Programming iOS 6, 3rd Edition

Tab Bar Controllers

A tab bar (UITabBar, see also Chapter 25) is a horizontal bar containing items. Each item (a UITabBarItem) displays, by default, an image and a title. At all times, exactly one of these items is selected (highlighted); when the user taps an item, it becomes the selected item.

If there are too many items to fit on a tab bar, the excess items are automatically subsumed into a final More item. When the user taps the More item, a list of the excess items appears, and the user can select one; the user can also be permitted to edit the tab bar, determining which items appear in the tab bar itself and which ones spill over into the More list.

A tab bar is an independent interface object, but it is most commonly used in conjunction with a tab bar controller (UITabBarController, a subclass of UIViewController) to form a tab bar interface. The tab bar controller displays the tab bar at the bottom of its own view. From the user’s standpoint, the tab bar items correspond to views; when the user selects a tab bar item, the corresponding view appears. The user is thus employing the tab bar to choose an entire area of your app’s functionality. In reality, the UITabBarController is a parent view controller; you give it child view controllers, which the tab bar controller then contains, and the views summoned by tapping the tab bar items are the views of those child view controllers.

Familiar examples of a tab bar interface on the iPhone are Apple’s Clock app, which has four tab ...