iOS label宽度自适应

    UILabel *lab = [[UILabel alloc] initWithFrame:CGRectMake(20, 100, 0, 20)];

    lab.font = [UIFont systemFontOfSize:14.0f];

    [self.view addSubview:lab];

    

    NSString *str = @"啦啦啦啦啦啦";

    lab.text = str;

    lab.backgroundColor = [UIColor redColor];

    CGSize maxSize = CGSizeMake(MAXFLOAT, 20);

    

    NSDictionary *params = @{

                             NSFontAttributeName : [UIFont systemFontOfSize:14.0f]

                             };

    

//    CGSize textSize = [str boundingRectWithSize:maxSize options:NSStringDrawingUsesLineFragmentOrigin attributes:params context:nil].size;

    

    CGSize textSize = [self getSizeWithMaxSize:maxSize text:str params:params];

    [lab setFrame:CGRectMake(lab.frame.origin.x, lab.frame.origin.y, textSize.width, lab.frame.size.height)];