毕业论文5000字英文翻译怎么找啊.docx
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毕业论文5000字英文翻译怎么找啊.docx
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毕业论文5000字英文翻译怎么找啊
毕业论文5000字英文翻译怎么找啊
篇一:
毕业设计的5000字英文文献翻译
外文及翻译
英语原文AndroidApplicationFundamentals
AndroidapplicationsarewrittenintheJavaprogramminglanguage.TheAndroidSDKtoolscompilethecode—alongwithanydataandresourcefiles—intoanAndroidpackage,anarchivefilewithan.apksuffix.Allthecodeinasingle.apkfileisconsideredtobeoneapplicationandisthefilethatAndroid-powereddevicesusetoinstalltheapplication.Onceinstalledonadevice,eachAndroidapplicationlivesinitsownsecuritysandbox:
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TheAndroidoperatingsystemisamulti-userLinuxsysteminwhicheach
applicationisadifferentuser.
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Bydefault,thesystemassignseachapplicationauniqueLinuxuserID(theIDisusedonlybythesystemandisunknowntotheapplication).Thesystemsets
permissionsforallthefilesinanapplicationsothatonlytheuserIDassignedtothatapplicationcanaccessthem.
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Eachprocesshasitsownvirtualmachine(VM),soanapplication'scoderunsinisolationfromotherapplications.
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Bydefault,everyapplicationrunsinitsownLinuxprocess.Androidstartstheprocesswhenanyoftheapplication'scomponentsneedtobeexecuted,thenshutsdowntheprocesswhenit'snolongerneededorwhenthesystemmustrecover
memoryforotherapplications.
Inthisway,theAndroidsystemimplementstheprincipleofleastprivilege.Thatis,eachapplication,bydefault,hasaccessonlytothecomponentsthatitrequirestodoitsworkandnomore.Thiscreatesaverysecureenvironmentinwhichanapplicationcannotaccesspartsofthesystemforwhichitisnotgivenpermission.
However,therearewaysforanapplicationtosharedatawithotherapplicationsandforanapplicationtoaccesssystemservices:
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It'spossibletoarrangefortwoapplicationstosharethesameLinuxuserID,inwhich
casetheyareabletoaccesseachother'sfiles.Toconservesystemresources,
applicationswiththesameuserIDcanalsoarrangetoruninthesameLinuxprocess
andsharethesameVM(theapplicationsmustalsobesignedwiththesame
certificate).
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Anapplicationcanrequestpermissiontoaccessdevicedatasuchastheuser's
contacts,SMSmessages,themountablestorage(SDcard),camera,Bluetooth,and
more.Allapplicationpermissionsmustbegrantedbytheuseratinstalltime.
ThatcoversthebasicsregardinghowanAndroidapplicationexistswithinthesystem.Therestofthisdocumentintroducesyouto:
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Thecoreframeworkcomponentsthatdefineyourapplication.
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Themanifestfileinwhichyoudeclarecomponentsandrequireddevicefeaturesfor
yourapplication.
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Resourcesthatareseparatefromtheapplicationcodeandallowyourapplicationto
gracefullyoptimizeitsbehaviorforavarietyofdeviceconfigurations.
ApplicationComponents
ApplicationcomponentsaretheessentialbuildingblocksofanAndroidapplication.Eachcomponentisadifferentpointthroughwhichthesystemcanenteryourapplication.Notallcomponentsareactualentrypointsfortheuserandsomedependoneachother,buteachoneexistsasitsownentityandplaysaspecificrole—eachoneisauniquebuildingblockthathelpsdefineyourapplication'soverallbehavior.
Therearefourdifferenttypesofapplicationcomponents.Eachtypeservesadistinctpurposeandhasadistinctlifecyclethatdefineshowthecomponentiscreatedanddestroyed.
Herearethefourtypesofapplicationcomponents:
Activities
Anactivityrepresentsasinglescreenwithauserinterface.Forexample,anemailapplicationmighthaveoneactivitythatshowsalistofnewemails,anotheractivitytocomposeanemail,andanotheractivityforreadingemails.Althoughtheactivitiesworktogethertoformacohesiveuserexperienceintheemailapplication,eachoneisindependentoftheothers.Assuch,adifferentapplicationcanstartanyoneofthese
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activities(iftheemailapplicationallowsit).Forexample,acameraapplicationcanstarttheactivityintheemailapplicationthatcomposesnewmail,inorderfortheusertoshareapicture.
AnactivityisimplementedasasubclassofActivityandyoucanlearnmoreaboutitintheActivitiesdeveloperguide.
Services
Aserviceisacomponentthatrunsinthebackgroundtoperformlong-runningoperationsortoperformworkforremoteprocesses.Aservicedoesnotprovideauserinterface.Forexample,aservicemightplaymusicinthebackgroundwhiletheuserisinadifferentapplication,oritmightfetchdataoverthenetworkwithoutblockinguserinteractionwithanactivity.Anothercomponent,suchasanactivity,canstarttheserviceandletitrunorbindtoitinordertointeractwithit.
AserviceisimplementedasasubclassofServiceandyoucanlearnmoreaboutitintheServicesdeveloperguide.Contentproviders
Acontentprovidermanagesasharedsetofapplicationdata.Youcanstorethedatainthefilesystem,anSQLitedatabase,ontheweb,oranyotherpersistentstoragelocationyourapplicationcanaccess.Throughthecontentprovider,otherapplicationscanqueryorevenmodifythedata(ifthecontentproviderallowsit).Forexample,theAndroidsystemprovidesacontentproviderthatmanagestheuser'scontactinformation.Assuch,anyapplicationwiththeproperpermissionscanquerypartofthecontentprovider(suchasContactsContract.Data)toreadandwriteinformationaboutaparticularperson.
Contentprovidersarealsousefulforreadingandwritingdatathatisprivatetoyourapplicationandnotshared.Forexample,theNotePadsampleapplicationusesacontentprovidertosavenotes.
AcontentproviderisimplementedasasubclassofContentProviderandmustimplementastandardsetofAPIsthatenableotherapplicationstoperformtransactions.Formoreinformation,seetheContentProvidersdeveloperguide.
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Broadcastreceivers
Abroadcastreceiverisacomponentthatrespondstosystem-widebroadcastaements.Manybroadcastsoriginatefromthesystem—forexample,abroadcastaingthatthescreenhasturnedoff,thebatteryislow,orapicturewascaptured.Applicationscanalsoinitiatebroadcasts—forexample,toletotherapplicationsknowthatsomedatahasbeendownloadedtothedeviceandisavailableforthemtouse.Althoughbroadcastreceiversdon'tdisplayauserinterface,theymaycreateastatusbarnotificationtoalerttheuserwhenabroadcasteventoccurs.Morely,though,abroadcastreceiverisjusta"gateway"toothercomponentsandisintendedtodoaveryminimalamountofwork.Forinstance,itmightinitiateaservicetoperformsomeworkbasedontheevent.
AbroadcastreceiverisimplementedasasubclassofBroadcastReceiverandeachbroadcastisdeliveredasanIntentobject.Formoreinformation,seetheBroadcastReceiverclass.
AuniqueaspectoftheAndroidsystemdesignisthatanyapplicationcanstartanotherapplication’scomponent.Forexample,ifyouwanttheusertocaptureaphotowiththedevicecamera,there'sprobablyanotherapplicationthatdoesthatandyourapplicationcanuseit,insteadofdevelopinganactivitytocaptureaphotoyourself.Youdon'tneedtoincorporateorevenlinktothecodefromthecameraapplication.Instead,youcansimplystarttheactivityinthecameraapplicationthatcapturesaphoto.Whencomplete,thephotoisevenreturnedtoyourapplicationsoyoucanuseit.Totheuser,itseemsasifthecameraisactuallyapartofyourapplication.
Whenthesystemstartsacomponent,itstartstheprocessforthatapplication(ifit'snotalreadyrunning)andinstantiatestheclassesneededforthecomponent.Forexample,ifyourapplicationstartstheactivityinthecameraapplicationthatcapturesaphoto,thatactivityrunsintheprocessthatbelongstothecameraapplication,notinyourapplication'sprocess.
Therefore,unlikeapplicationsonmostothersystems,Androidapplicationsdon'thaveasingleentrypoint(there'snomain()function,forexample).
Becausethesystemrunseachapplicationinaseparateprocesswithfilepermissionsthatrestrictaccesstootherapplications,yourapplicationcannotdirectlyactivateacomponentfromanotherapplication.TheAndroidsystem,however,can.So,toactivateacomponentin
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anotherapplication,youmustdeliveramessagetothesystemthatspecifiesyourintenttostartaparticularcomponent.Thesystemthenactivatesthecomponentforyou.
ActivatingComponents
Threeofthefourcomponenttypes—activities,services,andbroadcastreceivers—areactivatedbyanasynchronousmessagecalledanintent.Intentsbindindividualcomponentstoeachotheratruntime(youcanthinkofthemasthemessengersthatrequestanactionfromothercomponents),whetherthecomponentbelongstoyourapplicationoranother.
AnintentiscreatedwithanIntentobject,whichdefinesamessagetoactivateeitheraspecificcomponentoraspecifictypeofcomponent—anintentcanbeeitherexplicitorimplicit,respectively.
Foractivitiesandservices,anintentdefinestheactiontoperform(forexample,to"view"or"send"something)andmayspecifytheURIofthedatatoacton(amongotherthingsthatthecomponentbeingstartedmightneedtoknow).Forexample,anintentmightconveyarequestforanactivitytoshowanimageortoopenawebpage.Insomecases,youcanstartanactivitytoreceivearesult,inwhichcase,theactivityalsoreturnstheresultin
anIntent(forexample,youcanissueanintenttolettheuserpickapersonalcontactandhaveitreturnedtoyou—thereturnintentincludesaURIpointingtothechosencontact).
Forbroadcastreceivers,theintentsimplydefinestheaementbeingbroadcast(forexample,abroadcasttoindicatethe
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