iPhone Open Application Development

Transition Views

If there's one thing Apple is well known for, it's their devotion to aesthetics in their user interfaces. The effect of sliding pages left and right gives the user a sense of the flow of data through an application, or a sense of "forward" and "back." Even applications lacking a book type of structure can appreciate the smooth slide and fade transitions offered by UIKit. Transition views are objects that allow the current view on the screen to be swapped out smoothly and replaced by another view, with very little programming on the developer's part.

Creating a Transition

Transition views inherit from UIView, so they have most of the properties of a regular view, including a frame. To create a transition, the display region belonging to the view is passed to the transition's initWithFrame method.

UITransitionView *transitionView = [ [ UITransitionView alloc ]
    initWithFrame: viewRect ];

The same transition view can be used for multiple transition calls and even multiple transition types, so generally only one transition view is needed for a particular display region. If a navigation bar is being used, you must account for its presence by subtracting its height and coordinates from the transition view's display region:

UITransitionView *transitionView = [ [ UITransitionView alloc ]
     initWithFrame:
     CGRectMake(viewRect.origin.x, viewRect.origin.y + 48.0,
            viewRect.size.width, viewRect.size.height − 48.0
];

Once the transition has been created, it is added to the view in the ...