On state transitions can be responded to state changes in an appropriate way by calling corresponding methods on app's delegate object.

Example:

☛ applicationDidBecomeActive method can be used to prepare to run as the foreground app.

☛ applicationDidEnterBackground method can be used to execute some code when app is running in the background and may be suspended at any time.

☛ applicationWillEnterForeground method can be used to execute some code when your app is moving out of the background

☛ applicationWillTerminate method is called when your app is being terminated.