Question

Consider a UIViewController whose view contains the view of another UIViewController.

Is it correct to say that the parent UIViewController is responsible to call the lifecycle methods of the child controller? Methods such as:

- (void)viewWillAppear:(BOOL)animated;
- (void)viewDidAppear:(BOOL)animated;
- (void)viewWillDisappear:(BOOL)animated;
- (void)viewDidDisappear:(BOOL)animated;

For example:

- (void)viewWillAppear:(BOOL)animated {
    [super viewWillAppear:animated];
    [_childViewController viewWillAppear:animated];
}

If so, which methods must be called?

Is there a better way to do this? Clearly the above approach is not forward-compatible: if a new lifecycle method is added the parent class needs to be modified to propagate the call of the new method.

Or is nesting view controllers simply a bad idea and should be avoided?

Answer 1

The correct way to do this is to add the view controller as a child view controller. You need to maintain both a view hierarchy (adding the view as a subview) and a view controller hierarchy (adding the view controller as a child). All of the life cycle methods are then called for you.

The relevant methods are addChildViewController: and didMoveToParentViewController:.

There was a talk on view controller containment in WWDC 2011, I recommend watching the video.