overridePendingTransition的执行流程

 具体请看下面的表格：

♠ frameworks/base/core/java/android/app/ActivityManagerNative.java

§ ActivityManagerNative.getDefault() 很简单，获取gDefault

Java static public IActivityManager getDefault() { return gDefault.get(); } 1 2 3     static public IActivityManager getDefault() {         return gDefault.get();     }

§ gDefault 一个静态变量，是ActivityManagerService 的代理对象

Java private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() { protected IActivityManager create() { IBinder b = ServiceManager.getService("activity"); if (false) { Log.v("ActivityManager", "default service binder = " + b); } IActivityManager am = asInterface(b); if (false) { Log.v("ActivityManager", "default service = " + am); } return am; } }; 1 2 3 4 5 6 7 8 9 10 11 12 13     private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>() {         protected IActivityManager create() {             IBinder b = ServiceManager.getService("activity");             if (false) {                 Log.v("ActivityManager", "default service binder = " + b);             }             IActivityManager am = asInterface(b);             if (false) {                 Log.v("ActivityManager", "default service = " + am);             }             return am;         }     };

♠ frameworks/base/services/java/com/android/server/am/ActivityManagerService.java

ActivityRecord.isInStackLocked(token); 查询当前Activity是否还在Activity栈中？

Java static ActivityRecord isInStackLocked(IBinder token) { final ActivityRecord r = ActivityRecord.forToken(token); if (r != null) { return r.task.stack.isInStackLocked(token); } return null; } 1 2 3 4 5 6 7     static ActivityRecord isInStackLocked(IBinder token) {         final ActivityRecord r = ActivityRecord.forToken(token);         if (r != null) {             return r.task.stack.isInStackLocked(token);         }         return null;     }

如果还在继续执行Binder.clearCallingIdentity();保存此Activity在Binder中的id，稍候就会使用overridePendingAppTransition执行恢复的操作。

如果当前Activity的状态是活动状态或者将要暂停状态，执行WindowManagerService的overridePendingAppTransition

♠ frameworks/base/services/java/com/android/server/wm/WindowManagerService.java

调用AppTransition的overridePendingAppTransition方法（将动画的设置信息都放在AppTransition中了）

Java void overridePendingAppTransition(String packageName, int enterAnim, int exitAnim, IRemoteCallback startedCallback) { if (isTransitionSet()) { mNextAppTransitionType = NEXT_TRANSIT_TYPE_CUSTOM; mNextAppTransitionPackage = packageName; mNextAppTransitionThumbnail = null; mNextAppTransitionEnter = enterAnim; mNextAppTransitionExit = exitAnim; postAnimationCallback(); mNextAppTransitionCallback = startedCallback; } else { postAnimationCallback(); } } 1 2 3 4 5 6 7 8 9 10 11 12 13 14     void overridePendingAppTransition(String packageName, int enterAnim, int exitAnim,                                              IRemoteCallback startedCallback) {         if (isTransitionSet()) {             mNextAppTransitionType = NEXT_TRANSIT_TYPE_CUSTOM;             mNextAppTransitionPackage = packageName;             mNextAppTransitionThumbnail = null;             mNextAppTransitionEnter = enterAnim;             mNextAppTransitionExit = exitAnim;             postAnimationCallback();             mNextAppTransitionCallback = startedCallback;         } else {             postAnimationCallback();         }     }

然后WindowManagerService在进行Activity切换的时候就会根据AppTransition的动画设置来显示切换动画了。

 

总结：

1. 执行overridePendingTransition时的调用顺序ActivityManageService->WindowManageService

2. 最终设置的是WindowManagerService的overridePendingAppTransition

3. 和Windows编程中显示模式窗口不同，执行startActivity时并没有立即暂停当前Activity，而是通过Handler在下一个MessageQueue的处理中暂停的当前Activity