How to know if app is removed from background in SwiftUI?

Question

How to know if app is removed from background in SwiftUI? Is there any method just like Swift and how to use it?

Answer 1

I'd research the Scene protocol.

I quote...

The Scene protocol provides scene modifiers, defined as protocol methods with default implementations, that you use to configure a scene. For example, you can use the onChange(of:perform:) modifier to trigger an action when a value changes. The following code empties a cache when all of the scenes in the window group have moved to the background:

and to be clear this is the example provided by Apple...

struct MyScene: Scene {
    @Environment(\.scenePhase) private var scenePhase
    @StateObject private var cache = DataCache()

    var body: some Scene {
        WindowGroup {
            MyRootView()
        }
        .onChange(of: scenePhase) { newScenePhase in
            if newScenePhase == .background {
                cache.empty()
            }
        }
    }
}

I place this in my App file, like in the following example (with Core Data implementation):

import SwiftUI

@main
struct MyApp: App {

    let persistenceController = PersistenceController.shared
    
    @Environment(\.scenePhase) var scenePhase
    
    var body: some Scene {
        
        WindowGroup {
            
            NavigationView()
                .environment(\.managedObjectContext, persistenceController.container.viewContext)
        }
        .onChange(of: scenePhase) { _ in
            
            persistenceController.save()
        }
    }
}