When should I release the current UIViewController when transitioning to a new one?

Question

I am trying to understand how to properly release the view controller I'm currently in during a transition to a new one. Here's my code:

// First create a CATransition object to describe the transition
CATransition *transition = [CATransition animation];
transition.duration = 0.3;
...

// Add the transition to the current view's superview
[self.view.superview.layer addAnimation:transition forKey:nil];

// Put together the controllers for the new screen
MainMenuController *menu = [[MainMenuController alloc] initWithNibName:@"MainMenuController" bundle:[NSBundle mainBundle]];
UINavigationController *nav = [[UINavigationController alloc] initWithRootViewController:menu];

// Transition
[self.view.superview addSubview:nav.view];
[self.view removeFromSuperview];

// These can now be released
[menu release]; // <- This works okay
[nav release];  // <- This causes problems

The problem theoretically makes sense to me. The variable menu is okay to release, because when I assigned it as the root view controller of my newly minted UINavigationController, the nav controller retained the menu. But I don't see anywhere that nav itself is potentially being retained, and sure enough, when I release as above, my UI goes all wonky. (It doesn't crash, but the entire menu UI is missing.)

I guess what I don't understand is when I'm expected to release nav. I mean, the view controller executing this code is not long for this world, so it can't do it. Where should I put the call?

Answer 1

You shouldn't do it this way, for the reasons you have discovered.

You need a third controller, up above the two you're transitioning, to hold the nav controller, so that controller 1 can deallocate itself.

Answer 2

[self.view.superview addSubview:nav.view]; 

I don't feel good with this code. I think you can tell your superView's controller do this task by using delegate or notification.

The superView contain nav.view, so its controller should also retain nav.view's controller.