updating UILabel from appDelegate

Question

I have been having this issue from last couple of hours and did all the search that i could but unfortunately, i didnt find anything that resolves my issue.... Scenario: i have a CountDownTimer in TimerViewController, NSTimer and other methods are set up in AppDelegate which is suppose to update TimerViewController's Label... as per label's setter, i'm getting the value correctly and its showing in the NSLog HOWEVER, the label is not updating on the screen... this setter is being called from AppDelegate every second and the Label is suppose to show the Timer,

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

I have double checked the label, it hooked up with interface correctly, i tried to update the label from ViewDidLoad with test String, the label was showing me the string... Help please!

EDIT: AppDelegate Code:

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

I resolved this issue following the below code by jabobadilla

I actually solved it by performing a method that will go and retrieve the value that the NSTimer is updating in my AppDelegate, since the method firing the NSTimer is no longer in the main thread when I leave the view and come back to it. This method will loop as long as my NSTimer is valid. I also placed a delay, allowing for the UI to update the value, and then perform the method again. Here is the code in case it helps someone running into a similar issue. I got this idea from the suggestion provided by chandan, thanks!!

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];
    } 

}

Answer 2

There may be problem in your IBOutlet....

Try to create a programatic UILabel and pass the _mainTimerLabel value to that label....

This may help you..