ios - ラベルにカウントダウンタイマーを表示

Question

カウントダウンタイマーを表示したい。開始日と終了日があります。残り時間を次のように表示する必要があります

日 : 時 : 分 : 秒

このサイトからいくつかのコードを取得しましたが、終了日を過ぎるとマイナス記号が表示されます。誰か助けてください。

-(void) viewWillAppear:(BOOL)animated
{
    timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self     selector:@selector(updateCountdown) userInfo:nil repeats: YES];
}

-(void) updateCountdown 
{
    NSString *dateString = @"14-12-2012";
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

    [dateFormatter setDateFormat:@"dd-MM-yyyy"];
    NSDate *dateFromString = [[NSDate alloc] init];
    // voila!
    dateFromString = [dateFormatter dateFromString:dateString];

    NSDate *now = [NSDate date];
    NSCalendar *calendar = [NSCalendar currentCalendar];

    NSDateComponents *componentsHours = [calendar components:NSHourCalendarUnit fromDate:now];
    NSDateComponents *componentMint = [calendar components:NSMinuteCalendarUnit fromDate:now];    
    NSDateComponents *componentSec = [calendar components:NSSecondCalendarUnit fromDate:now];        

    NSCalendar *gregorianCalendar = [[NSCalendar alloc]      initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *componentsDaysDiff = [gregorianCalendar components:NSDayCalendarUnit
                                                        fromDate:now
                                                          toDate:dateFromString
                                                         options:0];

    lblDaysSetting.text=[NSString stringWithFormat:@"%02d",componentsDaysDiff.day];
    lblHouresSetting.text=[NSString stringWithFormat:@"%02d",(24-componentsHours.hour)];    
    lblMinitSetting.text=[NSString stringWithFormat:@"%02d",(60-componentMint.minute)];  
    lblSecSetting.text=[NSString stringWithFormat:@"%02d",(60-componentSec.second)];  
}