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。
