onMeasure()和onSizeChanged()

protected void onSizeChanged(int w, int h, int oldw, int oldh) protected void onMeasure(int widthMeasure, int heightMeasure)

首先onSizeChanged是设置大小的，而onMeasure是为了能够设置wrap_content或者是match_parent的属性。因此，如果我们希望自定义的View能够使用wrap_content或者是match_parent的属性，应该写成如下形式：

@Overrideprotected void onMeasure(int widthMeasure, int heightMeasure){    super.onMeasure(widthMeasure, heightMeasure);    setMeasuredDimension(getMeasuredWidth(), getMeasuredWidth());}