view onMeasure的源码如下：
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}
getDefaultSize(int size, int measureSpec)的源码如下：
public static int getDefaultSize(int size, int measureSpec) {
int result = size;
int specMode = MeasureSpec.getMode(measureSpec);
int specSize = MeasureSpec.getSize(measureSpec);
switch (specMode) {
case MeasureSpec.UNSPECIFIED:
result = size;
break;
case MeasureSpec.AT_MOST:
case MeasureSpec.EXACTLY:
result = specSize;
break;
}
return result;
}
getSuggestedMinimumWidth的源码如下：
protected int getSuggestedMinimumWidth() {
return (mBackground == null) ? mMinWidth : max(mMinWidth, mBackground.getMinimumWidth());
}
mMinWidth 是android：minWidth的属性，mBackground.getMinimumWidth()是background的width。
按照上述的源码进行测量，在MeasureSpec.AT_MOST和MeasureSpec.AT_MOST 两种模式测量下，view的宽度都应该等于getSuggestedMinimumWidth。如果view没有设置background和android：minWidth的属性，那么view的宽度应该等于0；而实际getwidth的宽度等于viewgroup的宽度。为什么会这样呢？
