IOS6上label文字空白

//实时清理累计天数

    if (!_totalDaysLabel) {

        _totalDaysLabel = [[UILabel alloc] init];

    }

    [self getTotalCleanDays];

    NSInteger totalDays = [[NSUserDefaults standardUserDefaults] integerForKey:KEYTOTALCLEANDAYS];

    NSString *totalDaysStr = [NSString stringWithFormat:@"%d天",totalDays];

    labelsize = [totalDaysStr sizeWithFont:font constrainedToSize:size lineBreakMode:GNLineBreakModeWordWrap];

    _totalDaysLabel.frame = CGRectMake(320.0f - (labelsize.width + SHOWINFORMATION_RIGHT), 44, labelsize.width, 44);

    _totalDaysLabel.textColor = [UIColor whiteColor];

    _totalDaysLabel.textAlignment = GNTextAlignmentRight;

    _totalDaysLabel.text = totalDaysStr;

    _totalDaysLabel.backgroundColor = [UIColor clearColor];   //奇怪了 在IOS6的系统上必须加上这句话才行，不然显示的是空白，在IOS7不加也正常

    [_showInformationView addSubview:_totalDaysLabel];