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ID:53254353
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页数:17页
时间:2020-04-02
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1、ApplicationFundamentalsAndroidapplicationsarewrittenintheJavaprogramminglanguage.ThecompiledJavacode—alongwithanydataandresourcefilesrequiredbytheapplication—isbundledbytheaapttoolintoanAndroidpackage,anarchivefilemarkedbyan.apksuffix.Thisfileisthevehiclefordistributingtheapplic
2、ationandinstallingitonmobiledevices;it'sthefileusersdownloadtotheirdevices.Allthecodeinasingle.apkfileisconsideredtobeoneapplication.Android应用基础:Android应用程序是通过java语言开发的,通过绑定一些应用所需要的东西,例如:编译的Java代码,加上数据和一些资源文件,使用一个apt的工具将所有的东西封装成一个android包,这个文件的文件后缀是.apk。这个文件是分发并安装应用程序到移动设备的载体,是用
3、户获得该应用程序所需要的下载的文件。ApplicationComponentsAcentralfeatureofAndroidisthatoneapplicationcanmakeuseofelementsofotherapplications(providedthoseapplicationspermitit).Forexample,ifyourapplicationneedstodisplayascrollinglistofimagesandanotherapplicationhasdevelopedasuitablescrollerandmade
4、itavailabletoothers,youcancalluponthatscrollertodothework,ratherthandevelopyourown.Yourapplicationdoesn'tincorporatethecodeoftheotherapplicationorlinktoit.Rather,itsimplystartsupthatpieceoftheotherapplicationwhentheneedarises.Forthistowork,thesystemmustbeabletostartanapplication
5、processwhenanypartofitisneeded,andinstantiatetheJavaobjectsforthatpart.Therefore,unlikeapplicationsonmostothersystems,Androidapplicationsdon'thaveasingleentrypointforeverythingintheapplication(nomain()function,forexample).Rather,theyhaveessentialcomponentsthatthesystemcaninstant
6、iateandrunasneeded.Therearefourtypesofcomponents:ActivitiesAnactivitypresentsavisualuserinterfaceforonefocusedendeavortheusercanundertake.Forexample,anactivitymightpresentalistofmenuitemsuserscanchoosefromoritmightdisplayphotographsalongwiththeircaptions.Atextmessagingapplicatio
7、nmighthaveoneactivitythatshowsalistofcontactstosendmessagesto,asecondactivitytowritethemessagetothechosencontact,andotheractivitiestoreviewoldmessagesorchangesettings.Thoughtheyworktogethertoformacohesiveuserinterface,eachactivityis共21页第16页independentoftheothers.Eachoneisimpleme
8、ntedasasubclassoftheActivitybaseclass.Anapplica
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