swiftui - Not Receiving scenePhase Changes

Question

I'm trying to execute some code I'd have previously put in my app delegate, such as saving my managed object context when entering the background. I put the call in the .onChange for the scenePhase, but I'm not getting anything. Here's a sample project:

import SwiftUI

@main
struct PhaseApp: App {
    @Environment(.scenePhase) private var scenePhase
    
    var body: some Scene {
        WindowGroup {
            Text("Hello, world.")
        }
        .onChange(of: scenePhase) { phase in
            switch phase {
            case .active:
                print("Active")
            case .background:
                print("Background")
            case .inactive:
                print("Inactive")
            @unknown default: break
            }
        }
    }
}

I'd expect to get a print command in the Simulator or on my test device whenever I press Home or tap the app, but nothing happens.

Answer 1

Use inside scene root view (usually ContentView)

Tested with Xcode 12 / iOS 14 as worked.

struct ContentView: View {
    @Environment(.scenePhase) private var scenePhase
    var body: some View {
        TestView()
            .onChange(of: scenePhase) { phase in
                switch phase {
                    case .active:
                        print(">> your code is here on scene become active")
                    case .inactive:
                        print(">> your code is here on scene become inactive")
                    case .background:
                        print(">> your code is here on scene go background")
                    default:
                        print(">> do something else in future")
                }
            }
    }
}