iOS 如何只给视图的左上角和右上角设置圆角

//懒加载之后返回的view即是设置完左上角和右上角设置完圆角之后的视图

//下面的bounds一定要传大小，不然就会出现视图不显示的情况。

-(UIView *)platFormBGV{

    if (!_platFormBGV) {

    _platFormBGV = [[UIView alloc] init];

    _platFormBGV.backgroundColor = [UIColor whiteColor];

    _platFormBGV.frame = CGRectMake(0, self.view.frame.size.height, APP_WIDTH, 220);

    // 左上和右上为圆角

    UIBezierPath *cornerRadiusPath = [UIBezierPath      bezierPathWithRoundedRect:_platFormBGV.bounds byRoundingCorners:UIRectCornerTopRight | UIRectCornerTopLeft cornerRadii:CGSizeMake(16, 16)];

    CAShapeLayer *cornerRadiusLayer = [ [CAShapeLayer alloc ] init];

    cornerRadiusLayer.frame = _platFormBGV.bounds;

    cornerRadiusLayer.path = cornerRadiusPath.CGPath;

    _platFormBGV.layer.mask = cornerRadiusLayer;

    }

    return _platFormBGV;

}