Some of the behaviours of UIApplications:
- It works along with the app delegate object which contains app-level logic.
- Control the app’s response to changes in interface orientation.
- Register for remote notifications.
- Extend the execution of the app so that it can finish a task in the background.
- Schedule and cancel local notifications.
- Coordinate the reception of remote-control events.
(A major role of a UIApplication object is to handle the initial routing of incoming user events. It also dispatches action messages forwarded to it by control objects (UIControl) to the appropriate target objects.)