IOS 文本文字下面添加下划线

    UILabel *infolabel = [[UILabel alloc] initWithFrame:CGRectMake(30*RATIO,260*RATIO, self.view.bounds.size.width-60*RATIO, 20*RATIO)];
    infolabel.text = @"[email protected]";
    infolabel.textColor = [UIColor whiteColor];
    infolabel.font = [UIFont systemFontOfSize:12*RATIO];
    infolabel.userInteractionEnabled = YES;
    NSMutableAttributedString *content = [[NSMutableAttributedString alloc]initWithString:[NSString stringWithFormat:@"[email protected]"]];
    NSRange contentRange = {0,[content length]};
    [content addAttribute:NSUnderlineStyleAttributeName value:[NSNumber numberWithInteger:NSUnderlineStyleSingle] range:contentRange];
    infolabel.attributedText = content;
    [self.view addSubview:infolabel];