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];