在开始本篇文章之前，我们先看一段代码：
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int expendSpec = MeasureSpec.makeMeasureSpec(Integer.MAX_VALUE >> 2, MeasureSpec.AT_MOST);
super.onMeasure(widthMeasureSpec, expendSpec);
} @Override
