I know that starting with iOS5 and the new UIViewController containment methods, you are supposed to call these methods together with addChildViewController:, removeFromParentViewController: and the transition method. I also know the proper order of calling them in the three scenarios. What I don't know is what exactly these methods do?
If these were merely override points for subclasses of UIViewController I guess we wouldn't be required to call super when overriding. What can/will go wrong if I don't call willMoveToParentViewController: nil before removing a view controller or didMoveToParentViewController: self?
In addition to what has been said, they do call some delegate methods:
addChildViewController
calls [child willMoveToParentViewController:self]
and removeFromParentViewController:
calls [child didMoveToParentViewController:nil]
Also, they modify the childViewControllers
property, which holds an array of child view controllers.