Up until recently, the iOS user interface paradigm supported showing only a limited amount of material on the screen at any point in time. In a Cocoa Touch application, there’s typically one view controller in focus at a time, and that view controller is in charge of the whole screen (or most of it). The notable exceptions are classes like UINavigationController and UITabBarController, which don’t display any interesting content on their own, but instead help developers organize other view controllers.
Unable to display preview. Download preview PDF.