需要借助UIBezierPath与CAShapeLayer进行实现

UIView *view = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];

view.backgroundColor = [UIColor redColor];

[self.view addSubview:view];

UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:view.bounds byRoundingCorners:UIRectCornerTopLeft | UIRectCornerBottomRight cornerRadii:CGSizeMake(20, 20)];

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

maskLayer.frame = view.bounds;

maskLayer.path = maskPath.CGPath;

view.layer.mask = maskLayer;

通过枚举类型UIRectCorner选择上下左右

typedef NS_OPTIONS(NSUInteger, UIRectCorner) {

UIRectCornerTopLeft = 1 << 0,

UIRectCornerTopRight = 1 << 1,

UIRectCornerBottomLeft = 1 << 2,

UIRectCornerBottomRight = 1 << 3,

UIRectCornerAllCorners = ~0UL

};

UILabel设置圆角可能出现问题

如果Uilabel设置圆角，在分辨率高的手机可能出现一条细线，因为label的宽度不是整数，取整数即可。