Transition between view controllers and rotation in iOS - iphone

Question

Consider a container view controller with two child view controllers (A and B), both added with addChildViewController:. Then:
A.view is added to the container view
B is displayed by doing transitionFromViewController from A to B. B receives viewWillLayoutSubviews and all is good with the world.
The device rotates while displaying B. Only B receives the rotation calls (willRotateToInterfaceOrientation: et all).
A is displayed by doing transitionFromViewController from B to A. A doesn't receive viewWillLayoutSubviews and thus the layout is broken.
Is this the expected behavior? If not, what might I be doing wrong? If yes, what should I do to notify A of the rotation change while displaying B?

Answer 1

As soon as you call addChildViewController: you are now a View Controller Container Implementer. This means you do have to do a little more work than a standard presentation call like presentViewController... This includes dealing with the frames of the views of the controllers you add as children, as your question suggests you might have expected.
For example, to implement a super basic example container, that just shows each child full screen, you could do something like this.
-(void)swapChildVCFrom:(UIViewController *)from to:(UIViewController *)to{
[self addChildViewController:to];
[from willMoveToParentViewController:nil];
// Adjust the new child view controller's view's frame
// For example here just set it to fill the parent view
to.view.frame = self.view.bounds;
[self transitionFromViewController:from
toViewController:to
duration:1.0
options:UIViewAnimationOptionTransitionFlipFromLeft
animations:nil
completion:^(BOOL b){
[to didMoveToParentViewController:self];
[from.view removeFromSuperview];
[from removeFromParentViewController];
}];
}

Answer 2

After A has been loaded and displayed, viewWillLayoutSubviews will not be called again unless A.view's bounds change. If you need your implementation to run each time the view comes on screen, you can try moving that code to viewWillAppear.

Answer 3

There are three solutions that I can think of:
Add all of your container's view controller's up front, and add their views, but hide all but the first one. Then in your method that transitions between the view controllers, you don't have to worry about the myriad containment related methods anymore (e.g. you don't need willMoveToParentViewController, addChildViewController, removeFromParentViewController, or didMoveToParentViewController), but rather just use the UIViewAnimationOptionShowHideTransitionViews option which will show or hide the appropriate views. This way, all the controllers get all the rotation notifications.
The second logical alternative would be to create only the first view controller up front. Then, when you want to transition to the second view controller, only then would you create it (and it's view). And make sure you don't keep a strong reference to the original controller (e.g. not only your own properties, but make sure to removeFromParentViewController, etc.). That will let it, and it's views, be deallocated. Thus, when you transition back, it will be recreated.
If you're creating your view controllers up front, but letting transitionFromViewController to add and remove their respective views to your container, then I think you'll probably have to invoke the appropriate child rotation events, like discussed in the Customizing Appearance and Rotation Callback Behavior in the View Controller Programming Guide.