android发现之旅之ViewRootImpl,Activity,Window,DecorView之间的关系

android复杂的概念,经常会弄的人晕头转向.本篇说说ui里几个概念的关系.

1. 从activity启动流程,可以看出各个对象的关系

大家都知道,这是android ui的核心概念.收的就是界面的一个活动交互界面.用startAcvitity的方式启动.省去中间状态:

在activity的attach接口中:

5063         mWindow = PolicyManager.makeNewWindow(this); 每个activity有一个Window对象.
  5064         mWindow.setCallback(this);  设置window对象的回调是activity

  5087         mWindow.setWindowManager(   设置window对象的manager
  5088                 (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
  5089                 mToken, mComponent.flattenToString(),
  5090                 (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
  5091         if (mParent != null) {
  5092             mWindow.setContainer(mParent.getWindow());
  5093         }
  5094         mWindowManager = mWindow.getWindowManager(); 保存windowmanager

在ActivityThread的handleResumeActivity接口里:

  2796                 r.window = r.activity.getWindow();
  2797                 View decor = r.window.getDecorView(); decorview是window子类, 通过window来获取
  2798                 decor.setVisibility(View.INVISIBLE);
  2799                 ViewManager wm = a.getWindowManager();
  2800                 WindowManager.LayoutParams l = r.window.getAttributes();
  2801                 a.mDecor = decor;  给activity的mDecor赋值           

  2804                 if (a.mVisibleFromClient) {
  2805                     a.mWindowAdded = true;
  2806                     wm.addView(decor, l);  这个调用会调用到WindowManagerGlobal的addView
  2807                 }

WindowManagerGlobal的addView会

16             root = new ViewRootImpl(view.getContext(), display);
6              root.setView(view, wparams, panelParentView);

也就是说, ViewRootImpl的mView其实是DecorView.

2.   总结

每个activity有个window,window被windowmanager管理.

每个window都有decorview.

每个window都有ViewRoot.

绘制发起从ViewRoot.

事件传递发起冲ViewRoot.

绘制传递canvas, canvas来自surface.