NSTimer crashes with EXC_BAD_ACCESS on Iphone when canceling

Question

I set two timers in my application that repeat every few seconds. Everything works fine, except when it's time to cancel the timers. When the phone is locked, I want to cancel these timers and then recreate them when the phone is unlocked.

I use notifications to figure out when to invalidate / create 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 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 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, I get an error. The strange thing is that if I switch the orders of the timers (for example, clockTicker is invalidated first). I still have an error in the second timer.

What can i do wrong?

Thanks Leonardo

Answer 1

invalidate , , . , ... , .

Answer 2

alarmTicker clockTicker , , , (alarmTicker), (clockTicker) .

Answer 3

, NULL , , -, -op. NULL, , , . : NULL vs nil in Objective-C