// 小于四个角 圆角

-(void)setbor{

    NSString *str = @" couldn't fit this all in a comment to @lomanf's answer. So I'm adding it as an answer.";

    //计算字符高度

    [Corner layoutHeightWithLable:self.label text:str];

    /*

     1.使用空白 view addSubView label

     2.得到类似 qq 聊天气泡，仅仅只是类似，还是有区别

     */

    UIView *view = [[UIView alloc]init];

    //view 的 frame 要比 label 大一点，不然切圆角会切到字符串

    view.frame = CGRectMake( ,  , _label.frame.size.width +  , _label.frame.size.height + );

    view.backgroundColor = [UIColor redColor];

    //圆角

    [Corner createCornerInView:view corners:UIRectCornerBottomLeft|UIRectCornerTopRight cgsize:CGSizeMake(, )];

    [self.view addSubview:view];

    [view addSubview:_label];

}

#import <UIKit/UIKit.h>

@interface Corner : UIView

+(void)createCornerInView:(UIView *)view corners:(UIRectCorner)corner cgsize:(CGSize)size;

+(void)layoutHeightWithLable:(UILabel *)label text:(NSString *)text;

@end

+(void)layoutHeightWithLable:(UILabel *)label text:(NSString *)text{

    label.numberOfLines = ;

    label.lineBreakMode = NSLineBreakByWordWrapping;

    CGSize maxSize = CGSizeMake(, MAXFLOAT);

    CGSize textSize = [text boundingRectWithSize:maxSize options:(NSStringDrawingUsesFontLeading | NSStringDrawingUsesLineFragmentOrigin) attributes:@{NSFontAttributeName:label.font} context:nil].size;

    label.frame = CGRectMake(label.frame.origin.x, label.frame.origin.y, textSize.width, textSize.height);

    label.text = text;

}

+(void)createCornerInView:(UIView *)view corners:(UIRectCorner)corner cgsize:(CGSize)size{

    /*

     typedef NS_OPTIONS(NSUInteger, UIRectCorner) {

     UIRectCornerTopLeft     = 1 << 0,  - 左上角

     UIRectCornerTopRight    = 1 << 1,  - 右上角

     UIRectCornerBottomLeft  = 1 << 2,  - 左下角

     UIRectCornerBottomRight = 1 << 3,  - 右下角

     UIRectCornerAllCorners  = ~0UL     - 四只角

     };

     */

    //贝塞尔曲线

    UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:view.bounds byRoundingCorners:corner cornerRadii:size];

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

    maskLayer.frame = view.bounds;

    maskLayer.path = bezierPath.CGPath;

    view.layer.mask = maskLayer;

}