iphone - 从 appDelegate 更新 UILabel

Question

过去几个小时我一直遇到这个问题，我做了所有我能做的搜索，但不幸的是，我没有找到任何可以解决我的问题的东西......场景:我在 TimerViewController 中有一个 CountDownTimer，在 AppDelegate 中设置了 NSTimer 和其他方法，它应该更新 TimerViewController 的标签......根据标签的 setter ，我正确地获取了值并且它在 NSLog 中显示但是，标签没有在屏幕上更新...每秒从 AppDelegate 调用此 setter 并且标签应该显示计时器，

- (void)setMainTimerLabel:(UILabel *)mainTimerLabel 
  {
    _mainTimerLabel = mainTimerLabel;
    NSLog(@"ValueUpdated %@",_mainTimerLabel); 
  }

我仔细检查了标签，它正确地连接了接口(interface)，我尝试用测试字符串从 ViewDidLoad 更新标签，标签向我显示了字符串...请帮忙!

编辑:AppDelegate代码:

AppDelegate.h

@property (nonatomic, strong) TimerViewController *TimerVC;

- (void)fireTimer;

AppDelegate.m

- (void)fireTimer
{
    self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(countDownTimer) userInfo:nil repeats:YES];
}

- (void) countDownTimer
{
    .......
   TimerVC = [[TimerViewController alloc]init];
    self.TimerVC.mainTimerLabel = [NSString stringWithFormat:@"%02d:%02d:%02d",hours,minutes,seconds];
    .......
}

Answer 1

我按照 jabobadilla 的以下代码解决了这个问题

我实际上通过执行一个方法来解决它，该方法将去检索 NSTimer 在我的 AppDelegate 中更新的值，因为当我离开 View 并返回它时，触发 NSTimer 的方法不再在主线程中.只要我的 NSTimer 有效，这个方法就会循环。我还放置了一个延迟，允许 UI 更新值，然后再次执行该方法。这是代码，以防它帮助遇到类似问题的人。我从 chandan 提供的建议中得到了这个想法，谢谢!!

AppDelegate.h

@interface AppDelegate : UIResponder <UIApplicationDelegate> {

}

@property (nonatomic, retain) NSTimer *countdownTimer;
@property (nonatomic, retain) NSString *timeString;

CountdownTimerViewController.h

@interface CountdownTimerViewController : UIViewController {

AppDelegate *appdelegate;

}

@property (strong, nonatomic) IBOutlet UILabel *labelCountdownTimer;

@property (strong, nonatomic) IBOutlet UIButton *buttonStartTimer;
@property (strong, nonatomic) IBOutlet UIButton *buttonStopTimer;

- (IBAction)startTimer:(id)sender;
- (IBAction)stopTimer:(id)sender;

CountdownTimerViewController.m

@implementation CountdownTimerViewController

@synthesize labelCountdownTimer;

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
        // Custom initialization
    }
    return self;
}

- (void)viewDidLoad
{
    [super viewDidLoad];
        // Do any additional setup after loading the view.

    //Instatiating Appdelegate
    if(!appdelegate)
        appdelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];

}

- (void) viewDidAppear:(BOOL)animated {

    if ([appdelegate.countdownTimer isValid]) {
        [self updateLabel];
    } else {
        labelCountdownTimer.text = @"00:00:00";
    }

}

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}

#pragma mark - Button Action Methods

- (IBAction)startTimer:(id)sender {

    [self updateCounter];

}

- (IBAction)stopTimer:(id)sender {

    [appdelegate.countdownTimer invalidate];
    labelCountdownTimer.text = @"00:00:00";

}

int countLimit=30; //seconds
NSDate *startDate;

- (void)updateCounter {

    labelCountdownTimer.text = @"00:00:00";
    startDate = [NSDate date];

    appdelegate.countdownTimer = [NSTimer scheduledTimerWithTimeInterval:1.0/10.0
                                                                  target:self
                                                                selector:@selector(countDown)
                                                                userInfo:nil
                                                                 repeats:YES];

}

  - (void)countDown {

    if([[NSDate date] timeIntervalSinceDate:startDate] >= countLimit) {
        [appdelegate.countdownTimer invalidate];
        return;
    }
    else {            
    NSDate *currentDate = [NSDate date];
    NSTimeInterval timeInterval = -([currentDate timeIntervalSinceDate:startDate]);
    NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval];
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"mm:ss"];
    [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];
    appdelegate.timeString = [dateFormatter stringFromDate:timerDate];
    labelCountdownTimer.text = appdelegate.timeString;
    }

} 


- (void) updateLabel {

    if ([appdelegate.countdownTimer isValid]) {
        labelCountdownTimer.text = appdelegate.timeString;
        [self performSelector:@selector(updateLabel) withObject:nil afterDelay:0.05];
    } 

}