viewgroup onMeasure例子

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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);        }    }

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。

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