle
ForegroundLifetime
F
o
r
eg
r
ou
n
d
Lif
et
im
e
oegou d et e
Theforegroundlifetime ofanactivityhappensbetweenacallto
onResume() untilacorrespondingcallto onPause().
Duringthistime,theactivityisinfrontofallotheractivitiesonscreen
andisinteractingwiththeuser.
Anactivitycanfrequentlytransitionbetweentheresumed andpaused
2626
states—forexample,
• onPause()iscalledwhenthedevicegoestosleeporwhenanew

activityisstarted,
• onResume()iscalledwhenanactivityresultoranewintentis
delivered.
9/12/2011
14
3.Android– Application'sLifeCycle
LifeCycleMethods
Method: onCreate()
• Calledwhentheactivityisfirstcreated.
• Thisiswhereyoushoulddoallofyournormalstaticsetup—
createviews,binddatatolists,andsoon.
• ThismethodispassedaBundle objectcontainingtheactivity's
previousstate,ifthatstatewascaptured.
• Alwa
y
sfollowedb
y
onStar
t
()
2727
y y
()
3.Android– Application'sLifeCycle
LifeCycleMethods
Method: onRestart()
• Calledaftertheactivityhasbeenstopped,justpriortoitbeing
startedagain.
• AlwaysfollowedbyonStart()
Method: onStart()

2828
• Calledjustbeforetheactivitybecomesvisibletotheuser.
• FollowedbyonResume()iftheactivitycomestotheforeground,
oronStop()ifitbecomeshidden.
9/12/2011
15
3.Android– Application'sLifeCycle
LifeCycleMethods
Method: onResume()
1. Calledjustbeforetheactivitystartsinteractingwiththeuser.
2. Atthispointtheactivityisatthetopoftheactivitystack,with
userinputgoingtoit.
3. AlwaysfollowedbyonPause().
2929
3.Android– Application'sLifeCycle
LifeCycleMethods
Method: onPause()
1. Calledwhenthesystemisabouttostartresuminganother
activity.
2. Thismethodistypicallyusedtocommit unsavedchangesto
persistentdata,stopanimationsandotherthingsthatmaybe
consumingCPU,andsoon.
3. Itshoulddowhateveritdoesver
y

q
uickl
y,
becausethenext
3030

y qy,
activitywillnotberesumeduntilitreturns.
4. FollowedeitherbyonResume()iftheactivityreturnsbacktothe
front,orbyonStop()ifitbecomesinvisibletotheuser.
5. Theactivityinthisstateiskillable bythesystem.
9/12/2011
16
3.Android– Application'sLifeCycle
LifeCycleMethods
Method: onStop()
1. Calledwhentheactivityisnolongervisibletotheuser.
2. Thismayhappenbecauseitisbeingdestroyed,orbecause
anotheractivity(eitheranexistingoneoranewone)hasbeen
resumedandiscoveringit.
3. FollowedeitherbyonRestart()iftheactivityiscomingbackto
interact
withtheuser
,
orb
y
onDestro
y
()
ifthisactivit
y
is
g
oin
g


3131
, y
y
() y gg
away.
4. Theactivityinthisstateiskillable bythesystem.
3.Android– Application'sLifeCycle
LifeCycleMethods
Method: onDestroy()
1. Calledbeforetheactivityisdestroyed.
2. Thisisthefinalcallthattheactivitywillreceive.
3. Itcouldbecalledeitherbecausetheactivityisfinishing(someone
calledfinish() onit),orbecausethesystemistemporarily
destroyingthisinstanceoftheactivitytosavespace.
4. Youcandistin
g
uishbetweenthesetwoscenarioswiththe
3232
g
isFinishing()method.
5. Theactivityinthisstateiskillable bythesystem.
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17
3.Android– Application'sLifeCycle
LifeCycleMethods
KillableStates
• Activitiesonkillablestatescanbeterminatedbythesystematany
timeafterthemethodreturns,withoutexecutinganotherlineofthe
activity'scode.
• Threemethods(onPause(),onStop(),andonDestroy())arekillable.

() h l h d b ll d bf h
3333
• onPause
()
ist
h
eon
l
yonet
h
atisguarantee
d
to
b
eca
ll
e
d

b
e
f
oret
h
e
processiskilled— onStop()andonDestroy()maynotbe.
• Therefore,youshoulduseonPause()towriteanypersistentdata
(suchasuseredits)tostorage.
Asanaside…
AndroidPreferences

3.Android– Application'sLifeCycle
LifeCycleMethods
Preferencesisalightweightmechanismtostoreandretrievekey‐value pairsof
primitivedatatypes.Itistypicallyusedtostoreapplicationpreferences,such
asadefaultgreetingoratextfonttobeloadedwhenevertheapplicationis
started.
CallContext.getSharedPreferences() toreadandwritevalues.
Assignanametoyoursetofpreferencesifyouwanttosharethemwithother
componentsinthesameapplication,oruse Activity.getPreferences()withno
nametokeepthemprivatetothecallingactivity.
Youcannotsharepreferencesacrossapplications(exceptbyusingacontent
provider).
3434
9/12/2011
18
3.Android– Application's LifeCycle
Example
LifeCycle
Example
LAYOUT
<?xmlversion="1.0"encoding="utf‐8"?>
<LinearLayout
xmlns:android=" />android:id="@+id/myScreen"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#ff000000"
>
<TextView
android:layout_width="fill_parent"

didl hih
"
"
Thefollowingapplication
demonstratessomeof
thestatetransitioning
situationsexperiencedin
thelife‐cycleofatypical
Androidactivity.
an
d
ro
id
:
l
ayout_
h
e
i
g
h
t=
"
wrap_content
"

android:text="@string/hello"
/>
<EditText
android:id="@+id/txtColorSelect"

android:hint="Backgroundcolor(red,green,blue)"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</EditText>
<TextView
android:id="@+id/txtToDo"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="#00000000">
<!‐‐ transparent‐‐>
/
TVi
3535
<
/
T
ext
Vi
ew>
<Button
android:text="Finish"
android:id="@+id/btnFinish"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
</Button>
</LinearLayout>
3.Android– Application'sLifeCycle
Example:LifeCycle
Code:LifeCycleDemo.Part1
Package cis493.lifecycle

import 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
()
3636
//
pro
t
ec
t
e
d
vo
id
on
St
ar
t
()
;
//protected void onRestart();
//protected void onResume();
//protected void onPause();
//protected void onStop();

//protected void onDestroy();
9/12/2011
19
3.Android– Application'sLifeCycle
Example:LifeCycle
Code:LifeCycleDemo.Part1
public
class
GoodLife
extends Activity {
public

class

GoodLife
extends

Activity

{
//classvariablesandconstants
publicstaticfinalStringMYPREFSID ="MyPrefs001";
publicstaticfinalint actMode =Activity.MODE_PRIVATE;
LinearLayout myScreen;
EditText txtColorSelect;
TextView txtToDo;
3737
Button btnFinish;
3.Android– Application'sLifeCycle
Example:LifeCycle

Code:LifeCycleDemo.Part2
@Override
public 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 > A
pp
Tab > re
-
e
xecute current a
pp

\
n
"
3838
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);
9/12/2011
20
Code:LifeCycleDemo.Part2
txtColorSelect = (EditText) findViewById(R.id.txtColorSelect);
// you may want to skip discussing the listener until later
ll
dd h d i
(
tth
(){
3.Android– Application'sLifeCycle
Example:LifeCycle
txtCo
l
orSe
l
ect.a
dd
TextC
h
ange
d
L
i
stener
(
n

e
w
T
ex
t
Wa
t
c
h
er
(){

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();
}

3939
3.Android– Application'sLifeCycle
Example:LifeCycle
Code:LifeCycleDemo.Part3
@Override
protected void onPause() {
super.onPause();
saveDataFromCurrentState();
Toast.makeText(this, "onPause", 1).show();
}
@Override
protected void onRestart() {
super.onRestart();
Toast.makeText(this, "onRestart", 1).show();
}
4040
}
@Override
protected void onResume() {
super.onResume();
Toast.makeText(this, "onResume", 1).show();
}
9/12/2011
21
3.Android– Application'sLifeCycle
Example:LifeCycle
Code:LifeCycleDemo.Part4
@Override
protected void onStart() {
// TODO Auto-generated method stub

super.onStart();
updateFromSavedState();
Toast.makeText(this, "onStart", 1).show();
}
@Override
protected void onDestroy() {
// TODO Auto-generated method stub
super.onDestroy();
4141
Toast.makeText(this, "
o
nDestroy
"
,
1).show();
}
@Override
protected void onStop() {
// TODO Auto-generated method stub
super.onStop();
Toast.makeText(this, "onStop", 1).show();
}
3.Android– Application'sLifeCycle
Example:LifeCycle
Code:LifeCycleDemo.Part5
protected void saveDataFromCurrentState() {
SharedPreferences myPrefs = getSharedPreferences(MYPREFSID, actMode);
hdf di
di
fdi

()
S
h
are
d
Pre
f
erences.E
di
tor
m
yE
di
tor
=

m
yPre
f
s.e
di
t
()
;
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
(
t
heChosenColor
)
;
4242
changeBackgroundColor(theChosenColor);
}
}// UpdateFromSavedState
protected void clearMyPreferences() {
SharedPreferences myPrefs = getSharedPreferences(MYPREFSID, actMode);
SharedPreferences.Editor myEditor = myPrefs.edit();
myEditor.clear();
myEditor.commit();
}
9/12/2011
22
3.Android– Application'sLifeCycle
Example:LifeCycle
Code:LifeCycleDemo.Part6
private void changeBackgroundColor (String theChosenColor){
//hbkdl
//
c
h
ange
b
ac

k
groun
d
co
l
or
if (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 preferences
clearMyPreferences();
myScreen.setBackgroundColor
(
0xff000000);
4343
}
}
3.Android– Application'sLifeCycle
Example:LifeCycle
Code:LifeCycleDemo.Part8
/*
protectedvoidonRestoreInstanceState(BundlesavedInstanceState)
ThismethodiscalledafteronStart()whentheactivityisbeingre‐initialized
fromapreviouslysavedstate.
Thedefaultimplementationofthismethodperformsarestoreofanyviewstate
thathadpreviouslybeenfrozenbyonSaveInstanceState(Bundle).

*/
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
Toast.makeText(getBaseContext(),
"onRestoreInstanceState
.
BUNDLING"
,
4444
,
Toast.LENGTH_LONG).show();
}
9/12/2011
23
3.Android– Application'sLifeCycle
Example:LifeCycle
Code:LifeCycleDemo.Part9
/*
d id
(dl
)
protecte
d
vo
id
onSaveInstanceState
(
Bun
dl

eoutState
)

Calledtoretrieveper‐instancestatefromanactivitybeforebeingkilled
sothatthestatecanberestoredin
onCreate(Bundle)or
onRestoreInstanceState(Bundle)(theBundlepopulatedbythismethod
willbepassedtoboth).
Thismethodiscalledbeforeanactivitymaybekilledsothatwhenitcomes
back
sometimeinthefutureitcanrestoreitsstate.Forexample,ifactivityB
islaunchedinfrontofactivityA,andatsomepointactivityAiskilledto
reclaimresources,activit
y
Awillhaveachancetosavethecurrentstateo
f

4545
y f
itsuserinterfaceviathismethodsothatwhentheuserreturnstoactivityA,
thestateoftheuserinterfacecanberestoredvia:
onCreate(Bundle)oronRestoreInstanceState(Bundle).
*/
3.Android– Application'sLifeCycle
Example:LifeCycle
Code:LifeCycleDemo.Part10
@Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Toast.makeText(getBaseContext(),

"onSaveInstanceState BUNDLING",
Toast.LENGTH_LONG).show();
} // onSaveInstanceState
}//LyfeCicleDemo
4646
9/12/2011
24
3.Android– Application'sLifeCycle
Example:LifeCycle
onCreate… onStart… onResume…
4747
3.Android– Application'sLifeCycle
Example:LifeCycle
onPause… onStop… onDestroy…
4848
Afterpressing“BackArrow”
9/12/2011
25
3.Android– Application'sLifeCycle
Example:LifeCycle
After
pressing“Home”
After
re‐executingAndLife2
After
“BackArrow”orFinish
onSavedInstanceState >
onPause >
onStop >
onRestart >

onStart >
onResume >
onPause >
onStop >
onDestroy >
PreservingStateInformation
1
Enter
data:
“
Hasta
la vista!
”
4949
EndofExample
1
.
Enter
data:

Hasta
la

vista!
2. ClickHomebutton
3. onSavedInstance >onPause >onStop
4. Readyour SMS
5. Executeaninstanceoftheapplication
6. onRestart >onStart >onResume
7. Youseethedataenteredinstep1

Application’sLifeCycle
Questions ?
Questions

?
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