If your app has more than one content view hierarchy, you need to be able to transition between them. For this, you’ll use a specialized type of view controller: a navigation controller (
UINavigationController). Anavigation controller manages transitions backward and forward through a series of view controllers, such as when a user navigates through email accounts, inbox messages, and individual emails in the iOS Mail app.
The set of view controllers managed by a particular navigation controller is called its navigation stack. Thenavigation stack is a last-in, first-out collection of custom view controller objects. The first item added to the stack becomes the root view controller and is never popped off the stack. Other view controllers can be pushed on or popped off the navigation stack.
Although a navigation controller’s primary job is to manage the presentation of your content view controllers, it’s also responsible for presenting custom views of its own. Specifically, it presents a navigation bar—the view at the top of the screen that provides context about the user’s place in the navigation hierarchy—which contains a back button and other buttons you can customize. Every view controller that’s added to the navigation stack presents this navigation bar. You are responsible for configuring the navigation bar.
You generally don’t have to do any work to pop a view controller off of the navigation stack; the back button provided by the navigation controller handles this for you. However, you do have to manually push a view controller onto the stack. You can do this using storyboards