ActivityThread是什么
ActivityThread在Android中它就代表了Android的主线程，但是并不是一个Thread类。
严格来说，UI主线程不是ActivityThread。ActivityThread类是Android APP进程的初始类，它的main函数是这个APP进程的入口。APP进程中UI事件的执行代码段都是由ActivityThread提供的。也就是说，Main Thread实例是存在的，只是创建它的代码我们不可见。ActivityThread的main函数就是在这个Main Thread里被执行的。
Java程序初始类中的main()方法，将作为该程序初始线程的起点，任何其他的线程都是由这个初始线程启动的。这个线程就是程序的主线程。
源码如下：
public final class ActivityThread {
//...
private static ActivityThread sCurrentActivityThread;
public static ActivityThread currentActivityThread() {
return sCurrentActivityThread;
}
private void attach(boolean system) {
sCurrentActivityThread = this;
//...
}
public static void main(String[] args) {
//....
//创建Looper和MessageQueue对象，用于处理主线程的消息
Looper.prepareMainLooper();
//创建ActivityThread对象
ActivityThread thread = new ActivityThread();
//建立Binder通道 (创建新线程)
thread.attach(false);
Looper.loop(); //消息循环运行
throw new RuntimeException("Main thread loop unexpectedly exited");
}
}
ApplicationThread是什么,有什么用？
ApplicationThread是ActivityThread的内部类，也是一个Binder对象。在此处它是作为Activitythread和AMS通信的桥梁.
private class ApplicationThread extends IApplicationThread.Stub {
public final void schedulePauseActivity(IBinder token, boolean finished,
boolean userLeaving, int configChanges, boolean dontReport) {
......
}
public final void scheduleStopActivity(IBinder token, boolean showWindow,
int configChanges) {
......
}
public final void scheduleLaunchActivity(Intent intent, IBinder token, int ident,
ActivityInfo info, Configuration curConfig, CompatibilityInfo compatInfo,
String referrer, IVoiceInteractor voiceInteractor, int procState, Bundle state,
PersistableBundle persistentState, List pendingResults,
List pendingNewIntents, boolean notResumed, boolean isForward,
ProfilerInfo profilerInfo) {
......
}
......
}
上述方法是用来启动activity的，除此外还有几种重要的方法，由此看来ApplicationThread的作用除了启动activity 和ams交互之外还用调用activity的生命周期方法，也就是我们看到的 几个activity生命周期方法。那么我们再看一下这些生命周期方法的调用过程。
schedulePauseActivity()
scheduleStopActivity()
scheduleResumeActivity()
scheduleSendResult()
scheduleLaunchActivity()
scheduleNewIntent()
scheduleDestroyActivity()
scheduleReceiver()
scheduleCreateService()
scheduleBindService()
scheduleUnbindService()
scheduleServiceArgs()
scheduleStopService()
bindApplication()
scheduleConfigurationChanged()
scheduleRegisteredReceiver()
scheduleInstallProvider()
ApplicationThread中的所有schedule方法内部都会调用一个sendMessage（）而其实际要调用到activtyThread中的H的实例对象mH中，mH中定义了很多消息类型，下图是其handlerMessage方法，这也印章了我上边的所说的ApplicationThread的桥梁作用，ams直接通过binder调用，实际调用到activityThread中的方法 。
private void sendMessage(int what, Object obj, int arg1, int arg2, int seq) {
if (DEBUG_MESSAGES) Slog.v(
TAG, "SCHEDULE " + mH.codeToString(what) + " arg1=" + arg1 + " arg2=" + arg2 +
"seq= " + seq);
Message msg = Message.obtain();
msg.what = what;
SomeArgs args = SomeArgs.obtain();
args.arg1 = obj;
args.argi1 = arg1;
args.argi2 = arg2;
args.argi3 = seq;
msg.obj = args;
mH.sendMessage(msg);
}
private class H extends Handler {
……
public void handleMessage(Message msg) {
if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));
switch (msg.what) {
case LAUNCH_ACTIVITY: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");
final ActivityClientRecord r = (ActivityClientRecord) msg.obj;
r.packageInfo = getPackageInfoNoCheck(
r.activityInfo.applicationInfo, r.compatInfo);
handleLaunchActivity(r, null, "LAUNCH_ACTIVITY");
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
case RELAUNCH_ACTIVITY: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityRestart");
ActivityClientRecord r = (ActivityClientRecord)msg.obj;
handleRelaunchActivity(r);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
case PAUSE_ACTIVITY: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityPause");
SomeArgs args = (SomeArgs) msg.obj;
handlePauseActivity((IBinder) args.arg1, false,
(args.argi1 & USER_LEAVING) != 0, args.argi2,
(args.argi1 & DONT_REPORT) != 0, args.argi3);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
case PAUSE_ACTIVITY_FINISHING: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityPause");
SomeArgs args = (SomeArgs) msg.obj;
handlePauseActivity((IBinder) args.arg1, true, (args.argi1 & USER_LEAVING) != 0,
args.argi2, (args.argi1 & DONT_REPORT) != 0, args.argi3);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
case STOP_ACTIVITY_SHOW: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStop");
SomeArgs args = (SomeArgs) msg.obj;
handleStopActivity((IBinder) args.arg1, true, args.argi2, args.argi3);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
case STOP_ACTIVITY_HIDE: {
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStop");
SomeArgs args = (SomeArgs) msg.obj;
handleStopActivity((IBinder) args.arg1, false, args.argi2, args.argi3);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
} break;
case SHOW_WINDOW:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityShowWindow");
handleWindowVisibility((IBinder)msg.obj, true);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case HIDE_WINDOW:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityHideWindow");
handleWindowVisibility((IBinder)msg.obj, false);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case RESUME_ACTIVITY:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityResume");
SomeArgs args = (SomeArgs) msg.obj;
handleResumeActivity((IBinder) args.arg1, true, args.argi1 != 0, true,
args.argi3, "RESUME_ACTIVITY");
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SEND_RESULT:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityDeliverResult");
handleSendResult((ResultData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case DESTROY_ACTIVITY:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityDestroy");
handleDestroyActivity((IBinder)msg.obj, msg.arg1 != 0,
msg.arg2, false);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case BIND_APPLICATION:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "bindApplication");
AppBindData data = (AppBindData)msg.obj;
handleBindApplication(data);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case EXIT_APPLICATION:
if (mInitialApplication != null) {
mInitialApplication.onTerminate();
}
Looper.myLooper().quit();
break;
case NEW_INTENT:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityNewIntent");
handleNewIntent((NewIntentData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case RECEIVER:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "broadcastReceiveComp");
handleReceiver((ReceiverData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case CREATE_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, ("serviceCreate: " + String.valueOf(msg.obj)));
handleCreateService((CreateServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case BIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceBind");
handleBindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case UNBIND_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceUnbind");
handleUnbindService((BindServiceData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case SERVICE_ARGS:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, ("serviceStart: " + String.valueOf(msg.obj)));
handleServiceArgs((ServiceArgsData)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
case STOP_SERVICE:
Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "serviceStop");
handleStopService((IBinder)msg.obj);
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
break;
}
Object obj = msg.obj;
if (obj instanceof SomeArgs) {
((SomeArgs) obj).recycle();
}
if (DEBUG_MESSAGES) Slog.v(TAG, "<<< done: " + codeToString(msg.what));
}
}
private void handleDestroyActivity(IBinder token, boolean finishing,
int configChanges, boolean getNonConfigInstance) {
ActivityClientRecord r = performDestroyActivity(token, finishing,
configChanges, getNonConfigInstance);
if (r != null) {
cleanUpPendingRemoveWindows(r, finishing);
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.mPreserveWindow) {
// Hold off on removing this until the new activity's
// window is being added.
r.mPendingRemoveWindow = r.window;
r.mPendingRemoveWindowManager = wm;
// We can only keep the part of the view hierarchy that we control,
// everything else must be removed, because it might not be able to
// behave properly when activity is relaunching.
r.window.clearContentView();
} else {
wm.removeViewImmediate(v);
}
}
if (wtoken != null && r.mPendingRemoveWindow == null) {
WindowManagerGlobal.getInstance().closeAll(wtoken,
r.activity.getClass().getName(), "Activity");
} else if (r.mPendingRemoveWindow != null) {
// We're preserving only one window, others should be closed so app views
// will be detached before the final tear down. It should be done now because
// some components (e.g. WebView) rely on detach callbacks to perform receiver
// unregister and other cleanup.
WindowManagerGlobal.getInstance().closeAllExceptView(token, v,
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 {
ActivityManager.getService().activityDestroyed(token);
} catch (RemoteException ex) {
throw ex.rethrowFromSystemServer();
}
}
mSomeActivitiesChanged = true;
}
ActivityClientRecord 上述代码太多我删掉了好多不熟悉的，我们看到了STOP_SERVICE，DESTROY_ACTIVITY，所以继续用我们比较熟悉的DESTROY_ACTIVITY为例进行分析。于是又抛出一个新的概念ActivityClientRecord（感觉我是写不完了。。。）因为上述代码已经拿到了activity window等我们熟知的对象，所以里边的方法就不继续深入讨论，下次有时间继续撸ActivityClientRecord 在activity启动中是如何发挥作用的。
static final class ActivityClientRecord {
IBinder token;
int ident;
Intent intent;
String referrer;
IVoiceInteractor voiceInteractor;
Bundle state;
PersistableBundle persistentState;
Activity activity;
Window window;
Activity parent;
String embeddedID;
Activity.NonConfigurationInstances lastNonConfigurationInstances;
……
ActivityClientRecord nextIdle;
ProfilerInfo profilerInfo;
ActivityInfo activityInfo;
CompatibilityInfo compatInfo;
LoadedApk packageInfo;
Window mPendingRemoveWindow;
WindowManager mPendingRemoveWindowManager;
boolean mPreserveWindow;
// Set for relaunch requests, indicates the order number of the relaunch operation, so it
// can be compared with other lifecycle operations.
int relaunchSeq = 0;
// Can only be accessed from the UI thread. This represents the latest processed message
// that is related to lifecycle events/
int lastProcessedSeq = 0;
ActivityClientRecord() {
parent = null;
embeddedID = null;
paused = false;
stopped = false;
hideForNow = false;
nextIdle = null;
configCallback = (Configuration overrideConfig, int newDisplayId) -> {
if (activity == null) {
throw new IllegalStateException(
"Received config update for non-existing activity");
}
activity.mMainThread.handleActivityConfigurationChanged(
new ActivityConfigChangeData(token, overrideConfig), newDisplayId);
};
}
……
}