Android应用程序启动过程源代码分析(2)
16lz
2021-12-04
Step 8. ActivityStack.startActivityLocked 这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityStack.java文件中:
再接下来,创建即将要启动的Activity的相关信息,并保存在r变量中:
从传进来的参数caller得到调用者的进程信息,并保存在callerApp变量中,这里就是Launcher应用程序的进程信息了。 前面说过,参数resultTo是Launcher这个Activity里面的一个Binder对象,通过它可以获得Launcher这个Activity的相关信息,保存在sourceRecord变量中。
- public classActivityStack{
- ......
- final intstartActivityLocked(IApplicationThreadcaller,
- Intentintent,StringresolvedType,
- Uri[]grantedUriPermissions,
- intgrantedMode,ActivityInfoaInfo,IBinderresultTo,
- StringresultWho, intrequestCode,
- intcallingPid, intcallingUid, booleanonlyIfNeeded,
- booleancomponentSpecified){
- interr=START_SUCCESS;
- ProcessRecordcallerApp= null;
- if(caller!= null){
- callerApp=mService.getRecordForAppLocked(caller);
- if(callerApp!= null){
- callingPid=callerApp.pid;
- callingUid=callerApp.info.uid;
- } else{
- ......
- }
- }
- ......
- ActivityRecordsourceRecord= null;
- ActivityRecordresultRecord= null;
- if(resultTo!= null){
- intindex=indexOfTokenLocked(resultTo);
- ......
- if(index>= 0){
- sourceRecord=(ActivityRecord)mHistory.get(index);
- if(requestCode>= 0&&!sourceRecord.finishing){
- ......
- }
- }
- }
- intlaunchFlags=intent.getFlags();
- if((launchFlags&Intent.FLAG_ACTIVITY_FORWARD_RESULT)!= 0
- &&sourceRecord!= null){
- ......
- }
- if(err==START_SUCCESS&&intent.getComponent()== null){
- ......
- }
- if(err==START_SUCCESS&&aInfo== null){
- ......
- }
- if(err!=START_SUCCESS){
- ......
- }
- ......
- ActivityRecordr= newActivityRecord(mService, this,callerApp,callingUid,
- intent,resolvedType,aInfo,mService.mConfiguration,
- resultRecord,resultWho,requestCode,componentSpecified);
- ......
- returnstartActivityUncheckedLocked(r,sourceRecord,
- grantedUriPermissions,grantedMode,onlyIfNeeded, true);
- }
- ......
- }
再接下来,创建即将要启动的Activity的相关信息,并保存在r变量中:
接着调用startActivityUncheckedLocked函数进行下一步操作。 Step 9. ActivityStack.startActivityUncheckedLocked 这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityStack.java文件中:
- ActivityRecordr= newActivityRecord(mService, this,callerApp,callingUid,
- intent,resolvedType,aInfo,mService.mConfiguration,
- resultRecord,resultWho,requestCode,componentSpecified);
函数首先获得intent的标志值,保存在launchFlags变量中。 这个intent的标志值的位Intent.FLAG_ACTIVITY_NO_USER_ACTION没有置位,因此 ,成员变量mUserLeaving的值为true。 这个intent的标志值的位Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP也没有置位,因此,变量notTop的值为null。 由于在这个例子的AndroidManifest.xml文件中,MainActivity没有配置launchMode属值,因此,这里的r.launchMode为默认值0,表示以标准(Standard,或者称为ActivityInfo.LAUNCH_MULTIPLE)的方式来启动这个Activity。Activity的启动方式有四种,其余三种分别是ActivityInfo.LAUNCH_SINGLE_INSTANCE、ActivityInfo.LAUNCH_SINGLE_TASK和ActivityInfo.LAUNCH_SINGLE_TOP,具体可以参考官方网站 http://developer.android.com/reference/android/content/pm/ActivityInfo.html。 传进来的参数r.resultTo为null,表示Launcher不需要等这个即将要启动的MainActivity的执行结果。 由于这个intent的标志值的位Intent.FLAG_ACTIVITY_NEW_TASK被置位,而且Intent.FLAG_ACTIVITY_MULTIPLE_TASK没有置位,因此,下面的if语句会被执行:
- public classActivityStack{
- ......
- final intstartActivityUncheckedLocked(ActivityRecordr,
- ActivityRecordsourceRecord,Uri[]grantedUriPermissions,
- intgrantedMode, booleanonlyIfNeeded, booleandoResume){
- finalIntentintent=r.intent;
- final intcallingUid=r.launchedFromUid;
- intlaunchFlags=intent.getFlags();
- //We'llinvokeonUserLeavingbeforeonPauseonlyifthelaunching
- //activitydidnotexplicitlystatethatthisisanautomatedlaunch.
- mUserLeaving=(launchFlags&Intent.FLAG_ACTIVITY_NO_USER_ACTION)== 0;
- ......
- ActivityRecordnotTop=(launchFlags&Intent.FLAG_ACTIVITY_PREVIOUS_IS_TOP)
- != 0?r: null;
- //IftheonlyIfNeededflagisset,thenwecandothisiftheactivity
- //beinglaunchedisthesameastheonemakingthecall...or,as
- //aspecialcase,ifwedonotknowthecallerthenwecountthe
- //currenttopactivityasthecaller.
- if(onlyIfNeeded){
- ......
- }
- if(sourceRecord== null){
- ......
- } else if(sourceRecord.launchMode==ActivityInfo.LAUNCH_SINGLE_INSTANCE){
- ......
- } else if(r.launchMode==ActivityInfo.LAUNCH_SINGLE_INSTANCE
- ||r.launchMode==ActivityInfo.LAUNCH_SINGLE_TASK){
- ......
- }
- if(r.resultTo!= null&&(launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK)!= 0){
- ......
- }
- booleanaddingToTask= false;
- if(((launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK)!= 0&&
- (launchFlags&Intent.FLAG_ACTIVITY_MULTIPLE_TASK)== 0)
- ||r.launchMode==ActivityInfo.LAUNCH_SINGLE_TASK
- ||r.launchMode==ActivityInfo.LAUNCH_SINGLE_INSTANCE){
- //Ifbringtofrontisrequested,andnoresultisrequested,and
- //wecanfindataskthatwasstartedwiththissame
- //component,theninsteadoflaunchingbringthatonetothefront.
- if(r.resultTo== null){
- //Seeifthereisatasktobringtothefront.Ifthisis
- //aSINGLE_INSTANCEactivity,therecanbeoneandonlyone
- //instanceofitinthehistory,anditisalwaysinitsown
- //uniquetask,sowedoaspecialsearch.
- ActivityRecordtaskTop=r.launchMode!=ActivityInfo.LAUNCH_SINGLE_INSTANCE
- ?findTaskLocked(intent,r.info)
- :findActivityLocked(intent,r.info);
- if(taskTop!= null){
- ......
- }
- }
- }
- ......
- if(r.packageName!= null){
- //Iftheactivitybeinglaunchedisthesameastheonecurrently
- //atthetop,thenweneedtocheckifitshouldonlybelaunched
- //once.
- ActivityRecordtop=topRunningNonDelayedActivityLocked(notTop);
- if(top!= null&&r.resultTo== null){
- if(top.realActivity.equals(r.realActivity)){
- ......
- }
- }
- } else{
- ......
- }
- booleannewTask= false;
- //Shouldthisbeconsideredanewtask?
- if(r.resultTo== null&&!addingToTask
- &&(launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK)!= 0){
- //todo:shoulddobettermanagementofintegers.
- mService.mCurTask++;
- if(mService.mCurTask<= 0){
- mService.mCurTask= 1;
- }
- r.task= newTaskRecord(mService.mCurTask,r.info,intent,
- (r.info.flags&ActivityInfo.FLAG_CLEAR_TASK_ON_LAUNCH)!= 0);
- ......
- newTask= true;
- if(mMainStack){
- mService.addRecentTaskLocked(r.task);
- }
- } else if(sourceRecord!= null){
- ......
- } else{
- ......
- }
- ......
- startActivityLocked(r,newTask,doResume);
- returnSTART_SUCCESS;
- }
- ......
- }
这段代码的逻辑是查看一下,当前有没有Task可以用来执行这个Activity。由于r.launchMode的值不为ActivityInfo.LAUNCH_SINGLE_INSTANCE,因此,它通过findTaskLocked函数来查找存不存这样的Task,这里返回的结果是null,即taskTop为null,因此,需要创建一个新的Task来启动这个Activity。 接着往下看:
- if(((launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK)!= 0&&
- (launchFlags&Intent.FLAG_ACTIVITY_MULTIPLE_TASK)== 0)
- ||r.launchMode==ActivityInfo.LAUNCH_SINGLE_TASK
- ||r.launchMode==ActivityInfo.LAUNCH_SINGLE_INSTANCE){
- //Ifbringtofrontisrequested,andnoresultisrequested,and
- //wecanfindataskthatwasstartedwiththissame
- //component,theninsteadoflaunchingbringthatonetothefront.
- if(r.resultTo== null){
- //Seeifthereisatasktobringtothefront.Ifthisis
- //aSINGLE_INSTANCEactivity,therecanbeoneandonlyone
- //instanceofitinthehistory,anditisalwaysinitsown
- //uniquetask,sowedoaspecialsearch.
- ActivityRecordtaskTop=r.launchMode!=ActivityInfo.LAUNCH_SINGLE_INSTANCE
- ?findTaskLocked(intent,r.info)
- :findActivityLocked(intent,r.info);
- if(taskTop!= null){
- ......
- }
- }
- }
这段代码的逻辑是看一下,当前在堆栈顶端的Activity是否就是即将要启动的Activity,有些情况下,如果即将要启动的Activity就在堆栈的顶端,那么,就不会重新启动这个Activity的别一个实例了,具体可以参考官方网站 http://developer.android.com/reference/android/content/pm/ActivityInfo.html 。现在处理堆栈顶端的Activity是Launcher,与我们即将要启动的MainActivity不是同一个Activity,因此,这里不用进一步处理上述介绍的情况。 执行到这里,我们知道,要在一个新的Task里面来启动这个Activity了,于是新创建一个Task:
- if(r.packageName!= null){
- //Iftheactivitybeinglaunchedisthesameastheonecurrently
- //atthetop,thenweneedtocheckifitshouldonlybelaunched
- //once.
- ActivityRecordtop=topRunningNonDelayedActivityLocked(notTop);
- if(top!= null&&r.resultTo== null){
- if(top.realActivity.equals(r.realActivity)){
- ......
- }
- }
- }
新建的Task保存在r.task域中,同时,添加到mService中去,这里的mService就是ActivityManagerService了。 最后就进入startActivityLocked(r, newTask, doResume)进一步处理了。这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityStack.java文件中:
- if(r.resultTo== null&&!addingToTask
- &&(launchFlags&Intent.FLAG_ACTIVITY_NEW_TASK)!= 0){
- //todo:shoulddobettermanagementofintegers.
- mService.mCurTask++;
- if(mService.mCurTask<= 0){
- mService.mCurTask= 1;
- }
- r.task= newTaskRecord(mService.mCurTask,r.info,intent,
- (r.info.flags&ActivityInfo.FLAG_CLEAR_TASK_ON_LAUNCH)!= 0);
- ......
- newTask= true;
- if(mMainStack){
- mService.addRecentTaskLocked(r.task);
- }
- }
这里的NH表示当前系统中历史任务的个数,这里肯定是大于0,因为Launcher已经跑起来了。当NH>0时,并且现在要切换新任务时,要做一些任务切的界面操作,这段代码我们就不看了,这里不会影响到下面启Activity的过程,有兴趣的读取可以自己研究一下。 这里传进来的参数doResume为true,于是调用resumeTopActivityLocked进一步操作。 Step 10. Activity.resumeTopActivityLocked 这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityStack.java文件中:
- public classActivityStack{
- ......
- private final voidstartActivityLocked(ActivityRecordr, booleannewTask,
- booleandoResume){
- final intNH=mHistory.size();
- intaddPos=- 1;
- if(!newTask){
- ......
- }
- //Placeanewactivityattopofstack,soitisnexttointeract
- //withtheuser.
- if(addPos< 0){
- addPos=NH;
- }
- //Ifwearenotplacingthenewactivityfrontmost,wedonotwant
- //todelivertheonUserLeavingcallbacktotheactualfrontmost
- //activity
- if(addPos<NH){
- ......
- }
- //Slottheactivityintothehistorystackandproceed
- mHistory.add(addPos,r);
- r.inHistory= true;
- r.frontOfTask=newTask;
- r.task.numActivities++;
- if(NH> 0){
- //Wewanttoshowthestartingpreviewwindowifweare
- //switchingtoanewtask,orthenextactivity'sprocessis
- //notcurrentlyrunning.
- ......
- } else{
- //Ifthisisthefirstactivity,don'tdoanyfancyanimations,
- //becausethereisnothingforittoanimateontopof.
- ......
- }
- ......
- if(doResume){
- resumeTopActivityLocked( null);
- }
- }
- ......
- }
函数先通过调用topRunningActivityLocked函数获得堆栈顶端的Activity,这里就是MainActivity了,这是在上面的Step 9设置好的,保存在next变量中。 接下来把mUserLeaving的保存在本地变量userLeaving中,然后重新设置为false,在上面的Step 9中,mUserLeaving的值为true,因此,这里的userLeaving为true。 这里的mResumedActivity为Launcher,因为Launcher是当前正被执行的Activity。 当我们处理休眠状态时,mLastPausedActivity保存堆栈顶端的Activity,因为当前不是休眠状态,所以mLastPausedActivity为null。 有了这些信息之后,下面的语句就容易理解了:
- public classActivityStack{
- ......
- /**
- *Ensurethatthetopactivityinthestackisresumed.
- *
- *@paramprevThepreviouslyresumedactivity,forwhenintheprocess
- *ofpausing;canbenulltocallfromelsewhere.
- *
- *@returnReturnstrueifsomethingisbeingresumed,orfalseif
- *nothinghappened.
- */
- final booleanresumeTopActivityLocked(ActivityRecordprev){
- //Findthefirstactivitythatisnotfinishing.
- ActivityRecordnext=topRunningActivityLocked( null);
- //Rememberhowwe'llprocessthispause/resumesituation,andensure
- //thatthestateisresethoweverwewindupproceeding.
- final booleanuserLeaving=mUserLeaving;
- mUserLeaving= false;
- if(next== null){
- ......
- }
- next.delayedResume= false;
- //Ifthetopactivityistheresumedone,nothingtodo.
- if(mResumedActivity==next&&next.state==ActivityState.RESUMED){
- ......
- }
- //Ifwearesleeping,andthereisnoresumedactivity,andthetop
- //activityispaused,wellthatisthestatewewant.
- if((mService.mSleeping||mService.mShuttingDown)
- &&mLastPausedActivity==next&&next.state==ActivityState.PAUSED){
- ......
- }
- ......
- //Ifwearecurrentlypausinganactivity,thendon'tdoanything
- //untilthatisdone.
- if(mPausingActivity!= null){
- ......
- }
- ......
- //Weneedtostartpausingthecurrentactivitysothetopone
- //canberesumed...
- if(mResumedActivity!= null){
- ......
- startPausingLocked(userLeaving, false);
- return true;
- }
- ......
- }
- ......
- }
它首先看要启动的Activity是否就是当前处理Resumed状态的Activity,如果是的话,那就什么都不用做,直接返回就可以了;否则再看一下系统当前是否休眠状态,如果是的话,再看看要启动的Activity是否就是当前处于堆栈顶端的Activity,如果是的话,也是什么都不用做。 上面两个条件都不满足,因此,在继续往下执行之前,首先要把当处于Resumed状态的Activity推入Paused状态,然后才可以启动新的Activity。但是在将当前这个Resumed状态的Activity推入Paused状态之前,首先要看一下当前是否有Activity正在进入Pausing状态,如果有的话,当前这个Resumed状态的Activity就要稍后才能进入Paused状态了,这样就保证了所有需要进入Paused状态的Activity串行处理。 这里没有处于Pausing状态的Activity,即mPausingActivity为null,而且mResumedActivity也不为null,于是就调用startPausingLocked函数把Launcher推入Paused状态去了。 Step 11. ActivityStack.startPausingLocked 这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityStack.java文件中:
- //Ifthetopactivityistheresumedone,nothingtodo.
- if(mResumedActivity==next&&next.state==ActivityState.RESUMED){
- ......
- }
- //Ifwearesleeping,andthereisnoresumedactivity,andthetop
- //activityispaused,wellthatisthestatewewant.
- if((mService.mSleeping||mService.mShuttingDown)
- &&mLastPausedActivity==next&&next.state==ActivityState.PAUSED){
- ......
- }
函数首先把mResumedActivity保存在本地变量prev中。在上一步Step 10中,说到mResumedActivity就是Launcher,因此,这里把Launcher进程中的ApplicationThread对象取出来,通过它来通知Launcher这个Activity它要进入Paused状态了。当然,这里的prev.app.thread是一个ApplicationThread对象的远程接口,通过调用这个远程接口的schedulePauseActivity来通知Launcher进入Paused状态。 参数prev.finishing表示prev所代表的Activity是否正在等待结束的Activity列表中,由于Laucher这个Activity还没结束,所以这里为false;参数prev.configChangeFlags表示哪些config发生了变化,这里我们不关心它的值。 Step 12.ApplicationThreadProxy.schedulePauseActivity 这个函数定义在frameworks/base/core/java/android/app/ApplicationThreadNative.java文件中:
- public classActivityStack{
- ......
- private final voidstartPausingLocked( booleanuserLeaving, booleanuiSleeping){
- if(mPausingActivity!= null){
- ......
- }
- ActivityRecordprev=mResumedActivity;
- if(prev== null){
- ......
- }
- ......
- mResumedActivity= null;
- mPausingActivity=prev;
- mLastPausedActivity=prev;
- prev.state=ActivityState.PAUSING;
- ......
- if(prev.app!= null&&prev.app.thread!= null){
- ......
- try{
- ......
- prev.app.thread.schedulePauseActivity(prev,prev.finishing,userLeaving,
- prev.configChangeFlags);
- ......
- } catch(Exceptione){
- ......
- }
- } else{
- ......
- }
- ......
- }
- ......
- }
这个函数通过Binder进程间通信机制进入到ApplicationThread.schedulePauseActivity函数中。 Step 13. ApplicationThread.schedulePauseActivity 这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中,它是ActivityThread的内部类:
- classApplicationThreadProxy implementsIApplicationThread{
- ......
- public final voidschedulePauseActivity(IBindertoken, booleanfinished,
- booleanuserLeaving, intconfigChanges) throwsRemoteException{
- Parceldata=Parcel.obtain();
- data.writeInterfaceToken(IApplicationThread.descriptor);
- data.writeStrongBinder(token);
- data.writeInt(finished? 1: 0);
- data.writeInt(userLeaving? 1: 0);
- data.writeInt(configChanges);
- mRemote.transact(SCHEDULE_PAUSE_ACTIVITY_TRANSACTION,data, null,
- IBinder.FLAG_ONEWAY);
- data.recycle();
- }
- ......
- }
这里调用的函数queueOrSendMessage是ActivityThread类的成员函数。 上面说到,这里的finished值为false,因此,queueOrSendMessage的第一个参数值为H.PAUSE_ACTIVITY,表示要暂停token所代表的Activity,即Launcher。 Step 14. ActivityThread.queueOrSendMessage 这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中:
- public final classActivityThread{
- ......
- private final classApplicationThread extendsApplicationThreadNative{
- ......
- public final voidschedulePauseActivity(IBindertoken, booleanfinished,
- booleanuserLeaving, intconfigChanges){
- queueOrSendMessage(
- finished?H.PAUSE_ACTIVITY_FINISHING:H.PAUSE_ACTIVITY,
- token,
- (userLeaving? 1: 0),
- configChanges);
- }
- ......
- }
- ......
- }
这里首先将相关信息组装成一个msg,然后通过mH成员变量发送出去,mH的类型是H,继承于Handler类,是ActivityThread的内部类,因此,这个消息最后由H.handleMessage来处理。 Step 15. H.handleMessage 这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中:
- public final classActivityThread{
- ......
- private final voidqueueOrSendMessage( intwhat,Objectobj, intarg1){
- queueOrSendMessage(what,obj,arg1, 0);
- }
- private final voidqueueOrSendMessage( intwhat,Objectobj, intarg1, intarg2){
- synchronized( this){
- ......
- Messagemsg=Message.obtain();
- msg.what=what;
- msg.obj=obj;
- msg.arg1=arg1;
- msg.arg2=arg2;
- mH.sendMessage(msg);
- }
- }
- ......
- }
这里调用ActivityThread.handlePauseActivity进一步操作,msg.obj是一个ActivityRecord对象的引用,它代表的是Launcher这个Activity。
- public final classActivityThread{
- ......
- private final classH extendsHandler{
- ......
- public voidhandleMessage(Messagemsg){
- ......
- switch(msg.what){
- ......
- casePAUSE_ACTIVITY:
- handlePauseActivity((IBinder)msg.obj, false,msg.arg1!= 0,msg.arg2);
- maybeSnapshot();
- break;
- ......
- }
- ......
- }
- ......
- }
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