Android View绘制流程

View绘制流程

相关对象介绍

ViewRootImpl

• 连接WindowManager 和 DecorView
• 完成View绘制的三大流程： measure、layout、draw
• implements ViewParent
• 分发底层传递的行为事件

DecorView

• Android 视图树的根节点,同时也是 FrameLayout 的子类

setContentView

1. Activity setContentView 调用了PhoneWindow的setContentView()
2. PhoneWindow的setContentView() 调用->installDecor() 调用->generateDecor()-> new DecorView()

流程

• ActivityThread的performLaunchActivity()调用 activity.attach()
• Activity的attach() 初始化了PhoneWindow和WindowManager new PhoneWindow setWindowManager()
• ActivityThread执行mInstrumentation.callActivityOnCreate()方法，然后执行Activity.onCreate()，再执行Activity setContentView
• Activity setContentView 调用了PhoneWindow的setContentView()
• PhoneWindow的setContentView() 调用->installDecor() 调用->generateDecor()-> new DecorView()
• 此时 DecorView PhoneWindow 都已经创建
• ActivityThread的handleResumeActivity() 调用WindowManagerImpl 的addView()
• WindowManagerImpl 的addView 实际是调用WindowManagerGlobal addView() , 在addView WindowManagerGlobal 中创建ViewRootImpl， 并将DecorView传入ViewRootImpl，完成windowManagerService和View的连接
• ViewRootImpl performTraversal()->performMeasure() performLayout() performDraw

//===========ActivityThread.java==========
final void handleResumeActivity(...) {
    ......
    //跟踪代码后发现其初始赋值为mWindow = new PhoneWindow(this, window, activityConfigCallback);
    r.window = r.activity.getWindow(); 
       //从PhoneWindow实例中获取DecorView  
    View decor = r.window.getDecorView();
    ......
    //跟踪代码后发现，vm值为上述PhoneWindow实例中获取的WindowManager。
    ViewManager wm = a.getWindowManager();
    ......
    //当前window的属性，从代码跟踪来看是PhoneWindow窗口的属性
    WindowManager.LayoutParams l = r.window.getAttributes();
    ......
    wm.addView(decor, l);
    ......
}

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

// =====================ViewRootImpl.java=================
private void performTraversals() {
   ......
   int childWidthMeasureSpec = getRootMeasureSpec(mWidth, lp.width);
   int childHeightMeasureSpec = getRootMeasureSpec(mHeight, lp.height);      
   ......
   // Ask host how big it wants to be
   performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
   ......
   performLayout(lp, mWidth, mHeight);
   ......
   performDraw();
}

View WindowManager Window关系图

View的绘制