解析: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

复制代码 代码如下:

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。