NSTimer crash with EXC_BAD_ACCESS on Iphone when invalidate

Question

I have setup two timers in my application which both repeats every a few seconds. Everything works fine except when is time to invalidate the timers. When the phone is locked, I want to invalidate those timers and then recreate them when the phone is unlocked.

Im using the notifications to realize when to invalidate/create the timers.

 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(notify_didBecomeActive:) name:UIApplicationDidBecomeActiveNotification object:nil];
 [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(notify_willResigneActive:) name:UIApplicationWillResignActiveNotification object:nil];

This is what the notify_didBecomeActive method contains:

clockTicker = [[NSTimer scheduledTimerWithTimeInterval: 1  
           target: self  
            selector: @selector(showActivity)  
            userInfo: nil  
             repeats: YES] retain];

alarmTicker = [[NSTimer scheduledTimerWithTimeInterval: CONST_ALARMTIMER  
              target: self  
            selector: @selector(checkAndLaunchAlarm)  
            userInfo: nil  
             repeats: YES] retain];

This the notify_willResigneActive method contains:

if (alarmTicker) {
 [alarmTicker invalidate];
 [alarmTicker release];
 alarmTicker = NULL;
}

if (clockTicker) {
 [clockTicker invalidate];
 [clockTicker release];
 clockTicker = NULL;
}

The problem is that when I debug this on the second timer invalidate I get the error. The weird thing is that if I switch the orders of the timers (like first invalidate the clockTicker).. I still got the error on the second timer.

What could I be doing wrong?

Thanks, Leonardo

Answer 1

invalidate releases the timer, no need to release after invalidating, thats why its crashing. But i just noticed that you are retaining the timer...im not sure that this is necessary either.

Answer 2

I'm not sure what setting the timer to NULL does as opposed to setting it to nil, but I know that if you make a call on a nil object, it's a no-op. If you make a call on a NULL object, it think it crashes, though I haven't verified this. This post might help: http://stackoverflow.com/questions/557582/null-vs-nil-in-objective-c