外文文献-android application fundamentals安卓应用基础1

毕业设计外文文献原文及译文学生姓名学号系别专业指导教师2015年5月计算机系网络工程ANDROIDAPPLICATIONFUNDAMENTALSANDROIDAPPLICATIONSAREWRITTENINTHEJAVAPROGRAMMINGLANGUAGETHEANDROIDSDKTOOLSCOMPILETHECODEALONGWITHANYDATAANDRESOURCEFILESINTOANANDROIDPACKAGE,ANARCHIVEFILEWITHANAPKSUFFIXALLTHECODEINASINGLEAPKFILEISCONSIDEREDTOBEONEAPPLICATIONANDISTHEFILETHATANDROIDPOWEREDDEVICESUSETOINSTALLTHEAPPLICATIONONCEINSTALLEDONADEVICE,EACHANDROIDAPPLICATIONLIVESINITSOWNSECURITYSANDBOXTHEANDROIDOPERATINGSYSTEMISAMULTIUSERLINUXSYSTEMINWHICHEACHAPPLICATIONISADIFFERENTUSERBYDEFAULT,THESYSTEMASSIGNSEACHAPPLICATIONAUNIQUELINUXUSERIDTHEIDISUSEDONLYBYTHESYSTEMANDISUNKNOWNTOTHEAPPLICATIONTHESYSTEMSETSPERMISSIONSFORALLTHEFILESINANAPPLICATIONSOTHATONLYTHEUSERIDASSIGNEDTOTHATAPPLICATIONCANACCESSTHEMEACHPROCESSHASITSOWNVIRTUALMACHINEVM,SOANAPPLICATIONSCODERUNSINISOLATIONFROMOTHERAPPLICATIONSBYDEFAULT,EVERYAPPLICATIONRUNSINITSOWNLINUXPROCESSANDROIDSTARTSTHEPROCESSWHENANYOFTHEAPPLICATIONSCOMPONENTSNEEDTOBEEXECUTED,THENSHUTSDOWNTHEPROCESSWHENITSNOLONGERNEEDEDORWHENTHESYSTEMMUSTRECOVERMEMORYFOROTHERAPPLICATIONSINTHISWAY,THEANDROIDSYSTEMIMPLEMENTSTHEPRINCIPLEOFLEASTPRIVILEGETHATIS,EACHAPPLICATION,BYDEFAULT,HASACCESSONLYTOTHECOMPONENTSTHATITREQUIRESTODOITSWORKANDNOMORETHISCREATESAVERYSECUREENVIRONMENTINWHICHANAPPLICATIONCANNOTACCESSPARTSOFTHESYSTEMFORWHICHITISNOTGIVENPERMISSIONHOWEVER,THEREAREWAYSFORANAPPLICATIONTOSHAREDATAWITHOTHERAPPLICATIONSANDFORANAPPLICATIONTOACCESSSYSTEMSERVICESITSPOSSIBLETOARRANGEFORTWOAPPLICATIONSTOSHARETHESAMELINUXUSERID,INWHICHCASETHEYAREABLETOACCESSEACHOTHERSFILESTOCONSERVESYSTEMRESOURCES,APPLICATIONSWITHTHESAMEUSERIDCANALSOARRANGETORUNINTHESAMELINUXPROCESSANDSHARETHESAMEVMTHEAPPLICATIONSMUSTALSOBESIGNEDWITHTHESAMECERTIFICATEANAPPLICATIONCANREQUESTPERMISSIONTOACCESSDEVICEDATASUCHASTHEUSERSCONTACTS,SMSMESSAGES,THEMOUNTABLESTORAGESDCARD,CAMERA,BLUETOOTH,ANDMOREALLAPPLICATIONPERMISSIONSMUSTBEGRANTEDBYTHEUSERATINSTALLTIMETHATCOVERSTHEBASICSREGARDINGHOWANANDROIDAPPLICATIONEXISTSWITHINTHESYSTEMTHERESTOFTHISDOCUMENTINTRODUCESYOUTOTHECOREFRAMEWORKCOMPONENTSTHATDEFINEYOURAPPLICATIONTHEMANIFESTFILEINWHICHYOUDECLARECOMPONENTSANDREQUIREDDEVICEFEATURESFORYOURAPPLICATIONRESOURCESTHATARESEPARATEFROMTHEAPPLICATIONCODEANDALLOWYOURAPPLICATIONTOGRACEFULLYOPTIMIZEITSBEHAVIORFORAVARIETYOFDEVICECONFIGURATIONSAPPLICATIONCOMPONENTSAPPLICATIONCOMPONENTSARETHEESSENTIALBUILDINGBLOCKSOFANANDROIDAPPLICATIONEACHCOMPONENTISADIFFERENTPOINTTHROUGHWHICHTHESYSTEMCANENTERYOURAPPLICATIONNOTALLCOMPONENTSAREACTUALENTRYPOINTSFORTHEUSERANDSOMEDEPENDONEACHOTHER,BUTEACHONEEXISTSASITSOWNENTITYANDPLAYSASPECIFICROLEEACHONEISAUNIQUEBUILDINGBLOCKTHATHELPSDEFINEYOURAPPLICATIONSOVERALLBEHAVIORTHEREAREFOURDIFFERENTTYPESOFAPPLICATIONCOMPONENTSEACHTYPESERVESADISTINCTPURPOSEANDHASADISTINCTLIFECYCLETHATDEFINESHOWTHECOMPONENTISCREATEDANDDESTROYEDHEREARETHEFOURTYPESOFAPPLICATIONCOMPONENTSACTIVITIESANACTIVITYREPRESENTSASINGLESCREENWITHAUSERINTERFACEFOREXAMPLE,ANEMAILAPPLICATIONMIGHTHAVEONEACTIVITYTHATSHOWSALISTOFNEWEMAILS,ANOTHERACTIVITYTOCOMPOSEANEMAIL,ANDANOTHERACTIVITYFORREADINGEMAILSALTHOUGHTHEACTIVITIESWORKTOGETHERTOFORMACOHESIVEUSEREXPERIENCEINTHEEMAILAPPLICATION,EACHONEISINDEPENDENTOFTHEOTHERSASSUCH,ADIFFERENTAPPLICATIONCANSTARTANYONEOFTHESEACTIVITIESIFTHEEMAILAPPLICATIONALLOWSITFOREXAMPLE,ACAMERAAPPLICATIONCANSTARTTHEACTIVITYINTHEEMAILAPPLICATIONTHATCOMPOSESNEWMAIL,INORDERFORTHEUSERTOSHAREAPICTUREANACTIVITYISIMPLEMENTEDASASUBCLASSOFACTIVITYANDYOUCANLEARNMOREABOUTITINTHEACTIVITIESDEVELOPERGUIDESERVICESASERVICEISACOMPONENTTHATRUNSINTHEBACKGROUNDTOPERFORMLONGRUNNINGOPERATIONSORTOPERFORMWORKFORREMOTEPROCESSESASERVICEDOESNOTPROVIDEAUSERINTERFACEFOREXAMPLE,ASERVICEMIGHTPLAYMUSICINTHEBACKGROUNDWHILETHEUSERISINADIFFERENTAPPLICATION,ORITMIGHTFETCHDATAOVERTHENETWORKWITHOUTBLOCKINGUSERINTERACTIONWITHANACTIVITYANOTHERCOMPONENT,SUCHASANACTIVITY,CANSTARTTHESERVICEANDLETITRUNORBINDTOITINORDERTOINTERACTWITHITASERVICEISIMPLEMENTEDASASUBCLASSOFSERVICEANDYOUCANLEARNMOREABOUTITINTHESERVICESDEVELOPERGUIDECONTENTPROVIDERSACONTENTPROVIDERMANAGESASHAREDSETOFAPPLICATIONDATAYOUCANSTORETHEDATAINTHEFILESYSTEM,ANSQLITEDATABASE,ONTHEWEB,ORANYOTHERPERSISTENTSTORAGELOCATIONYOURAPPLICATIONCANACCESSTHROUGHTHECONTENTPROVIDER,OTHERAPPLICATIONSCANQUERYOREVENMODIFYTHEDATAIFTHECONTENTPROVIDERALLOWSITFOREXAMPLE,THEANDROIDSYSTEMPROVIDESACONTENTPROVIDERTHATMANAGESTHEUSERSCONTACTINFORMATIONASSUCH,ANYAPPLICATIONWITHTHEPROPERPERMISSIONSCANQUERYPARTOFTHECONTENTPROVIDERSUCHASCONTACTSCONTRACTDATATOREADANDWRITEINFORMATIONABOUTAPARTICULARPERSONCONTENTPROVIDERSAREALSOUSEFULFORREADINGANDWRITINGDATATHATISPRIVATETOYOURAPPLICATIONANDNOTSHAREDFOREXAMPLE,THENOTEPADSAMPLEAPPLICATIONUSESACONTENTPROVIDERTOSAVENOTESACONTENTPROVIDERISIMPLEMENTEDASASUBCLASSOFCONTENTPROVIDERANDMUSTIMPLEMENTASTANDARDSETOFAPISTHATENABLEOTHERAPPLICATIONSTOPERFORMTRANSACTIONSFORMOREINFORMATION,SEETHECONTENTPROVIDERSDEVELOPERGUIDEBROADCASTRECEIVERSABROADCASTRECEIVERISACOMPONENTTHATRESPONDSTOSYSTEMWIDEBROADCASTANNOUNCEMENTSMANYBROADCASTSORIGINATEFROMTHESYSTEMFOREXAMPLE,ABROADCASTANNOUNCINGTHATTHESCREENHASTURNEDOFF,THEBATTERYISLOW,ORAPICTUREWASCAPTUREDAPPLICATIONSCANALSOINITIATEBROADCASTSFOREXAMPLE,TOLETOTHERAPPLICATIONSKNOWTHATSOMEDATAHASBEENDOWNLOADEDTOTHEDEVICEANDISAVAILABLEFORTHEMTOUSEALTHOUGHBROADCASTRECEIVERSDONTDISPLAYAUSERINTERFACE,THEYMAYCREATEASTATUSBARNOTIFICATIONTOALERTTHEUSERWHENABROADCASTEVENTOCCURSMORECOMMONLY,THOUGH,ABROADCASTRECEIVERISJUSTA“GATEWAY“TOOTHERCOMPONENTSANDISINTENDEDTODOAVERYMINIMALAMOUNTOFWORKFORINSTANCE,ITMIGHTINITIATEASERVICETOPERFORMSOMEWORKBASEDONTHEEVENTABROADCASTRECEIVERISIMPLEMENTEDASASUBCLASSOFBROADCASTRECEIVERANDEACHBROADCASTISDELIVEREDASANINTENTOBJECTFORMOREINFORMATION,SEETHEBROADCASTRECEIVERCLASSAUNIQUEASPECTOFTHEANDROIDSYSTEMDESIGNISTHATANYAPPLICATIONCANSTARTANOTHERAPPLICATIONSCOMPONENTFOREXAMPLE,IFYOUWANTTHEUSERTOCAPTUREAPHOTOWITHTHEDEVICECAMERA,THERESPROBABLYANOTHERAPPLICATIONTHATDOESTHATANDYOURAPPLICATIONCANUSEIT,INSTEADOFDEVELOPINGANACTIVITYTOCAPTUREAPHOTOYOURSELFYOUDONTNEEDTOINCORPORATEOREVENLINKTOTHECODEFROMTHECAMERAAPPLICATIONINSTEAD,YOUCANSIMPLYSTARTTHEACTIVITYINTHECAMERAAPPLICATIONTHATCAPTURESAPHOTOWHENCOMPLETE,THEPHOTOISEVENRETURNEDTOYOURAPPLICATIONSOYOUCANUSEITTOTHEUSER,ITSEEMSASIFTHECAMERAISACTUALLYAPARTOFYOURAPPLICATIONWHENTHESYSTEMSTARTSACOMPONENT,ITSTARTSTHEPROCESSFORTHATAPPLICATIONIFITSNOTALREADYRUNNINGANDINSTANTIATESTHECLASSESNEEDEDFORTHECOMPONENTFOREXAMPLE,IFYOURAPPLICATIONSTARTSTHEACTIVITYINTHECAMERAAPPLICATIONTHATCAPTURESAPHOTO,THATACTIVITYRUNSINTHEPROCESSTHATBELONGSTOTHECAMERAAPPLICATION,NOTINYOURAPPLICATIONSPROCESSTHEREFORE,UNLIKEAPPLICATIONSONMOSTOTHERSYSTEMS,ANDROIDAPPLICATIONSDONTHAVEASINGLEENTRYPOINTTHERESNOMAINFUNCTION,FOREXAMPLEBECAUSETHESYSTEMRUNSEACHAPPLICATIONINASEPARATEPROCESSWITHFILEPERMISSIONSTHATRESTRICTACCESSTOOTHERAPPLICATIONS,YOURAPPLICATIONCANNOTDIRECTLYACTIVATEACOMPONENTFROMANOTHERAPPLICATIONTHEANDROIDSYSTEM,HOWEVER,CANSO,TOACTIVATEACOMPONENTINANOTHERAPPLICATION,YOUMUSTDELIVERAMESSAGETOTHESYSTEMTHATSPECIFIESYOURINTENTTOSTARTAPARTICULARCOMPONENTTHESYSTEMTHENACTIVATESTHECOMPONENTFORYOUACTIVATINGCOMPONENTSTHREEOFTHEFOURCOMPONENTTYPESACTIVITIES,SERVICES,ANDBROADCASTRECEIVERSAREACTIVATEDBYANASYNCHRONOUSMESSAGECALLEDANINTENTINTENTSBINDINDIVIDUALCOMPONENTSTOEACHOTHERATRUNTIMEYOUCANTHINKOFTHEMASTHEMESSENGERSTHATREQUESTANACTIONFROMOTHERCOMPONENTS,WHETHERTHECOMPONENTBELONGSTOYOURAPPLICATIONORANOTHERANINTENTISCREATEDWITHANINTENTOBJECT,WHICHDEFINESAMESSAGETOACTIVATEEITHERASPECIFICCOMPONENTORASPECIFICTYPEOFCOMPONENTANINTENTCANBEEITHEREXPLICITORIMPLICIT,RESPECTIVELYFORACTIVITIESANDSERVICES,ANINTENTDEFINESTHEACTIONTOPERFORMFOREXAMPLE,TO“VIEW“OR“SEND“SOMETHINGANDMAYSPECIFYTHEURIOFTHEDATATOACTONAMONGOTHERTHINGSTHATTHECOMPONENTBEINGSTARTEDMIGHTNEEDTOKNOWFOREXAMPLE,ANINTENTMIGHTCONVEYAREQUESTFORANACTIVITYTOSHOWANIMAGEORTOOPENAWEBPAGEINSOMECASES,YOUCANSTARTANACTIVITYTORECEIVEARESULT,INWHICHCASE,THEACTIVITYALSORETURNSTHERESULTINANINTENTFOREXAMPLE,YOUCANISSUEANINTENTTOLETTHEUSERPICKAPERSONALCONTACTANDHAVEITRETURNEDTOYOUTHERETURNINTENTINCLUDESAURIPOINTINGTOTHECHOSENCONTACTFORBROADCASTRECEIVERS,THEINTENTSIMPLYDEFINESTHEANNOUNCEMENTBEINGBROADCASTFOREXAMPLE,ABROADCASTTOINDICATETHEDEVICEBATTERYISLOWINCLUDESONLYAKNOWNACTIONSTRINGTHATINDICATES“BATTERYISLOW“THEOTHERCOMPONENTTYPE,CONTENTPROVIDER,ISNOTACTIVATEDBYINTENTSRATHER,ITISACTIVATEDWHENTARGETEDBYAREQUESTFROMACONTENTRESOLVERTHECONTENTRESOLVERHANDLESALLDIRECTTRANSACTIONSWITHTHECONTENTPROVIDERSOTHATTHECOMPONENTTHATSPERFORMINGTRANSACTIONSWITHTHEPROVIDERDOESNTNEEDTOANDINSTEADCALLSMETHODSONTHECONTENTRESOLVEROBJECTTHISLEAVESALAYEROFABSTRACTIONBETWEENTHECONTENTPROVIDERANDTHECOMPONENTREQUESTINGINFORMATIONFORSECURITYTHEREARESEPARATEMETHODSFORACTIVATINGEACHTYPEOFCOMPONENTYOUCANSTARTANACTIVITYORGIVEITSOMETHINGNEWTODOBYPASSINGANINTENTTOSTARTACTIVITYORSTARTACTIVITYFORRESULTWHENYOUWANTTHEACTIVITYTORETURNARESULTYOUCANSTARTASERVICEORGIVENEWINSTRUCTIONSTOANONGOINGSERVICEBYPASSINGANINTENTTOSTARTSERVICEORYOUCANBINDTOTHESERVICEBYPASSINGANINTENTTOBINDSERVICEYOUCANINITIATEABROADCASTBYPASSINGANINTENTTOMETHODSLIKESENDBROADCAST,SENDORDEREDBROADCAST,ORSENDSTICKYBROADCASTYOUCANPERFORMAQUERYTOACONTENTPROVIDERBYCALLINGQUERYONACONTENTRESOLVERFORMOREINFORMATIONABOUTUSINGINTENTS,SEETHEINTENTSANDINTENTFILTERSDOCUMENTMOREINFORMATIONABOUTACTIVATINGSPECIFICCOMPONENTSISALSOPROVIDEDINTHEFOLLOWINGDOCUMENTSACTIVITIES,SERVICES,BROADCASTRECEIVERANDCONTENTPROVIDERSDECLARINGCOMPONENTSTHEPRIMARYTASKOFTHEMANIFESTISTOINFORMTHESYSTEMABOUTTHEAPPLICATIONSCOMPONENTSFOREXAMPLE,AMANIFESTFILECANDECLAREANACTIVITYASFOLLOWSINTHEELEMENT,THEANDROIDICONATTRIBUTEPOINTSTORESOURCESFORANICONTHATIDENTIFIESTHEAPPLICATIONINTHEELEMENT,THEANDROIDNAMEATTRIBUTESPECIFIESTHEFULLYQUALIFIEDCLASSNAMEOFTHEACTIVITYSUBCLASSANDTHEANDROIDLABELATTRIBUTESSPECIFIESASTRINGTOUSEASTHEUSERVISIBLELABELFORTHEACTIVITYYOUMUSTDECLAREALLAPPLICATIONCOMPONENTSTHISWAYELEMENTSFORACTIVITIESELEMENTSFORSERVICESELEMENTSFORBROADCASTRECEIVERSELEMENTSFORCONTENTPROVIDERSACTIVITIES,SERVICES,ANDCONTENTPROVIDERSTHATYOUINCLUDEINYOURSOURCEBUTDONOTDECLAREINTHEMANIFESTARENOTVISIBLETOTHESYSTEMAND,CONSEQUENTLY,CANNEVERRUNHOWEVER,BROADCASTRECEIVERSCANBEEITHERDECLAREDINTHEMANIFESTORCREATEDDYNAMICALLYINCODEASBROADCASTRECEIVEROBJECTSANDREGISTEREDWITHTHESYSTEMBYCALLINGREGISTERRECEIVERDECLARINGCOMPONENTCAPABILITIESASDISCUSSEDABOVE,INACTIVATINGCOMPONENTS,YOUCANUSEANINTENTTOSTARTACTIVITIES,SERVICES,ANDBROADCASTRECEIVERSYOUCANDOSOBYEXPLICITLYNAMINGTHETARGETCOMPONENTUSINGTHECOMPONENTCLASSNAMEINTHEINTENTHOWEVER,THEREALPOWEROFINTENTSLIESINTHECONCEPTOFINTENTACTIONSWITHINTENTACTIONS,YOUSIMPLYDESCRIBETHETYPEOFACTIONYOUWANTTOPERFORMANDOPTIONALLY,THEDATAUPONWHICHYOUDLIKETOPERFORMTHEACTIONANDALLOWTHESYSTEMTOFINDACOMPONENTONTHEDEVICETHATCANPERFORMTHEACTIONANDSTARTITIFTHEREAREMULTIPLECOMPONENTSTHATCANPERFORMTHEACTIONDESCRIBEDBYTHEINTENT,THENTHEUSERSELECTSWHICHONETOUSETHEWAYTHESYSTEMIDENTIFIESTHECOMPONENTSTHATCANRESPONDTOANINTENTISBYCOMPARINGTHEINTENTRECEIVEDTOTHEINTENTFILTERSPROVIDEDINTHEMANIFESTFILEOFOTHERAPPLICATIONSONTHEDEVICEWHENYOUDECLAREACOMPONENTINYOURAPPLICATIONSMANIFEST,YOUCANOPTIONALLYINCLUDEINTENTFILTERSTHATDECLARETHECAPABILITIESOFTHECOMPONENTSOITCANRESPONDTOINTENTSFROMOTHERAPPLICATIONSYOUCANDECLAREANINTENTFILTERFORYOURCOMPONENTBYADDINGANELEMENTASACHILDOFTHECOMPONENTSDECLARATIONELEMENTFOREXAMPLE,ANEMAILAPPLICATIONWITHANACTIVITYFORCOMPOSINGANEWEMAILMIGHTDECLAREANINTENTFILTERINITSMANIFESTENTRYTORESPONDTO“SEND“INTENTSINORDERTOSENDEMAILANACTIVITYINYOURAPPLICATIONCANTHENCREATEANINTENTWITHTHE“SEND”ACTIONACTION_SEND,WHICHTHESYSTEMMATCHESTOTHEEMAILAPPLICATIONS“SEND”ACTIVITYANDLAUNCHESITWHENYOUINVOKETHEINTENTWITHSTARTACTIVITYFORMOREABOUTCREATINGINTENTFILTERS,SEETHEINTENTSANDINTENTFILTERSDOCUMENTDECLARINGAPPLICATIONREQUIREMENTSTHEREAREAVARIETYOFDEVICESPOWEREDBYANDROIDANDNOTALLOFTHEMPROVIDETHESAMEFEATURESANDCAPABILITIESINORDERTOPREVENTYOURAPPLICATIONFROMBEINGINSTALLEDONDEVICESTHATLACKFEATURESNEEDEDBYYOURAPPLICATION,ITSIMPORTANTTHATYOUCLEARLYDEFINEAPROFILEFORTHETYPESOFDEVICESYOURAPPLICATIONSUPPORTSBYDECLARINGDEVICEANDSOFTWAREREQUIREMENTSINYOURMANIFESTFILEMOSTOFTHESEDECLARATIONSAREINFORMATIONALONLYANDTHESYSTEMDOESNOTREADTHEM,BUTEXTERNALSERVICESSUCHASGOOGLEPLAYDOREADTHEMINORDERTOPROVIDEFILTERINGFORUSERSWHENTHEYSEARCHFORAPPLICATIONSFROMTHEIRDEVICEFOREXAMPLE,IFYOURAPPLICATIONREQUIRESACAMERAANDUSESAPISINTRODUCEDINANDROID21APILEVEL7,YOUSHOULDDECLARETHESEASREQUIREMENTSINYOURMANIFESTFILETHATWAY,DEVICESTHATDONOTHAVEACAMERAANDHAVEANANDROIDVERSIONLOWERTHAN21CANNOTINSTALLYOURAPPLICATIONFROMGOOGLEPLAYHOWEVER,YOUCANALSODECLARETHATYOURAPPLICATIONUSESTHECAMERA,BUTDOESNOTREQUIREITINTHATCASE,YOURAPPLICATIONMUSTPERFORMACHECKATRUNTIMETODETERMINEIFTHEDEVICEHASACAMERAANDDISABLEANYFEATURESTHATUSETHECAMERAIFONEISNOTAVAILABLEHEREARESOMEOFTHEIMPORTANTDEVICECHARACTERISTICSTHATYOUSHOULDCONSIDERASYOUDESIGNANDDEVELOPYOURAPPLICATIONSCREENSIZEANDDENSITYINORDERTOCATEGORIZEDEVICESBYTHEIRSCREENTYPE,ANDROIDDEFINESTWOCHARACTERISTICSFOREACHDEVICESCREENSIZETHEPHYSICALDIMENSIONSOFTHESCREENANDSCREENDENSITYTHEPHYSICALDENSITYOFTHEPIXELSONTHESCREEN,ORDPIDOTSPERINCHTOSIMPLIFYALLTHEDIFFERENTTYPESOFSCREENCONFIGURATIONS,THEANDROIDSYSTEMGENERALIZESTHEMINTOSELECTGROUPSTHATMAKETHEMEASIERTOTARGETTHESCREENSIZESARESMALL,NORMAL,LARGE,ANDEXTRALARGETHESCREENDENSITIESARELOWDENSITY,MEDIUMDENSITY,HIGHDENSITY,ANDEXTRAHIGHDENSITYBYDEFAULT,YOURAPPLICATIONISCOMPATIBLEWITHALLSCREENSIZESANDDENSITIES,BECAUSETHEANDROIDSYSTEMMAKESTHEAPPROPRIATEADJUSTMENTSTOYOURUILAYOUTANDIMAGERESOURCESHOWEVER,YOUSHOULDCREATESPECIALIZEDLAYOUTSFORCERTAINSCREENSIZESANDPROVIDESPECIALIZEDIMAGESFORCERTAINDENSITIES,USINGALTERNATIVELAYOUTRESOURCES,ANDBYDECLARINGINYOURMANIFESTEXACTLYWHICHSCREENSIZESYOURAPPLICATIONSUPPORTSWITHTHEELEMENTFORMOREINFORMATION,SEETHESUPPORTINGMULTIPLESCREENSDOCUMENTINPUTCONFIGURATIONSMANYDEVICESPROVIDEADIFFERENTTYPEOFUSERINPUTMECHANISM,SUCHASAHARDWAREKEYBOARD,ATRACKBALL,ORAFIVEWAYNAVIGATIONPADIFYOURAPPLICATIONREQUIRESAPARTICULARKINDOFINPUTHARDWARE,THENYOUSHOULDDECLAREITINYOURMANIFESTWITHTHEELEMENTHOWEVER,ITISRARETHATANAPPLICATIONSHOULDREQUIREACERTAININPUTCONFIGURATIONDEVICEFEATURESTHEREAREMANYHARDWAREANDSOFTWAREFEATURESTHATMAYORMAYNOTEXISTONAGIVENANDROIDPOWEREDDEVICE,SUCHASACAMERA,ALIGHTSENSOR,BLUETOOTH,ACERTAINVERSIONOFOPENGL,ORTHEFIDELITYOFTHETOUCHSCREENYOUSHOULDNEVERASSUMETHATACERTAINFEATUREISAVAILABLEONALLANDROIDPOWEREDDEVICESOTHERTHANTHEAVAILABILITYOFTHESTANDARDANDROIDLIBRARY,SOYOUSHOULDDECLAREANYFEATURESUSEDBYYOURAPPLICATIONWITHTHEELEMENTPLATFORMVERSIONDIFFERENTANDROIDPOWEREDDEVICESOFTENRUNDIFFERENTVERSIONSOFTHEANDROIDPLATFORM,SUCHASANDROID16ORANDROID23EACHSUCCESSIVEVERSIONOFTENINCLUDESADDITIONALAPISNOTAVAILABLEINTHEPREVIOUSVERSIONINORDERTOINDICATEWHICHSETOFAPISAREAVAILABLE,EACHPLATFORMVERSIONSPECIFIESANAPILEVELFOREXAMPLE,ANDROID10ISAPILEVEL1ANDANDROID23ISAPILEVEL9IFYOUUSEANYAPISTHATWEREADDEDTOTHEPLATFORMAFTERVERSION10,YOUSHOULDDECLARETHEMINIMUMAPILEVELINWHICHTHOSEAPISWEREINTRODUCEDUSINGTHEELEMENTITSIMPORTANTTHATYOUDECLAREALLSUCHREQUIREMENTSFORYOURAPPLICATION,BECAUSE,WHENYOUDISTRIBUTEYOURAPPLICATIONONGOOGLEPLAY,THESTOREUSESTHESEDECLARATIONSTOFILTERWHICHAPPLICATIONSAREAVAILABLEONEACHDEVICEASSUCH,YOURAPPLICATIONSHOULDBEAVAILABLEONLYTODEVICESTHATMEETALLYOURAPPLICATIONREQUIREMENTSFORMOREINFORMATIONABOUTHOWGOOGLEPLAYFILTERSAPPLICATIONSBASEDONTHESEANDOTHERREQUIREMENTS,SEETHEFILTERSONGOOGLEPLAYDOCUMENTAPPLICATIONRESOURCESANANDROIDAPPLICATIONISCOMPOSEDOFMORETHANJUSTCODEITREQUIRESRESOURCESTHATARESEPARATEFROMTHESOURCECODE,SUCHASIMAGES,AUDIOFILES,ANDANYTHINGRELATINGTOTHEVISUALPRESENTATIONOFTHEAPPLICATIONFOREXAMPLE,YOUSHOULDDEFINEANIMATIONS,MENUS,STYLES,COLORS,ANDTHELAYOUTOFACTIVITYUSERINTERFACESWITHXMLFILESUSINGAPPLICATIONRESOURCESMAKESITEASYTOUPDATEVARIOUSCHARACTERISTICSOFYOURAPPLICATIONWITHOUTMODIFYINGCODEANDBYPROVIDINGSETSOFALTERNATIVERESOURCESENABLESYOUTOOPTIMIZEYOURAPPLICATIONFORAVARIETYOFDEVICECONFIGURATIONSSUCHASDIFFERENTLANGUAGESANDSCREENSIZESFOREVERYRESOURCETHATYOUINCLUDEINYOURANDROIDPROJECT,THESDKBUILDTOOLSDEFINEAUNIQUEINTEGERID,WHICHYOUCANUSETOREFERENCETHERESOURCEFROMYOURAPPLICATIONCODEORFROMOTHERRESOURCESDEFINEDINXMLFOREXAMPLE,IFYOURAPPLICATIONCONTAINSANIMAGEFILENAMEDLOGOPNGSAVEDINTHERES/DRAWABLE/DIRECTORY,THESDKTOOLSGENERATEARESOURCEIDNAMEDRDRAWABLELOGO,WHICHYOUCANUSETOREFERENCETHEIMAGEANDINSERTITINYOURUSERINTERFACEONEOFTHEMOSTIMPORTANTASPECTSOFPROVIDINGRESOURCESSEPARATEFROMYOURSOURCECODEISTHEABILITYFORYOUTOPROVIDEALTERNATIVERESOURCESFORDIFFERENTDEVICECONFIGURATIONSFOREXAMPLE,BYDEFININGUISTRINGSINXML,YOUCANTRANSLATETHESTRINGSINTOOTHERLANGUAGESANDSAVETHOSESTRINGSINSEPARATEFILESTHEN,BASEDONALANGUAGEQUALIFIERTHATYOUAPPENDTOTHERESOURCEDIRECTORYSNAMESUCHASRES/VALUESFR/FORFRENCHSTRINGVALUESANDTHEUSERSLANGUAGESETTING,THEANDROIDSYSTEMAPPLIESTHEAPPROPRIATELANGUAGESTRINGSTOYOURUIANDROIDSUPPORTSMANYDIFFERENTQUALIFIERSFORYOURALTERNATIVERESOURCESTHEQUALIFIERISASHORTSTRINGTHATYOUINCLUDEINTHENAMEOFYOURRESOURCEDIRECTORIESINORDERTODEFINETHEDEVICECONFIGURATIONFORWHICHTHOSERESOURCESSHOULDBEUSEDASANOTHEREXAMPLE,YOUSHOULDOFTENCREATEDIFFERENTLAYOUTSFORYOURACTIVITIES,DEPENDINGONTHEDEVICESSCREENORIENTATIONANDSIZEFOREXAMPLE,WHENTHEDEVICESCREENISINPORTRAITORIENTATIONTALL,YOUMIGHTWANTALAYOUTWITHBUTTONSTOBEVERTICAL,BUTWHENTHESCREENISINLANDSCAPEORIENTATIONWIDE,THEBUTTONSSHOULDBEALIGNEDHORIZONTALLYTOCHANGETHELAYOUTDEPENDINGONTHEORIENTATION,YOUCANDEFINETWODIFFERENTLAYOUTSANDAPPLYTHEAPPROPRIATEQUALIFIERTOEACHLAYOUTSDIRECTORYNAMETHEN,THESYSTEMAUTOMATICALLYAPPLIESTHEAPPROPRIATELAYOUTDEPENDINGONTHECURRENTDEVICEORIENTATIONFORMOREABOUTTHEDIFFERENTKINDSOFRESOURCESYOUCANINCLUDEINYOURAPPLICATIONANDHOWTOCREATEALTERNATIVERESOURCESFORVARIOUSDEVICECONFIGURATIONS,SEETHEAPPLICATIONRESOURCESDEVELOPERGUIDE安卓应用基础ANDROID应用程序是用JAVA编程语言编写的，ANDROID的SDK工具编译成代码和数据和资源文件放到一个ANDROID的包，一个归档文件档案资源的APK后缀，所有的在一个单一的代码APK文件被认为是一个应用程序，是ANDROID的文件，供电设备来安装应用程序。一旦安装在设备上，每个ANDROID应用程序的生命在它自己的安全沙箱而ANDROID操作系统是一个多用户LINUX系统中，每个应用程序是一个不同的用户。默认情况下，每个应用程序的系统分配一个唯一的LINUX用户ID（该ID仅用于由系统是未知的应用程序），系统设置所有的应用程序中的文件权限，以便只有用户ID分配给该应用程序可以访问它们。每个进程都有它自己的虚拟机（VM），因此应用程序的代码在从其他应用程序隔离运行。默认情况下，每个应用程序运行在它自己的LINUX进程。ANDROID的启动过程时，应用程序的任何组件需要被执行，然后关闭该进程时，它不