NSTimer disables dealloc in UIView

Question

@interface someview:UIView{
  NSTimer* timer;
}
@end

@implementation someview

-(void)dealloc{
  NSLog(@"dealloc someview");
  [timer invalidate];
  timer = nil;
}
-(void)runTimer{
//
}
-(void)someMethod{

  timer = [NSTimer timerWithTimeInterval:2.0f target:self selector:@selector(runTimer) userInfo:nil repeats:YES];
}

@end

Releasing someview will NOT call dealloc and the timer keeps on running.

If I comment out the "timer = [NSTimer schedule...." part, dealloc will be called. Which means all the other part of my code is working properly and the timer is the culprit. The runTimer method is empty, which means it's just the timer messing with me.

Answer 1

As mentioned above, Timers retain their targets. Until the timer is invalidated, there is a retain cycle between the timer and the view, so the view will not be deallocated.

I would invalidate the timer when it's removed from the view hierarchy by subclassing didMoveToSuperview, this gets called by the system when there is a View-Related Change (e.g superview changes). The 'removeFromSuperview' is only called when removeFromSuperview is called on UIView

- (void)didMoveToSuperview
{
    [super didMoveToSuperview];

    if (!self.superview)
    {
        [timer invalidate];
        timer = nil;
    }
}

Answer 2

I think the best solution when using an NSTimer inside of a UIView is to override the removeFromSuperview method;

- (void)removeFromSuperview
{
    [timer invalidate];
    timer = nil;

    [super removeFromSuperview];
}

The only thing to keep in mind here is that you need to ensure that timer is not a nil object because removeFromSuperview can also get automatically called from other UIView's super dealloc methods. You could wrap in a conditional to check.

Answer 3

NSTimer retains the target. Therefore, the timer must be invalidated before your view is dealloc'd.