详解Android.activity销毁流程的工作原理

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我是靠谱客的博主自觉棒棒糖，最近开发中收集的这篇文章主要介绍详解Android.activity销毁流程的工作原理，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

继续我们的源码解析，上一篇文章我们介绍了Activity的启动流程，一个典型的场景就是Activity a 启动了一个Activity b，他们的生命周期回调方法是：

onPause(a) –> onCreate(b) –> onStart(b) –> onResume(b) –> onStop(a)

而我们根据源码也验证了这样的生命周期调用序列，那么Activity的销毁流程呢？它的生命周期的调用顺序又是这样的呢？

这里我们我做一个简单的demo，让一个Activity a启动Activity b，然后在b中调用finish()方法，它们的生命周期执行顺序是：

onPause(b)
onRestart(a)
onStart(a)
onResume(a)
onStop(b)
onDestory(b)

好吧，根据我们测试的生命周期方法的回调过程开始对Activity销毁流程的分析，一般而言当我们需要销毁Activity的时候都会调用其自身的finish方法，所以我们的流程开始是以finish方法开始的。

一：请求销毁当前Activity

MyActivity.finish()
Activity.finish()
ActivityManagerNative.getDefault().finishActivity()
ActivityManagerService.finishActivity()
ActivityStack.requestFinishActivityLocked()
ActivityStack.finishActivityLocked()
ActivityStack.startPausingLocked()

首先我们在自己的Activity调用了finish方法，它实际上调用的是Activity的finish方法：

public void finish() {
 finish(false);
}

然后我们可以发现其调用了finish方法的重载方法，并且传递了一个参数值：

private void finish(boolean finishTask) {
  if (mParent == null) {
   int resultCode;
   Intent resultData;
   synchronized (this) {
    resultCode = mResultCode;
    resultData = mResultData;
   }
   if (false) Log.v(TAG, "Finishing self: token=" + mToken);
   try {
    if (resultData != null) {
     resultData.prepareToLeaveProcess();
    }
    if (ActivityManagerNative.getDefault()
      .finishActivity(mToken, resultCode, resultData, finishTask)) {
     mFinished = true;
    }
   } catch (RemoteException e) {
    // Empty
   }
  } else {
   mParent.finishFromChild(this);
  }
 }

好吧，这个参数值似乎并没什么用。。。这里就不在讨论了，然后调用了ActivityManagerNative.getDefault().finishActivity方法，好吧，根据上一篇文章的介绍，我们知道了ActivityManagerNative是一个Binder对象，这里调用的方法最终会被ActivityManagerService执行，所以这了的finishActivity最终被执行的是ActivityManagerService.finishActivity方法，好吧，我们来看一下ActivityManagerService的finishActivity方法的执行逻辑。。。

@Override
public final boolean finishActivity(IBinder token, int resultCode, Intent resultData, boolean finishTask) {
  ...
  res = tr.stack.requestFinishActivityLocked(token, resultCode,resultData, "app-request", true);
  ...
}

这里我们可以发现，经过一系列逻辑判断之后，最终调用了ActivityStack的requestFinishActivityLocked方法，这里应该就是执行finish Activity的逻辑了。

final boolean requestFinishActivityLocked(IBinder token, int resultCode,
   Intent resultData, String reason, boolean oomAdj) {
  ActivityRecord r = isInStackLocked(token);
  if (DEBUG_RESULTS || DEBUG_STATES) Slog.v(TAG_STATES,
    "Finishing activity token=" + token + " r="
    + ", result=" + resultCode + ", data=" + resultData
    + ", reason=" + reason);
  if (r == null) {
   return false;
  }

  finishActivityLocked(r, resultCode, resultData, reason, oomAdj);
  return true;
 }

这个方法体里面又调用了finishActivityLocked方法，那我们继续看一下finishActivityLocked方法的实现：

final boolean finishActivityLocked(ActivityRecord r, int resultCode, Intent resultData,
   String reason, boolean oomAdj) {
  ...
  startPausingLocked(false, false, false, false);
  ...
  return false;
 }

好吧，在这里调用了startPausingLocked方法，看名字应该是开始要执行Activity的onPause方法请求了，然后我们看一下startPausingLocked方法的实现：

final boolean startPausingLocked(boolean userLeaving, boolean uiSleeping, boolean resuming, boolean dontWait) {
  ...
   try {
    EventLog.writeEvent(EventLogTags.AM_PAUSE_ACTIVITY,
      prev.userId, System.identityHashCode(prev),
      prev.shortComponentName);
    mService.updateUsageStats(prev, false);
    prev.app.thread.schedulePauseActivity(prev.appToken, prev.finishing,
      userLeaving, prev.configChangeFlags, dontWait);
   } catch (Exception e) {
    // Ignore exception, if process died other code will cleanup.
    Slog.w(TAG, "Exception thrown during pause", e);
    mPausingActivity = null;
    mLastPausedActivity = null;
    mLastNoHistoryActivity = null;
   }
  ...
 }

这样从应用程序调用finish方法，ActivityManagerService接收请求并执行startPausingLocked方法。

二：执行当前Activity的onPause方法

IApplicationThread.schedulePauseActivity()
ActivityThread.schedulePauseActivity()
ActivityThread.sendMessage()
ActivityThread.H.sendMessage()
ActivityThread.H.handleMessage()
ActivityThread.handlePauseActivity()
ActivityThread.performPauseActivity()
Instrumentation.callActivityOnPause()
Activity.performPause()
Activity.onPause()
ActivityManagerNative.getDefault().activityPaused()
ActivityManagerService.activityPaused()
ActivityStack.activityPausedLocked()
ActivityStack.completePauseLocked()

在方法startPausingLocked中我们调用了：prev.app.thread.schedulePauseActivity这里实际上调用的是IApplicationThread的schedulePauseActivity方法，IApplicationThread也是一个Binder对象，它是ActivityThread中ApplicationThread的Binder client端，所以最终会调用的是ApplicationThread的schedulePauseActivity方法，好吧我们看一下ActivityThread的schedulePauseActivity方法的具体实现：

public final void schedulePauseActivity(IBinder token, boolean finished, boolean userLeaving, int configChanges, boolean dontReport) {
 sendMessage(
  finished ? H.PAUSE_ACTIVITY_FINISHING : H.PAUSE_ACTIVITY,
  token, (userLeaving ? 1 : 0) | (dontReport ? 2 : 0),
     configChanges);
}

然后调用了ActivityThread的sendMessage方法：

private void sendMessage(int what, Object obj, int arg1, int arg2) {
  sendMessage(what, obj, arg1, arg2, false);
 }

然后又回调了sendMessage的重载方法。。

private void sendMessage(int what, Object obj, int arg1, int arg2, boolean async) {
  if (DEBUG_MESSAGES) Slog.v(
   TAG, "SCHEDULE " + what + " " + mH.codeToString(what)
   + ": " + arg1 + " / " + obj);
  Message msg = Message.obtain();
  msg.what = what;
  msg.obj = obj;
  msg.arg1 = arg1;
  msg.arg2 = arg2;
  if (async) {
   msg.setAsynchronous(true);
  }
  mH.sendMessage(msg);
 }

最终调用mH发送异步消息，然后在mH的handleMessge方法中处理异步消息并调用handlePauseActivity方法：

private void handlePauseActivity(IBinder token, boolean finished,
   boolean userLeaving, int configChanges, boolean dontReport) {
  ActivityClientRecord r = mActivities.get(token);
  if (r != null) {
   //Slog.v(TAG, "userLeaving=" + userLeaving + " handling pause of " + r);
   if (userLeaving) {
    performUserLeavingActivity(r);
   }

   r.activity.mConfigChangeFlags |= configChanges;
   performPauseActivity(token, finished, r.isPreHoneycomb());

   // Make sure any pending writes are now committed.
   if (r.isPreHoneycomb()) {
    QueuedWork.waitToFinish();
   }

   // Tell the activity manager we have paused.
   if (!dontReport) {
    try {
     ActivityManagerNative.getDefault().activityPaused(token);
    } catch (RemoteException ex) {
    }
   }
   mSomeActivitiesChanged = true;
  }
 }

好吧，这里回调了performPauseActivity方法，上篇文章中我们已经分析过了这段代码：

performPauseActivity()
Instrumentation.callActivityOnPause()
Activity.performPause()
Activity.onPause()

这样我们就回调了第一个生命周期方法：onPause。。。

在handlePauseActivity方法中我们调用了ActivityManagerNative.getDefault().activityPaused(token)方法，好吧又是回调ActivityManagerService的方法，这样最终会调用ActivityManagerService的activityPaused方法：

@Override
 public final void activityPaused(IBinder token) {
  final long origId = Binder.clearCallingIdentity();
  synchronized(this) {
   ActivityStack stack = ActivityRecord.getStackLocked(token);
   if (stack != null) {
    stack.activityPausedLocked(token, false);
   }
  }
  Binder.restoreCallingIdentity(origId);
 }

这样，我们继续看一下activityPausedLocked方法的实现：

final void activityPausedLocked(IBinder token, boolean timeout) {
  ...
  completePauseLocked(true);
  ...
}

里面又经过一系列的逻辑判断之后，开始执行completePauseLocked方法：

private void completePauseLocked(boolean resumeNext) {
 ...     mStackSupervisor.resumeTopActivitiesLocked(topStack, null, null);
 ...
 }

这样栈顶Activity的onPause操作就执行完成了，接下来就就是开始执行上一个Activity的onResume操作了。。。

三：执行上一个Activity的onResume操作

这样调用了ActivityStackSupervisor.resumeTopActivitiesLocked方法。。，又开始调用这个方法，通过上一篇文章的介绍，我们知道这个方法实际上是执行Activity的初始化，我们看一下其具体的调用过程：

ActivityStack.resumeTopActivityLocked()
ActivityStack.resumeTopInnerLocked()
IApplicationThread.scheduleResumeActivity()
ActivityThread.scheduleResumeActivity()
ActivityThread.sendMessage()
ActivityTherad.H.sendMessage()
ActivityThread.H.handleMessage()
ActivityThread.H.handleResumeMessage()
Activity.performResume()
Activity.performRestart()
Instrumentation.callActivityOnRestart()
Activity.onRestart()
Activity.performStart()
Instrumentation.callActivityOnStart()
Activity.onStart()
Instrumentation.callActivityOnResume()
Activity.onResume()

好吧，这个过程其实上一篇文章中已经做了介绍，这里不做过多的分析了，通过这样调用过程我们最终执行了当前栈顶Activity上一个Activity的onRestart方法，onStart方法，onResume方法等，下面我们将调用栈顶Activity的onStop方法，onDestory方法。

四：执行栈顶Activity的销毁操作

Looper.myQueue().addIdleHandler(new Idler())
ActivityManagerNative.getDefault().activityIdle()
ActivityManagerService.activityIdle()
ActivityStackSupervisor.activityIdleInternalLocked()
ActivityStack.destroyActivityLocked()
IApplicationThread.scheduleDestoryActivity()
ActivityThread.scheduleDestoryActivity()
ActivityThread.sendMessage()
ActivityThread.H.sendMessage()
ActivityThread.H.handleMessage()
ActivityThread.handleDestoryActivity()
ActivityThread.performDestoryActivity()
Activity.performStop()
Instrumentation.callActivityOnStop()
Activity.onStop()
Instrumentation.callActivityOnDestory()
Activity.performDestory()
Acitivity.onDestory()
ActivityManagerNative.getDefault().activityDestoryed()
ActivityManagerService.activityDestoryed()
ActivityStack.activityDestoryedLocked()

我们在ActivityThread.handleResumeActivity方法中调用了Looper.myQueue().addIdleHandler(new Idler())，下面看一下这个方法的实现：

private class Idler implements MessageQueue.IdleHandler {
  @Override
  public final boolean queueIdle() {
   ActivityClientRecord a = mNewActivities;
   boolean stopProfiling = false;
   if (mBoundApplication != null && mProfiler.profileFd != null
     && mProfiler.autoStopProfiler) {
    stopProfiling = true;
   }
   if (a != null) {
    mNewActivities = null;
    IActivityManager am = ActivityManagerNative.getDefault();
    ActivityClientRecord prev;
    do {
     if (localLOGV) Slog.v(
      TAG, "Reporting idle of " + a +
      " finished=" +
      (a.activity != null && a.activity.mFinished));
     if (a.activity != null && !a.activity.mFinished) {
      try {
       am.activityIdle(a.token, a.createdConfig, stopProfiling);
       a.createdConfig = null;
      } catch (RemoteException ex) {
       // Ignore
      }
     }
     prev = a;
     a = a.nextIdle;
     prev.nextIdle = null;
    } while (a != null);
   }
   if (stopProfiling) {
    mProfiler.stopProfiling();
   }
   ensureJitEnabled();
   return false;
  }
 }

内部有一个queueIdle的回调方法，当它被添加到MessageQueue之后就会回调该方法，我们可以发现在这个方法体中调用了ActivityManagerNative.getDefault.activityIdle方法，通过上一篇文章以及上面的讲解，我们应该知道这了最终调用的是ActivityManagerService.activityIdle方法，好吧，这里看一下activityIdle方法的具体实现：

public final void activityIdle(IBinder token, Configuration config, boolean stopProfiling) {
  final long origId = Binder.clearCallingIdentity();
  synchronized (this) {
   ActivityStack stack = ActivityRecord.getStackLocked(token);
   if (stack != null) {
    ActivityRecord r =
      mStackSupervisor.activityIdleInternalLocked(token, false, config);
    if (stopProfiling) {
     if ((mProfileProc == r.app) && (mProfileFd != null)) {
      try {
       mProfileFd.close();
      } catch (IOException e) {
      }
      clearProfilerLocked();
     }
    }
   }
  }
  Binder.restoreCallingIdentity(origId);
 }

可以发现这里又调用了ActivityStackSupervisor.activityIdleInternalLocked方法，然后我们看一下activityIdleInternalLocked方法的具体实现：

final ActivityRecord activityIdleInternalLocked(final IBinder token, boolean fromTimeout, Configuration config) {
 .... 
 stack.destroyActivityLocked(r, true, "finish-idle");
 .... 
}

可以看到这里调用ActivityStack.destroyActivityLocked方法，可以看一下其具体实现：

final boolean destroyActivityLocked(ActivityRecord r, boolean removeFromApp, String reason) {
  ...
  r.app.thread.scheduleDestroyActivity(r.appToken, r.finishing, r.configChangeFlags);
  ...  
}

好吧，这里又开始执行IApplicationThread.scheduleDestoryActivity方法，上文已经做了说明这里最终调用的是ActivityThread.scheduleDestroyActivity方法，好吧，看一下ActivityThread.scheduleDestryActivity方法的实现：

public final void scheduleDestroyActivity(IBinder token, boolean finishing, int configChanges) {
 sendMessage(H.DESTROY_ACTIVITY, token, finishing ? 1 : 0,
     configChanges);
}

这里有开始执行sendMessage方法，通过一系列的调用sendMessage方法最终调用了handleDestroyActivity方法：

private void handleDestroyActivity(IBinder token, boolean finishing,
   int configChanges, boolean getNonConfigInstance) {
  ActivityClientRecord r = performDestroyActivity(token, finishing,
    configChanges, getNonConfigInstance);
  if (r != null) {
   cleanUpPendingRemoveWindows(r);
   WindowManager wm = r.activity.getWindowManager();
   View v = r.activity.mDecor;
   if (v != null) {
    if (r.activity.mVisibleFromServer) {
     mNumVisibleActivities--;
    }
    IBinder wtoken = v.getWindowToken();
    if (r.activity.mWindowAdded) {
     if (r.onlyLocalRequest) {
      // Hold off on removing this until the new activity's
      // window is being added.
      r.mPendingRemoveWindow = v;
      r.mPendingRemoveWindowManager = wm;
     } else {
      wm.removeViewImmediate(v);
     }
    }
    if (wtoken != null && r.mPendingRemoveWindow == null) {
     WindowManagerGlobal.getInstance().closeAll(wtoken,
       r.activity.getClass().getName(), "Activity");
    }
    r.activity.mDecor = null;
   }
   if (r.mPendingRemoveWindow == null) {
    // If we are delaying the removal of the activity window, then
    // we can't clean up all windows here. Note that we can't do
    // so later either, which means any windows that aren't closed
    // by the app will leak. Well we try to warning them a lot
    // about leaking windows, because that is a bug, so if they are
    // using this recreate facility then they get to live with leaks.
    WindowManagerGlobal.getInstance().closeAll(token,
      r.activity.getClass().getName(), "Activity");
   }

   // Mocked out contexts won't be participating in the normal
   // process lifecycle, but if we're running with a proper
   // ApplicationContext we need to have it tear down things
   // cleanly.
   Context c = r.activity.getBaseContext();
   if (c instanceof ContextImpl) {
    ((ContextImpl) c).scheduleFinalCleanup(
      r.activity.getClass().getName(), "Activity");
   }
  }
  if (finishing) {
   try {
    ActivityManagerNative.getDefault().activityDestroyed(token);
   } catch (RemoteException ex) {
    // If the system process has died, it's game over for everyone.
   }
  }
  mSomeActivitiesChanged = true;
 }

可以看到这里调用了performDestroyActivity方法，用来执行Avtivity的onDestroy方法：

private ActivityClientRecord performDestroyActivity(IBinder token, boolean finishing,
   int configChanges, boolean getNonConfigInstance) {
  ...  
  r.activity.performStop();
  ...
  mInstrumentation.callActivityOnDestroy(r.activity);
  ...
 }

然后调用了Activity.performStop()方法，查看performStop方法：

final void performStop() {
  ...
  mInstrumentation.callActivityOnStop(this);
  ...
}

然后调用了Instrumentation.callActivityOnStop()方法：

public void callActivityOnStop(Activity activity) {
  activity.onStop();
 }

好吧，终于调用了Activity的onStop方法。。。

我们继续看一下Instrumentation.callActivityOnDestroy()。。。。又是通过Instrumentation来调用Activity的onDestroy方法：

public void callActivityOnDestroy(Activity activity) {
 ...
 activity.performDestroy();
 ...
}

然后看一下Activity的performDestroy()方法的实现：

final void performDestroy() {
  mDestroyed = true;
  mWindow.destroy();
  mFragments.dispatchDestroy();
  onDestroy();
  mFragments.doLoaderDestroy();
  if (mVoiceInteractor != null) {
   mVoiceInteractor.detachActivity();
  }
 }

O(∩_∩)O哈哈~，终于回调了Activity的onDestroy方法。。。。

总结：

Activity的销毁流程是从finish方法开始的

Activity销毁过程是：onPause –> onRestart –> onStart –> onResume –> onStop –> onDestroy

Activity的销毁流程是ActivityThread与ActivityManagerService相互配合销毁的

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持靠谱客。