Chris Pietschmann

public partial class App : Application
{
    protected override void OnStartup(StartupEventArgs e)
    {
        // Get Reference to the current Process
        Process thisProc = Process.GetCurrentProcess();
        // Check how many total processes have the same name as the current one
        if (Process.GetProcessesByName(thisProc.ProcessName).Length > 1)
        {
            // If ther is more than one, than it is already running.
            MessageBox.Show("Application is already running.");
            Application.Current.Shutdown();
            return;
        }

        base.OnStartup(e);
    }
}

namespace SingleInstanceDetection
{
    public class EntryPoint
    {
        [STAThread]
        public static void Main(string[] args)
        {
            SingleInstanceManager manager = new SingleInstanceManager();
            manager.Run(args);
        }
    }

    // Using VB bits to detect single instances and process accordingly:
    //  * OnStartup is fired when the first instance loads
    //  * OnStartupNextInstance is fired when the application is re-run again
    //    NOTE: it is redirected to this instance thanks to IsSingleInstance
    public class SingleInstanceManager : WindowsFormsApplicationBase
    {
        SingleInstanceApplication app;

        public SingleInstanceManager()
        {
            this.IsSingleInstance = true;
        }

        protected override bool OnStartup(Microsoft.VisualBasic.ApplicationServices.StartupEventArgs e)
        {
            // First time app is launched
            app = new SingleInstanceApplication();
            app.Run();
            return false;
        }

        protected override void OnStartupNextInstance(StartupNextInstanceEventArgs eventArgs)
        {
            // Subsequent launches
            base.OnStartupNextInstance(eventArgs);
            app.Activate();
        }
    }

    public class SingleInstanceApplication : Application
    {
        protected override void OnStartup(System.Windows.StartupEventArgs e)
        {
            base.OnStartup(e);

            // Create and show the application's main window
            MainWindow window = new MainWindow();
            window.Show();
        }

        public void Activate()
        {
            // Reactivate application's main window
            this.MainWindow.Activate();
        }
    }
}

<r:Ribbon>
    <r:RibbonTab Label="Banking">
        <r:RibbonGroup>
            <r:RibbonButton Command="me:AppCommands.Cut"/>
            <r:RibbonButton Command="me:AppCommands.Copy"/>
            <r:RibbonButton Command="me:AppCommands.Paste"/>
        </r:RibbonGroup>

        <r:RibbonGroup>
            <r:RibbonButton Command="me:AppCommands.AddNew"/>
            <r:RibbonButton Command="me:AppCommands.Clear" />
            <r:RibbonButton Command="me:AppCommands.Delete"/>
        </r:RibbonGroup>

        <r:RibbonGroup>
            <r:RibbonButton Command="me:AppCommands.DownloadStatements"/>
            <r:RibbonButton Command="me:AppCommands.DownloadCreditCards"/>
            <r:RibbonButton Command="me:AppCommands.Transfer"/>
        </r:RibbonGroup>
    </r:RibbonTab>
</r:Ribbon>

using System;
using System.Windows;
using System.Runtime.InteropServices;
using System.Windows.Interop;

namespace WpfApplication3
{
    /// <summary>
    /// Interaction logic for Window1.xaml
    /// </summary>
    public partial class Window1 : Window
    {
        #region Win32 API Stuff

        // Define the Win32 API methods we are going to use
        [DllImport("user32.dll")]
        private static extern IntPtr GetSystemMenu(IntPtr hWnd, bool bRevert);

        [DllImport("user32.dll")]
        private static extern bool InsertMenu(IntPtr hMenu, Int32 wPosition, Int32 wFlags, Int32 wIDNewItem, string lpNewItem);

        /// Define our Constants we will use
        public const Int32 WM_SYSCOMMAND = 0x112;
        public const Int32 MF_SEPARATOR = 0x800;
        public const Int32 MF_BYPOSITION = 0x400;
        public const Int32 MF_STRING = 0x0;

        #endregion

        // The constants we'll use to identify our custom system menu items
        public const Int32 _SettingsSysMenuID = 1000;
        public const Int32 _AboutSysMenuID = 1001;

        /// <summary>
        /// This is the Win32 Interop Handle for this Window
        /// </summary>
        public IntPtr Handle
        {
            get
            {
                return new WindowInteropHelper(this).Handle;
            }
        }

        public Window1()
        {
            InitializeComponent();

            this.Loaded += new RoutedEventHandler(Window1_Loaded);
        }

        private void Window1_Loaded(object sender, RoutedEventArgs e)
        {
            /// Get the Handle for the Forms System Menu
            IntPtr systemMenuHandle = GetSystemMenu(this.Handle, false);

            /// Create our new System Menu items just before the Close menu item
            InsertMenu(systemMenuHandle, 5, MF_BYPOSITION | MF_SEPARATOR, 0, string.Empty); // <-- Add a menu seperator
            InsertMenu(systemMenuHandle, 6, MF_BYPOSITION, _SettingsSysMenuID, "Settings...");
            InsertMenu(systemMenuHandle, 7, MF_BYPOSITION, _AboutSysMenuID, "About...");

            // Attach our WndProc handler to this Window
            HwndSource source = HwndSource.FromHwnd(this.Handle);
            source.AddHook(new HwndSourceHook(WndProc));
        }

        private static IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
        {
            // Check if a System Command has been executed
            if (msg == WM_SYSCOMMAND)
            {
                // Execute the appropriate code for the System Menu item that was clicked
                switch (wParam.ToInt32())
                {
                    case _SettingsSysMenuID:
                        MessageBox.Show("\"Settings\" was clicked");
                        handled = true;
                        break;
                    case _AboutSysMenuID:
                        MessageBox.Show("\"About\" was clicked");
                        handled = true;
                        break;
                }
            }

            return IntPtr.Zero;
        }
    }
}