继承ViewGroup后的子类如何重写onMeasure方法

1.首先贴上我试验成功的代码

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		
		int measureWidth = MeasureSpec.getSize(widthMeasureSpec);
		int measureHeigth = MeasureSpec.getSize(heightMeasureSpec);
		setMeasuredDimension(measureWidth, measureHeigth);
		// TODO Auto-generated method stub
		for(int i= 0;i<getChildCount();i++){
			View v = getChildAt(i);
			Log.v(TAG, "measureWidth is " +v.getMeasuredWidth() + "measureHeight is " +v.getMeasuredHeight());
			int widthSpec = 0;
			int heightSpec = 0;
			LayoutParams params = v.getLayoutParams();
			if(params.width > 0){
				widthSpec = MeasureSpec.makeMeasureSpec(params.width, MeasureSpec.EXACTLY);
			}else if (params.width == -1) {
				widthSpec = MeasureSpec.makeMeasureSpec(measureWidth, MeasureSpec.EXACTLY);
			} else if (params.width == -2) {
				widthSpec = MeasureSpec.makeMeasureSpec(measureWidth, MeasureSpec.AT_MOST);
			}
			
			if(params.height > 0){
				heightSpec = MeasureSpec.makeMeasureSpec(params.height, MeasureSpec.EXACTLY);
			}else if (params.height == -1) {
				heightSpec = MeasureSpec.makeMeasureSpec(measureHeigth, MeasureSpec.EXACTLY);
			} else if (params.height == -2) {
				heightSpec = MeasureSpec.makeMeasureSpec(measureWidth, MeasureSpec.AT_MOST);
			}
			v.measure(widthSpec, heightSpec);
			
		}
	}

解释一下：

首先判断params.width的值是多少，有三种情况。

如果是大于零的话，及传递的就是一个具体的值，那么，构造MeasupreSpec的时候可以直接用EXACTLY。

如果为-1的话，就是MatchParent的情况，那么，获得父View的宽度，再用EXACTLY来构造MeasureSpec。

如果为-2的话，就是wrapContent的情况，那么，构造MeasureSpec的话直接用一个负数就可以了。