Note: in this post I discuss sceneDidEnterBackground/WillResignActive but I assume any guidance provided would also apply to the now deprecated applicationDidEnterBackground/applicationWillResignActive and SwiftUI's ScenePhase (please call out if that's not the case!).
A common pattern for applications with sensitive user data (banking, health, private journals, etc.) is to obsurce content in the app switcher. Different apps appear to implement this in two common patterns. Either immediately upon becoming inactive (near immediately upon moving to task switcher) or only upon becoming backgrounded (not until you've gone to another app or back to the home screen).
I’d like to make sure we’re aligned with Apple’s intended best practices and am wondering if an anti-pattern of using sceneWillResignActive(_:) may be becoming popularized and has minor user experience inconviences (jarring transitions to the App Switcher/Control Center/Notification Center and when the system presents alerts.)
Our applications current implementation uses sceneDidEnterBackground(_:) to obscure sensitive elements instead of sceneWillResignActive(_:), based on the recomendations from tech note QA1838 and the documentation in sceneDidEnterBackground(_:)
... Shortly after this method [sceneWillEnterBackground] returns, UIKit takes a snapshot of your scene’s interface for display in the app switcher. Make sure your interface doesn’t contain sensitive user information.
Both QA1838 and the sceneDidEnterBackground documentation seem to indicate backgrounding is the appropriate event to respond to for this pattern but I am wondering if "to display in the app switcher" may be causing confusion since your app can also display in the app switcher upon becoming inactive and if some guidance could be added to sceneWillResignActive that it is not nesscary to obsure content during this state (if that is true).
In our testing, apps seems to continue to play any in-progress animations when entering the app switcher from the application (inactive state), suggesting no snapshot capture. We also discovered that it appears sceneWillResignActive not always be called (it usually is) but occasionally you can swipe into the app switcher without it being called but that sceneDidEnterBackground is triggered more consistently.
It appears the Wallet app behaves as I'd expect with sceneDidEnterBackground on card details screens as well (ejecting you to the card preview if you switch apps) but will keep you on the card details screen upon becoming inactive.
Questions:
- Is sceneDidEnterBackground(_:) still Apple’s recommended place to obscure sensitive content, or should apps handle this earlier (e.g. on inactive)?
- Would it actually be recommended against using sceneWillResignActive active given it seems to not be gauranteed to be called?
Ask:
- Provide an updated version of QA1838 to solidfy the extrapolation of applicationDidEnterBackground -> sceneDidEnterBackground
- Consider adding explicit guidance to sceneWillResignActive documentation