Track scenes state on SwiftUI with visionOS

README.md

Track scenes state on SwiftUI with visionOS

Sometimes, a window is closed and you don't know it's closed.

In example:

• a detail window will be opened from main window
• user will close main window
• and there is no way to go back to main window.

This sample helps me to fix it on my own apps.

If you think it can be improved, don't hesitate to comment. ^^

MyApp.swift

import SwiftUI

/// Main Window content
private struct MainView: View {
    @Environment(\.appState) private var appState
    @Environment(\.openWindow) private var openWindow

    var body: some View {
        NavigationStack {
            VStack {
                Text("Main View")
                    .navigationTitle("Main Window")
                Button {
                    if !appState.visibleScenes.contains(.detailWindow) {
                        openWindow(id: AppState.AppSceneId.detailWindow.rawValue)
                    }
                } label: {
                    Text("Open detail")
                }
            }
        }
        .visibilityTracker(for: .mainWindow)
    }
}

/// Detail Window content
private struct DetailView: View {
    @Environment(\.appState) private var appState
    @Environment(\.openWindow) private var openWindow

    var body: some View {
        NavigationStack {
            Text("Detail View")
                .navigationTitle("Detail Window")
        }
        .visibilityTracker(for: .detailWindow)
        .onChange(of: appState.visibleScenes) { _, newValue in
            // if everything is closed, re-open main window
            if newValue.isEmpty {
                openWindow(id: AppState.AppSceneId.mainWindow.rawValue)
            }
        }
    }
}

@main
struct MyApp: App {
    @State private var appState = AppState()
    
    var body: some Scene {
        // The main view
        WindowGroup(id: AppState.AppSceneId.mainWindow.rawValue) {
            MainView()
        }
        .windowResizability(.contentSize)
        .environment(\.appState, appState)
  
    
        // The detail view
        WindowGroup(id: AppState.AppSceneId.detailWindow.rawValue) {
            DetailView()
        }
        .windowResizability(.contentSize)
        .environment(\.appState, appState)
    }
    
}

VisibilityTrackerModifier.swift

import Foundation
import Observation
import SwiftUI

/// A global App State
@Observable final class AppState {
    /// Identifier for a scene
    enum AppSceneId: String {
        case mainWindow
        case detailWindow
    }

    /// Currently displayed scenes (automatically updated)
    fileprivate(set) var visibleScenes: Set<AppSceneId> = [.mainWindow]
}

// MARK: - SwiftUI

/// Modifier used to track visibility of current window or immersive space
private struct VisibilityTrackerModifier: ViewModifier {
    /// The scene we want to track
    let trackedScene: AppState.AppSceneId

    @Environment(\.appState) private var appState
    @Environment(\.scenePhase) private var scenePhase

    func body(content: Content) -> some View {
        content
            .onAppear {
                // Forever called
                appState.visibleScenes.insert(trackedScene)
            }
            .onDisappear {
                // Called sometimes
                appState.visibleScenes.remove(trackedScene)
            }
            .onChange(of: scenePhase) { _, newScenePhase in
                // Forever called
                if newScenePhase == .background || newScenePhase == .inactive {
                    appState.visibleScenes.remove(trackedScene)
                }
            }
    }
}


// MARK: - SwiftUI helpers

extension View {
    func visibilityTracker(for trackedScene: AppState.AppSceneId) -> some View {
        modifier(VisibilityTrackerModifier(trackedScene: trackedScene))
    }
}

private struct AppStateEnvironmentKey: EnvironmentKey {
    static let defaultValue = AppState()
}

extension EnvironmentValues {
    var appState: AppState {
        get {
            self[AppStateEnvironmentKey.self]
        }
        set {
            self[AppStateEnvironmentKey.self] = newValue
        }
    }
}