Android之WMS

WindowManagerService简称WMS，WMS是属于Android系统的其他服务，但是它的重要性和AMS在同一级别，作为“窗口管理员”，它负责窗口的创建、调度、显示以及触摸事件分发。也是一个Android程序猿必须了解的系统服务。

在SyetemServer启动时会调用startOtherServices:

private void startOtherServices() {
            WindowManagerService wm = null;
       
      //InputManagerService
            traceBeginAndSlog("StartInputManagerService");
      inputManager = new InputManagerService(context);
      Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);

      traceBeginAndSlog("StartWindowManagerService");
      
      wm = WindowManagerService.main(context, inputManager,
      mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL,
      !mFirstBoot, mOnlyCore);
      ServiceManager.addService(Context.WINDOW_SERVICE, wm);
      ServiceManager.addService(Context.INPUT_SERVICE, inputManager);
      Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
      
      mActivityManagerService.setWindowManager(wm);

      inputManager.setWindowManagerCallbacks(wm.getInputMonitor());
      inputManager.start();
      
      wm.displayReady();
      wm.systemReady();
}

可以看到，InputManagerService作为参数传递给了WMS，而WMS又作为参数传给了AMS

WMS.main

public static WindowManagerService main(final Context context,
            final InputManagerService im,
            final boolean haveInputMethods, final boolean showBootMsgs,
            final boolean onlyCore) {
        final WindowManagerService[] holder = new WindowManagerService[1];
        //运行在"android.display"线程
        DisplayThread.getHandler().runWithScissors(new Runnable() {
            @Override
            public void run() {
                holder[0] = new WindowManagerService(context, im,
                        haveInputMethods, showBootMsgs, onlyCore);
            }
        }, 0);
        return holder[0];
    }

WindowManagerService

private WindowManagerService(Context context, InputManagerService inputManager,
           boolean haveInputMethods, boolean showBootMsgs, boolean onlyCore) {
       mContext = context;
       mHaveInputMethods = haveInputMethods;
       mAllowBootMessages = showBootMsgs;
       mOnlyCore = onlyCore;
    
       ......
       //保存传进来的IMS
       mInputManager = inputManager; 
       mDisplayManagerInternal = LocalServices.getService(DisplayManagerInternal.class);
       mDisplaySettings = new DisplaySettings();
       mDisplaySettings.readSettingsLocked();

       mDisplayManager = (DisplayManager)context.getSystemService(Context.DISPLAY_SERVICE);
       // 获取Display数组，每个显示设备对应一个Display
       mDisplays = mDisplayManager.getDisplays();
       for (Display display : mDisplays) {
           // 创建DisplayContent,用于支持多屏幕的功能
           createDisplayContentLocked(display);
       }
     
       mActivityManager = ActivityManagerNative.getDefault();     

       //创建WindowAnimator，用于管理所有的窗口动画
       mAnimator = new WindowAnimator(this);
       mAllowTheaterModeWakeFromLayout = context.getResources().getBoolean(
               com.android.internal.R.bool.config_allowTheaterModeWakeFromWindowLayout);

       LocalServices.addService(WindowManagerInternal.class, new LocalService());
  
       //初始化窗口管理策略接口类WindowManagerPolicy
       initPolicy();

       // Add ourself to the Watchdog monitors.
       Watchdog.getInstance().addMonitor(this);
       ......

   }

initPolicy

private void initPolicy() {
    //运行在"android.ui"线程
    UiThread.getHandler().runWithScissors(new Runnable() {
        @Override
        public void run() {
            WindowManagerPolicyThread.set(Thread.currentThread(), Looper.myLooper());

            mPolicy.init(mContext, WindowManagerService.this, WindowManagerService.this);
        }
    }, 0);
}

在initPolicy中，mPolicy实际为PhoneWindowManager。

final WindowManagerPolicy mPolicy = new PhoneWindowManager();

"system_server"线程中会调用WMS的main方法，main方法中会创建WMS，创建WMS的过程运行在"android.display"线程中，它的优先级更高一些，因此要等创建WMS完毕后才会唤醒处于等待状态的"system_server"线程。

WMS初始化时会执行initPolicy方法，initPolicy方法会调用PWM的init方法，这个init方法运行在"android.ui"线程，并且优先级更高，因此要先执行完PWM的init方法后，才会唤醒处于等待状态的"android.display"线程。