ios - NSTimer 和 NSDateFormatter 麻烦。我的 timerLabel 刷新后消失了吗？

Question

我在一个 viewController 上有一个 UIDatePicker，它允许用户以(7 月 22 日星期日下午 2:33)的形式设置日历日期、小时和分钟，以便在单独的 viewController 中使用计时器。在单独的 viewController 上，我尝试将计时器以“dd:hh:mm:ss”的形式显示在 UIImagePickerController 上的叠加层中，位于当前 NSDate(今天的日期/时间)和所选 datePicker 日期之间。基本上，它是一个倒计时器，当相机加载时，从选定的选择器日期开始倒计时天、小时、分钟、秒。我的问题是，一旦相机加载，计时器就会以正确的格式显示正确的剩余时间，但当它到达我的refreshLabel方法时很快就会消失。我记录了timerLabel的值，它在日志中正确显示，但是一旦循环运行，它就会为所有内容返回Null。昨晚我得到了一些帮助，确定我的问题很可能与字符串中日期的格式有关，但我不知道这可能是什么错误，因为相机首次加载时最初显示了正确的日期。这是我的第一个 viewController 中的代码，其中包含设置 timerLabels 时间的 datePicker:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
    if ([segue.identifier isEqualToString:@"showDate"]) {
        NSString *textFieldContents = self.textField.text;
        NSString *counterContents = self.counter;
        NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
        NSString *deadline = [NSString stringWithFormat:@"%@/deadline.txt",
                              documentsDirectory];
        NSString *flashName = [NSString stringWithFormat:@"%@/flashName.txt",
                               documentsDirectory];
        NSError *fileError;
        [textFieldContents writeToFile:flashName
                            atomically:YES
                              encoding:NSStringEncodingConversionAllowLossy
                                 error:&fileError];
        [counterContents writeToFile:deadline
                           atomically:YES
                             encoding:NSStringEncodingConversionAllowLossy
                                error:&fileError];
        if(fileError.code == 0){
            NSLog(@"deadline.txt was written successfully with these contents: %@,", 
                  counterContents);
            NSLog(@"flashName.txt was written successfully with these contents: %@,",
                  textFieldContents);}
        else
            [self performSegueWithIdentifier:@"showDate" sender:self];}
}

-(IBAction)refreshLabel; {

        NSDate *selected = [NSDate dateWithTimeIntervalSince1970:[picker.date timeIntervalSince1970] - 1];
        self.counter = [self.formatter stringFromDate:selected];
        NSLog(@"selected is: %@", selected);
        NSDate *todaysDate = [NSDate 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.counter = [NSString stringWithFormat:@"%ld:%02ld:%02ld:%02ld", (long)days, (long)hours, (long)minutes, (long)seconds];
        NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
        NSString *deadline = [NSString stringWithFormat:@"%@/deadline.txt", documentsDirectory];
        NSInteger success = [NSKeyedArchiver archiveRootObject:selected toFile:deadline];
        NSLog(@"success is: %d",success);
    }e *selected = [NSDate dateWithTimeIntervalSince1970:[[picker date] timeIntervalSince1970] - 1];

- (void)viewDidLoad
{   [super viewDidLoad];
    self.textField.delegate = self;

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

    NSDate *now = [NSDate date];

    picker.minimumDate = [NSDate date];
    picker.maximumDate = [now dateByAddingTimeInterval:604800];

    [picker setDate:now animated:YES];
    self.counter = [now description];

    self.now = [NSDate date];
    self.counter = [self.formatter stringFromDate:self.now];}

这是我的 UIImagePickerController 的 viewController 代码，我需要它来显示计时器标签并正确倒计时:

  - (IBAction)startCamera:(id)sender {
    if (self.image == nil &&  [self.videoFilePath length] == 0) {
        self.imagePickerController = [[UIImagePickerController alloc] init];
        self.imagePickerController.delegate = self;
        self.imagePickerController.allowsEditing = NO;
        self.imagePickerController.videoMaximumDuration = 10;

        if ([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {
            self.imagePickerController.sourceType = UIImagePickerControllerSourceTypeCamera;
        }
        else {
            self.imagePickerController.sourceType = UIImagePickerControllerSourceTypePhotoLibrary;
        }
        self.imagePickerController.mediaTypes = [UIImagePickerController availableMediaTypesForSourceType:self.imagePickerController.sourceType];
        [self presentViewController:self.imagePickerController animated:NO completion:nil];}

    [[NSBundle mainBundle] loadNibNamed:@"OverlayView" owner:self options:nil];
    self.overlayView.frame = CGRectMake(160,8,0,0);
    self.imagePickerController.cameraOverlayView = self.overlayView;

    NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSString *deadline = [NSString stringWithFormat:@"%@/deadline.txt",
                          documentsDirectory];
    NSString *flashName = [NSString stringWithFormat:@"%@/flashName.txt",
                           documentsDirectory];
    NSError *fileError;
    titleLabel.text = [NSString stringWithContentsOfFile:flashName
                                                encoding:NSASCIIStringEncoding
                                                   error:&fileError];
    timerLabel.text = [NSString stringWithContentsOfFile:deadline
                                                encoding:NSASCIIStringEncoding
                                                   error:&fileError];
    if(fileError.code == 0){
        NSLog(@"deadline.txt was read successfully with these contents: %@,",
              timerLabel.text);
        NSLog(@"flashName.txt was read successfully with these contents: %@,",
              titleLabel.text);}

    self.startDate = [NSKeyedUnarchiver unarchiveObjectWithFile:deadline];
    [self refreshLabel];

    [NSTimer scheduledTimerWithTimeInterval:1
                                     target:self
                                   selector:@selector(refreshLabel)
                                   userInfo:nil
                                    repeats:YES];
}

-(void)refreshLabel {

    NSDate *todaysDate = [NSDate date];

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

    NSUInteger unitFlags = NSDayCalendarUnit | NSMinuteCalendarUnit | NSHourCalendarUnit | NSSecondCalendarUnit;
    NSDateComponents *dateComparisonComponents = [gregorian components:unitFlags fromDate:todaysDate toDate:self.startDate options:NSWrapCalendarComponents];
    NSInteger days = [dateComparisonComponents day];
    NSInteger hours = [dateComparisonComponents hour];
    NSInteger minutes = [dateComparisonComponents minute];
    NSInteger seconds = [dateComparisonComponents second];

    self.timerLabel.text = [NSString stringWithFormat:@"%ld:%02ld:%02ld:%02ld", (long)days, (long)hours, (long)minutes, (long)seconds];
    if (days == 0 && hours == 0 && minutes == 0 && seconds == 0) {
        [self.timer invalidate];
        NSLog(@"Time's up!");
    }
}

Answer 1

根据我们昨晚的讨论，您不能以这种方式使用日期格式化程序，因为您查看的是 future 的时间，例如 1 天 2 小时 5 分钟，而不是日期。一种方法是将选取器的选定日期传递给图像选取器 Controller ，并执行与在第一个 Controller 中所做的几乎相同的操作来获取日期组件。所以在第一个 Controller 中，将选择器日期保存到文件而不是字符串:

-(IBAction)refreshLabel; {

    NSDate *selected = [NSDate dateWithTimeIntervalSince1970:[picker.date timeIntervalSince1970] - 1];
    self.counter = [self.formatter stringFromDate:selected];
    NSLog(@"selected is: %@", selected);
    NSDate *todaysDate = [NSDate date];

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

    NSUInteger unitFlags = NSDayCalendarUnit | NSMinuteCalendarUnit | NSHourCalendarUnit | NSSecondCalendarUnit;
    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.counter = [NSString stringWithFormat:@"%ld:%02ld:%02ld:%02ld", (long)days, (long)hours, (long)minutes, (long)seconds];
    self.textField.text = self.counter;
    NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSString *deadline = [NSString stringWithFormat:@"%@/deadline.txt", documentsDirectory];
    NSInteger success = [NSKeyedArchiver archiveRootObject:selected toFile:deadline];
    NSLog(@"success is: %d",success);
}

然后在图像选择器 Controller 中(我只显示计时器标签所需的代码):

- (IBAction)startCamera:(id)sender {

    NSString *documentsDirectory = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
    NSString *deadline = [NSString stringWithFormat:@"%@/deadline.txt", documentsDirectory];
    NSError *fileError;
    self.startDate = [NSKeyedUnarchiver unarchiveObjectWithFile:deadline];
    [self refreshLabel];
    if(fileError.code == 0){
        NSLog(@"deadline.txt was read successfully with these contents: %@,", self.timerLabel.text);
        self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(refreshLabel) userInfo:nil repeats:YES];
    }
}


-(void)refreshLabel{
    NSDate *todaysDate = [NSDate date];

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

    NSUInteger unitFlags = NSDayCalendarUnit | NSMinuteCalendarUnit | NSHourCalendarUnit | NSSecondCalendarUnit;
    NSDateComponents *dateComparisonComponents = [gregorian components:unitFlags fromDate:todaysDate toDate:self.startDate options:NSWrapCalendarComponents];
    NSInteger days = [dateComparisonComponents day];
    NSInteger hours = [dateComparisonComponents hour];
    NSInteger minutes = [dateComparisonComponents minute];
    NSInteger seconds = [dateComparisonComponents second];

    self.timerLabel.text = [NSString stringWithFormat:@"%ld:%02ld:%02ld:%02ld", (long)days, (long)hours, (long)minutes, (long)seconds];
    if (days == 0 && hours == 0 && minutes == 0 && seconds == 0) {
        [self.timer invalidate];
        NSLog(@"Time's up!");
    }
}