詳解Android.activity銷毀流程的工作原理
繼續(xù)我們的源碼解析，上一篇文章我們介紹了Activity的啟動(dòng)流程，一個(gè)典型的場(chǎng)景就是Activity a 啟動(dòng)了一個(gè)Activity b，他們的生命周期回調(diào)方法是：
onPause(a) –> onCreate(b) –> onStart(b) –> onResume(b) –> onStop(a)
而我們根據(jù)源碼也驗(yàn)證了這樣的生命周期調(diào)用序列，那么Activity的銷毀流程呢？它的生命周期的調(diào)用順序又是這樣的呢？
這里我們我做一個(gè)簡(jiǎn)單的demo，讓一個(gè)Activity a啟動(dòng)Activity b，然后在b中調(diào)用finish()方法，它們的生命周期執(zhí)行順序是：
onPause(b)
onRestart(a)
onStart(a)
onResume(a)
onStop(b)
onDestory(b)
好吧，根據(jù)我們測(cè)試的生命周期方法的回調(diào)過(guò)程開(kāi)始對(duì)Activity銷毀流程的分析，一般而言當(dāng)我們需要銷毀Activity的時(shí)候都會(huì)調(diào)用其自身的finish方法，所以我們的流程開(kāi)始是以finish方法開(kāi)始的。
一：請(qǐng)求銷毀當(dāng)前Activity
MyActivity.finish()
Activity.finish()
ActivityManagerNative.getDefault().finishActivity()
ActivityManagerService.finishActivity()
ActivityStack.requestFinishActivityLocked()
ActivityStack.finishActivityLocked()
ActivityStack.startPausingLocked()
首先我們?cè)谧约旱腁ctivity調(diào)用了finish方法，它實(shí)際上調(diào)用的是Activity的finish方法：
public void finish() {
finish(false);
}
然后我們可以發(fā)現(xiàn)其調(diào)用了finish方法的重載方法，并且傳遞了一個(gè)參數(shù)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，這個(gè)參數(shù)值似乎并沒(méi)什么用。。。這里就不在討論了，然后調(diào)用了ActivityManagerNative.getDefault().finishActivity方法，好吧，根據(jù)上一篇文章的介紹，我們知道了ActivityManagerNative是一個(gè)Binder對(duì)象，這里調(diào)用的方法最終會(huì)被ActivityManagerService執(zhí)行，所以這了的finishActivity最終被執(zhí)行的是ActivityManagerService.finishActivity方法，好吧，我們來(lái)看一下ActivityManagerService的finishActivity方法的執(zhí)行邏輯。。。
@Override
public final boolean finishActivity(IBinder token, int resultCode, Intent resultData, boolean finishTask) {
...
res = tr.stack.requestFinishActivityLocked(token, resultCode,resultData, "app-request", true);
...
}
這里我們可以發(fā)現(xiàn)，經(jīng)過(guò)一系列邏輯判斷之后，最終調(diào)用了ActivityStack的requestFinishActivityLocked方法，這里應(yīng)該就是執(zhí)行finish Activity的邏輯了。
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;
}
這個(gè)方法體里面又調(diào)用了finishActivityLocked方法，那我們繼續(xù)看一下finishActivityLocked方法的實(shí)現(xiàn)：
final boolean finishActivityLocked(ActivityRecord r, int resultCode, Intent resultData,
String reason, boolean oomAdj) {
...
startPausingLocked(false, false, false, false);
...
return false;
}
好吧，在這里調(diào)用了startPausingLocked方法，看名字應(yīng)該是開(kāi)始要執(zhí)行Activity的onPause方法請(qǐng)求了，然后我們看一下startPausingLocked方法的實(shí)現(xiàn)：
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;
}
...
}
這樣從應(yīng)用程序調(diào)用finish方法，ActivityManagerService接收請(qǐng)求并執(zhí)行startPausingLocked方法。
二：執(zhí)行當(dāng)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中我們調(diào)用了：prev.app.thread.schedulePauseActivity這里實(shí)際上調(diào)用的是IApplicationThread的schedulePauseActivity方法，IApplicationThread也是一個(gè)Binder對(duì)象，它是ActivityThread中ApplicationThread的Binder client端，所以最終會(huì)調(diào)用的是ApplicationThread的schedulePauseActivity方法，好吧我們看一下ActivityThread的schedulePauseActivity方法的具體實(shí)現(xiàn)：
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);
}
然后調(diào)用了ActivityThread的sendMessage方法：
private void sendMessage(int what, Object obj, int arg1, int arg2) {
sendMessage(what, obj, arg1, arg2, false);
}
然后又回調(diào)了sendMessage的重載方法。。
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);
}
最終調(diào)用mH發(fā)送異步消息，然后在mH的handleMessge方法中處理異步消息并調(diào)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，這里回調(diào)了performPauseActivity方法，上篇文章中我們已經(jīng)分析過(guò)了這段代碼：
performPauseActivity()
Instrumentation.callActivityOnPause()
Activity.performPause()
Activity.onPause()
這樣我們就回調(diào)了第一個(gè)生命周期方法：onPause。。。
在handlePauseActivity方法中我們調(diào)用了ActivityManagerNative.getDefault().activityPaused(token)方法，好吧又是回調(diào)ActivityManagerService的方法，這樣最終會(huì)調(diào)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);
}
這樣，我們繼續(xù)看一下activityPausedLocked方法的實(shí)現(xiàn)：
final void activityPausedLocked(IBinder token, boolean timeout) {
...
completePauseLocked(true);
...
}
里面又經(jīng)過(guò)一系列的邏輯判斷之后，開(kāi)始執(zhí)行completePauseLocked方法：
private void completePauseLocked(boolean resumeNext) {
... mStackSupervisor.resumeTopActivitiesLocked(topStack, null, null);
...
}
這樣棧頂Activity的onPause操作就執(zhí)行完成了，接下來(lái)就就是開(kāi)始執(zhí)行上一個(gè)Activity的onResume操作了。。。
三：執(zhí)行上一個(gè)Activity的onResume操作
這樣調(diào)用了ActivityStackSupervisor.resumeTopActivitiesLocked方法。。，又開(kāi)始調(diào)用這個(gè)方法，通過(guò)上一篇文章的介紹，我們知道這個(gè)方法實(shí)際上是執(zhí)行Activity的初始化，我們看一下其具體的調(diào)用過(guò)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，這個(gè)過(guò)程其實(shí)上一篇文章中已經(jīng)做了介紹，這里不做過(guò)多的分析了，通過(guò)這樣調(diào)用過(guò)程我們最終執(zhí)行了當(dāng)前棧頂Activity上一個(gè)Activity的onRestart方法，onStart方法，onResume方法等，下面我們將調(diào)用棧頂Activity的onStop方法，onDestory方法。
四：執(zhí)行棧頂Activity的銷毀操作
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()
我們?cè)贏ctivityThread.handleResumeActivity方法中調(diào)用了Looper.myQueue().addIdleHandler(new Idler())，下面看一下這個(gè)方法的實(shí)現(xiàn)：
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;
}
}
內(nèi)部有一個(gè)queueIdle的回調(diào)方法，當(dāng)它被添加到MessageQueue之后就會(huì)回調(diào)該方法，我們可以發(fā)現(xiàn)在這個(gè)方法體中調(diào)用了ActivityManagerNative.getDefault.activityIdle方法，通過(guò)上一篇文章以及上面的講解，我們應(yīng)該知道這了最終調(diào)用的是ActivityManagerService.activityIdle方法，好吧，這里看一下activityIdle方法的具體實(shí)現(xiàn)：
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);
}
可以發(fā)現(xiàn)這里又調(diào)用了ActivityStackSupervisor.activityIdleInternalLocked方法，然后我們看一下activityIdleInternalLocked方法的具體實(shí)現(xiàn)：
final ActivityRecord activityIdleInternalLocked(final IBinder token, boolean fromTimeout, Configuration config) {
....
stack.destroyActivityLocked(r, true, "finish-idle");
....
}
可以看到這里調(diào)用ActivityStack.destroyActivityLocked方法，可以看一下其具體實(shí)現(xiàn)：
final boolean destroyActivityLocked(ActivityRecord r, boolean removeFromApp, String reason) {
...
r.app.thread.scheduleDestroyActivity(r.appToken, r.finishing, r.configChangeFlags);
...
}
好吧，這里又開(kāi)始執(zhí)行IApplicationThread.scheduleDestoryActivity方法，上文已經(jīng)做了說(shuō)明這里最終調(diào)用的是ActivityThread.scheduleDestroyActivity方法，好吧，看一下ActivityThread.scheduleDestryActivity方法的實(shí)現(xiàn)：
public final void scheduleDestroyActivity(IBinder token, boolean finishing, int configChanges) {
sendMessage(H.DESTROY_ACTIVITY, token, finishing ? 1 : 0,
configChanges);
}
這里有開(kāi)始執(zhí)行sendMessage方法，通過(guò)一系列的調(diào)用sendMessage方法最終調(diào)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;
}
可以看到這里調(diào)用了performDestroyActivity方法，用來(lái)執(zhí)行Avtivity的onDestroy方法：
private ActivityClientRecord performDestroyActivity(IBinder token, boolean finishing,
int configChanges, boolean getNonConfigInstance) {
...
r.activity.performStop();
...
mInstrumentation.callActivityOnDestroy(r.activity);
...
}
然后調(diào)用了Activity.performStop()方法，查看performStop方法：
final void performStop() {
...
mInstrumentation.callActivityOnStop(this);
...
}
然后調(diào)用了Instrumentation.callActivityOnStop()方法：
public void callActivityOnStop(Activity activity) {
activity.onStop();
}
好吧，終于調(diào)用了Activity的onStop方法。。。
我們繼續(xù)看一下Instrumentation.callActivityOnDestroy()。。。。又是通過(guò)Instrumentation來(lái)調(diào)用Activity的onDestroy方法：
public void callActivityOnDestroy(Activity activity) {
...
activity.performDestroy();
...
}
然后看一下Activity的performDestroy()方法的實(shí)現(xiàn)：
final void performDestroy() {
mDestroyed = true;
mWindow.destroy();
mFragments.dispatchDestroy();
onDestroy();
mFragments.doLoaderDestroy();
if (mVoiceInteractor != null) {
mVoiceInteractor.detachActivity();
}
}
O(∩_∩)O哈哈~，終于回調(diào)了Activity的onDestroy方法。。。。
總結(jié)：
Activity的銷毀流程是從finish方法開(kāi)始的
Activity銷毀過(guò)程是：onPause –> onRestart –> onStart –> onResume –> onStop –> onDestroy
Activity的銷毀流程是ActivityThread與ActivityManagerService相互配合銷毀的
以上就是本文的全部?jī)?nèi)容，希望對(duì)大家的學(xué)習(xí)有所幫助，也希望大家多多支持腳本之家。
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