iOS: Fire method at gradually increasing speed

Question

My game plays a ticking clock sound every second. I would like the sound to slowly speed up throughout the game. My initial thought was to use an NSTimer and update the speed when the method fires, like this:

static float soundDelay = 1.0;
timer = [NSTimer scheduledTimerWithTimeInterval:clickClackDelay
                                                     target:self
                                                   selector:@selector(playSound)
                                                   userInfo:nil
                                                    repeats:YES];

- (void)playSound {
    soundDelay -= 0.1;
    NSLog(@"Play sound");
}

This didn't work, and it seems like NSTimer isn't really meant to be used that way. Any other suggestions on how I could accomplish this?

Answer 1

You can implement it by calling the playSound method from itself. You can do it in the following way.

- (void)playSound
{
   static float soundDelay = 1.0;
   if([timer isValid])
   {
     [timer invalidate];
     timer = nil;
   }
   timer = [NSTimer scheduledTimerWithTimeInterval:clickClackDelay
                                                     target:self
                                                   selector:@selector(playSound)
                                                   userInfo:nil
                                                    repeats:NO];
    soundDelay -= 0.1;
    if(soundDelay <=0)   //when sound delay is zero invalidate timer
    {
       [timer invalidate];
       timer = nil;
    }
    NSLog(@"Play sound");
}