How a view controller know when it is dismissed or popped out of the navigation controller stack?

My view controller needs to know when it is popped out of the 开发者_StackOverflow社区navigation controller stack, so that it can retain itself, wait and release itself later with another notification.

I intend to do like that when the view is sent dealloc message:

- (void)dealloc {
    if (self.isPerformingSomeTask) {
        self.isPopedOut = YES;
        [self retain];
        return;
    }
    [super dealloc];
}

But I think this is not a good solution?

This is an extremely bad idea.

1. "-dealloc" is not the place to retain the object that is deallocated. If you want to be absolutely sure, that your object is not deallocated, then retain it upon construction, e.g. in "-viewDidLoad"
2. "-dealloc" is not a way to detect that a view is popped from the navigation stack. You could be deallocated for any reason or the deallocation could be delayed even though you were popped from the stack
3. If you want to detect, that the view is not displayed anymore, you should look for "-viewWillDisappear:"
4. The pope has nothing to do with it, so don't pope out your views :-)
5. If you need some object to receive the results of a long running task, probably your AppDelegate is a better receiver, not the view controller

EDIT: The following code refers to my comment below:

So you code should look like this

- (void) startMyLongTask {
  [self retain];
  // start the task
}

- (void) longRunningTaskReturns {
  // process results
  [self release];
}

- (void) dealloc {
  // as long as longRunningTaskReturns is not called
  // you will never come here
  [super dealloc];
}