NSTimer automatically increases when I change view controller - ios

Question

In my viewController I inserted a timer for a calculation of numbers taken directly from my database of Parse.com.
The timer is working correctly, were inserted in viewDidAppear and in ViewDidDisappear in such a way as to lock the sequence when changing view controller.
The problem I have is that when I change the view controller with the Push the timer does not stop you give an example:
I open the application and the calculation is done correctly with the animation of NSTimer.
Change View, and then I go back with the back button to view where the timer at this point I see that the numbers contiunano to increase every time I change view and go back ...
Can you explain where I'm wrong?
-(void)viewDidAppear:(BOOL)animated {
[[UIApplication sharedApplication] setStatusBarHidden:NO withAnimation:UIStatusBarAnimationSlide];
[self.navigationController.navigationBar setBackgroundImage:[UIImage new]forBarMetrics:UIBarMetricsDefault];
self.navigationController.navigationBar.shadowImage = [UIImage new];
[self.navigationController.navigationBar setBackgroundColor:[UIColor clearColor]];
self.title = NSLocalizedString(#"", nil);
[self animatelayertopoint:0];
[self AnimationMenuView:600];
[self QueryForViewPrincipal];
[self QueryForCollectionView];
[self ShowBadgeNumber];
[self Timer];
[collectionView reloadData];
}
-(void)Timer{
timer = [NSTimer scheduledTimerWithTimeInterval:0.012 target:self selector:#selector(CalcoloMediadiLaurea) userInfo:nil repeats:YES];
}
-(void) CalcoloMediadiLaurea{
PFUser *CurrentUser = [PFUser currentUser];
NSNumber *NumeroUndici = [NSNumber numberWithInt:11];
NSNumber *NumeroTre = [NSNumber numberWithInt:3];
NSNumber *ValoreMediaPonderata = [CurrentUser objectForKey:FF_USER_MEDIA_PONDERATA];
int FFValoreTre = [NumeroTre intValue];
int FFValoreUndici = [NumeroUndici intValue];
double MediaPonderata = [ValoreMediaPonderata doubleValue];
double RisultatoMoltiplicazioneValoriPonderataUndici;
RisultatoMoltiplicazioneValoriPonderataUndici = MediaPonderata * FFValoreUndici;
double RisultatoMediaLaurea;
RisultatoMediaLaurea = RisultatoMoltiplicazioneValoriPonderataUndici / FFValoreTre;
CalcoloMediaLaureaLabel.text = [NSString stringWithFormat:#"%.1f", FFTickValoreMediaLaurea ];
FFTickValoreMediaLaurea++;
if(FFTickValoreMediaLaurea > RisultatoMediaLaurea){
[timer invalidate];
timer = nil;
}
}
-(void)viewDidDisappear:(BOOL)animated {
[self animatelayertopoint:0];
[self AnimationMenuView:600];
[self CalcoloMediadiLaurea];
}

Answer 1

The timer get rescheduled again on view did appear without getting invalidated to the previous one.You should make instance of timer in .h and then hold the reference of timer in it .And on view did appear when you are scheduling the timer just invalidate it and then schedule it again.
if([self.timer isValid])
{
[self.timer invalidate];
self.timer=nil;
self.timer=[NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:#selector(CalcoloMediadiLaurea:) userInfo:nil repeats:YES];
}

Answer 2

This worked for me which is along the lines of the above answer but a little more explicitly stated.
- (void)viewWillAppear:(BOOL)animated
{
NSTimeInterval secondsBetween = [endDate timeIntervalSinceDate:currentTime];
secondsLeft = secondsBetween;
[self countdownTimer];
}
- (void)viewDidDisappear:(BOOL)animated
{
[self.timer invalidate];
self.timer = nil;
}
//Initiates timer
- (void)countdownTimer
{
[self.timer invalidate];
self.timer = nil;
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:#selector(updateCounter:) userInfo:nil repeats:YES];
}

Answer 3

It's because you are creating new timers without invalidating old ones. The timers don't get invalidated automatically, you have to do it yourself. So if U go on second view and return before your invalidate condition is true you will create new timer and have two of them :)... And so on.