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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,ANDTHELAYOUTOFACTIVITYUSERINTERFACESWITHXMLFILESUSINGAPPLICATIONRESOURCESMAKESITEASYTOUPDATEVARIOUSCHARACTERISTICSOFYOURAPPLICATIONWITHOUTMODIFYINGCODEANDBYPROVIDINGSETSOFALTERNATIVERESOURCESENABLESYOUTOOPTIMIZEYOURAPPLICATIONFORAVARIETYOFDEVICECONFIGURATIONSSUCHASDIFFERENTLANGUAGESANDSCREENSIZESFOREVER
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