-(void)btnClick:(id)sender

{
    NSLog(@"btnClick");


    dispatch_queue_t queue=dispatch_get_global_queue(0, 0);
    dispatch_source_t timer=dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0), 2*NSEC_PER_SEC, 1*NSEC_PER_SEC);

    dispatch_source_set_event_handler(timer, ^{

        dispatch_async(dispatch_get_main_queue(), ^{
            self.label1.text=[NSString stringWithFormat:@"%d", arc4random_uniform(1000000)];
        });
    });

    dispatch_resume(timer);
}

//Define member varialbe for timer in header file
NSTimer* timerForLocationUpdate;

//Call createTimer to create timer that will execute in each 1 min

- (void) createTimer
{
    timerForLocationUpdate = [NSTimer scheduledTimerWithTimeInterval:60 /*Number of seconds*/
                                                              target:self
                                                            selector:@selector(updateLocation)
                                                            userInfo:nil
                                                             repeats:YES];

    [[NSRunLoop currentRunLoop] addTimer:timerForLocationUpdate
                                 forMode:NSRunLoopCommonModes];
}

//Method is called in each 1 min
- (void) updateLocation
{

}

NSTimer *t = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(yourMethod) userInfo:nil repeats:YES];
NSRunLoop *runner = [NSRunLoop currentRunLoop];
[runner addTimer:t forMode: NSDefaultRunLoopMode];

-(void)yourMethod{
    Self.label1.text = [NSString stringWithFormat:@"%d", arc4random_uniform(1000000)];
}

-(void)btnClick:(id)sender

{
    NSLog(@"btnClick");

    static dispatch_source_t timer;

    dispatch_queue_t queue=dispatch_get_global_queue(0, 0);
    timer=dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, 0, 0, queue);
    dispatch_source_set_timer(timer, dispatch_walltime(NULL, 0), 2*NSEC_PER_SEC, 1*NSEC_PER_SEC);

    dispatch_source_set_event_handler(timer, ^{

        dispatch_async(dispatch_get_main_queue(), ^{
            self.label1.text=[NSString stringWithFormat:@"%d", arc4random_uniform(1000000)];
        });
    });

    dispatch_resume(timer);
}