fired when an iOS application will stop being the focus.
This includes not only the user leaving the application, but also pauses due to notifications or calls. See applicationWillResignActive for the exact behavior that triggers this event.
Note that making calls to functions which modify the UI during this event may cause execution UP TO the UI call before the suspension, but then execute the REMAINDER of the callback after the application is resumed (but before the resume event is triggered).
Source object that fired the event.
Name of the event fired.