added single instancing

TheXamlGuy.TaskbarGroup/LifeCycles/ApplicationHost.cs

@@ -2,7 +2,6 @@
 using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
-using System.Windows;
 using TheXamlGuy.TaskbarGroup.Core;
 
 namespace TheXamlGuy.TaskbarGroup
@@ -11,20 +10,13 @@ namespace TheXamlGuy.TaskbarGroup
     {
         private readonly TaskbarButtonFlyoutWindow flyoutWindow;
         private readonly IEnumerable<IInitializable> initializables;
-        private readonly IMediator mediator;
         private bool isInitialized;
 
         public ApplicationHost(IEnumerable<IInitializable> initializables,
-            IMessenger messenger,
-            IMediator mediator,
             TaskbarButtonFlyoutWindow flyoutWindow)
         {
             this.initializables = initializables;
-            this.mediator = mediator;
             this.flyoutWindow = flyoutWindow;
-
-            messenger.Subscribe<TaskbarButtonInvoked>(OnTaskbarButtonInvoked);
-            messenger.Subscribe<TaskbarButtonDragEnter>(OnTaskbarButtonDragEnter);
         }
 
         public async Task StartAsync(CancellationToken cancellationToken)
@@ -40,6 +32,7 @@ namespace TheXamlGuy.TaskbarGroup
         {
             await Task.CompletedTask;
         }
+
         private async Task InitializeAsync()
         {
             if (!isInitialized)
@@ -53,21 +46,6 @@ namespace TheXamlGuy.TaskbarGroup
             }
         }
 
-        private void OnTaskbarButtonDragEnter(TaskbarButtonDragEnter args)
-        {
-            Application.Current.Dispatcher.Invoke(() => Open(args.Button));
-        }
-
-        private void OnTaskbarButtonInvoked(TaskbarButtonInvoked args)
-        {
-            Application.Current.Dispatcher.Invoke(() => Open(args.Button));
-        }
-
-        private void Open(TaskbarButton button)
-        {
-            mediator.Handle(new TaskbarButtonFlyoutActivation(button));
-        }
-
         private async Task StartupAsync()
         {
             if (!isInitialized)

TheXamlGuy.TaskbarGroup/Program.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Threading;
+
+namespace TheXamlGuy.TaskbarGroup
+{
+    public class Program
+    {
+        [STAThread()]
+        public static void Main()
+        {
+            using (new Mutex(true, "TheXamlGuy.TaskbarGroup", out var createdNew))
+            {
+                if (createdNew)
+                {
+                    using (new Flyout.App())
+                    {
+                        var app = new App();
+                        app.Run();
+                    }
+                }
+                else
+                {
+                    Environment.Exit(0);
+                }
+            }
+        }
+    }
+}

TheXamlGuy.TaskbarGroup/Properties/Program.cs

@@ -1,17 +0,0 @@
-using System;
-
-namespace TheXamlGuy.TaskbarGroup
-{
-    public class Program
-    {
-        [STAThread()]
-        public static void Main()
-        {
-            using (new Flyout.App())
-            {
-                var app = new App();
-                app.Run();
-            }
-        }
-    }
-}

TheXamlGuy.TaskbarGroup/TheXamlGuy.TaskbarGroup.csproj

@@ -5,7 +5,9 @@
 		<UseWPF>true</UseWPF>
 		<StartupObject>TheXamlGuy.TaskbarGroup.Program</StartupObject>
 		<AssetTargetFallback>uap10.0.19041</AssetTargetFallback>
+		<TargetPlatformVersion>10.0.19041</TargetPlatformVersion>
 		<Platforms>x64;x86</Platforms>
+		<RuntimeIdentifiers>win10-x64;win10-x86</RuntimeIdentifiers>
 		<LangVersion>10.0</LangVersion>
 		<Nullable>enable</Nullable>
 	</PropertyGroup>

TheXamlGuy.TaskbarGroup/Windows/TaskbarButtonFlyoutWindow.cs

@@ -1,16 +1,19 @@
 using System;
-using System.Windows;
-using System.Windows.Media;
 using System.Windows.Threading;
+using TheXamlGuy.TaskbarGroup.Core;
 using TheXamlGuy.TaskbarGroup.Flyout.Controls;
 
 namespace TheXamlGuy.TaskbarGroup
 {
     public class TaskbarButtonFlyoutWindow : TransparentXamlWindow<TaskbarButtonFlyout>
     {
-        public TaskbarButtonFlyoutWindow()
+        private readonly IMediator mediator;
+
+        public TaskbarButtonFlyoutWindow(IMessenger messenger,
+            IMediator mediator)
         {
-            Deactivated += OnDeactivated;
+            this.mediator = mediator;
+
             Topmost = true;
             Width = 258;
             Height = 258;
@@ -19,15 +22,36 @@ namespace TheXamlGuy.TaskbarGroup
             {
                 Hide();
             }), DispatcherPriority.ContextIdle, null);
+
+            messenger.Subscribe<TaskbarButtonInvoked>(OnTaskbarButtonInvoked);
+            messenger.Subscribe<TaskbarButtonDragEnter>(OnTaskbarButtonDragEnter);
         }
 
-        private void OnDeactivated(object? sender, EventArgs args)
+        protected override void OnDeactivated(EventArgs args)
         {
             if (XamlContent is TaskbarButtonFlyout flyout)
             {
                 flyout.Close();
                 Hide();
             }
-        }
+
+            base.OnDeactivated(args);
+        }
+
+        private void Open(TaskbarButton button)
+        {
+            mediator.Handle(new TaskbarButtonFlyoutActivation(button));
+        }
+
+        private void OnTaskbarButtonDragEnter(TaskbarButtonDragEnter args)
+        {
+            Dispatcher.Invoke(() => Open(args.Button));
+        }
+
+        private void OnTaskbarButtonInvoked(TaskbarButtonInvoked args)
+        {
+            Dispatcher.Invoke(() => Open(args.Button));
+        }
+
     }
 }