iPhone Open Application Development

Navigation Bars

The iPhone doesn't support toolbars in the traditional desktop sense. Because each screen of an application is considered a page in a book, Apple has made their version of the toolbar for iPhone to appear more book-like as well. In contrast to toolbars, which can display a clutter of different icons, navigation bars are limited to include a page title (e.g., "Saved Messages"), directional buttons to parent pages, and text buttons for context-sensitive functions such as turning on the speakerphone or clearing a list of items. Navigation bars can also support controls to add tabbed buttons such as the "All" and "Missed" call buttons when viewing recent calls.

Creating a Navigation Bar

To create a navigation bar, instantiate it as an object and call its initWithFrame method—just like a UIView.

UINavigationBar *navBar = [ [UINavigationBar alloc]
    initWithFrame: CGRectMake(0, 0, 320, 48)
];

The above creates a navigation bar 48 pixels high (the default) at position 0x0 (the upper-left corner of its parent view). This is the general convention, but a navigation bar can be created anywhere within the window. By using a different vertical offset, you can place the navigation bar at the bottom of the window or underneath another navigation bar.

To know when something happens on the navigation bar, such as a button press, use the navigation bar's delegate. A delegate is an object that acts on behalf of another object. By setting the navigation bar's delegate to self, you can ...