A Navigation Controller is a special kind of view controller that manages a stack of view controllers and their corresponding views. It's an ideal way to display hierarchical data.

The Navigation Controller is always initialized with a root view controller; this will be the starting view at the bottom of the stack. As the user presses buttons in that view, you can then push a new view controller onto the stack to show a new view. When the user is done with the new view and presses a button to go back, you then pop that controller of the stack to return to the root view. (A Navigation Controller can be used with or without a Navigation Bar.)

A navigation controller’s primary job is to manage the presentation of your content view controllers, and it is also responsible for presenting some custom views of its own. Specifically, it presents a navigation bar, which contains a back button and some buttons you can customize. A navigation controller can also optionally present a navigation toolbar view and populate it with custom buttons.

A navigation controller uses several objects to implement the navigation interface. You are responsible for providing some of these objects and the rest are created by the navigation controller itself. 

Specifically, you are responsible for providing the view controllers with the content you want to present. If you want to respond to notifications from the navigation controller, you can also provide a delegate object. The navigation controller creates the views—such as the navigation bar and toolbar—that are used for the navigation interface, and it is responsible for managing those views.

Objects managed by the navigation controller

For navigation bar and toolbar objects associated with a navigation controller, you can only customize some aspects of their appearance and behavior. The navigation controller alone is responsible for configuring and displaying them. In addition, a navigation controller object automatically assigns itself as the delegate of its UINavigationBar object and prevents other objects from changing that relationship.

You can modify the delegate and the other view controllers on the navigation stack. The navigation stack is a last-in, first-out collection of custom view controller objects that are managed by the navigation controller. The first item added to the stack becomes the root view controller and is never popped off the stack. Additional items can be added to the stack using the methods of the UINavigationController class.