设置控件圆角，只设置上面两个角的圆角，下面两个角依然是直角，如图效果：

代码（通过贝塞尔曲线重绘layer层）：

UIImageView *picImageView = [[UIImageView alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];  
picImageView.backgroundColor = [UIColor greenColor];  
[self.view addSubview:picImageView];  
          
// UIRectCornerBottomRight通过这个设置 
UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:picImageView.bounds 
                                               byRoundingCorners:UIRectCornerTopLeft|UIRectCornerTopRight 
                                                     cornerRadii:CGSizeMake(10, 10)];  
      
CAShapeLayer *maskLayer = [CAShapeLayer layer];  
maskLayer.frame = picImageView.bounds;  
maskLayer.path = maskPath.CGPath;  
      
picImageView.layer.mask = maskLayer;