improve single instance support

App.xaml.cs

@@ -15,15 +15,16 @@ public partial class App : Application
         public static Win_Format fb;
         internal const int MaxWindowCount = 2;//need to set this to 4 while debugging if you use live debug toolbar in vs2015.
         public const string MutexString = @"{39622D35-176E-453D-B1FD-E4EC1EAF31DC}";
+        private System.Threading.Mutex mtx;
 
         [DllImport("shlwapi.dll")]
         private static extern bool PathIsNetworkPath(string pszPath);
 
         private void RunCheck(object sender1, StartupEventArgs e1)
         {
-            if (SingleInstance.CheckExist(MutexString))
-            {asdfasfasdf
-                SingleInstance.SendNotifyMessage(SingleInstance.HWND_BROADCAST, SingleInstance.RegisteredMsg, IntPtr.Zero, IntPtr.Zero);
+            if (SingleInstance.CheckExist(MutexString, ref mtx))
+            {
+                SingleInstance.SendNotifyMessage(SingleInstance.HWND_BROADCAST, SingleInstance.RegisteredWM, IntPtr.Zero, IntPtr.Zero);
                 Current.Shutdown();
                 return;
             }
@@ -88,6 +89,11 @@ private void RunCheck(object sender1, StartupEventArgs e1)
             mainwin.Show();
         }
 
-
+        protected override void OnExit(ExitEventArgs e)
+        {
+            base.OnExit(e);
+            mtx?.Close();
+        }
+
     }
 }

MainWindow.xaml.cs

@@ -18,7 +18,7 @@ public partial class MainWindow : Window
         private object Lock_Save = new object();
         private static int CountDown = 0;
         Point mousepos;
-                        
+
         public MainWindow()
         {
             InitializeComponent();
@@ -501,7 +501,6 @@ private void Win_Main_Loaded(object sender, RoutedEventArgs e)
             RTB_Main.IsUndoEnabled = true;
             //without the above two lines, Load actions can be undone.
 
-
             currScrnRect = new GetCurrentMonitor().GetInfo();
 
             var task_save = new Thread(SaveNotes);
@@ -514,9 +513,10 @@ private void Win_Main_Loaded(object sender, RoutedEventArgs e)
 
         private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
         {
-            if (msg == SingleInstance.RegisteredMsg)
+            if (msg == SingleInstance.RegisteredWM)
             {
-                MessageBox.Show("Body text", "Title text", MessageBoxButton.OK, MessageBoxImage.Exclamation);
+                Activate();
+                UnDock();
             }
             return IntPtr.Zero;
         }

SingleInstance.cs

@@ -11,7 +11,9 @@ namespace DesktopNote
     class SingleInstance
     {
         public static readonly IntPtr HWND_BROADCAST = (IntPtr)0xffff;
-        public static readonly int RegisteredMsg = RegisterWindowMessage("WM_SHOW_DESKTOPNOTE");
+        //from MSDN: If two different applications register the same message string, the applications return the same message value.
+        //The message remains registered until the session ends.
+        public static readonly int RegisteredWM = RegisterWindowMessage("WM_SHOW_DESKTOPNOTE");
         //[DllImport("user32")] //not working when ShowInTaskbar set to false.
         //public static extern bool PostMessage(IntPtr hwnd, int msg, IntPtr wparam, IntPtr lparam);
         [DllImport("user32.dll", CharSet = CharSet.Auto)]
@@ -22,12 +24,16 @@ class SingleInstance
         public enum MutexScope { Local, Global }
 
         /// <summary>
-        /// Return created mutex if the mutex name does not exist. Returns null if the mutex name exists.
+        /// Return false and the created mutex if the mutex name does not exist. Otherwise returns true and null.
         /// </summary>
-        public static bool CheckExist(string uniquestr, MutexScope scope = MutexScope.Global)
-        {sdrsfsdf
+        public static bool CheckExist(string uniquestr, ref Mutex mtx, MutexScope scope = MutexScope.Global)
+        {
             bool createdNew;
-            new Mutex(true, scope.ToString() + @"\" + uniquestr, out createdNew);
+            var newmtx = new Mutex(false, scope.ToString() + @"\" + uniquestr, out createdNew);
+            if (createdNew)
+                mtx = newmtx;
+            else
+                newmtx.Close();
             return !createdNew;
         }
     }