外文文献Android Application Fundamentals安卓应用基础.docx

外文文献Android Application Fundamentals安卓应用基础.docx

《外文文献Android Application Fundamentals安卓应用基础.docx》由会员分享，可在线阅读，更多相关《外文文献Android Application Fundamentals安卓应用基础.docx（25页珍藏版）》请在冰点文库上搜索。

外文文献AndroidApplicationFundamentals安卓应用基础

外文文献-AndroidApplicationFundamentals安卓应用基础

毕业设计

外文文献原文及译文

AndroidApplicationFundamentals

安卓应用基础

学生姓名:

学号:

计算机系系别:

网络工程专业:

指导教师:

2015年5月

中北大学信息商务学院2015届毕业设计外文文献原文及译文

AndroidApplicationFundamentals

AndroidapplicationsarewrittenintheJavaprogramminglanguage.TheAndroidSDKtoolscompilethecode—alongwithanydataandresourcefiles—intoanAndroidpackage,

anarchivefilewithan.apksuffix.Allthecodeinasingle.apkfileisconsideredtobeoneapplicationandisthefilethatAndroid-powereddevicesusetoinstalltheapplication.

Onceinstalledonadevice,eachAndroidapplicationlivesinitsownsecuritysandbox:

TheAndroidoperatingsystemisamulti-userLinuxsysteminwhicheach

applicationisadifferentuser.

Bydefault,thesystemassignseachapplicationauniqueLinuxuserID（theIDis

usedonlybythesystemandisunknowntotheapplication）.Thesystemsets

permissionsforallthefilesinanapplicationsothatonlytheuserIDassignedto

thatapplicationcanaccessthem.

Eachprocesshasitsownvirtualmachine（VM）,soanapplication'scoderunsin

isolationfromotherapplications.

Bydefault,everyapplicationrunsinitsownLinuxprocess.Androidstartsthe

processwhenanyoftheapplication'scomponentsneedtobeexecuted,thenshuts

downtheprocesswhenit'snolongerneededorwhenthesystemmustrecover

memoryforotherapplications.

Inthisway,theAndroidsystemimplementstheprincipleofleastprivilege.Thatis,

eachapplication,bydefault,hasaccessonlytothecomponentsthatitrequirestodoitsworkandnomore.Thiscreatesaverysecureenvironmentinwhichanapplicationcannotaccesspartsofthesystemforwhichitisnotgivenpermission.

However,therearewaysforanapplicationtosharedatawithotherapplicationsandforanapplicationtoaccesssystemservices:

It'spossibletoarrangefortwoapplicationstosharethesameLinuxuserID,in

whichcasetheyareabletoaccesseachother'sfiles.Toconservesystemresources,

中北大学信息商务学院2015届毕业设计外文文献原文及译文

applicationswiththesameuserIDcanalsoarrangetoruninthesameLinux

processandsharethesameVM（theapplicationsmustalsobesignedwiththe

samecertificate）.

Anapplicationcanrequestpermissiontoaccessdevicedatasuchastheuser's

contacts,SMSmessages,themountablestorage（SDcard）,camera,Bluetooth,and

more.Allapplicationpermissionsmustbegrantedbytheuseratinstalltime.ThatcoversthebasicsregardinghowanAndroidapplicationexistswithinthesystem.Therestofthisdocumentintroducesyouto:

Thecoreframeworkcomponentsthatdefineyourapplication.

Themanifestfileinwhichyoudeclarecomponentsandrequireddevicefeatures

foryourapplication.

Resourcesthatareseparatefromtheapplicationcodeandallowyourapplication

togracefullyoptimizeitsbehaviorforavarietyofdeviceconfigurations.

ApplicationComponents

ApplicationcomponentsaretheessentialbuildingblocksofanAndroidapplication.Eachcomponentisadifferentpointthroughwhichthesystemcanenteryourapplication.Notallcomponentsareactualentrypointsfortheuserandsomedependoneachother,buteachoneexistsasitsownentityandplaysaspecificrole—eachoneisauniquebuilding

blockthathelpsdefineyourapplication'soverallbehavior.

Therearefourdifferenttypesofapplicationcomponents.Eachtypeservesadistinctpurposeandhasadistinctlifecyclethatdefineshowthecomponentiscreatedanddestroyed.

Herearethefourtypesofapplicationcomponents:

Activities

Anactivityrepresentsasinglescreenwithauserinterface.Forexample,anemail

applicationmighthaveoneactivitythatshowsalistofnewemails,anotheractivity

中北大学信息商务学院2015届毕业设计外文文献原文及译文

tocomposeanemail,andanotheractivityforreadingemails.Althoughtheactivitiesworktogethertoformacohesiveuserexperienceintheemailapplication,eachoneisindependentoftheothers.Assuch,adifferentapplicationcanstartanyoneoftheseactivities（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.

Contentprovidersarealsousefulforreadingandwritingdatathatisprivatetoyour

中北大学信息商务学院2015届毕业设计外文文献原文及译文

applicationandnotshared.Forexample,theNotePadsampleapplicationusesa

contentprovidertosavenotes.

AcontentproviderisimplementedasasubclassofContentProviderandmust

implementastandardsetofAPIsthatenableotherapplicationstoperform

transactions.Formoreinformation,seetheContentProvidersdeveloperguide.Broadcastreceivers

Abroadcastreceiverisacomponentthatrespondstosystem-widebroadcast

announcements.Manybroadcastsoriginatefromthesystem—forexample,a

broadcastannouncingthatthescreenhasturnedoff,thebatteryislow,orapicture

wascaptured.Applicationscanalsoinitiatebroadcasts—forexample,toletother

applicationsknowthatsomedatahasbeendownloadedtothedeviceandis

availableforthemtouse.Althoughbroadcastreceiversdon'tdisplayauser

interface,theymaycreateastatusbarnotificationtoalerttheuserwhenabroadcast

eventoccurs.Morecommonly,though,abroadcastreceiverisjusta"gateway"to

othercomponentsandisintendedtodoaveryminimalamountofwork.For

instance,itmightinitiateaservicetoperformsomeworkbasedontheevent.

AbroadcastreceiverisimplementedasasubclassofBroadcastReceiverandeach

broadcastisdeliveredasanIntentobject.Formoreinformation,see

theBroadcastReceiverclass.

AuniqueaspectoftheAndroidsystemdesignisthatanyapplicationcanstartanotherapplication’scomponent.Forexample,ifyouwanttheusertocaptureaphotowiththedevicecamera,there'sprobablyanotherapplicationthatdoesthatandyourapplicationcanuseit,insteadofdevelopinganactivitytocaptureaphotoyourself.Youdon'tneedtoincorporateorevenlinktothecodefromthecameraapplication.Instead,youcansimplystarttheactivityinthecameraapplicationthatcapturesaphoto.Whencomplete,thephotoisevenreturnedtoyourapplicationsoyoucanuseit.Totheuser,itseemsasifthecameraisactuallyapartofyourapplication.

中北大学信息商务学院2015届毕业设计外文文献原文及译文

Whenthesystemstartsacomponent,itstartstheprocessforthatapplication（ifit'snotalreadyrunning）andinstantiatestheclassesneededforthecomponent.Forexample,ifyourapplicationstartstheactivityinthecameraapplicationthatcapturesaphoto,thatactivityrunsintheprocessthatbelongstothecameraapplication,notinyourapplication'sprocess.Therefore,unlikeapplicationsonmostothersystems,Androidapplicationsdon'thaveasingleentrypoint（there'snomain（）function,forexample）.

Becausethesystemrunseachapplicationinaseparateprocesswithfilepermissionsthatrestrictaccesstootherapplications,yourapplicationcannotdirectlyactivateacomponentfromanotherapplication.TheAndroidsystem,however,can.So,toactivateacomponentinanotherapplication,youmustdeliveramessagetothesystemthatspecifiesyourintenttostartaparticularcomponent.Thesystemthenactivatesthecomponentforyou.

ActivatingComponents

Threeofthefourcomponenttypes—activities,services,andbroadcastreceivers—are

activatedbyanasynchronousmessagecalledanintent.Intentsbindindividualcomponents

toeachotheratruntime（youcanthinkofthemasthemessengersthatrequestanactionfromothercomponents）,whetherthecomponentbelongstoyourapplicationoranother.

AnintentiscreatedwithanIntentobject,whichdefinesamessagetoactivateeitheraspecificcomponentoraspecifictypeofcomponent—anintentcanbeeitherexplicitor

implicit,respectively.

Foractivitiesandservices,anintentdefinestheactiontoperform（forexample,to"view"or"send"something）andmayspecifytheURIofthedatatoacton（amongotherthingsthatthecomponentbeingstartedmightneedtoknow）.Forexample,anintentmightconveyarequestforanactivitytoshowanimageortoopenawebpage.Insomecases,youcanstartanactivitytoreceivearesult,inwhichcase,theactivityalsoreturnsth