Activity启动流程

一直都想过要去看一看一个activity是怎么启动起来的，但一直都没有静下心去认真看一看，现在趁着有时间好好阅读了一下源码，加上网上一些同志的分享，终于吧代码撸的比较清楚了，怕时间一久，又忘记了，赶紧记下来，如果有什么错误和遗漏的话，看官们也请指出。（本文中源码出自Android API 23）

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首先我们打开activity的startActivity方法：

@Override
public voidstartActivity(Intent intent) {
    mBase.startActivity(intent);
}

Activity继承于 Context，这是个抽象类，里面并没有实现 startActivity（） 这个方法，查了一下它的子类，嗯哼，就看了 ContextWrapper实现了它，但是，这个 mBase 又是什么鬼？嗯，也是一个 Context对象，但具体是那个类呢，查了一下 Context的继承关系，找到了 ContentImpl这个类，看一下这个类的介绍：

/**
 * Common implementation of Context API, which provides the base
 * context object for Activity and other application components.
 */
classContextImplextendsContext {...}

这个类就是Context的Api的共同的实现类了，上面说到的 mBase 对象实际上说的就是这个类的实例了，那么这个对象是怎么来的，啥时候实例化的？不急，往下看，迟早要知道的。

好了，现在来看一下 ContentImpl中 startActivity()的实现：

@Override
public voidstartActivity(Intent intent) {
    warnIfCallingFromSystemProcess();
    startActivity(intent,null);
}

@Override
public voidstartActivity(Intent intent, Bundle options) {
   warnIfCallingFromSystemProcess();
   if((intent.getFlags()&Intent.FLAG_ACTIVITY_NEW_TASK) ==0) {
       throw newAndroidRuntimeException(
               "Calling startActivity() from outside of an Activity "
               +" context requires the FLAG_ACTIVITY_NEW_TASK flag."
               +" Is this really what you want?");
   }
   mMainThread.getInstrumentation().execStartActivity(
           getOuterContext(),mMainThread.getApplicationThread(),null,
           (Activity)null, intent, -1, options);
}

看红色代码部分，mMainThread就是 ActivityThread类的实例，整个app进程的入口main()函数也是在这个类中的，这个 mMainThread提供了一个 Instrumentation对象

/**
 * Base class for implementing application instrumentation code.  When running
 * with instrumentation turned on, this class will be instantiated for you
 * before any of the application code, allowing you to monitor all of the
 * interaction the system has with the application.  An Instrumentation
 * implementation is described to the system through an AndroidManifest.xml's
 *<instrumentation> tag.
 */
public classInstrumentation {...}

简单的说，它就是用来监控应用中各种交互行为，从注释上看，我们可以通过 Manifest来指定一个我们自己实现的 Instrumentation类，好了这个不是重点，让我们看一下一个类怎么 startActivity的吧：

publicActivityResult execStartActivity(
       Context who, IBinder contextThread, IBinder token, Activity target,
       Intent intent,intrequestCode, Bundle options) {
   //...
   //前面的不是重点

   try{
       intent.migrateExtraStreamToClipData();
       intent.prepareToLeaveProcess();
       intresult =ActivityManagerNative.getDefault()
           .startActivity(whoThread, who.getBasePackageName(), intent,
                   intent.resolveTypeIfNeeded(who.getContentResolver()),
                   token, target !=null? target.mEmbeddedID:null,
                   requestCode,0,null, options);
       checkStartActivityResult(result, intent);
   }catch(RemoteException e) {
       throw newRuntimeException("Failure from system", e);
   }
   return null;
}

好吧，怎么这家伙又把启动 activity的事情交给别人做了。。。再点进去看：咦，怎么。。怎么是 IActivityManager的接口方法，好吧，又要找它的实现类了，but 貌似找到的这个家伙 ActivityManagerProxy 并没有认真的做事情啊，它找了一个代理去 startActivity（）去了，那我们就去找这个代理去，从 IActivityManager extends IInterface 这个类的继承方式我们就能发现这其实就是Android中的Binder机制，跨进程的通信机制，ActivityManagerProxy找的代理其实就是 ActivityManagerService，ActivityManagerService属于系统进程，它对手机中所有的activity进行了统一的管理，源码中就是这么个获取的：

IBinder b = ServiceManager.getService("activity");
IActivityManager am =asInterface(b);

熟悉的 aidl嘛，好了好了，感觉有点跑偏，往回扯，来看看 AMS 怎么实现 startActivity() 的：

@Override
public final intstartActivity(IApplicationThread caller, String callingPackage,
        Intent intent, String resolvedType, IBinder resultTo, String resultWho,intrequestCode,
        intstartFlags, ProfilerInfo profilerInfo, Bundle options) {
    returnstartActivityAsUser(caller, callingPackage, intent, resolvedType, resultTo,
        resultWho, requestCode, startFlags, profilerInfo, options,
        UserHandle.getCallingUserId());
}

@Override
public final intstartActivityAsUser(IApplicationThread caller, String callingPackage,
        Intent intent, String resolvedType, IBinder resultTo, String resultWho,intrequestCode,
        intstartFlags, ProfilerInfo profilerInfo, Bundle options,intuserId) {
    enforceNotIsolatedCaller("startActivity");
    userId = handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(), userId,
            false,ALLOW_FULL_ONLY,"startActivity",null);
    //TODO: Switch to user app stacks here.
    returnmStackSupervisor.startActivityMayWait(caller, -1, callingPackage, intent,
            resolvedType,null,null, resultTo, resultWho, requestCode, startFlags,
            profilerInfo,null,null, options,false, userId,null,null);
}

找到了，一个 mStackSupervisor对象，这又是干啥的？字面上的意思就是活动栈的管理器，先不管了，让我们先看看它的实现（...啊，代码不是一般的长，咱们只划重点）：

final intstartActivityMayWait(IApplicationThread caller,intcallingUid,
       String callingPackage, Intent intent, String resolvedType,
       IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
       IBinder resultTo, String resultWho,intrequestCode,intstartFlags,
       ProfilerInfo profilerInfo, WaitResult outResult, Configuration config,
       Bundle options,booleanignoreTargetSecurity,intuserId,
       IActivityContainer iContainer, TaskRecord inTask) {
   // Refuse possible leaked file descriptors
   if(intent !=null&& intent.hasFileDescriptors()) {
       throw newIllegalArgumentException("File descriptors passed in Intent");
   }
   booleancomponentSpecified = intent.getComponent() !=null;

   // Don't modify the client's object!
   intent =newIntent(intent);

   // Collect information about the target of the Intent.
   ActivityInfo aInfo =
           resolveActivity(intent, resolvedType, startFlags, profilerInfo, userId);

   ActivityContainer container = (ActivityContainer)iContainer;
   synchronized(mService) {
       if(container !=null&& container.mParentActivity!=null&&
               container.mParentActivity.state!= RESUMED) {
           // Cannot start a child activity if the parent is not resumed.
           returnActivityManager.START_CANCELED;
       }
       final intrealCallingPid = Binder.getCallingPid();
       final intrealCallingUid = Binder.getCallingUid();
       intcallingPid;
       if(callingUid >=0) {
           callingPid = -1;
       }else if(caller ==null) {
           callingPid = realCallingPid;
           callingUid = realCallingUid;
       }else{
           callingPid = callingUid = -1;
       }

       finalActivityStack stack;
       if(container ==null|| container.mStack.isOnHomeDisplay()) {
           stack =mFocusedStack;
       }else{
           stack = container.mStack;
       }
       stack.mConfigWillChange= config !=null&&mService.mConfiguration.diff(config) !=0;
       if(DEBUG_CONFIGURATION) Slog.v(TAG_CONFIGURATION,
               "Starting activity when config will change = "+ stack.mConfigWillChange);

       final longorigId = Binder.clearCallingIdentity();

       if(aInfo !=null&&
               (aInfo.applicationInfo.privateFlags
                       &ApplicationInfo.PRIVATE_FLAG_CANT_SAVE_STATE) !=0) {
           // This may be a heavy-weight process!  Check to see if we already
           // have another, different heavy-weight process running.
           if(aInfo.processName.equals(aInfo.applicationInfo.packageName)) {
               if(mService.mHeavyWeightProcess!=null&&
                       (mService.mHeavyWeightProcess.info.uid!= aInfo.applicationInfo.uid||
                       !mService.mHeavyWeightProcess.processName.equals(aInfo.processName))) {
                   intappCallingUid = callingUid;
                   if(caller !=null) {
                       Proce***ecord callerApp =mService.getRecordForAppLocked(caller);
                       if(callerApp !=null) {
                           appCallingUid = callerApp.info.uid;
                       }else{
                           Slog.w(TAG,"Unable to find app for caller "+ caller
                                 +" (pid="+ callingPid +") when starting: "
                                 + intent.toString());
                           ActivityOptions.abort(options);
                           returnActivityManager.START_PERMISSION_DENIED;
                       }
                   }

                   IIntentSender target =mService.getIntentSenderLocked(
                           ActivityManager.INTENT_SENDER_ACTIVITY,"android",
                           appCallingUid, userId,null,null,0,newIntent[] { intent },
                           newString[] { resolvedType }, PendingIntent.FLAG_CANCEL_CURRENT
                           | PendingIntent.FLAG_ONE_SHOT,null);

                   Intent newIntent =newIntent();
                   if(requestCode >=0) {
                       // Caller is requesting a result.
                       newIntent.putExtra(HeavyWeightSwitcherActivity.KEY_HAS_RESULT,true);
                   }
                   newIntent.putExtra(HeavyWeightSwitcherActivity.KEY_INTENT,
                           newIntentSender(target));
                   if(mService.mHeavyWeightProcess.activities.size() >0) {
                       ActivityRecord hist =mService.mHeavyWeightProcess.activities.get(0);
                       newIntent.putExtra(HeavyWeightSwitcherActivity.KEY_CUR_APP,
                               hist.packageName);
                       newIntent.putExtra(HeavyWeightSwitcherActivity.KEY_CUR_TASK,
                               hist.task.taskId);
                   }
                   newIntent.putExtra(HeavyWeightSwitcherActivity.KEY_NEW_APP,
                           aInfo.packageName);
                   newIntent.setFlags(intent.getFlags());
                   newIntent.setClassName("android",
                           HeavyWeightSwitcherActivity.class.getName());
                   intent = newIntent;
                   resolvedType =null;
                   caller =null;
                   callingUid = Binder.getCallingUid();
                   callingPid = Binder.getCallingPid();
                   componentSpecified =true;
                   try{
                       ResolveInfo rInfo =
                           AppGlobals.getPackageManager().resolveIntent(
                                   intent,null,
                                   PackageManager.MATCH_DEFAULT_ONLY
                                   | ActivityManagerService.STOCK_PM_FLAGS, userId);
                       aInfo = rInfo !=null? rInfo.activityInfo:null;
                       aInfo =mService.getActivityInfoForUser(aInfo, userId);
                   }catch(RemoteException e) {
                       aInfo =null;
                   }
               }
           }
       }

       int res = startActivityLocked(caller, intent, resolvedType, aInfo,
               voiceSession, voiceInteractor, resultTo, resultWho,
               requestCode, callingPid, callingUid, callingPackage,
               realCallingPid, realCallingUid, startFlags, options, ignoreTargetSecurity,
               componentSpecified, null, container, inTask);

       Binder.restoreCallingIdentity(origId);

       if(stack.mConfigWillChange) {
           // If the caller also wants to switch to a new configuration,
           // do so now.  This allows a clean switch, as we are waiting
           // for the current activity to pause (so we will not destroy
           // it), and have not yet started the next activity.
           mService.enforceCallingPermission(android.Manifest.permission.CHANGE_CONFIGURATION,
                   "updateConfiguration()");
           stack.mConfigWillChange=false;
           if(DEBUG_CONFIGURATION) Slog.v(TAG_CONFIGURATION,
                   "Updating to new configuration after starting activity.");
           mService.updateConfigurationLocked(config,null,false,false);
       }

       if(outResult !=null) {
           outResult.result= res;
           if(res == ActivityManager.START_SUCCESS) {
               mWaitingActivityLaunched.add(outResult);
               do{
                   try{
                       mService.wait();
                   }catch(InterruptedException e) {
                   }
               }while(!outResult.timeout&& outResult.who==null);
           }else if(res == ActivityManager.START_TASK_TO_FRONT) {
               ActivityRecord r = stack.topRunningActivityLocked(null);
               if(r.nowVisible&& r.state== RESUMED) {
                   outResult.timeout=false;
                   outResult.who=newComponentName(r.info.packageName, r.info.name);
                   outResult.totalTime=0;
                   outResult.thisTime=0;
               }else{
                   outResult.thisTime= SystemClock.uptimeMillis();
                   mWaitingActivityVisible.add(outResult);
                   do{
                       try{
                           mService.wait();
                       }catch(InterruptedException e) {
                       }
                   }while(!outResult.timeout&& outResult.who==null);
               }
           }
       }

       returnres;
   }
}

继续往里走~~

final intstartActivityLocked(IApplicationThread caller,
       Intent intent, String resolvedType, ActivityInfo aInfo,
       IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,
       IBinder resultTo, String resultWho,intrequestCode,
       intcallingPid,intcallingUid, String callingPackage,
       intrealCallingPid,intrealCallingUid,intstartFlags, Bundle options,
       booleanignoreTargetSecurity,booleancomponentSpecified, ActivityRecord[] outActivity,
       ActivityContainer container, TaskRecord inTask) {
   interr = ActivityManager.START_SUCCESS;


   //...
   //中间各种逻辑判断，这里就不贴出来了，贼多。。。我们依旧划个重点

   doPendingActivityLaunchesLocked(false);

   err = startActivityUncheckedLocked(r, sourceRecord, voiceSession, voiceInteractor,
           startFlags,true, options, inTask);//这里记住一下倒数第3个参数是true。

   if(err <0) {
       // If someone asked to have the keyguard dismissed on the next
       // activity start, but we are not actually doing an activity
       // switch...  just dismiss the keyguard now, because we
       // probably want to see whatever is behind it.
       notifyActivityDrawnForKeyguard();
   }
   returnerr;
}

还得往里走。。。好多层：

final intstartActivityUncheckedLocked(finalActivityRecord r, ActivityRecord sourceRecord,
        IVoiceInteractionSession voiceSession, IVoiceInteractor voiceInteractor,intstartFlags,
        booleandoResume, Bundle options, TaskRecord inTask) {
    //前面N个判断...

    mService.grantUriPermissionFromIntentLocked(callingUid, r.packageName,
            intent, r.getUriPermissionsLocked(), r.userId);

    if(sourceRecord !=null&& sourceRecord.isRecentsActivity()) {
        r.task.setTaskToReturnTo(RECENTS_ACTIVITY_TYPE);
    }
    if(newTask) {
        EventLog.writeEvent(EventLogTags.AM_CREATE_TASK, r.userId, r.task.taskId);
    }
    ActivityStack.logStartActivity(EventLogTags.AM_CREATE_ACTIVITY, r, r.task);
    targetStack.mLastPausedActivity=null;
    targetStack.startActivityLocked(r, newTask, doResume, keepCurTransition, options);
    if(!launchTaskBehind) {
        // Don't set focus on an activity that's going to the back.
        mService.setFocusedActivityLocked(r,"startedActivity");
    }
    returnActivityManager.START_SUCCESS;
}

这个方法就屌的不行了，好几百行，一行行看下来绝对的心力交瘁，换个角度来看，这个方法的返回值比较有特点，他们都是 ActiviyManager中的常量，让我们看一看这些常量代表的意思：

/**
 * Result for IActivityManaqer.startActivity: the activity was started
 * successfully as normal.
 * @hide
 */
public static final intSTART_SUCCESS=0;

/**
 * Result for IActivityManaqer.startActivity: the caller asked that the Intent not
 * be executed if it is the recipient, and that is indeed the case.
 * @hide
 */
public static final intSTART_RETURN_INTENT_TO_CALLER=1;

/**
 * Result for IActivityManaqer.startActivity: activity wasn't really started, but
 * a task was simply brought to the foreground.
 * @hide
 */
public static final intSTART_TASK_TO_FRONT=2;

/**
 * Result for IActivityManaqer.startActivity: activity wasn't really started, but
 * the given Intent was given to the existing top activity.
 * @hide
 */
public static final intSTART_DELIVERED_TO_TOP=3;

好了，就贴几个，可以看出这些都是我们启动以后 activity的返回的各种结果，可想而知前面的各种逻辑是干嘛的了。那么这样我们就只找成功的那一个常量值 START_SUCCESS，在 startActivityLocked（） 我们发现之后方法末尾返回了 START_SUCCESS，其余都不是，那么关键代码也就比较好找了，请看上面红色的重点~~，好了继续走你，这回就来到了 ActivityStack 这个类了：

final voidstartActivityLocked(ActivityRecord r,booleannewTask,
       booleandoResume,booleankeepCurTransition, Bundle options) {
   //逻辑判断。。比如Home键什么的

   if(doResume) {
       mStackSupervisor.resumeTopActivitiesLocked(this, r, options);
   }
}

还记得前面划重点的参数吧，就是doResume，前面的一些逻辑代码咱们就不谈了，有兴趣的小盆友有时间可以慢慢看，咱们继续往下走 ActivityStackSupervisor.resumeTopActivitiesLocked()：

booleanresumeTopActivitiesLocked(ActivityStack targetStack, ActivityRecord target,
        Bundle targetOptions) {
    if(targetStack ==null) {
        targetStack =mFocusedStack;
    }
    // Do targetStack first.
    booleanresult =false;
    if(isFrontStack(targetStack)) {
        result = targetStack.resumeTopActivityLocked(target, targetOptions);
    }

    for(intdisplayNdx =mActivityDisplays.size() -1; displayNdx >=0; --displayNdx) {
        finalArrayList stacks =mActivityDisplays.valueAt(displayNdx).mStacks;
        for(intstackNdx = stacks.size() -1; stackNdx >=0; --stackNdx) {
            finalActivityStack stack = stacks.get(stackNdx);
            if(stack == targetStack) {
                // Already started above.
                continue;
            }
            if(isFrontStack(stack)) {
                stack.resumeTopActivityLocked(null);
            }
        }
    }
    returnresult;
}

这个方法代码量比较少，关键的地方就是 resumeTopActivityLocked 了，感觉越来越接近目标了，还有点小激动。。。ActivityStack.resumeTopActivityLocked():

final booleanresumeTopActivityLocked(ActivityRecord prev, Bundle options) {
    if(mStackSupervisor.inResumeTopActivity) {
        // Don't even start recursing.
        return false;
    }

    booleanresult =false;
    try{
        // Protect against recursion.
        mStackSupervisor.inResumeTopActivity=true;
        if(mService.mLockScreenShown== ActivityManagerService.LOCK_SCREEN_LEAVING) {
            mService.mLockScreenShown= ActivityManagerService.LOCK_SCREEN_HIDDEN;
            mService.updateSleepIfNeededLocked();
        }
        result = resumeTopActivityInnerLocked(prev, options);
    }finally{
        mStackSupervisor.inResumeTopActivity=false;
    }
    returnresult;
}

嗯，是一个内部具体实现方法：

private booleanresumeTopActivityInnerLocked(ActivityRecord prev, Bundle options) {
     //.....
    ActivityStack lastStack = mStackSupervisor.getLastStack();
   if (next.app != null && next.app.thread != null) {

           //.........
        try{
            
            //...........
          
        }catch(Exception e) {
            // Whoops, need to restart this activity!
            if(DEBUG_STATES) Slog.v(TAG_STATES,"Resume failed; resetting state to "
                    + lastState +": "+ next);
            next.state= lastState;
            if(lastStack !=null) {
                lastStack.mResumedActivity= lastResumedActivity;
            }
            Slog.i(TAG,"Restarting because process died: "+ next);
            if(!next.hasBeenLaunched) {
                next.hasBeenLaunched=true;
            }else  if(SHOW_APP_STARTING_PREVIEW&& lastStack !=null&&
                    mStackSupervisor.isFrontStack(lastStack)) {
                mWindowManager.setAppStartingWindow(
                        next.appToken, next.packageName, next.theme,
                        mService.compatibilityInfoForPackageLocked(next.info.applicationInfo),
                        next.nonLocalizedLabel, next.labelRes, next.icon, next.logo,
                        next.windowFlags,null,true);
            }
            mStackSupervisor.startSpecificActivityLocked(next,true,false);
            if(DEBUG_STACK)mStackSupervisor.validateTopActivitiesLocked();
            return true;
        }

        // From this point on, if something goes wrong there is no way
        // to recover the activity.
        try{
            next.visible=true;
            completeResumeLocked(next);
        }catch(Exception e) {
            // If any exception gets thrown, toss away this
            // activity and try the next one.
            Slog.w(TAG,"Exception thrown during resume of "+ next, e);
            requestFinishActivityLocked(next.appToken, Activity.RESULT_CANCELED,null,
                    "resume-exception",true);
            if(DEBUG_STACK)mStackSupervisor.validateTopActivitiesLocked();
            return true;
        }
        next.stopped=false;

    }else{
        // Whoops, need to restart this activity!
        if(!next.hasBeenLaunched) {
            next.hasBeenLaunched=true;
        }else{
            if(SHOW_APP_STARTING_PREVIEW) {
                mWindowManager.setAppStartingWindow(
                        next.appToken, next.packageName, next.theme,
                        mService.compatibilityInfoForPackageLocked(
                                next.info.applicationInfo),
                        next.nonLocalizedLabel,
                        next.labelRes, next.icon, next.logo, next.windowFlags,
                        null,true);
            }
            if(DEBUG_SWITCH) Slog.v(TAG_SWITCH,"Restarting: "+ next);
        }
        if(DEBUG_STATES) Slog.d(TAG_STATES,"resumeTopActivityLocked: Restarting "+ next);
        mStackSupervisor.startSpecificActivityLocked(next,true,true);
    }

    if(DEBUG_STACK)mStackSupervisor.validateTopActivitiesLocked();
    return true;
}

阿西吧，将近400行。。老衲差点就要圆寂在这源码上面了。。耐着性子看了好几遍，还是让老衲找出了重点，前面的判断大概都有比如从 activity 后台到前台，从暂停到恢复，回到home页，屏幕旋转,切换到不同栈 activity 等等各种情况，但是这个不是咱们要的，咱就是要一个 activity 从无到有，所以咱只留相关的代码，ActivityStackSupervisor.startSpecificActivityLocked():

voidstartSpecificActivityLocked(ActivityRecord r,
        booleanandResume,booleancheckConfig) {
    // Is this activity's application already running?
    Proce***ecord app =mService.getProce***ecordLocked(r.processName,
            r.info.applicationInfo.uid,true);

    r.task.stack.setLaunchTime(r);

    if(app !=null&& app.thread!=null) {
        try{
            if((r.info.flags&ActivityInfo.FLAG_MULTIPROCESS) ==0
                    || !"android".equals(r.info.packageName)) {
                // Don't add this if it is a platform component that is marked
                // to run in multiple processes, because this is actually
                // part of the framework so doesn't make sense to track as a
                // separate apk in the process.
                app.addPackage(r.info.packageName, r.info.applicationInfo.versionCode,
                        mService.mProcessStats);
            }
            realStartActivityLocked(r, app, andResume, checkConfig);
            return;
        }catch(RemoteException e) {
            Slog.w(TAG,"Exception when starting activity "
                    + r.intent.getComponent().flattenToShortString(), e);
        }

        // If a dead object exception was thrown -- fall through to
        // restart the application.
    }

    mService.startProcessLocked(r.processName, r.info.applicationInfo,true,0,
            "activity", r.intent.getComponent(),false,false,true);
}

啊，终于找到一个比较少代码的方法了，从逻辑判断上看 realStartActivityLocked 才是开启我们应用内的方法嘛，至于 startProcessLocked，它是启动应用进程的，咱们先不管，下一篇文章再理它，看看 realStartActivityLocked 怎么个实现的：

final booleanrealStartActivityLocked(ActivityRecord r,
       Proce***ecord app,booleanandResume,booleancheckConfig)
       throwsRemoteException {

   //...check..
   app.thread.scheduleLaunchActivity(newIntent(r.intent), r.appToken,
           System.identityHashCode(r), r.info,newConfiguration(mService.mConfiguration),
           newConfiguration(stack.mOverrideConfig), r.compat, r.launchedFromPackage,
           task.voiceInteractor, app.repProcState, r.icicle, r.persistentState, results,
           newIntents, !andResume,mService.isNextTransitionForward(), profilerInfo);

   // do other things...
   return true;
}

忽略掉其他的代码，我们只看重点，这个 thread 是谁呢？还记得我们的 ActivityThread 吧，这个thread其实就是 ActivityThread中的内部类对象 ApplicationThread，我们去看一下这个方法的实现，看了那么多代码，这里其实已经很接近了：

public final voidscheduleLaunchActivity(Intent intent, IBinder token,intident,
        ActivityInfo info, Configuration curConfig, Configuration overrideConfig,
        CompatibilityInfo compatInfo, String referrer, IVoiceInteractor voiceInteractor,
        intprocState, Bundle state, PersistableBundle persistentState,
        List pendingResults, List pendingNewIntents,
        booleannotResumed,booleanisForward, ProfilerInfo profilerInfo) {

    updateProcessState(procState,false);

    ActivityClientRecord r =newActivityClientRecord();

    r.token= token;
    r.ident= ident;
    r.intent= intent;
    r.referrer= referrer;
    r.voiceInteractor= voiceInteractor;
    r.activityInfo= info;
    r.compatInfo= compatInfo;
    r.state= state;
    r.persistentState= persistentState;

    r.pendingResults= pendingResults;<            
            
                            

                网站题目：Activity启动流程                

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