Follow sequence when a child view controller is removed

[singh88]

• (void) hideContentController: (UIViewController*) content {
  [content willMoveToParentViewController:nil];
  [content.view removeFromSuperview];
  [content removeFromParentViewController];
  }

https://developer.apple.com/library/archive/featuredarticles/ViewControllerPGforiPhoneOS/ImplementingaContainerViewController.html