Multitasking is supported in iOS 4 or above. When the user exits from an app by pressing the device's home button, the app is moved into the background rather than being fully closed. This can also occur for a variety of other reasons, such as the user accepting an incoming call or the app itself launching another application.
When the user, or some other application, launches the app again, it can simply continue where it left off rather than being completely re-loaded. This also significantly reduces the start-up time when you return to the app.
Events are dispatched when your application is moved to the background, or resumed by the operating system. This recipe will explain how to listen for and capture these events.