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How to detect when your app moves to the background or foreground with scenePhase

Paul Hudson    @twostraws   

Updated for Xcode 13.0

New in iOS 14

SwiftUI provides a scenePhase environment key that is automatically updated as your app moves between the foreground, background, and inactive states. You can watch for these in your App struct itself, or in any SwiftUI view.

First, add a property to track the key:

@Environment(\.scenePhase) var scenePhase

And now either add any logic you want to your body, or use onChange() to observe changes directly.

As an example, we could write a view that monitors scenePhase and prints out some text into Xcode’s debug console whenever the phase changes:

struct ContentView: View {
    @Environment(\.scenePhase) var scenePhase

    var body: some View { 
        Text("Example Text")
            .onChange(of: scenePhase) { newPhase in
                if newPhase == .inactive {
                    print("Inactive")
                } else if newPhase == .active {
                    print("Active")
                } else if newPhase == .background {
                    print("Background")
                }
            }
    }
}

Download this as an Xcode project

As you can see, there are three states:

  1. The Active state is used when your app is in the foreground and interactive for the user, meaning that they are using it right now.
  2. The Background state is used when your app isn’t currently visible, so you should cut back the amount of work you do.
  3. The Inactive state is used when your app is visible, but not directly interactive to the user. For example, if you enter multi-tasking mode while running the app – you can see your app’s window alongside others, but you’re not directly using it.
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