深入理解Activity——Token之旅
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Token是ActivityRecord的内部静态类，我们先来看下Token的继承关系，Token extends IApplicationToken.Stub，从IApplicationToken.Stub类进行继承，根据Binder的机制可以知道Token是一个匿名Binder实体类，这个匿名Binder实体会传递给其他进程，其他进程会拿到Token的代理端。
我们知道匿名Binder有两个比较重要的用途，一个是拿到Binder代理端后可跨Binder调用实体端的函数接口，另一个作用便是在多个进程中标识同一个对象。往往这两个作用是同时存在的，比如我们这里研究的Token就同时存在这两个作用，但最重要的便是后者，Token标识了一个ActivityRecord对象，即间接标识了一个Activity。
下面这个图是Token的传递，首先会传递到WMS中，接着会传递到应用进程ActivityThread中，下面来具体分析这个传递流程。
1、Token对象的创建
- ActivityRecord(ActivityManagerService _service, ProcessRecord _caller,
- int _launchedFromUid, String _launchedFromPackage, Intent _intent, String _resolvedType,
- ActivityInfo aInfo, Configuration _configuration,
- ActivityRecord _resultTo, String _resultWho, int _reqCode,
- boolean _componentSpecified, ActivityStackSupervisor supervisor,
- ActivityContainer container, Bundle options) {
- service = _service;
- appToken = new Token(this);
- ........
2、AMS调用WMS的addAPPToken()接口
在启动一个Activity时，会调用startActivityLocked()来在WMS中添加一个AppWindowToken对象；
- final void startActivityLocked(ActivityRecord r, boolean newTask,
- boolean doResume, boolean keepCurTransition, Bundle options) {
- ......
- mWindowManager.addAppToken(task.mActivities.indexOf(r), r.appToken,
- r.task.taskId, mStackId, r.info.screenOrientation, r.fullscreen,
- (r.info.flags & ActivityInfo.FLAG_SHOW_ON_LOCK_SCREEN) != 0, r.userId,
- r.info.configChanges, task.voiceSession != null, r.mLaunchTaskBehind);
- ......
- }
- public void addAppToken(int addPos, IApplicationToken token, int taskId, int stackId,
- int requestedOrientation, boolean fullscreen, boolean showWhenLocked, int userId,
- int configChanges, boolean voiceInteraction, boolean launchTaskBehind) {
- ......
-
- synchronized(mWindowMap) {
- AppWindowToken atoken = findAppWindowToken(token.asBinder());
- if (atoken != null) {
- Slog.w(TAG, "Attempted to add existing app token: " + token);
- return;
- }
- atoken = new AppWindowToken(this, token, voiceInteraction);
- ......
- Task task = mTaskIdToTask.get(taskId);
- if (task == null) {
- createTask(taskId, stackId, userId, atoken);
- } else {
- task.addAppToken(addPos, atoken);
- }
- mTokenMap.put(token.asBinder(), atoken);
-
- atoken.hidden = true;
- atoken.hiddenRequested = true;
-
- }
- }
3、AMS跨Binder调用应用进程的scheduleLaunchActivity()将Token传递给上层应用进程- final boolean realStartActivityLocked(ActivityRecord r,
- ProcessRecord app, boolean andResume, boolean checkConfig)
- throws RemoteException {
- ......
- app.thread.scheduleLaunchActivity(new Intent(r.intent), r.appToken,
- System.identityHashCode(r), r.info, new Configuration(mService.mConfiguration),
- r.compat, r.launchedFromPackage, r.task.voiceInteractor, app.repProcState,
- r.icicle, r.persistentState, results, newIntents, !andResume,
- mService.isNextTransitionForward(), profilerInfo);
- ......
- }
这个是通过调用app.thread.scheduleLaunchActivity()完成的，可以知道对端接收到的便是Token的代理对象。
我们来看下ApplicationThread中scheduleLaunchActivity()的实现：
- 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<ResultInfo> pendingResults,
- List<ReferrerIntent> pendingNewIntents, boolean notResumed, boolean isForward,
- ProfilerInfo profilerInfo) {
- updateProcessState(procState, false);
- ActivityClientRecord r = new ActivityClientRecord();
- 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;
- r.pendingIntents = pendingNewIntents;
- r.startsNotResumed = notResumed;
- r.isForward = isForward;
- r.profilerInfo = profilerInfo;
- updatePendingConfiguration(curConfig);
- sendMessage(H.LAUNCH_ACTIVITY, r);
- }
4、Activity窗口添加
ViewRootImpl.setView()函数中添加Activity窗口时在参数mWindowAttributes中携带Token代理对象。
- public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
- synchronized (this) {
- if (mView == null) {
- mView = view;
- ......
- mWindowAttributes.copyFrom(attrs);
- ......
- try {
- ......
- res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
- getHostVisibility(), mDisplay.getDisplayId(),
- mAttachInfo.mContentInsets, mAttachInfo.mStableInsets, mInputChannel);
- } catch (RemoteException e) {
- ......
- } finally {
- ......
- }
- ......
- }
- }
- }
- public int addWindow(Session session, IWindow client, int seq,
- WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
- Rect outContentInsets, Rect outStableInsets, InputChannel outInputChannel) {
- ......
- boolean addToken = false;
- WindowToken token = mTokenMap.get(attrs.token);
- ......
- win = new WindowState(this, session, client, token,
- attachedWindow, appOp[0], seq, attrs, viewVisibility, displayContent);
-
- mWindowMap.put(client.asBinder(), win);
- ......
- }
根据Binder机制可以知道从上层应用传递过来的Token代理对象会转换成SystemServer进程中的Token本地对象，后者与第2步中从Token对象是同一个对象，所以上面调用mTokenMap.get(attrs.token)时便能返回正确返回一个WindowToken（这个WindowToken其实是一个APPWindowToken），这样添加的窗口也就跟Activity关联上了。
转自：http://blog.csdn.net/guoqifa29/article/details/46819377#comments
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