Sporadic zombie NSTimer - ios

Question

I have a timer in a UIViewController:
#interface MyViewController : UIViewController <UITableViewDataSource,UITableViewDelegate, MFMailComposeViewControllerDelegate>
...
#property (nonatomic, assign) int m_remaining_time;
...
#end
In .m file:
#interface MyViewController ()
{
NSTimer *m_timer;
}
The timer starts on viewDidAppear()
m_timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:#selector(decrementSpin) userInfo:nil repeats:YES];
The method decrementSpin simply decrements the counter and prints a log:
- (void)decrementSpin
{
self.m_remaining_time--;
if(self.m_remaining_time > 0) {
NSLog(#"[TIMER] >> %d", self.m_remaining_time);
}
else {
NSLog(#"[TIMER] >> Time finished!");
[m_timer invalidate];
m_timer = nil;
}
}
I destroy the timer in every case the ViewController will close:
In appDidEnterInBackground, viewDidDisappear, when a button that closes the view has been pushed (goind to next view for ex)
The problem is that, in some cases, I have seen in the simulator the log [TIMER] >> %d that keeps printing even after I closed the view.
It is not always the case, but sometimes it keeps counting.
Any clues ?
Edit:
#skaak, I do the following code in appDidEnterInBackground, viewDidDisappear:
if(m_timer) {
[m_timer invalidate];
m_timer = nil;
}
Then when the player pushes the "Next" and "Home" buttons.
For example the case of "Home" button:
-(IBAction)homeButtonPressed:(id)sender{
if(m_timer) {
[m_timer invalidate];
m_timer = nil;
}
[[NSNotificationCenter defaultCenter] removeObserver:self];
InitScreenViewController* initVc = [self.storyboard instantiateViewControllerWithIdentifier:#"initScreenViewController"];
UINavigationController *navVC = [[UINavigationController alloc] initWithRootViewController:initVc];
[navVC setNavigationBarHidden:true];
[UIView transitionWithView:[AppDelegate getShareInstance].window duration:0.1f options:UIViewAnimationOptionTransitionCrossDissolve animations:^{
[AppDelegate getShareInstance].window.rootViewController = navVC;
}completion:nil];
}
Edit #2:
I added the following flag:
#property (assign, nonatomic) BOOL isCurrentlyViewShowed;
Which is set on viewDidAppear (along with your suggestion):
self.isCurrentlyViewShowed = TRUE;
if(m_timer) {
[m_timer invalidate];
m_timer = nil;
}
m_timer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:#selector(decrementSpin) userInfo:nil repeats:YES];
Then, it is set to off everytime the view is closed:
if(m_timer) {
[m_timer invalidate];
m_timer = nil;
}
self.isCurrentlyViewShowed = FALSE;
And finally, on decrementSpin:
if(self.isCurrentlyViewShowed == FALSE){
if(m_timer) {
[m_timer invalidate];
m_timer = nil;
}
}
self.m_remaining_time--;
if(self.m_remaining_time > 0) {
NSLog(#"[TIMER] (%p)>> %d (FLAG: %d)", m_timer, self.m_remaining_time, self.isCurrentlyViewShowed);
}
else {
NSLog(#"[TIMER] (%p)>> Time finished (FLAG: %d)", m_timer, self.isCurrentlyViewShowes);
[m_timer invalidate];
m_timer = nil;
AudioServicesPlaySystemSound(kSystemSoundID_Vibrate);
}
I did repeated the test like 100 times and I managed to reproduce it once!
I left this view, and I saw on the log the line:
[TIMER] (0x2818ecfc0)>> 58 (FLAG: 1)
[TIMER] (0x2818ecfc0)>> 57 (FLAG: 1)
...
It means that somehow the View object is re-initialized ? I don't get it..

Answer 1

This is tricky, and need the whole code to try and isolate it. But here is an idea that might help. In fact, I think you need to do it like this anyhow. Change your viewDidAppear to something like below.
- viewDidAppear
{
if ( ! m_timer )
{
m_timer = ...
}
}
or, depending on the logic, to
- viewDidAppear
{
if ( m_timer )
{
[m_timer invalidate];
m_timer = nil;
}
m_timer = ...
}
In either case you will be sure you have only one timer running at a time which may be your problem.