Android系统App Widgets英文资料外文翻译文献Word文档下载推荐.docx

Android系统App Widgets英文资料外文翻译文献Word文档下载推荐.docx

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Viewlayout

DefinestheinitiallayoutfortheAppWidget,definedinXML.

Additionally,youcanimplementanAppWidgetconfigurationActivity.ThisisanoptionalActivitythatlauncheswhentheuseraddsyourAppWidgetandallowshimorhertomodifyAppWidgetsettingsatcreate-time.

Thefollowingsectionsdescribehowtosetupeachofthesecomponents.

DeclaringanAppWidgetintheManifest

First,declaretheAppWidgetProviderclassinyourapplication'

sAndroidManifest.xmlfile.Forexample:

<

receiverandroid:

name="

ExampleAppWidgetProvider"

>

<

intent-filter>

actionandroid:

android.appwidget.action.APPWIDGET_UPDATE"

/>

/intent-filter>

meta-dataandroid:

android.appwidget.provider"

android:

resource="

@xml/example_appwidget_info"

/receiver>

The<

receiver>

elementrequirestheandroid:

nameattribute,whichspecifiestheAppWidgetProviderusedbytheAppWidget.

elementmustincludean<

action>

elementwiththeandroid:

nameattribute.ThisattributespecifiesthattheAppWidgetProvideracceptstheACTION_APPWIDGET_UPDATEbroadcast.Thisistheonlybroadcastthatyoumustexplicitlydeclare.TheAppWidgetManagerautomaticallysendsallotherAppWidgetbroadcaststotheAppWidgetProviderasnecessary.

meta-data>

elementspecifiestheAppWidgetProviderInforesourceandrequiresthefollowingattributes:

•android:

name-Specifiesthemetadataname.Useandroid.appwidget.providertoidentifythedataastheAppWidgetProviderInfodescriptor.

resource-SpecifiestheAppWidgetProviderInforesourcelocation.

AddingtheAppWidgetProviderInfoMetadata

TheAppWidgetProviderInfodefinestheessentialqualitiesofanAppWidget,suchasitsminimumlayoutdimensions,itsinitiallayoutresource,howoftentoupdatetheAppWidget,and（optionally）aconfigurationActivitytolaunchatcreate-time.DefinetheAppWidgetProviderInfoobjectinanXMLresourceusingasingle<

appwidget-provider>

elementandsaveitintheproject'

sres/xml/folder.

Forexample:

appwidget-providerxmlns:

android="

minWidth="

294dp"

!

--density-independentpixels-->

minHeight="

72dp"

updatePeriodMillis="

86400000"

--onceperday-->

initialLayout="

@layout/example_appwidget"

configure="

com.example.android.ExampleAppWidgetConfigure"

/appwidget-provider>

Here'

sasummaryofthe<

attributes:

•ThevaluesfortheminWidthandminHeightattributesspecifytheminimumarearequiredbytheAppWidget'

slayout.

ThedefaultHomescreenpositionsAppWidgetsinitswindowbasedonagridofcellsthathaveadefinedheightandwidth.IfthevaluesforanAppWidget'

sminimumwidthorheightdon'

tmatchthedimensionsofthecells,thentheAppWidgetdimensionsrounduptothenearestcellsize.（SeetheAppWidgetDesignGuidelinesformoreinformationontheHomescreencellsizes.）

BecausetheHomescreen'

slayoutorientation（andthus,thecellsizes）canchange,asaruleofthumb,youshouldassumetheworst-casecellsizeof74pixelsfortheheightandwidthofacell.However,youmustsubtract2fromthefinaldimensiontoaccountforanyintegerroundingerrorsthatoccurinthepixelcount.Tofindyourminimumwidthandheightindensity-independentpixels（dp）,usethisformula:

（numberofcells*74）–2

Followingthisformula,youshoulduse72dpforaheightofonecell,294dpandforawidthoffourcells.

•TheupdatePeriodMillisattributedefineshowoftentheAppWidgetframeworkshouldrequestanupdatefromtheAppWidgetProviderbycallingtheonUpdate（）method.Theactualupdateisnotguaranteedtooccurexactlyontimewiththisvalueandwesuggestupdatingasinfrequentlyaspossible—perhapsnomorethanonceanhourtoconservethebattery.Youmightalsoallowtheusertoadjustthefrequencyinaconfiguration—somepeoplemightwantastocktickertoupdateevery15minutes,ormaybeonlyfourtimesaday.

Note:

Ifthedeviceisasleepwhenitistimeforanupdate（asdefinedbyupdatePeriodMillis）,thenthedevicewillwakeupinordertoperformtheupdate.Ifyoudon'

tupdatemorethanonceperhour,thisprobablywon'

tcausesignificantproblemsforthebatterylife.If,however,youneedtoupdatemorefrequentlyand/oryoudonotneedtoupdatewhilethedeviceisasleep,thenyoucaninsteadperformupdatesbasedonanalarmthatwillnotwakethedevice.Todoso,setanalarmwithanIntentthatyourAppWidgetProviderreceives,usingtheAlarmManager.SetthealarmtypetoeitherELAPSED_REALTIMEorRTC,whichwillonlydeliverthealarmwhenthedeviceisawake.ThensetupdatePeriodMillistozero（"

0"

）.

•TheinitialLayoutattributepointstothelayoutresourcethatdefinestheAppWidgetlayout.

•TheconfigureattributedefinestheActivitytolaunchwhentheuseraddstheAppWidget,inorderforhimorhertoconfigureAppWidgetproperties.Thisisoptional（readCreatinganAppWidgetConfigurationActivitybelow）.

SeetheAppWidgetProviderInfoclassformoreinformationontheattributesacceptedbythe<

element.

CreatingtheAppWidgetLayout

YoumustdefineaninitiallayoutforyourAppWidgetinXMLandsaveitintheproject'

sres/layout/directory.YoucandesignyourAppWidgetusingtheViewobjectslistedbelow,butbeforeyoubegindesigningyourAppWidget,pleasereadandunderstandtheAppWidgetDesignGuidelines.

CreatingtheAppWidgetlayoutissimpleifyou'

refamiliarwithDeclaringLayoutinXML.However,youmustbeawarethatAppWidgetlayoutsarebasedonRemoteViews,whichdonotsupporteverykindoflayoutorviewwidget.

ARemoteViewsobject（and,consequently,anAppWidget）cansupportthefollowinglayoutclasses:

•FrameLayout

•LinearLayout

•RelativeLayout

Andthefollowingwidgetclasses:

•AnalogClock

•Button

•Chronometer

•ImageButton

•ImageView

•ProgressBar

•TextView

Descendantsoftheseclassesarenotsupported.

UsingtheAppWidgetProviderClass

YoumustdeclareyourAppWidgetProviderclassimplementationasabroadcastreceiverusingthe<

elementintheAndroidManifest（seeDeclaringanAppWidgetintheManifestabove）.

TheAppWidgetProviderclassextendsBroadcastReceiverasaconvenienceclasstohandletheAppWidgetbroadcasts.TheAppWidgetProviderreceivesonlytheeventbroadcaststhatarerelevanttotheAppWidget,suchaswhentheAppWidgetisupdated,deleted,enabled,anddisabled.Whenthesebroadcasteventsoccur,theAppWidgetProviderreceivesthefollowingmethodcalls:

onUpdate（Context,AppWidgetManager,int[]）

ThisiscalledtoupdatetheAppWidgetatintervalsdefinedbytheupdatePeriodMillisattributeintheAppWidgetProviderInfo（seeAddingtheAppWidgetProviderInfoMetadataabove）.ThismethodisalsocalledwhentheuseraddstheAppWidget,soitshouldperformtheessentialsetup,suchasdefineeventhandlersforViewsandstartatemporaryService,ifnecessary.However,ifyouhavedeclaredaconfigurationActivity,thismethodisnotcalledwhentheuseraddstheAppWidget,butiscalledforthesubsequentupdates.ItistheresponsibilityoftheconfigurationActivitytoperformthefirstupdatewhenconfigurationisdone.（SeeCreatinganAppWidgetConfigurationActivitybelow.）

onDeleted（Context,int[]）

ThisiscalledeverytimeanAppWidgetisdeletedfromtheAppWidgethost.

onEnabled（Context）

ThisiscalledwhenaninstancetheAppWidgetiscreatedforthefirsttime.Forexample,iftheuseraddstwoinstancesofyourAppWidget,thisisonlycalledthefirsttime.IfyouneedtoopenanewdatabaseorperformothersetupthatonlyneedstooccuronceforallAppWidgetinstances,thenthisisagoodplacetodoit.

onDisabled（Context）

ThisiscalledwhenthelastinstanceofyourAppWidgetisdeletedfromtheAppWidgethost.ThisiswhereyoushouldcleanupanyworkdoneinonEnabled（Context）,suchasdeleteatemporarydatabase.

onReceive（Context,Intent）

Thisiscalledforeverybroadcastandbeforeeachoftheabovecallbackmethods.Younormallydon'

tneedtoimplementthismethodbecausethedefaultAppWidgetProviderimplementationfiltersallAppWidgetbroadcastsandcallstheabovemethodsasappropriate.

InAndroid1.5,thereisaknownissueinwhichtheonDeleted（）methodwillnotbecalledwhenitshouldbe.Toworkaroundthisissue,youcanimplementonReceive（）asdescribedinthisGroupposttoreceivetheonDeleted（）callback.

ThemostimportantAppWidgetProvidercallbackisonUpdated（）becauseitiscalledwheneachAppWidgetisaddedtoahost（unlessyouuseaconfigurationActivity）.IfyourAppWidgetacceptsanyuserinteraction