UIView设置少于四个的圆角

　　最近的需求中有个label需要设置右下角为圆角，其余三个为直角，一开始用的是重写drawRect，然后用绘图重绘每个角的样子，计算起来还是麻烦

　　后来发现了下面的方法：

　　

 UILabel *courseStyleLabel = [[UILabel alloc] initWithFrame:CGRectMake(, , , )];
         courseStyleLabel.backgroundColor = CreateColorByRGB(TitleBgImgViewColor);
         courseStyleLabel.textColor = [UIColor whiteColor];
         courseStyleLabel.textAlignment = NSTextAlignmentCenter;
         courseStyleLabel.font = [UIFont systemFontOfSize:12.0];
         courseStyleLabel.layer.masksToBounds = YES;

         UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:courseStyleLabel.bounds
                                                        byRoundingCorners:UIRectCornerBottomRight
                                                              cornerRadii:CGSizeMake(, )];
         CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
         maskLayer.frame = courseStyleLabel.bounds;
         maskLayer.path = maskPath.CGPath;
         courseStyleLabel.layer.mask = maskLayer;
         [courseImage addSubview:courseStyleLabel];

　　显示效果是右下角有个 弧度为 3 的小圆角

　　

UIRectCornerTopLeft     =  << ,
    UIRectCornerTopRight    =  << ,
    UIRectCornerBottomLeft  =  << ,
    UIRectCornerBottomRight =  << ,
    UIRectCornerAllCorners  = ~0UL

　　通过这个枚举值判断画哪个圆角