Programming iOS 6, 3rd Edition

Container View Controllers

Built-in view controller subclasses such as UITabBarController, UINavigationController, and UIPageViewController are parent view controllers: they accept and maintain child view controllers and manage swapping their views into and out of the interface. Such abilities and behaviors are formalized and generalized into the notion of a container view controller, so that your own custom UIViewController subclasses can do the same thing.

A UIViewController has a childViewControllers array, which is maintained for you. To act as a parent view controller, your UIViewController subclass must fulfill certain responsibilities.

When a view controller is to become your view controller’s child, your view controller must do these things, in this order:

• Send addChildViewController: to itself, with the child as argument. The child is automatically added to your childViewControllers array and is retained.
• Get the child view controller’s view into the interface (as a subview of your view controller’s view), if that’s what adding a child view controller means.
• Send didMoveToParentViewController: to the child with your view controller as its argument.

When a view controller is to cease being your view controller’s child, your view controller must do these things, in this order:

• Send willMoveToParentViewController: to the child with a nil argument.
• Remove the child view controller’s view from your interface.
• Send removeFromParentViewController to the child. The child is automatically ...