NSTimer not firing the selector

Could also be a threading problem:

if

[NSThread isMainThread]

is false then start the timer like this:

dispatch_async(dispatch_get_main_queue(), ^{        timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(tick:) userInfo:nil repeats:YES];    })

You seem to be a bit mixed up with your timer variable.

You initialize a new timer but you aren't actually using it. Do you want to use the timer you initialized or do you want to you ApplicationDelegate.timer?

Here are the two possible solutions.

Option One (assuming that you have a class instance titled ApplicationDelegate and that it has a timer property):

ApplicationDelegate.timer = [NSTimer scheduledTimerWithTimeInterval:5.0 target:self selector:@selector(updateModel:) userInfo:str repeats:YES];[[NSRunLoop currentRunLoop] addTimer:ApplicationDelegate.timer forMode:NSRunLoopCommonModes];

Option Two:

NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:5.0 target:self selector:@selector(updateModel:) userInfo:str repeats:YES];[[NSRunLoop currentRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];

I catch the same issue and I fire timer in main queue to solve it:

[NSURLConnection sendAsynchronousRequest:request queue:_operationQueue    completionHandler:^(NSURLResponse *response, NSData *data, NSError *error){         [self loopUpUpdateStart];}];-(void)loopUpUpdateStart{    dispatch_async(dispatch_get_main_queue(), ^{        _loopTimerForUpRevision =           NSTimer scheduledTimerWithTimeInterval: kNetworkLoopIntervalUpRev                                          target: self                                        selector: @selector(myCoolMethod)                                        userInfo: nil                                         repeats: YES];        TRACE(@"Start Up updates");    });}