Question

Consider a container view controller with two child view controllers (A and B), both added with addChildViewController:. Then:

1. A.view is added to the container view
2. B is displayed by doing transitionFromViewController from A to B. B receives viewWillLayoutSubviews and all is good with the world.
3. The device rotates while displaying B. Only B receives the rotation calls (willRotateToInterfaceOrientation: et all).
4. 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];
                            }];
}