Android 自定义View onMeasure

// MeasureSpec 源码 删除了注释
public static class MeasureSpec
    {
        private static final int MODE_SHIFT = 30;
        private static final int MODE_MASK = 0x3 << MODE_SHIFT;
        public static final int UNSPECIFIED = 0 << MODE_SHIFT;
        public static final int EXACTLY = 1 << MODE_SHIFT;
        public static final int AT_MOST = 2 << MODE_SHIFT;

        public static int makeMeasureSpec(int size, int mode)
        {
            return size + mode;
        }

        public static int getMode(int measureSpec)
        {
            return (measureSpec & MODE_MASK);
        }

        public static int getSize(int measureSpec)
        {
            return (measureSpec & ~MODE_MASK);
        }

        public static String toString(int measureSpec)
        {
            int mode = getMode(measureSpec);
            int size = getSize(measureSpec);
            StringBuilder sb = new StringBuilder("MeasureSpec: ");
            if (mode == UNSPECIFIED)
            {
                sb.append("UNSPECIFIED ");
            } else if (mode == EXACTLY)
            {
                sb.append("EXACTLY ");
            } else if (mode == AT_MOST)
            {
                sb.append("AT_MOST ");
            } else
            {
                sb.append(mode).append(" ");
            }
            sb.append(size);
            return sb.toString();
        }
    }

    // MeasureSpec.AT_MOST (wrap_content) 代表的是最大可获得的空间
    // MeasureSpec.EXACTLY (fill_parent/match_parent) 代表的是精确的尺寸
    // MeasureSpec.UNSPECIFIED 对于控件尺寸来说，没有任何参考意义。

    // 指定自定义View的最小宽高
    private static int MIN_WIDTH_SIZE = 50;
    private static int MIN_HEIGHT_SIZE = 50;

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    { // 测量方法
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int width = MeasureSpec.getSize(widthMeasureSpec);
        int height = MeasureSpec.getSize(heightMeasureSpec);
        int wmode = MeasureSpec.getMode(widthMeasureSpec);
        int hmode = MeasureSpec.getMode(heightMeasureSpec);
        int w = 0, h = 0;
        w = this.measureSize(wmode, width, MIN_WIDTH_SIZE);
        h = this.measureSize(hmode, height, MIN_HEIGHT_SIZE);
        // 设置测量大小
        super.setMeasuredDimension(w, h);
    }

    // 计算测量大小
    public int measureSize(int mode, int measureSize, int minSize)
    {
        int size = 0;
        if (mode == MeasureSpec.AT_MOST)
        {
            size = minSize;
        } else if (mode == MeasureSpec.EXACTLY)
        {
            size = measureSize;
        } else
        { // UNSPECIFIED
            size = minSize;
        }
        return size;
    }

PS：关于MeasureSpec的解释来自网上搜索