Question

Ok i want to create MULTIPLE timers that all start at a different time (25, 50,1 min, 1min 30s…) but i dont know how to make it stop when it reaches 0 and when it does reach zero, bring the “Player” to another view.

Heres my .h file

@interface ViewController :UIViewController {

IBOutlet UILabel *seconds;

NSTimer *timer;

int MainInt;
}

@end

And heres my .m file

@implementation ViewController

-(void)countDownDuration {

MainInt -= 1;

seconds.text = [NSString stringWithFormat:@"%i", MainInt];

}

-(IBAction)start:(id)sender {

MainInt = 25;

timer = [NSTimer scheduledTimerWithTimeInterval:1.0

                                         target:self
                                       selector:@selector(countDownDuration)
                                       userInfo:nil
                                        repeats:YES];
}

@end

Answer 1

NSTimer doesn’t do this automatically, but it’s trivial to add it to your countDownDuration method. For example:

-(void)countDownDuration {
  MainInt -= 1;
  seconds.text = [NSString stringWithFormat:@"%i", MainInt];
  if (MainInt <= 0) {
    [timer invalidate];
    [self bringThePlayerToAnotherView];
  }
}

Of course you want to create multiple timers. You could store each one in a different variable and give each one a different selector. But if you look at the documentation for NSTimer, the callback method actually takes the timer object as a selector; you’re ignoring it, but you shouldn’t be.

And meanwhile, you can store an object of any type you want as the userInfo for the timer, so that’s a good place to stash a separate current countdown value for each timer.

So, you can do something like this:

-(void)countDownDuration:(NSTimer *)timer {
  int countdown = [[timer userInfo] reduceCountdown];
  seconds.text = [NSString stringWithFormat:@"%i", countdown];
  if (countdown <= 0) {
    [timer invalidate];
    [self bringThePlayerToAnotherView];
  }
}

-(IBAction)start:(id)sender {
  id userInfo = [[MyCountdownClass alloc] initWithCountdown:25];
  timer = [NSTimer scheduledTimerWithTimeInterval:1.0
                                           target:self
                                         selector:@selector(countDownDuration:)
                                         userInfo:userInfo
                                          repeats:YES];
}

I’ve left a few details unwritten (like the definition of MyCountdownClass—which has to include method initWithCountdown: and reduceCountdown that do the right thing), but they should all be pretty simple. (Also, presumably you want a userInfo that stores more than just the countdown value—e.g., if each timer sends the player to a different view, you’ve got to stash the view there as well.)

PS, notice that you now need @selector(countDownDuration:). Newcomers to ObjC screw this up all the time. countDownDuration: and countDownDuration are completely unrelated selectors.

PPS, the full definition of MyCountdownClass will have to be visible in countDownDuration: (unless you have some other class with the same selectors). You may want to explicitly cast the result of userInfo to MyCountdownClass * to make things clearer.