View简要工作原理

ViewRootImpl对象=>performTraversals()

private void performTraversals() {
//上下近800行代码。
  performMeasure();
  performLayout();
  performDraw();
}

private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
//mView是DecorView对象
  mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);     
}

layout和draw同理，下面是measure,layout,draw的机制==>

measure

layout

draw