android源码解析之（十五）-->Activity销毁流程

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：

@Override
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