copy from : http://gityuan.com/2017/04/16/activity-with-window/
I. Overview
AMS is one of the most core Android system service, whose duties include management of the four core components and processes, and the most complicated of the four components in the Activity. Its complexity is needed for the UI with user interaction (involving Window), WMS its main responsibilities is to work between window management, as well as with the App, SurfaceFlinger and other modules to each other together. in short:
- App UI is mainly specific business needs
- AMS is a management system of the four components and process management, especially Activity stack and various other management state switch;
- WMS is Activiy the corresponding window management system (system window and nested sub-window);
- SurfaceFlinger sucked applied to the UI drawing FrameBuffer (frame buffer), and finally completed by the hardware rendering to the screen;
1.1 WMS whole picture
Description: Click to enlarge
- WMS inherited
IWindowManager.Stub, as Binder server; - WMS member variables mSessions holds all the Session object, Session inherited
IWindowSession.Stub, as Binder server; - Member variables mPolicy: instance of an object is PhoneWindowManager, used to implement a variety of strategies associated with a window;
- Member variable mChoreographer: for animation control window, the screen rotation and other operations;
- Member variables mDisplayContents: Record a group DisplayContent objects associated with this multi-screen output;
- Member variables mTokenMap: Save all WindowToken objects; to IBinder is key, may be IAppWindowToken or other Bp end of Binder;
- The other end of the case: ActivityRecord.Token extends IApplicationToken.Stub
- 成员变量mWindowMap: 保存所有的WindowState对象;以IBinder为key, 是IWindow的Bp端;
- 另一端情况: ViewRootImpl.W extends IWindow.Stub
- 一般地,每一个窗口都对应一个WindowState对象, 该对象的成员变量mClient用于跟应用端交互,成员变量mToken用于跟AMS交互.
二. Activity与Window
2.1 Binder服务
上图是Window调用过程所涉及的Binder服务：
| Binder服务端 | 接口 | 所在进程 |
|---|---|---|
| WindowManagerService | IWindowManager | system_server |
| Session | IWindowSession | system_server |
| ViewRootImpl.W | IWindow | app进程 |
| ActivityRecord.Token | IApplicationToken | system_server |
Activity启动过程会执行组件的生命周期回调以及UI相关对象的创建。UI工作通过向AMS服务来 创建WindowState对象完成，该对象用于描述窗口各种状态属性，以及跟WMS通信。
- WindowManagerService: Activity通过其成员变量mWindowManager(数据类型WindowManagerImpl)，再调用WindowManagerGlobal对象，经过binder call跟WMS通信；
- Session：ViewRootImp创建的用于跟WMS中的Session进行通信；
- ViewRootImpl.W：app端创建的binder服务；
- ActivityRecord.Token: startActivity过程通过binder call进入system_server进程，在该进程执行ASS.startActivityLocked()方法中会创建相应的ActivityRecord对象，该对象初始化时会创建数据类型为ActivityRecord.Token的成员变量appToken，然后会将该对象传递到ActivityThread.
2.2 核心对象
2.2.1 Activity对象
[-> Activity.java]
下面列举Activity对象的部分常见成员变量：
- mWindow：数据类型为PhoneWindow，继承于Window对象；
- mWindowManager：数据类型为WindowManagerImpl，实现WindowManager接口;
- mMainThread：数据类型为ActivityThread, 并非真正的线程，只是运行在主线程的对象。
- mUiThread: 数据类型为Thread，当前activity所在线程，即主线程;
- mHandler：数据类型为Handler, 当前主线程的handler;
- mDecor: 数据类型为View, Activity执行完resume之后创建的视图对象；
另外说明：WindowManagerImpl与Window这两个对象相互保存对方的信息：
- WindowManagerImpl.mParentWindowWindow 指向Window对象；
- Window.mWindowManager 指向WindowManagerImpl对象；
2.2.2 ViewRootImpl对象
- mWindowSession: 数据类型为IWindowSession, 同一进程中所有的ViewRootImpl对象只对应唯一相同的Session代理对象。
- mWindow: 数据类型为IWindow.Stub，每个创建对应一个该对象。
2.2.3 WindowState对象
WindowState对象代表一个窗口，记录在system_server.
- mSession: 数据类型为Session，是system_server的binder服务端；
- mClient: 数据类型为IWindow，是app端的ViewRootImpl.W服务的binder代理对象；
2.3 数量关系
- 每一个Activity对应一个应用窗口；每一个窗口对应一个ViewRootImpl对象；
- 每一个App进程对应唯一的WindowManagerGlobal对象；
- WindowManagerGlobal.sWindowManagerService用于跟WMS交互
- WindowManagerGlobal.sWindowSession用于跟Session交互；
- 每一个App进程对应唯一的相同Session代理对象；
- App可以没有Activity/PhoneWindow/DecorView，例如带悬浮窗口的Service；
- Activity运行在ActivityThread所在的主线程；
- DecorView是Activity所要显示的视图内容；
- ViewRootImpl：管理DecorView跟WMS的交互；每次调用addView()添加窗口时，则都会创建一个ViewRootImpl对象；
2.4 AMS与WMS的对于关系
Activity与Window有一些对象具有一定的对应关系：
| AMS | WMS |
|---|---|
| ActivityRecord | AppWindowToken |
| TaskRecord | Task |
| ActivityStack | TaskStack |
2.5 交互
- App跟AMS通信，会建立Session连接到WMS，后续便通过IWindowSesson跟WMS通信；
- WMS跟SF通信，WMS建立SurfaceComposerClient，然后会在SF中创建Client与之对应， 后续便通过ISurfaceComposerClient跟SF通信；
2.6 IWindow死亡回调
[-> WindowState.java]
private class DeathRecipient implements IBinder.DeathRecipient { public void binderDied() { try { synchronized(mService.mWindowMap) { WindowState win = mService.windowForClientLocked(mSession, mClient, false); Slog.i(TAG, "WIN DEATH: " + win); if (win != null) { mService.removeWindowLocked(win); } else if (mHasSurface) { Slog.e(TAG, "!!! LEAK !!! Window removed but surface still valid."); mService.removeWindowLocked(WindowState.this); } } } catch (IllegalArgumentException ex) { ... } } } App end when the process dies, run IWindow Agent system_server will receive death callback, to handle the removal of the corresponding window information.
III. Summary
Chat also focused on how the main thread to interact with the UI.
To be continued ...