关于Android的外文文献Word下载.docx
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Android:
AProgrammer’sGuide
1WhatIsAndroid
1.1KeySkills&
Concepts
●Historyofembeddeddeviceprogramming
●ExplanationofOpenHandsetAlliance
●FirstlookattheAndroidhomescreen
Itcanbesaidthat,forawhile,traditionaldesktopapplicationdevelopershavebeenspoiled.Thisisnottosaythattraditionaldesktopapplicationdevelopmentiseasierthanotherformsofdevelopment.However,astraditionaldesktopapplicationdevelopers,wehavehadtheabilitytocreatealmostanykindofapplicationwecanimagine.IamincludingmyselfinthisgroupingbecauseIgotmystartindesktopprogramming.
Oneaspectthathasmadedesktopprogrammingmoreaccessibleisthatwehavehadtheabilitytointeractwiththedesktopoperatingsystem,andthusinteractwithanyunderlyinghardware,prettyfreely(oratleastwithminimalexceptions).Thiskindoffreedomtoprogramindependently,however,hasneverreallybeenavailabletothesmallgroupofprogrammerswhodaredtoventureintothemurkywatersofcellphonedevelopment.
NOTE:
Irefertotwodifferentkindsofdevelopersinthisdiscussion:
traditionaldesktopapplicationdevelopers,whoworkinalmostanylanguageandwhoseendproduct,applications,arebuilttorunonany“desktop”operatingsystem;
andAndroiddevelopers,JavadeveloperswhodevelopfortheAndroidplatform.Thisisnotforthepurposesofsayingoneisbyanymeansbetterorworsethantheother.Rather,thedistinctionismadeforpurposesofcomparingthedevelopmentstylesandtoolsofdesktopoperatingsystemenvironmentstothemobileoperatingsystemenvironment,
1.2BriefHistoryofEmbeddedDeviceProgramming
Foralongtime,cellphonedeveloperscomprisedasmallsectofaslightlylargergroupofdevelopersknownasembeddeddevicedevelopers.Seenasaless“glamorous”siblingtodesktop—andlaterweb—development,embeddeddevicedevelopmenttypicallygottheproverbialshortendofthestickasfarashardwareandoperatingsystemfeatures,becauseembeddeddevicemanufacturerswerenotoriouslystingyonfeaturesupport.
Embeddeddevicemanufacturerstypicallyneededtoguardtheirhardwaresecretsclosely,sotheygaveembeddeddevicedevelopersfewlibrariestocallwhentryingtointeractwithaspecificdevice.Embeddeddevicesdifferfromdesktopsinthatanembeddeddeviceistypicallya“computeronachip.”Forexample,consideryourstandardtelevisionremotecontrol;
itisnotreallyseenasanoverwhelmingachievementoftechnologicalcomplexity.Whenanybuttonispressed,achipinterpretsthesignalinawaythathasbeenprogrammedintothedevice.Thisallowsthedevicetoknowwhattoexpectfromtheinputdevice(keypad),andhowtorespondtothosecommands(forexample,turnonthetelevision).Thisisasimpleformofembeddeddeviceprogramming.However,believeitornot,simpledevicessuchasthesearedefinitelyrelatedtotherootsofearlycellphonedevicesanddevelopment.
Mostembeddeddevicesran(andinsomecasesstillrun)proprietaryoperatingsystems.Thereasonforchoosingtocreateaproprietaryoperatingsystemratherthanuseanyconsumersystemwasreallyaproductofnecessity.Simpledevicesdidnotneedveryrobustandoptimizedoperatingsystems.
Asaproductofdeviceevolution,manyofthemorecomplexembeddeddevices,suchasearlyPDAs,householdsecuritysystems,andGPSs,movedtosomewhatstandardizedoperatingsystemplatformsaboutfiveyearsago.Small-footprintoperatingsystemssuchasLinux,orevenanembeddedversionofMicrosoftWindows,havebecomemoreprevalentonmanyembeddeddevices.Aroundthistimeindeviceevolution,cellphonesbranchedfromotherembeddeddevicesontotheirownpath.Thisbranchingisevidentwhenyouexaminetheirarchitecture.
Nearlysincetheirinception,cellphoneshavebeenfringedevicesinsofarastheyrunonproprietarysoftware—softwarethatisownedandcontrolledbythemanufacturer,andisalmostalwaysconsideredtobea“closed”system.Thepracticeofmanufacturersusingproprietaryoperatingsystemsbeganmoreoutofnecessitythananyotherreason.Thatis,cellphonemanufacturerstypicallyusedhardwarethatwascompletelydevelopedin-house,oratleasthardwarethatwasspecificallydevelopedforthepurposesofrunningcellphoneequipment.Asaresult,therewerenoopenlyavailable,off-the-shelfsoftwarepackagesorsolutionsthatwouldreliablyinteractwiththeirhardware.Sincethemanufacturersalsowantedtoguardverycloselytheirhardwaretradesecrets,someofwhichcouldberevealedbyallowingaccesstothesoftwarelevelofthedevice,thecommonpracticewas,andinmostcasesstillis,tousecompletelyproprietaryandclosedsoftwaretoruntheirdevices.Thedownsidetothisisthatanyonewhowantedtodevelopapplicationsforcellphonesneededtohaveintimate