Feature: Add confirmation when the app closes.

Speculator/CSharp.Utils/UI/AppCloseHandler.cs

@@ -0,0 +1,88 @@
+// Code authored by Dean Edis (DeanTheCoder).
+// Anyone is free to copy, modify, use, compile, or distribute this software,
+// either in source code form or as a compiled binary, for any non-commercial
+// purpose.
+//
+// If you modify the code, please retain this copyright header,
+// and consider contributing back to the repository or letting us know
+// about your modifications. Your contributions are valued!
+//
+// THE SOFTWARE IS PROVIDED AS IS, WITHOUT WARRANTY OF ANY KIND.
+
+using Avalonia.Controls;
+using Avalonia.Controls.ApplicationLifetimes;
+using Material.Icons;
+
+namespace CSharp.Utils.UI;
+
+/// <summary>
+/// Closing an app, especially on the Mac, is a bit of a mess.
+/// Closing the main app window triggers close events that can be cancelled.
+/// Closing using the Mac app menu or Command-Q will close the app window
+/// and kill the UI thread, preventing the window from triggering a confirmation
+/// dialog.
+///
+/// This class ensures both types of closure play nicely with each other.
+/// </summary>
+public class AppCloseHandler
+{
+    private bool m_isCloseConfirmed;
+    private bool m_isConfirmationDialogActive;
+    private IClassicDesktopStyleApplicationLifetime m_desktop;
+
+    public static AppCloseHandler Instance { get; } = new AppCloseHandler();
+
+    /// <summary>
+    /// Call from App.axaml.cs as early as possible.
+    /// </summary>
+    public void Init(IClassicDesktopStyleApplicationLifetime desktop)
+    {
+        m_desktop = desktop;
+
+        // Triggered when the user hits Command-Q or uses the Mac app menu.
+        desktop.ShutdownRequested += (_, args) =>
+        {
+            if (m_isCloseConfirmed)
+                return;
+
+            args.Cancel = true;
+            PromptForConfirmationAsync();
+        };
+    }
+
+    /// <summary>
+    /// Subscribe this to the main window's Closing event.
+    /// </summary>
+    public void OnMainWindowClosing(WindowClosingEventArgs args)
+    {
+        if (m_isCloseConfirmed)
+            return; // Allow the close.
+
+        args.Cancel = true;
+        if (!m_isConfirmationDialogActive)
+        {
+            // User hasn't seen the confirmation dialog yet, so show it.
+            PromptForConfirmationAsync();
+        }
+    }
+
+    private void PromptForConfirmationAsync()
+    {
+        m_isConfirmationDialogActive = true;
+        DialogService.Instance.Warn(
+            "Confirm Exit?",
+            "Any unsaved changes will be lost.",
+            "CANCEL",
+            "EXIT",
+            confirmed =>
+            {
+                m_isConfirmationDialogActive = false;
+                if (confirmed)
+                {
+                    m_isCloseConfirmed = true;
+                    m_desktop.Shutdown(); // Repeat the shutdown request, confirmed this time.
+                }
+            },
+            MaterialIconKind.CloseBold);
+    }
+}

Speculator/Speculator/Views/App.axaml.cs

@@ -14,6 +14,7 @@
 using Avalonia.Controls;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Markup.Xaml;
+using CSharp.Utils.UI;
 using Speculator.ViewModels;
 
 namespace Speculator.Views;
@@ -37,6 +38,8 @@ public override void OnFrameworkInitializationCompleted()
     {
         if (ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
         {
+            AppCloseHandler.Instance.Init(desktop);
+
             var viewModel = new MainWindowViewModel();
             desktop.MainWindow = new MainWindow
             {

Speculator/Speculator/Views/MainWindow.axaml.cs

@@ -15,6 +15,7 @@
 using Avalonia.Input;
 using Avalonia.Interactivity;
 using Avalonia.Threading;
+using CSharp.Utils.UI;
 using Material.Icons.Avalonia;
 using Speculator.ViewModels;
 // ReSharper disable UnusedParameter.Local
@@ -30,6 +31,7 @@ public MainWindow()
     {
         InitializeComponent();
 
+        Closing += (_, args) => AppCloseHandler.Instance.OnMainWindowClosing(args);
         Closed += (_, _) => (DataContext as IDisposable)?.Dispose();
     }
 
@@ -75,4 +77,4 @@ private void OnKeyboardIconLoaded(object sender, RoutedEventArgs e)
         };
         icon.PointerExited += (_, _) => Keyboard.Opacity = 0.0;
     }
-}
+}