In iOS 13, what events do I get when the user swipes my app up in the app switcher?

Question

I\'m finding it extraordinarily difficult to categorize and account for what events I get (or don\'t get) when the user swipes my app up in the app switcher on iOS 13. This

Answer 1

in my case, I want to save user state when the app is terminated by the user or the system, applicationWillTerminate(_:) does not being called for me most of the time.

I achieved what I want by using sceneWillResignActive(_ scene: UIScene)

Answer 2

Let's assume that your app supports window scenes. So what the user is swiping up in the app switcher is really a scene, not your app as a whole. Then the possibilities appear to be as follows.

On an iPhone

If the scene was frontmost:

• sceneDidEnterBackground
• applicationWillTerminate(_:)

But if the scene was not frontmost, you'll get nothing; you already received sceneDidEnterBackground, and you won't get applicationWillTerminate(_:) now because the app isn't running.

On an iPad, if the app does not support multiple windows

If the scene was frontmost:

• sceneDidDisconnect(_:)
• application(_:didDiscardSceneSessions:)
• applicationWillTerminate(_:)

But if the scene was not frontmost, you'll get nothing; you already received sceneDidEnterBackground, and you won't get applicationWillTerminate(_:) now because the app isn't running.

On an iPad, if the app does support multiple windows

If the scene was frontmost:

• sceneDidEnterBackground
• applicationWillTerminate(_:) (perhaps)

But if the scene was not frontmost, you'll get nothing; you already received sceneDidEnterBackground, and you won't get applicationWillTerminate(_:) now because either the app isn't running or the app isn't terminating (if there's another window). If the app is still running, you might get sceneDidDisconnect(_:) and possibly application(_:didDiscardSceneSessions:) later.

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Conclusions

What's the odd-man-out here? It's the case where we're running on an iPad and we support scenes but not multiple windows. We don't get sceneDidEnterBackground! I regard that as incoherent. Since we don't support multiple windows, this is basically an iPhone app and it should behave like an iPhone app. I shouldn't have to double up my code just because my app runs on both iPhone and iPad.