Changes

Navigation based applications present a hierarchical approach to displaying information to the user. Such applications typically take the form of a navigation bar (UINavigationBar) and a series of Table based views (UITableView). Selecting an item from the table list causes the view associated with that selection to be displayed. The navigation bar will display a title corresponding to the currently displayed view together with a button that returns the user to the previous view when selected. For an example of this concept in action, spend some time using the iPhone ''Mail '' or ''Settings '' applications.

When developing a navigation based application the central component of the architecture is the ''navigation controller''. In addition, each screen has a table view and a corresponding view controller. The navigation controller maintains a stack of these view controllers. When a new view is displayed it is ''pushed '' onto the navigation controller’s stackand becomes the currently active controller. When the user selects the button in the navigation bar to move back to the previous level, that view controller is ''popped '' off the stack and the view controller beneath it moved to the top as the currently active controller.

The view controller that represents for the first table view that appears when the application is started is called the ''root view controller''.