Question

I’ve tried the following:

- (void)setupTimer {    
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(doSomething) userInfo:nil repeats:YES];
    objc_setAssociatedObject(self, &key, timer, OBJC_ASSOCIATION_RETAIN);
    [timer invalidate];
}

- (void)doSomething { /* ... */ }
- (void)afterDoingSomething { [objc_getAssociatedObject(self, &key) invalidate]; }

Yet, the timer doesn’t tick (I didn’t expected it to do so; this code just didn’t look much right to me) for some reason. Is there a way to make it… work?

Answer 1

You’re invalidating the timer immediately after creating and scheduling it. Remove the [timer invalidate]; line in -setupTimer:

- (void)setupTimer {    
    NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(doSomething) userInfo:nil repeats:YES];
    objc_setAssociatedObject(self, &key, timer, OBJC_ASSOCIATION_RETAIN);
}

From the documentation:

[invalidate] stops the receiver from ever firing again and requests
its removal from its run loop.

Am I correct in assuming that this code is in a category? Otherwise, I can’t think of a good reason to make the timer an associated object instead of just using a regular instance variable for it.