Which function is called when iPhone app is terminated?

Question

I'm working on a project in Xcode version 4.2.1 and in iOS 5.0. I'm wondering which function will be called when you completely terminate an application, which means even the time when an users force the app running on background to be terminated from home screen. I was assuming that

(void)applicationWillTerminate:(UIApplication *)application

would be called, but it turned out it was not called even after terminating the app on background. What I basically want to do is to call a method that I created just before the app is completely terminated, so need to know which function is called at the end of the app.

Thank you.

Solution 1

"applicationWillTerminate" method will be called only when application is not in suspended state while being terminated.

To understand this, considering currently your application is in foreground active state, go through following two cases:

Case 1: When you single tap Home button, app directly goes to suspended state by calling methods - (1) applicationWillResignActive and then (2) applicationDidEnterBackground.

Now when you try to quit/terminate app, by double tapping home button and then swiping up the current app screen from recent app screens, app is in suspended state. So, "applicationWillTerminate" method will not be called.

Case 2: When you double tap Home button, app goes to inactive state by calling method - (1) applicationWillResignActive.

Now when you try to quit/terminate app, by swiping up the current app screen from recent app screens, app is in inactive state (not in suspended state) while being terminated. So, "applicationWillTerminate" method will be called.

Look what Apple say:

For more info on this look - Apple's Official Documentation on applicationWillTerminate(_:)

Solution 2

Here's a good overview of the application lifecycle notifications & delegate messages on iOS 4.0 and newer. In short...

Your app will generally never see willTerminate, because the system generally only terminates your app once it's already suspended (in the background). Once your app is suspended, it gets no further chance to act(*), so there's no callback for that.

The didEnterBackground delegate message or notification should be considered your last chance to clean things up or save state before possible termination.

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(*) Okay, your app can do stuff if it's in one of the supported background execution modes, like audio, VoIP, or navigation, but in that case it either hasn't been suspended yet or it's been un-suspended with an entry point specific to that background mode.

Solution 3

If the app is already suspended, it will not receive further notifications. Watch for the didEnterBackground notification.