stringWithFormat，dateFromString，＆stringFromDate不工作

Question

我試圖顯示UIDatePicker輸入和真實世界時間的IBOutlet標籤dd:hh:mm:ss形式的時差。我有我的NSLog顯示正確的信息，但我很難得到相同的數據顯示在我的標籤。 截至目前，我的UILabel中沒有顯示任何內容，但正確的數據在NSLog中。 當我改變

[self.formatter stringFromDate:timeDif]; 

到

[self.formatter stringFromDate:selected]; 

顯示當前的DatePicker選擇時間（這是不是我想要的），但仍NSLog的正確顯示的時間差。我知道這是我的格式化序列或某事有什麼問題，但我一直無法知道我哪裏出錯了。

- (IBAction)displayDate:(id)sender { 

    NSDate *timeDif = [self.formatter dateFromString:self.string]; 
    NSDate *todaysDate = [NSDate date]; 
    NSDate *selected = [picker date]; 

    self.formatter = [NSDateFormatter new]; 
    [self.formatter setDateFormat:@"dd:hh:mm:ss"]; 

    [picker setDate:selected animated:YES]; 

    self.label.text = [self.formatter stringFromDate:timeDif]; 

    NSDateComponents *dateComponents = [[NSDateComponents alloc] init]; 

    NSCalendar *gregorian = [[NSCalendar alloc] 
          initWithCalendarIdentifier:NSGregorianCalendar]; 

    NSUInteger unitFlags = NSDayCalendarUnit | NSMinuteCalendarUnit | NSHourCalendarUnit | NSSecondCalendarUnit; 

    NSDateComponents *dateComparisonComponents = [gregorian components:unitFlags 
                   fromDate:todaysDate 
                   toDate:selected 
                   options:NSWrapCalendarComponents]; 

    NSInteger days = [dateComparisonComponents day]; 
    NSInteger hours = [dateComparisonComponents hour]; 
    NSInteger minutes = [dateComparisonComponents minute]; 
    NSInteger seconds = [dateComparisonComponents second]; 

    dateComponents.day = days; 
    dateComponents.hour = hours; 
    dateComponents.minute = minutes; 
    dateComponents.second = seconds; 

    self.string = [NSString stringWithFormat:@"%1d:%1d:%1d:%1d", 
               dateComparisonComponents.day, 
               dateComparisonComponents.hour, 
               dateComparisonComponents.minute, 
               dateComparisonComponents.second]; 

    NSLog(@"%1d:%1d:%1d:%1d", 
          dateComparisonComponents.day, 
          dateComparisonComponents.hour, 
          dateComparisonComponents.minute, 
          dateComparisonComponents.second); 
} 

Answer 1

你有很多額外和不必要的代碼。只是這樣做：

- (IBAction)displayDate:(id)sender { 
    NSDate *todaysDate = [NSDate date]; 
    NSDate *selected = [picker date]; 

    NSCalendar *gregorian = [[NSCalendar alloc] 
          initWithCalendarIdentifier:NSGregorianCalendar]; 

    NSUInteger unitFlags = NSDayCalendarUnit |NSMinuteCalendarUnit | NSHourCalendarUnit | NSSecondCalendarUnit; 
    NSDateComponents *dateComparisonComponents = [gregorian components:unitFlags 
                   fromDate:todaysDate 
                   toDate:selected 
                   options:NSWrapCalendarComponents]; 

    NSInteger days = [dateComparisonComponents day]; 
    NSInteger hours = [dateComparisonComponents hour]; 
    NSInteger minutes = [dateComparisonComponents minute]; 
    NSInteger seconds = [dateComparisonComponents second]; 

    self.label.text = [NSString stringWithFormat:@"%ld:%02ld:%02ld:%02ld", 
               days, 
               hours, 
               minutes, 
               seconds]; 
} 

在你的原代碼，self.formatter甚至不會設置第一次運行代碼。這意味着timeDif將首次成爲nil。您還可以獲取選擇器的日期，然後將選擇器的日期設置爲相同的值。沒有理由。並且你沒有已知的理由使用dateComponents。最後，什麼是self.string？