Question

I have an NSTimer object that I need to repeatedly execute. The code that it calls is ultimately toggles a setting in my application through 4 various states. Each time the state changes, I want my interval to change on my timer. This loop should continue throughout the lifetime of the application.

As far as I can tell, you can not update the interval property on an NSTimer. I believe this means that I need to add code to create a new NSTimer object each time I toggle my state within my timer code. The following implementation is what I am thinking:

//Consider that in my containing class, there is an NSTimer property, named myTimer.

//My selector method, used by myTimer
-(void) updateState:(NSTimer *) timer
{
    switch (AppState)
    {
    case state_1:
        //Update current state to state_2
        [self setMyTimer:[NSTimer scheduledTimerWithTimeInterval:30.0 
                                                          target:self 
                                                        selector:@selector(updateState:) 
                                            userInfo:nil repeats:NO];
        break;
    case state_2:
        //Update current state to state_3
        [self setMyTimer:[NSTimer scheduledTimerWithTimeInterval:5.0 
                                                          target:self 
                                                        selector:@selector(updateState:) 
                                            userInfo:nil repeats:NO];
        break;
    case state_3:
        //Update current state to state_4
        [self setMyTimer:[NSTimer scheduledTimerWithTimeInterval:30.0 
                                                          target:self 
                                                        selector:@selector(updateState:) 
                                            userInfo:nil repeats:NO];
        break;
    case state_4:
        //Update current state back to state_1
        [self setMyTimer:[NSTimer scheduledTimerWithTimeInterval:5.0 
                                                          target:self 
                                                        selector:@selector(updateState:) 
                                            userInfo:nil repeats:NO];
        break;
    }
}

Is this the most optimal solution or can the creation of all these timers cause any form trouble for my application as it continuously executes?

Also, I have ARC cut on within my project. In this case, will I still need to destroy the previous NSTimer objects?

Answer 1

can the creation of all these timers cause any form trouble for my application as it continuously executes?

Not as long as you’re managing the memory correctly. Using a synthesized setter will take care of this for you.

In this case, will I still need to destroy the previous NSTimer objects?

Not explicitly. When a non-repeating timer fires, it invalidates itself, and the run loop sends release (because it had retained it). If you’ve got a claim on it, you’ll need to release it too, which you do using the setter.

Since none of these timers are repeating, you could drop the ivar and instead use performSelector:withObject:afterDelay:

- (void)updateState {

    NSTimeInterval delay = 30;
    switch(AppState)
    {
        case 1: { break; }
        case 2: { delay = 5.0;
                  break; }
        case 3: { break; }
        case 4: { delay = 5.0;
                  break; }
    }

    [self performSelector:@selector(updateState) 
               withObject:nil 
               afterDelay:delay];

}

(By the way, I assume you’ve got breaks in your real code. You definitely should if you don’t.)