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

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。