NSTimer doesn't stop

问题:

I've got a timer which fires when the viewWillAppear method is being called and invalidates when the viewDidDisappear method is being called. But after a certain amount of switching between views the timer continues firing even after it was invalidated. What's the problem?

Here is my code:

NSTimer *timer;

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    timer = [NSTimer scheduledTimerWithTimeInterval: 0.2f
                     target: self
                     selector:@selector( timerAction )
                     userInfo:nil
                     repeats:YES];
}

-(void)viewDidDisappear:(BOOL)animated {
    [super viewDidDisappear:animated];
    [timer invalidate];
    timer = nil;
}

-(void) timerAction
{
    NSLog(@"timerAction");
}

回答1:

I should have been keeping a link to the timer by retaining it. :) I've asked this question 5 months ago, and it's amazing, how much more experience I acquired. :)

timer = [ [NSTimer scheduledTimerWithTimeInterval: ...] retain];
...
...
[timer invalidate];
[timer release];

回答2:

This is an absolute solution. None of the ones above worked for me, so I did this,

where you want to start the timer,

[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerMethod) userInfo:nil repeats:NO];

The method that the timer calls,

-(void)timerMethod
{
    // do what you need to do

    if (needs to be called again) {

        [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(timerMethod) userInfo:nil repeats:NO];        
    }
}

hope this helps,

回答3:

A method called by a timer should have the definition

- (void)methodName:(NSTimer *)aTimer;

This way the method has the instance of timer which was fired. The way you are doing it, the method will not know whether the timer was invalidated or not.

Try changing your timer initialization to

timer = [NSTimer scheduledTimerWithTimeInterval: 0.2f target: self selector:@selector(timerAction:) userInfo:nil repeats:YES]

and the method to

-(void) timerAction:(NSTimer *)aTimer{...}

Hope that helps

回答4:

This may not be the issue, but you need to retain the reference to timer that is returned from scheduledTimerWithInterval:. Without doing this, your pointer to the timer might be invalid by the time you go to stop it.

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    timer = [[NSTimer scheduledTimerWithTimeInterval:0.2f target:self selector:@selector(timerAction) userInfo:nil repeats:YES] retain];
}

- (void)viewDidDisappear:(BOOL)animated
{
    [timer invalidate];
    [timer release];
    timer = nil;
    [super viewDidDisappear:animated];
}

- (void)dealloc
{
    [timer invalidate];
    [timer release];
    timer = nil;
    [super dealloc];
}

Also, try setting a breakpoint in viewDidDisappear and make sure it's getting called!

回答5:

**In .h class**

@interface 
{
NSTimer * theTimer;

}


**in .m class**

//put this code where you want to calling the NSTimer function

        theTimer = [NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:@selector(updateCounter:) userInfo:nil repeats:YES];



- (void)updateCounter:(NSTimer *)theTimer 
{

   // write your code here for counter update 

}


// put this code to Stop timer:

    [theTimer invalidate];
    theTimer = nil;

回答6:

This did the trick to me in Swift

override func viewWillDisappear(animated: Bool) {
    super.viewWillDisappear(animated)

    dispatch_async(dispatch_get_main_queue(),{ [weak self] in

        self?.idleTimer?.invalidate()
        self?.idleTimer = nil

    })

}

回答7:

You have forgotten to release the timer in viewWillDisappear:

- (void)viewDidDisappear:(BOOL)animated
{
    [super viewDidDisappear:animated];
    [timer invalidate];
    [timer release];
    timer = nil;
}

_{This shouldn't cause the timer to keep firing though...}

回答8:

Of invalidate the doco says

"The run loop removes and releases the timer, either just before the invalidate method returns or at some later point."

I suppose yours is getting removed at some later point.

回答9:

I had the same problem.

I can't dealloc my instance if the timer is still running, so I have to stop it before calling :

- (void)stopTimer
{
    [timer invalidate];
    [timer release];
    timer = nil;
}

After calling this method my timer really stop

回答10:

- (void)viewWillAppear:(BOOL)animated gets called again.

In fact it gets called every time you switch views or after you dismiss a modal view. Basically any time your view actually reappears on screen, not just the first time.

So in this case the timer gets restarted, even though is was invalidated before.

回答11:

After creating your timer just register it to run in NSRunLoopCommonModes:

[[NSRunLoop currentRunLoop] addTimer:myTimer forMode:NSRunLoopCommonModes];

Then invalidate method will work.

回答12:

This works for me

dispatch_async(dispatch_get_main_queue(), ^{
    [timer invalidate];
});