applicationWillEnterForeground()
Tells the delegate that the app is about to transition from the background to the foreground.
Declaration
optional func applicationWillEnterForeground()Discussion
The system calls this method when the app transitions from the background to the foreground. Override this method to undo many of the changes you made to your app upon entering the background. The call to this method is invariably followed by a call to the applicationDidBecomeActive() method, as the app moves from the inactive to the active state.