构建你的第一个Android应用程序.docx

构建你的第一个Android应用程序.docx

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构建你的第一个Android应用程序

编写你的第一个Android应用程序

2012-10-3翻译：

罗奕聪

注意：

這篇文章的一部分基於Android開放原始碼計劃（AndroidOpenSourceProject），這部分內容在知識共享姓名標示2.5（CCBY2.5）許可下發佈此內容在知識共享姓名標示-非商業性-相同方式分享3.0Unported（CCBY-NC-SA3.0）許可下發佈。

一、创建一个Android工程

AnAndroidprojectcontainsallthefilesthatcomprisethesourcecodeforyourAndroidapp.TheAndroidSDKtoolsmakeiteasytostartanewAndroidprojectwithasetofdefaultprojectdirectoriesandfiles.

ThislessonshowshowtocreateanewprojecteitherusingEclipse（withtheADTplugin）orusingtheSDKtoolsfromacommandline.

CreateaProjectwithEclipse

InEclipse,clickNewAndroidAppProject 

 inthetoolbar.

Figure1. TheNewAndroidAppProjectwizardinEclipse.

1.Fillintheformthatappears:

oApplicationName istheappnamethatappearstousers.Forthisproject,use"MyFirstApp."

oProjectName isthenameofyourprojectdirectoryandthenamevisibleinEclipse.

oPackageName isthepackagenamespaceforyourapp（followingthesamerulesaspackagesintheJavaprogramminglanguage）.YourpackagenamemustbeuniqueacrossallpackagesinstalledontheAndroidsystem.Forthisreason,it'sgenerallybestifyouuseanamethatbeginswiththereversedomainnameofyourorganizationorpublisherentity.Forthisproject,youcanusesomethinglike"com.example.myfirstapp."However,youcannotpublishyourapponGooglePlayusingthe"com.example"namespace.

oBuildSDK istheplatformversionagainstwhichyouwillcompileyourapp.Bydefault,thisissettothelatestversionofAndroidavailableinyourSDK.（ItshouldbeAndroid4.1orgreater;ifyoudon'thavesuchaversionavailable,youmustinstalloneusingthe SDKManager）.Youcanstillbuildyourapptosupportolderversions,butsettingthebuildtargettothelatestversionallowsyoutoenablenewfeaturesandoptimizeyourappforagreatuserexperienceonthelatestdevices.

oMinimumRequiredSDK isthelowestversionofAndroidthatyourappsupports.Tosupportasmanydevicesaspossible,youshouldsetthistothelowestversionavailablethatallowsyourapptoprovideitscorefeatureset.IfanyfeatureofyourappispossibleonlyonnewerversionsofAndroidandit'snotcriticaltotheapp'scorefeatureset,youcanenablethefeatureonlywhenrunningontheversionsthatsupportit.

Leavethissettothedefaultvalueforthisproject.

2.Click Next.

3.Thefollowingscreenprovidestoolstohelpyoucreatealaunchericonforyourapp.

Youcancustomizeaniconinseveralwaysandthetoolgeneratesaniconforallscreendensities.Beforeyoupublishyourapp,youshouldbesureyouriconmeetsthespecificationsdefinedinthe Iconography designguide.

Click Next.

4.Nowyoucanselectanactivitytemplatefromwhichtobeginbuildingyourapp.

Forthisproject,select BlankActivity andclick Next.

5.Leaveallthedetailsfortheactivityintheirdefaultstateandclick Finish.

YourAndroidprojectisnowsetupwithsomedefaultfilesandyou’rereadytobeginbuildingtheapp.Continuetothe nextlesson.

CreateaProjectwithCommandLineTools

Ifyou'renotusingtheEclipseIDEwiththeADTplugin,youcaninsteadcreateyourprojectusingtheSDKtoolsfromacommandline:

1.ChangedirectoriesintotheAndroidSDK’s tools/ path.

2.Execute:

androidlisttargets

ThisprintsalistoftheavailableAndroidplatformsthatyou’vedownloadedforyourSDK.Findtheplatformagainstwhichyouwanttocompileyourapp.Makeanoteofthetargetid.Werecommendthatyouselectthehighestversionpossible.Youcanstillbuildyourapptosupportolderversions,butsettingthebuildtargettothelatestversionallowsyoutooptimizeyourappforthelatestdevices.

Ifyoudon'tseeanytargetslisted,youneedtoinstallsomeusingtheAndroidSDKManagertool.See AddingPlatformsandPackages.

3.Execute:

androidcreateproject--target--nameMyFirstApp\--path/MyFirstApp--activityMainActivity\--packagecom.example.myfirstapp

Replace  withanidfromthelistoftargets（fromthepreviousstep）andreplace  withthelocationinwhichyouwanttosaveyourAndroidprojects.

YourAndroidprojectisnowsetupwithseveraldefaultconfigurationsandyou’rereadytobeginbuildingtheapp.Continuetothe nextlesson.

Tip:

 Addthe platform-tools/ aswellasthe tools/ directorytoyour PATH environmentvariable.

RunningYourApp

Ifyoufollowedthe previouslesson tocreateanAndroidproject,itincludesadefaultsetof"HelloWorld"sourcefilesthatallowyoutoimmediatelyruntheapp.

Howyourunyourappdependsontwothings:

whetheryouhavearealAndroid-powereddeviceandwhetheryou’reusingEclipse.ThislessonshowsyouhowtoinstallandrunyourapponarealdeviceandontheAndroidemulator,andinbothcaseswitheitherEclipseorthecommandlinetools.

Beforeyourunyourapp,youshouldbeawareofafewdirectoriesandfilesintheAndroidproject:

AndroidManifest.xml

The manifestfile describesthefundamentalcharacteristicsoftheappanddefineseachofitscomponents.You'lllearnaboutvariousdeclarationsinthisfileasyoureadmoretrainingclasses.

src/

Directoryforyourapp'smainsourcefiles.Bydefault,itincludesan Activity classthatrunswhenyourappislaunchedusingtheappicon.

res/

Containsseveralsub-directoriesfor appresources.Herearejustafew:

drawable-hdpi/

Directoryfordrawableobjects（suchasbitmaps）thataredesignedforhigh-density（hdpi）screens.Otherdrawabledirectoriescontainassetsdesignedforotherscreendensities.

layout/

Directoryforfilesthatdefineyourapp'suserinterface.

values/

DirectoryforothervariousXMLfilesthatcontainacollectionofresources,suchasstringandcolordefinitions.

WhenyoubuildandrunthedefaultAndroidapp,thedefault Activity classstartsandloadsalayoutfilethatsays"HelloWorld."Theresultisnothingexciting,butit'simportantthatyouunderstandhowtorunyourappbeforeyoustartdeveloping.

RunonaRealDevice

IfyouhavearealAndroid-powereddevice,here'showyoucaninstallandrunyourapp:

1.PluginyourdevicetoyourdevelopmentmachinewithaUSBcable.Ifyou’redevelopingonWindows,youmightneedtoinstalltheappropriateUSBdriverforyourdevice.Forhelpinstallingdrivers,seethe OEMUSBDrivers document.

2.Ensurethat USBdebugging isenabledinthedeviceSettings（openSettingsandnavitageto Applications>Development onmostdevices,orclick Developeroptions onAndroid4.0andhigher）.

ToruntheappfromEclipse,openoneofyourproject'sfilesandclickRun 

 fromthetoolbar.Eclipseinstallstheapponyourconnecteddeviceandstartsit.

Ortorunyourappfromacommandline:

1.

antdebug

ChangedirectoriestotherootofyourAndroidprojectandexecute:

2.

adbinstallbin/MyFirstApp-debug.apk

MakesuretheAndroidSDK platform-tools/ directoryisincludedinyour PATH environmentvariable,thenexecute:

3.Onyourdevice,locate MyFirstActivity andopenit.

That'showyoubuildandrunyourAndroidapponadevice!

Tostartdeveloping,continuetothe nextlesson.

RunontheEmulator

Whetheryou’reusingEclipseorthecommandline,torunyourappontheemulatoryouneedtofirstcreateanAndroidVirtualDevice （AVD）.AnAVDisadeviceconfigurationfortheAndroidemulatorthatallowsyoutomodeldifferentdevices.

Figure1. TheAVDManagershowingafewvirtualdevices.

TocreateanAVD:

1.LaunchtheAndroidVirtualDeviceManager:

a.InEclipse,clickAndroidVirtualDeviceManager 

fromthetoolbar.

b.

androidavd

Fromthecommandline,changedirectoriesto/tools/ andexecute:

2.Inthe AndroidVirtualDeviceManager panel,click New.

3.FillinthedetailsfortheAVD.Giveitaname,aplatformtarget,anSDcardsize,andaskin（HVGAisdefault）.

4.Click CreateAVD.

5.SelectthenewAVDfromthe AndroidVirtualDeviceManager andclick Start.

6.Aftertheemulatorbootsup,unlocktheemulatorscreen.

ToruntheappfromEclipse,openoneofyourproject'sfilesandclickRun 

 fromthetoolbar.EclipseinstallstheapponyourAVDandstartsit.

Ortorunyourappfromthecommandline:

1.ChangedirectoriestotherootofyourAndroidprojectandexecute:

antdebug

2.MakesuretheAndroidSDK platform-tools/ directoryisincludedinyour PATH environmentvariable,thenexecute:

adbinstallbin/MyFirstApp-debug.apk

3.Ontheemulator,locate MyFirstActivity andopenit.

That'showyoubuildandrunyourAndroidappontheemulator!

Tostartdeveloping,continuetothe nextlesson.

BuildingaSimpleUserInterface

AlternativeLayouts

DeclaringyourUIlayoutinXMLratherthanruntimecodeisusefulforseveralreasons,butit'sespeciallyimportantsoyoucancreatedifferentlayoutsfordifferentscreensizes.Forexample,youcancreatetwoversionsofalayoutandtellthesystemtouseoneon"small"screensandtheotheron"large"screens.Formoreinformation,seetheclassabout SupportingDifferentDevices.

ThegraphicaluserinterfaceforanAndroidappisbuiltusingahierarchyof View and ViewGroup objects. View objectsareusuallyUIwidgetssuchas buttons or textfields andViewGroup objectsareinvisibleviewcontainersthatdefinehowthechildviewsarelaidout,suchasinagridoraverticallist.

AndroidprovidesanXMLvocabularythatcorrespondstothesubclassesof View and ViewGroup soyoucandefineyourUIinXMLusingahierarchyofUIelements.

Figure1. Illustrationofhow ViewGroup objectsformbranchesinthelayoutandcontainother View objects.

Inthislesson,you'llcreatealayoutinXMLthatincludesatextfieldandabutton.Int