android – 绘制具有圆角的LinearLayout

我试图实现一个LinearLayout子类,它使用圆角绘制自己.从我的研究中,我设置setwillNotDraw(false)并覆盖onDraw()在画布中绘制一个圆角矩形：

@Override
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);

    int sc = canvas.saveLayer(0,getWidth(),getHeight(),drawPaint,Canvas.MATRIX_SAVE_FLAG | Canvas.CLIP_SAVE_FLAG | Canvas.HAS_ALPHA_LAYER_SAVE_FLAG
            | Canvas.FULL_COLOR_LAYER_SAVE_FLAG | Canvas.CLIP_TO_LAYER_SAVE_FLAG);
    canvas.drawRoundRect(bounds,mCornerRadius,roundPaint);
    canvas.restoretoCount(sc);
}

哪里：

drawPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
drawPaint.setColor(0xffffffff);
drawPaint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.DST_IN));

roundPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
roundPaint.setColor(0xffffffff);

DST_IN在这里是正确的选择(根据APIDemos的例子),但是应该是透明的区域(圆角的)改为黑色背景,孩子的角落仍然可见.这是使用Android 4.2.2的galaxy Nexus的结果：

任何提示？

编辑：这是我想要实现的,对于拍摄的粗鲁感到遗憾:)

编辑2：我向GitHub添加了一个可运行的示例项目：https://github.com/venator85/RoundClippingLayout

谢谢