欢迎大家下载我个人开发的app安琪花园

其基本思路是：

1. 通过自定义属性，作用于PercentRelativeLayout的子控件上面 
2. 重写PercentRelativeLayout 静态内部类LayoutParams继承自RelativeLayout.LayoutParams
3. 在重写的LayoutParams里面解析出新增加的属性
4. 重写PercentRelatvieLayoutParams里面的generateLayoutParams(AttributeSet attrs)方法，并返回我们自己定义 的LayoutParams实例
5. 重写percentRelativeLayout的onmeasure方法，计算出控件的真正宽高。

接下来看一下具体的代码

第一步：
<declare-styleable name="Percent">
        <attr name="width_percent" format="float"></attr>
       <attr name="height_percent" format="float"></attr>
    </declare-styleable>

第二步， 第三步： 位于自定义控件PercentRelativeLayout下面
public static class LayoutParams extends RelativeLayout.LayoutParams {

        public float width;
        public float height;

        public LayoutParams(Context c, AttributeSet attrs) {
            super(c, attrs);
            TypedArray array = c.obtainStyledAttributes(attrs, R.styleable.Percent);
            width = array.getFloat(R.styleable.Percent_width_percent, 0);
            height = array.getFloat(R.styleable.Percent_height_percent, 0);
            array.recycle();
        }

    }

第四步：返回了自己写的LayoutParams实例

    @Override
    public RelativeLayout.LayoutParams generateLayoutParams(AttributeSet attrs) {
        return new LayoutParams(getContext(), attrs);
    }

第五步： 重写onMeasure方法，  计算出真正的宽高
@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);
        int count = getChildCount();
        for(int i = 0; i < count; i++){
            View view = getChildAt(i);
            ViewGroup.LayoutParams params = view.getLayoutParams();
            if(checkLayoutParams(params)){
                LayoutParams params1 = (LayoutParams) params;
                if(params1.width > 0){
                    params.width = (int) (width * params1.width);
                }

                if(params1.height > 0){
                    params.height = (int) (height * params1.height);
                }
                view.setLayoutParams(params);
            }
        }
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    }

github地址