view 部分设置圆角

UIImage *img = [UIImage ly_imageWithColor:[UIColor redColor]];
self.imgView = [[UIImageView alloc] initWithImage:img];
self.imgView.frame = CGRectMake(100, 100, 100, 100);
[self.view addSubview:self.imgView];

UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:self.imgView.bounds byRoundingCorners:UIRectCornerTopLeft|UIRectCornerTopRight cornerRadii:CGSizeMake(10, 10)];
CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
maskLayer.frame = self.imgView.bounds;
maskLayer.path = maskPath.CGPath;
self.imgView.layer.mask = maskLayer;

关于参数：

第二个参数byRoundingCorners:(UIRectCorner)corners允许指定矩形的部分角为圆角，而其余的角为直角，取值来自枚举:

  typedef NS_OPTIONS(NSUInteger, UIRectCorner) {
    UIRectCornerTopLeft     = 1 << 0,
    UIRectCornerTopRight    = 1 << 1,
    UIRectCornerBottomLeft  = 1 << 2,
    UIRectCornerBottomRight = 1 << 3,
    UIRectCornerAllCorners  = ~0UL
};

其最后一个参数cornerRadii:(CGSize)cornerRadii指定了圆角的半径，但这里需要注意，这个参数的取值是 CGSize类型，也就意味着这里需要给出的是椭圆的半径。