Android应用程序启动过程源代码分析（4）
Step 28. ActivityStack.realStartActivityLocked 这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityStack.java文件中： publicclassActivityStack{ ...... finalbooleanrealStartActivityLocked(ActivityRecordr, ProcessRecordapp,booleanandResume,booleancheckConfig) throwsRemoteException{ ...... r.app=app; ...... intidx=app.activities.indexOf(r); if(idx<0){ app.activities.add(r); } ...... try{ ...... List<ResultInfo>results=null; List<Intent>newIntents=null; if(andResume){ results=r.results; newIntents=r.newIntents; } ...... app.thread.scheduleLaunchActivity(newIntent(r.intent),r, System.identityHashCode(r), r.info,r.icicle,results,newIntents,!andResume, mService.isNextTransitionForward()); ...... }catch(RemoteExceptione){ ...... } ...... returntrue; } ...... } 这里最终通过app.thread进入到ApplicationThreadProxy的scheduleLaunchActivity函数中，注意，这里的第二个参数r，是一个ActivityRecord类型的Binder对象，用来作来这个Activity的token值。 Step 29.ApplicationThreadProxy.scheduleLaunchActivity 这个函数定义在frameworks/base/core/java/android/app/ApplicationThreadNative.java文件中： classApplicationThreadProxyimplementsIApplicationThread{ ...... publicfinalvoidscheduleLaunchActivity(Intentintent,IBindertoken,intident, ActivityInfoinfo,Bundlestate,List<ResultInfo>pendingResults, List<Intent>pendingNewIntents,booleannotResumed,booleanisForward) throwsRemoteException{ Parceldata=Parcel.obtain(); data.writeInterfaceToken(IApplicationThread.descriptor); intent.writeToParcel(data,0); data.writeStrongBinder(token); data.writeInt(ident); info.writeToParcel(data,0); data.writeBundle(state); data.writeTypedList(pendingResults); data.writeTypedList(pendingNewIntents); data.writeInt(notResumed?1:0); data.writeInt(isForward?1:0); mRemote.transact(SCHEDULE_LAUNCH_ACTIVITY_TRANSACTION,data,null, IBinder.FLAG_ONEWAY); data.recycle(); } ...... } 这个函数最终通过Binder驱动程序进入到ApplicationThread的scheduleLaunchActivity函数中。 Step 30.ApplicationThread.scheduleLaunchActivity 这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中： publicfinalclassActivityThread{ ...... privatefinalclassApplicationThreadextendsApplicationThreadNative{ ...... //weusetokentoidentifythisactivitywithouthavingtosendthe //activityitselfbacktotheactivitymanager.(mattersmorewithipc) publicfinalvoidscheduleLaunchActivity(Intentintent,IBindertoken,intident, ActivityInfoinfo,Bundlestate,List<ResultInfo>pendingResults, List<Intent>pendingNewIntents,booleannotResumed,booleanisForward){ ActivityClientRecordr=newActivityClientRecord(); r.token=token; r.ident=ident; r.intent=intent; r.activityInfo=info; r.state=state; r.pendingResults=pendingResults; r.pendingIntents=pendingNewIntents; r.startsNotResumed=notResumed; r.isForward=isForward; queueOrSendMessage(H.LAUNCH_ACTIVITY,r); } ...... } ...... } 函数首先创建一个ActivityClientRecord实例，并且初始化它的成员变量，然后调用ActivityThread类的queueOrSendMessage函数进一步处理。 Step 31.ActivityThread.queueOrSendMessage 这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中： publicfinalclassActivityThread{ ...... privatefinalclassApplicationThreadextendsApplicationThreadNative{ ...... //ifthethreadhasn'tstartedyet,wedon'thavethehandler,sojust //savethemessagesuntilwe'reready. privatefinalvoidqueueOrSendMessage(intwhat,Objectobj){ queueOrSendMessage(what,obj,0,0); } ...... privatefinalvoidqueueOrSendMessage(intwhat,Objectobj,intarg1,intarg2){ synchronized(this){ ...... Messagemsg=Message.obtain(); msg.what=what; msg.obj=obj; msg.arg1=arg1; msg.arg2=arg2; mH.sendMessage(msg); } } ...... } ...... } 函数把消息内容放在msg中，然后通过mH把消息分发出去，这里的成员变量mH我们在前面已经见过，消息分发出去后，最后会调用H类的handleMessage函数。 Step 32. H.handleMessage 这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中： publicfinalclassActivityThread{ ...... privatefinalclassHextendsHandler{ ...... publicvoidhandleMessage(Messagemsg){ ...... switch(msg.what){ caseLAUNCH_ACTIVITY:{ ActivityClientRecordr=(ActivityClientRecord)msg.obj; r.packageInfo=getPackageInfoNoCheck( r.activityInfo.applicationInfo); handleLaunchActivity(r,null); }break; ...... } ...... } ...... } 这里最后调用ActivityThread类的handleLaunchActivity函数进一步处理。 Step 33.ActivityThread.handleLaunchActivity 这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中： publicfinalclassActivityThread{ ...... privatefinalvoidhandleLaunchActivity(ActivityClientRecordr,IntentcustomIntent){ ...... Activitya=performLaunchActivity(r,customIntent); if(a!=null){ r.createdConfig=newConfiguration(mConfiguration); BundleoldState=r.state; handleResumeActivity(r.token,false,r.isForward); ...... }else{ ...... } } ...... } 这里首先调用performLaunchActivity函数来加载这个Activity类，即shy.luo.activity.MainActivity，然后调用它的onCreate函数，最后回到handleLaunchActivity函数时，再调用handleResumeActivity函数来使这个Activity进入Resumed状态，即会调用这个Activity的onResume函数，这是遵循Activity的生命周期的。 Step 34.ActivityThread.performLaunchActivity 这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中： publicfinalclassActivityThread{ ...... privatefinalActivityperformLaunchActivity(ActivityClientRecordr,IntentcustomIntent){ ActivityInfoaInfo=r.activityInfo; if(r.packageInfo==null){ r.packageInfo=getPackageInfo(aInfo.applicationInfo, Context.CONTEXT_INCLUDE_CODE); } ComponentNamecomponent=r.intent.getComponent(); if(component==null){ component=r.intent.resolveActivity( mInitialApplication.getPackageManager()); r.intent.setComponent(component); } if(r.activityInfo.targetActivity!=null){ component=newComponentName(r.activityInfo.packageName, r.activityInfo.targetActivity); } Activityactivity=null; try{ java.lang.ClassLoadercl=r.packageInfo.getClassLoader(); activity=mInstrumentation.newActivity( cl,component.getClassName(),r.intent); r.intent.setExtrasClassLoader(cl); if(r.state!=null){ r.state.setClassLoader(cl); } }catch(Exceptione){ ...... } try{ Applicationapp=r.packageInfo.makeApplication(false,mInstrumentation); ...... if(activity!=null){ ContextImplappContext=newContextImpl(); appContext.init(r.packageInfo,r.token,this); appContext.setOuterContext(activity); CharSequencetitle=r.activityInfo.loadLabel(appContext.getPackageManager()); Configurationconfig=newConfiguration(mConfiguration); ...... activity.attach(appContext,this,getInstrumentation(),r.token, r.ident,app,r.intent,r.activityInfo,title,r.parent, r.embeddedID,r.lastNonConfigurationInstance, r.lastNonConfigurationChildInstances,config); if(customIntent!=null){ activity.mIntent=customIntent; } r.lastNonConfigurationInstance=null; r.lastNonConfigurationChildInstances=null; activity.mStartedActivity=false; inttheme=r.activityInfo.getThemeResource(); if(theme!=0){ activity.setTheme(theme); } activity.mCalled=false; mInstrumentation.callActivityOnCreate(activity,r.state); ...... r.activity=activity; r.stopped=true; if(!r.activity.mFinished){ activity.performStart(); r.stopped=false; } if(!r.activity.mFinished){ if(r.state!=null){ mInstrumentation.callActivityOnRestoreInstanceState(activity,r.state); } } if(!r.activity.mFinished){ activity.mCalled=false; mInstrumentation.callActivityOnPostCreate(activity,r.state); if(!activity.mCalled){ thrownewSuperNotCalledException( "Activity"+r.intent.getComponent().toShortString()+ "didnotcallthroughtosuper.onPostCreate()"); } } } r.paused=true; mActivities.put(r.token,r); }catch(SuperNotCalledExceptione){ ...... }catch(Exceptione){ ...... } returnactivity; } ...... } 函数前面是收集要启动的Activity的相关信息，主要package和component信息： ActivityInfoaInfo=r.activityInfo; if(r.packageInfo==null){ r.packageInfo=getPackageInfo(aInfo.applicationInfo, Context.CONTEXT_INCLUDE_CODE); } ComponentNamecomponent=r.intent.getComponent(); if(component==null){ component=r.intent.resolveActivity( mInitialApplication.getPackageManager()); r.intent.setComponent(component); } if(r.activityInfo.targetActivity!=null){ component=newComponentName(r.activityInfo.packageName, r.activityInfo.targetActivity); } 然后通过ClassLoader将shy.luo.activity.MainActivity类加载进来： Activityactivity=null; try{ java.lang.ClassLoadercl=r.packageInfo.getClassLoader(); activity=mInstrumentation.newActivity( cl,component.getClassName(),r.intent); r.intent.setExtrasClassLoader(cl); if(r.state!=null){ r.state.setClassLoader(cl); } }catch(Exceptione){ ...... } 接下来是创建Application对象，这是根据AndroidManifest.xml配置文件中的Application标签的信息来创建的： Applicationapp=r.packageInfo.makeApplication(false,mInstrumentation); 后面的代码主要创建Activity的上下文信息，并通过attach方法将这些上下文信息设置到MainActivity中去： activity.attach(appContext,this,getInstrumentation(),r.token, r.ident,app,r.intent,r.activityInfo,title,r.parent, r.embeddedID,r.lastNonConfigurationInstance, r.lastNonConfigurationChildInstances,config); 最后还要调用MainActivity的onCreate函数： mInstrumentation.callActivityOnCreate(activity,r.state); 这里不是直接调用MainActivity的onCreate函数，而是通过mInstrumentation的callActivityOnCreate函数来间接调用，前面我们说过，mInstrumentation在这里的作用是监控Activity与系统的交互操作，相当于是系统运行日志。 本文转自 Luoshengyang 51CTO博客，原文链接：http://blog.51cto.com/shyluo/965992，如需转载请自行联系原作者
