COM 教程 计算机 英文.docx

IntroductionFormanypeople,learningCOMandDCOMistough.YouknowthatlearningCOMistherightthingtodo-youhearconstanthypeandyouknowthatmanyofMicrosoft,sproductsandprogrammertoolsarebasedonCOM,soitisobviouslysomethingthatisimportant.ButyoualsoknowthatCOMisreallyhard.YoumayhavealreadytriedtolearnCOMonce,ormaybeevenseveraltimes.Youmayhaveslidthroughacoupleofbooks,playedwithsomewizards,etc.Butitjustdoesn,tmakeanysense.Everythingseemsextremelycomplicatedandmuchharderthanitneedstobe.There,salsothevocabulary:"marshalling","apartmentthreads”,z,singletonobjects“andsoon.Whatisthis?ThepurposeofthissetoftutorialsistohelpyoutoquicklyunderstandwhatisgoingonintheworldofDCOMsothatyoucancreateCOMclientsandserverseasily.Wedothatstartingatthebeginningandlayingthingsoutforyousimplyandintherightorder.BythetimeyoufinishthesetutorialsyouwillunderstandallofthebasicconceptsdrivingDCOMandyouwillbeabletoproceedquicklytolearntherest.YouwillbeamazedathoweasyDCOMcanbeonceyougetagoodstart. TheBaSiCSOfCOM-thebestplacetostartisatthebeginning. SimDIeCoMCIientS-COMclientsareeasy SimPIeCOMSerVerS-usingtheAT1.wizardtobuildaserverTheBasicsofCOMUnderstandinghowCOMworkscanbeintimidatingatfirst.OnereasonforthisintimidationisthefactthatCOMusesitsownvocabulary.AsecondreasonisthatCOMcontainsanumberofnewconcepts.OneoftheeasiestwaystomasterthevocabularyandconceptsistocompareCOMobjectstonormalC+objectstoidentifythesimilaritiesanddifferences.YoucanalsomapunfamiliarconceptsfromCOMintothestandardC+modelthatyoualreadyunderstand.Thiswillgiveyouacomfortablestartingpoint,fromwhichwelllookatCOM'sfundamentalconcepts.Oncewehavedonethis,theexamplepresentedinthefollowingsectionswillbeextremelyeasytounderstand.ClassesandObjectsImaginethatyouhavecreatedasimpleclassinC+calledxxx.Ithasseveralmemberfunctions,namedMethodA,MethodB,andMethodC.Eachmemberfunctionacceptsparametersandreturnsaresult.Theclassdeclarationisshownhere:classxxxpublic:intMethodA(inta);intMethodB(floatb);floatMethodC(floatc);；Theclassdeclarationitselfdescribestheclass.Whenyouneedtousetheclass,youmustcreateaninstanceoftheobject.Instantiationsaretheactualobjects;classesarejustthedefinitions.Eachobjectiscreatedeitherasavariable(localorglobal)oritiscreateddynamicallyusingthenewstatement.Thenewstatementdynamicallycreatesthevariableontheheapandreturnsapointertoit.Whenyoucallmemberfunctions,youdosobydereferencingthepointer.Forexample:xxx*px;/px=newxxx;/p->MethodA(l);/deletepx;/pointertoxxxclasscreateobjectonheapcallmethodfreeobjectItisimportantforyoutounderstandandrecognizethatCOMfollowsthissameobjectedorientedmodel.COMhasclasses,memberfunctionsandinstantiationsjustlikeC+objectsdo.AlthoughyounevercallnewonaCOMobject,youmuststillcreateitinmemory.YouaccessCOMobjectswithpointers,andyoumustde-allocatethemwhenyouarefinished.WhenwewriteCOMcode,wewon'tbeusingnewanddelete.Althoughwe,regoingtouseC+asourlanguage,we'llhaveawholenewsyntax.COMisimplementedbycallstotheCOMAPI,whichprovidesfunctionsthatcreateanddestroyCOMobjects.Here'sanexampleCOMprogramwritteninpsedo-COMcode.ixx*pi/CoCreateInstance(,&pi)/pi->MethodA();/pi->Release();/pointertoxxxCOMinterfacecreateinterfacecallmethodfreeinterfaceInthisexample,we'llcallclassixxan"interface".Thevariablepiisapointertotheinterface.ThemethodCoCreateInstancecreatesaninstanceoftypeixx.Thisinterfacepointerisusedtomakemethodcalls.Releasedeletestheinterface.vepurposelyomittedtheparameterstoCoCreateInstance.Ididthissoasnottoobscurethebasicsimplicityoftheprogram.CoCreateInstancetakesanumberofarguments,allofwhichneedsomemoredetailedcoverage.Fornow,let'stakeastepbackandlookatthebiggerissueswithCOM.HowCOMIsDifferentCOMisnotC+,andforgoodreason.COMobjectsaresomewhatmorecomplicatedthentheirC+brethren.Mostofthiscomplicationisnecessarybecauseofnetworkconsiderations.TherearefourbasicfactorsdictatingthedesignofCOM:C+objectsalwaysruninthesameprocessspace.COMobjectscanrunacrossprocessesoracrosscomputers. COMmethodscanbecalledacrossanetwork.C+methodnamesmustbeuniqueinagivenprocessspace.COMobjectnamesmustbeuniquethroughouttheworld. COMserversmaybewritteninavarietyofdifferentlanguagesandonentirelydifferentoperatingsystems,whileC÷+objectsarealwayswritteninC+.1.et'slookatwhatthesedifferencesbetweenCOMandC+meantoyouasaprogrammer.COMcanrunacrossprocessesInCOM,youastheprogrammerareallowedtocreateobjectsinotherprocesses,andonanymachineonthenetwork.ThatdoesnotmeanthatyouW川alwaysdoit(inmanycasesyouwon't).However,thepossibilitymeansthatyoucan'tcreateaCOMobjectusingthenormalC+newstatement,andcallingitsmethodswithlocalprocedurecallswon'tsuffice.TocreateaCOMobject,someexecutingentity(anEXEoraService)willhavetoperformremotememoryallocationandobjectcreation.Thisisaverycomplextask.Byremote,wemeaninanotherprocessoronanotherprocess.ThisproblemissolvedbycreatingaconceptcalledaCOMserver.ThisotherentityW川havetomaintaintightcommunicationwiththeclient.COMmethodscanbecalledacrossanetworkIfyouhaveaccesstoamachineo