Keeping track of visionOS windows being opened/closed

WindowWatchingApp.Swift

import SwiftUI
import RealityKit
import RealityKitContent

@main
struct WindowWatchingApp: App {
    @State private var windowManager: WindowManager
    
    init() {
        _windowManager = State(initialValue: WindowManager())
    }
    
    var body: some SwiftUI.Scene {
        WindowGroup(id: "WindowA") {
            WindowA()
                .environment(windowManager)
        }
        .windowResizability(.contentSize)
        
        WindowGroup(id: "WindowB") {
            WindowB()
                .environment(windowManager)
        }
        .windowResizability(.contentSize)
    }
}

@Observable
class WindowManager {
    var isWindowAOpen: Bool = false
    var isWindowBOpen: Bool = false
}

struct WindowA: View {
    @Environment(WindowManager.self) var windowManager
    @Environment(\.openWindow) var openWindow
    @Environment(\.scenePhase) private var scenePhase
    
    var body: some View {
        VStack {
            Text("Window A").font(.title)
            Button(action: {
                openWindow(id: "WindowB")
            }, label: {
                Text("Open Window B")
            })
            .disabled(windowManager.isWindowBOpen)
        }
        .padding()
        .onAppear {
            windowManager.isWindowAOpen = true
            print("onAppear: windowManager.isWindowAOpen = \(windowManager.isWindowAOpen)")
        }
        .onDisappear {
            windowManager.isWindowAOpen = false
            print("onDisappear: windowManager.isWindowAOpen = \(windowManager.isWindowAOpen)")
        }
        .onChange(of: scenePhase) { oldValue, newValue in
            print("Window A scene: \(newValue)")
            if newValue == .background && !windowManager.isWindowBOpen {
                // if you need to do something when the last window is closed
                print("ALL WINDOWS ARE CLOSED")
                windowManager.isWindowAOpen = false
            } else if newValue == .active {
                windowManager.isWindowAOpen = true
            }
        }
    }
}

struct WindowB: View {
    @Environment(WindowManager.self) var windowManager
    @Environment(\.openWindow) var openWindow
    @Environment(\.scenePhase) private var scenePhase
    
    var body: some View {
        VStack {
            Text("Window B").font(.title)
            Button(action: {
                openWindow(id: "WindowA")
            }, label: {
                Text("Open Window A")
            })
            .disabled(windowManager.isWindowAOpen)
        }
        .padding()
        .onAppear {
            windowManager.isWindowBOpen = true
            print("onAppear: windowManager.isWindowBOpen = \(windowManager.isWindowBOpen)")
        }
        .onDisappear {
            windowManager.isWindowBOpen = false
            print("onDisappear: windowManager.isWindowBOpen = \(windowManager.isWindowBOpen)")
        }
        .onChange(of: scenePhase) { oldValue, newValue in
            print("Window B scene: \(newValue)")
            if newValue == .background && !windowManager.isWindowAOpen {
                // if you need to do something when the last window is closed
                print("ALL WINDOWS ARE CLOSED")
                windowManager.isWindowBOpen = false
            } else if newValue == .active {
                windowManager.isWindowBOpen = true
            }
        }
    }
}