iOS Programming: The Big Nerd Ranch Guide, 6th Edition

Launch Screen

Another item you should set for the project is the launch image, which appears while an application is loading. The launch image has a specific role in iOS: It conveys to the user that the application is indeed launching and depicts the UI that the user will interact with once the application loads. Therefore, a good launch image is a content-less screenshot of the application. For example, the Clock application’s launch image shows the four tabs along the bottom, all in the unselected state. Once the application loads, the correct tab is selected and the content becomes visible. (Keep in mind that the launch image is replaced after the application has launched; it does not become the background image of the application.) ...