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NSTimer not working on StopWatch App ONLY ON SIMULATOR (Shows static strange number)
#import <UIKit/UIKit.h>

@interface ViewController : UIViewController
{
    NSTimer *stopWatchTimer;
    NSDate *startDate;
}


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

- (IBAction)startButtonTapped:(id)sender;

- (IBAction)stopButtonTapped:(id)sender;

-(void)updateTimer;

@end

- (IBAction)startButtonTapped:(id)sender {

    stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:1.0
                                                      target:self
                                                    selector:@selector(updateTimer)
                                                    userInfo:nil
                                                     repeats:YES];
}


- (void)updateTimer
{
    NSDate *currentDate = [NSDate date];
    NSTimeInterval timeInterval = [currentDate timeIntervalSinceDate:startDate];
    NSDate *timerDate = [NSDate dateWithTimeIntervalSince1970:timeInterval];

    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"HH:mm"];
    [dateFormatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0.0]];

    NSString *timeString=[dateFormatter stringFromDate:timerDate];
    stopWatchLabel.text = timeString;
}


- (IBAction)stopButtonTapped:(id)sender {

    [stopWatchTimer invalidate];
}

- (IBAction)startButtonTapped:(id)sender {
    startDate = [NSDate date];

    stopWatchTimer = [NSTimer scheduledTimerWithTimeInterval:1.0
                                                      target:self
                                                    selector:@selector(updateTimer)
                                                    userInfo:nil
                                                     repeats:YES];
}

- (void)updateTimer
{
    NSDate *currentDate = [NSDate date];
    NSTimeInterval timeInterval = [currentDate timeIntervalSinceDate:startDate];

    NSInteger minutes = floor(timeInterval/60);
    NSInteger seconds = trunc(timeInterval - minutes * 60);

    NSString *timeString=[NSString stringWithFormat:@"%i:%02i", minutes, seconds];
    stopWatchLabel.text = timeString;
}

- (void)updateTimer
{
    NSDate *currentDate = [NSDate date];
    NSCalendar *calendar = [[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
    NSDateComponents *components = [calendar components:NSSecondCalendarUnit|NSMinuteCalendarUnit fromDate:startDate toDate:currentDate options:0];
    NSInteger minutes = [components minute];
    NSInteger seconds = [components second];

    NSString *timeString=[NSString stringWithFormat:@"%i:%02i", minutes, seconds];
    stopWatchLabel.text = timeString;
 }