title: How can I detect if the notification center was opened
body: <p>In a cocos2dx project, on iOS 10 devices, when the notification center is swiped down then up, a huge frame rate drop happens. As a result, when the animations resume ui elements whose motion depends on the delta t are moved to invalid positions. It looks to me that the OS is putting the app in some kind of a background mode but the <code>applicationDidEnterBackground</code> is not called.
  Is there a way to receive an event when the notification center is swiped down/up?</p>