NSTimer not firing the selector

问题:

In ios5.0 with ARC, in my rootviewcontroller I call a method in a security manager object that is held by the app delegate. In that method I setup the timer as below

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

However, this never fires the selector ie. updateModel: never gets called. What may be wrong? Is there another more efficient way I can do this without using NStimer?

回答1:

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];

回答2:

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];
    })

回答3:

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");
    });
}

回答4:

This line has several problems:

[[NSRunLoop currentRunLoop] addTimer:ApplicationDelegate.timer forMode:NSRunLoopCommonModes]; 

First, it should not be required at all. -scheduledTimerWithTimeInterval:... already adds the timer to the runloop. You do not need to add it again.

Second, the local variable timer is unrelated to the property ApplicationDelegate.timer (which is presumably nil at this point).

If you're talking to the application delegate so much that you've created something called ApplicationDelegate (a global? a macro?), you're talking to it too much. The application delegate is the delegate for the application; it assists in the application starting and stopping and responding to system events. The application delegate is not a place to store global variables. A timer is definitely not the kind of thing you'd fetch from another object in any case.