Android系统App Widgets英文资料外文翻译文献.docx

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Android系统App Widgets英文资料外文翻译文献.docx

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Android系统App Widgets英文资料外文翻译文献.docx

Android系统AppWidgets英文资料外文翻译文献

AppWidgets

AppWidgetsareminiatureapplicationviewsthatcanbeembeddedinotherapplications（suchastheHomescreen）andreceiveperiodicupdates.TheseviewsarereferredtoasWidgetsintheuserinterface,andyoucanpublishonewithanAppWidgetprovider.AnapplicationcomponentthatisabletoholdotherAppWidgetsiscalledanAppWidgethost.ThescreenshotbelowshowstheMusicAppWidget.

ThisdocumentdescribeshowtopublishanAppWidgetusinganAppWidgetprovider.

TheBasics

TocreateanAppWidget,youneedthefollowing:

AppWidgetProviderInfoobject

DescribesthemetadataforanAppWidget,suchastheAppWidget'slayout,updatefrequency,andtheAppWidgetProviderclass.ThisshouldbedefinedinXML.

AppWidgetProviderclassimplementation

DefinesthebasicmethodsthatallowyoutoprogrammaticallyinterfacewiththeAppWidget,basedonbroadcastevents.Throughit,youwillreceivebroadcastswhentheAppWidgetisupdated,enabled,disabledanddeleted.

Viewlayout

DefinestheinitiallayoutfortheAppWidget,definedinXML.

Additionally,youcanimplementanAppWidgetconfigurationActivity.ThisisanoptionalActivitythatlauncheswhentheuseraddsyourAppWidgetandallowshimorhertomodifyAppWidgetsettingsatcreate-time.

Thefollowingsectionsdescribehowtosetupeachofthesecomponents.

DeclaringanAppWidgetintheManifest

First,declaretheAppWidgetProviderclassinyourapplication'sAndroidManifest.xmlfile.Forexample:

name="ExampleAppWidgetProvider">

name="android.appwidget.action.APPWIDGET_UPDATE"/>

name="android.appwidget.provider"

android:

resource="@xml/example_appwidget_info"/>

Theelementrequirestheandroid:

nameattribute,whichspecifiestheAppWidgetProviderusedbytheAppWidget.

Theelementmustincludeanelementwiththeandroid:

nameattribute.ThisattributespecifiesthattheAppWidgetProvideracceptstheACTION_APPWIDGET_UPDATEbroadcast.Thisistheonlybroadcastthatyoumustexplicitlydeclare.TheAppWidgetManagerautomaticallysendsallotherAppWidgetbroadcaststotheAppWidgetProviderasnecessary.

TheelementspecifiestheAppWidgetProviderInforesourceandrequiresthefollowingattributes:

•android:

name-Specifiesthemetadataname.Useandroid.appwidget.providertoidentifythedataastheAppWidgetProviderInfodescriptor.

•android:

resource-SpecifiestheAppWidgetProviderInforesourcelocation.

AddingtheAppWidgetProviderInfoMetadata

TheAppWidgetProviderInfodefinestheessentialqualitiesofanAppWidget,suchasitsminimumlayoutdimensions,itsinitiallayoutresource,howoftentoupdatetheAppWidget,and（optionally）aconfigurationActivitytolaunchatcreate-time.DefinetheAppWidgetProviderInfoobjectinanXMLresourceusingasingleelementandsaveitintheproject'sres/xml/folder.

Forexample:

android="

android:

minWidth="294dp"

--density-independentpixels-->

android:

minHeight="72dp"

android:

updatePeriodMillis="86400000"

--onceperday-->

android:

initialLayout="@layout/example_appwidget"

android:

configure="com.example.android.ExampleAppWidgetConfigure">

Here'sasummaryoftheattributes:

•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）.

SeetheAppWidgetProviderInfoclassformoreinformationontheattributesacceptedbytheelement.

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

YoumustdeclareyourAppWidgetProviderclassimplementationasabroadcastreceiverusingtheelementintheAndroidManifest（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.

Note:

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

ThemostimportantAppWidgetProvidercallbackisonUpdated（）becauseitiscalledwheneachAppWidgetisaddedtoahost（unlessyouuseaconfigurationActivity）.IfyourAppWidgetacceptsanyuserinteraction

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