that the app which is running in foreground goes to inactive state and then it transitions to background state.he foreground app transitions to the inactive state and then to the background state. When the app goes to inactive state,app delegate's applicationWillResignActive: is called and when the app goes to background state,app delegate's applicationDidEnterBackground: method is called.
Apps that is waiting for some background tasks (such as playing music) or that has requested for some extra execution time from system may continue some background task for a while .
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