內容來自：https://codereview.stackexchange.com/questions/20871/single-instance-wpf-application

第一步：添加System.RunTime.Remoting引用

第二步：新建一個類class1.cs(按自己想法命名)

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
 
using System.Runtime.Remoting;
using System.Runtime.Remoting.Channels;
using System.Runtime.Remoting.Channels.Ipc;
using System.Runtime.Serialization.Formatters;
using System.Security;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Threading;

 
namespace SingleWPF
{
    internal enum WM
    {
        NULL = 0x0000,
        CREATE = 0x0001,
        DESTROY = 0x0002,
        MOVE = 0x0003,
        SIZE = 0x0005,
        ACTIVATE = 0x0006,
        SETFOCUS = 0x0007,
        KILLFOCUS = 0x0008,
        ENABLE = 0x000A,
        SETREDRAW = 0x000B,
        SETTEXT = 0x000C,
        GETTEXT 
 
= 0x000D,
        GETTEXTLENGTH = 0x000E,
        PAINT = 0x000F,
        CLOSE = 0x0010,
        QUERYENDSESSION = 0x0011,
        QUIT = 0x0012,
        QUERYOPEN = 0x0013,
        ERASEBKGND = 0x0014,
        SYSCOLORCHANGE = 0x0015,
        SHOWWINDOW = 0x0018,
        ACTIVATEAPP = 0x001C,
        SETCURSOR = 0x0020,
        MOUSEACTIVATE = 0x0021,
        CHILDACTIVATE = 0x0022,
        QUEUESYNC = 0x0023,
        GETMINMAXINFO = 0x0024,

        WINDOWPOSCHANGING = 0x0046,
        WINDOWPOSCHANGED = 0x0047,

        CONTEXTMENU = 0x007B,
        STYLECHANGING = 0x007C,
        STYLECHANGED = 0x007D,
        DISPLAYCHANGE = 0x007E,
        GETICON = 0x007F,
        SETICON = 0x0080,
        NCCREATE = 0x0081,
        NCDESTROY = 0x0082,
        NCCALCSIZE = 0x0083,
        NCHITTEST = 0x0084,
        NCPAINT = 0x0085,
        NCACTIVATE = 0x0086,
        GETDLGCODE = 0x0087,
        SYNCPAINT = 0x0088,
        NCMOUSEMOVE = 0x00A0,
        NCLBUTTONDOWN = 0x00A1,
        NCLBUTTONUP = 0x00A2,
        NCLBUTTONDBLCLK = 0x00A3,
        NCRBUTTONDOWN = 0x00A4,
        NCRBUTTONUP = 0x00A5,
        NCRBUTTONDBLCLK = 0x00A6,
        NCMBUTTONDOWN = 0x00A7,
        NCMBUTTONUP = 0x00A8,
        NCMBUTTONDBLCLK = 0x00A9,

        SYSKEYDOWN = 0x0104,
        SYSKEYUP = 0x0105,
        SYSCHAR = 0x0106,
        SYSDEADCHAR = 0x0107,
        COMMAND = 0x0111,
        SYSCOMMAND = 0x0112,

        MOUSEMOVE = 0x0200,
        LBUTTONDOWN = 0x0201,
        LBUTTONUP = 0x0202,
        LBUTTONDBLCLK = 0x0203,
        RBUTTONDOWN = 0x0204,
        RBUTTONUP = 0x0205,
        RBUTTONDBLCLK = 0x0206,
        MBUTTONDOWN = 0x0207,
        MBUTTONUP = 0x0208,
        MBUTTONDBLCLK = 0x0209,
        MOUSEWHEEL = 0x020A,
        XBUTTONDOWN = 0x020B,
        XBUTTONUP = 0x020C,
        XBUTTONDBLCLK = 0x020D,
        MOUSEHWHEEL = 0x020E,


        CAPTURECHANGED = 0x0215,

        ENTERSIZEMOVE = 0x0231,
        EXITSIZEMOVE = 0x0232,

        IME_SETCONTEXT = 0x0281,
        IME_NOTIFY = 0x0282,
        IME_CONTROL = 0x0283,
        IME_COMPOSITIONFULL = 0x0284,
        IME_SELECT = 0x0285,
        IME_CHAR = 0x0286,
        IME_REQUEST = 0x0288,
        IME_KEYDOWN = 0x0290,
        IME_KEYUP = 0x0291,

        NCMOUSELEAVE = 0x02A2,

        DWMCOMPOSITIONCHANGED = 0x031E,
        DWMNCRENDERINGCHANGED = 0x031F,
        DWMCOLORIZATIONCOLORCHANGED = 0x0320,
        DWMWINDOWMAXIMIZEDCHANGE = 0x0321,

        #region Windows 7
        DWMSENDICONICTHUMBNAIL = 0x0323,
        DWMSENDICONICLIVEPREVIEWBITMAP = 0x0326,
        #endregion

        USER = 0x0400,

        // This is the hard-coded message value used by WinForms for Shell_NotifyIcon.
        // It‘s relatively safe to reuse.
        TRAYMOUSEMESSAGE = 0x800, //WM_USER + 1024
        APP = 0x8000,
    }

    [SuppressUnmanagedCodeSecurity]
    internal static class NativeMethods
    {
        /// <summary>
        /// Delegate declaration that matches WndProc signatures.
        /// </summary>
        public delegate IntPtr MessageHandler(WM uMsg, IntPtr wParam, IntPtr lParam, out bool handled);

        [DllImport("shell32.dll", EntryPoint = "CommandLineToArgvW", CharSet = CharSet.Unicode)]
        private static extern IntPtr _CommandLineToArgvW([MarshalAs(UnmanagedType.LPWStr)] string cmdLine, out int numArgs);


        [DllImport("kernel32.dll", EntryPoint = "LocalFree", SetLastError = true)]
        private static extern IntPtr _LocalFree(IntPtr hMem);


        public static string[] CommandLineToArgvW(string cmdLine)
        {
            IntPtr argv = IntPtr.Zero;
            try
            {
                int numArgs = 0;

                argv = _CommandLineToArgvW(cmdLine, out numArgs);
                if (argv == IntPtr.Zero)
                {
                    throw new Win32Exception();
                }
                var result = new string[numArgs];

                for (int i = 0; i < numArgs; i++)
                {
                    IntPtr currArg = Marshal.ReadIntPtr(argv, i * Marshal.SizeOf(typeof(IntPtr)));
                    result[i] = Marshal.PtrToStringUni(currArg);
                }

                return result;
            }
            finally
            {

                IntPtr p = _LocalFree(argv);
                // Otherwise LocalFree failed.
                // Assert.AreEqual(IntPtr.Zero, p);
            }
        }

    }

    public interface ISingleInstanceApp
    {
        bool SignalExternalCommandLineArgs(IList<string> args);
    }

    /// <summary>
    /// This class checks to make sure that only one instance of 
    /// this application is running at a time.
    /// </summary>
    /// <remarks>
    /// Note: this class should be used with some caution, because it does no
    /// security checking. For example, if one instance of an app that uses this class
    /// is running as Administrator, any other instance, even if it is not
    /// running as Administrator, can activate it with command line arguments.
    /// For most apps, this will not be much of an issue.
    /// </remarks>
    public static class SingleInstance<TApplication>
                where TApplication : Application, ISingleInstanceApp

    {
        #region Private Fields

        /// <summary>
        /// String delimiter used in channel names.
        /// </summary>
        private const string Delimiter = ":";

        /// <summary>
        /// Suffix to the channel name.
        /// </summary>
        private const string ChannelNameSuffix = "SingeInstanceIPCChannel";

        /// <summary>
        /// Remote service name.
        /// </summary>
        private const string RemoteServiceName = "SingleInstanceApplicationService";

        /// <summary>
        /// IPC protocol used (string).
        /// </summary>
        private const string IpcProtocol = "ipc://";

        /// <summary>
        /// Application mutex.
        /// </summary>
        private static Mutex singleInstanceMutex;

        /// <summary>
        /// IPC channel for communications.
        /// </summary>
        private static IpcServerChannel channel;

        /// <summary>
        /// List of command line arguments for the application.
        /// </summary>
        private static IList<string> commandLineArgs;

        #endregion

        #region Public Properties

        /// <summary>
        /// Gets list of command line arguments for the application.
        /// </summary>
        public static IList<string> CommandLineArgs
        {
            get { return commandLineArgs; }
        }

        #endregion

        #region Public Methods

        /// <summary>
        /// Checks if the instance of the application attempting to start is the first instance. 
        /// If not, activates the first instance.
        /// </summary>
        /// <returns>True if this is the first instance of the application.</returns>
        public static bool InitializeAsFirstInstance(string uniqueName)
        {
            commandLineArgs = GetCommandLineArgs(uniqueName);

            // Build unique application Id and the IPC channel name.
            string applicationIdentifier = uniqueName + Environment.UserName;

            string channelName = String.Concat(applicationIdentifier, Delimiter, ChannelNameSuffix);

            // Create mutex based on unique application Id to check if this is the first instance of the application. 
            bool firstInstance;
            singleInstanceMutex = new Mutex(true, applicationIdentifier, out firstInstance);
            if (firstInstance)
            {
                CreateRemoteService(channelName);
            }
            else
            {
                SignalFirstInstance(channelName, commandLineArgs);
            }

            return firstInstance;
        }

        /// <summary>
        /// Cleans up single-instance code, clearing shared resources, mutexes, etc.
        /// </summary>
        public static void Cleanup()
        {
            if (singleInstanceMutex != null)
            {
                singleInstanceMutex.Close();
                singleInstanceMutex = null;
            }

            if (channel != null)
            {
                ChannelServices.UnregisterChannel(channel);
                channel = null;
            }
        }

        #endregion

        #region Private Methods

        /// <summary>
        /// Gets command line args - for ClickOnce deployed applications, command line args may not be passed directly, they have to be retrieved.
        /// </summary>
        /// <returns>List of command line arg strings.</returns>
        private static IList<string> GetCommandLineArgs(string uniqueApplicationName)
        {
            string[] args = null;
            if (AppDomain.CurrentDomain.ActivationContext == null)
            {
                // The application was not clickonce deployed, get args from standard API‘s
                args = Environment.GetCommandLineArgs();
            }
            else
            {
                // The application was clickonce deployed
                // Clickonce deployed apps cannot recieve traditional commandline arguments
                // As a workaround commandline arguments can be written to a shared location before 
                // the app is launched and the app can obtain its commandline arguments from the 
                // shared location               
                string appFolderPath = Path.Combine(
                    Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), uniqueApplicationName);

                string cmdLinePath = Path.Combine(appFolderPath, "cmdline.txt");
                if (File.Exists(cmdLinePath))
                {
                    try
                    {
                        using (TextReader reader = new StreamReader(cmdLinePath, System.Text.Encoding.Unicode))
                        {
                            args = NativeMethods.CommandLineToArgvW(reader.ReadToEnd());
                        }

                        File.Delete(cmdLinePath);
                    }
                    catch (IOException)
                    {
                    }
                }
            }

            if (args == null)
            {
                args = new string[] { };
            }

            return new List<string>(args);
        }

        /// <summary>
        /// Creates a remote service for communication.
        /// </summary>
        /// <param name="channelName">Application‘s IPC channel name.</param>
        private static void CreateRemoteService(string channelName)
        {
            BinaryServerFormatterSinkProvider serverProvider = new BinaryServerFormatterSinkProvider();
            serverProvider.TypeFilterLevel = TypeFilterLevel.Full;
            IDictionary props = new Dictionary<string, string>();

            props["name"] = channelName;
            props["portName"] = channelName;
            props["exclusiveAddressUse"] = "false";

            // Create the IPC Server channel with the channel properties
            channel = new IpcServerChannel(props, serverProvider);

            // Register the channel with the channel services
            ChannelServices.RegisterChannel(channel, true);

            // Expose the remote service with the REMOTE_SERVICE_NAME
            IPCRemoteService remoteService = new IPCRemoteService();
            RemotingServices.Marshal(remoteService, RemoteServiceName);
        }

        /// <summary>
        /// Creates a client channel and obtains a reference to the remoting service exposed by the server - 
        /// in this case, the remoting service exposed by the first instance. Calls a function of the remoting service 
        /// class to pass on command line arguments from the second instance to the first and cause it to activate itself.
        /// </summary>
        /// <param name="channelName">Application‘s IPC channel name.</param>
        /// <param name="args">
        /// Command line arguments for the second instance, passed to the first instance to take appropriate action.
        /// </param>
        private static void SignalFirstInstance(string channelName, IList<string> args)
        {
            IpcClientChannel secondInstanceChannel = new IpcClientChannel();
            ChannelServices.RegisterChannel(secondInstanceChannel, true);

            string remotingServiceUrl = IpcProtocol + channelName + "/" + RemoteServiceName;

            // Obtain a reference to the remoting service exposed by the server i.e the first instance of the application
            IPCRemoteService firstInstanceRemoteServiceReference = (IPCRemoteService)RemotingServices.Connect(typeof(IPCRemoteService), remotingServiceUrl);

            // Check that the remote service exists, in some cases the first instance may not yet have created one, in which case
            // the second instance should just exit
            if (firstInstanceRemoteServiceReference != null)
            {
                // Invoke a method of the remote service exposed by the first instance passing on the command line
                // arguments and causing the first instance to activate itself
                firstInstanceRemoteServiceReference.InvokeFirstInstance(args);
            }
        }

        /// <summary>
        /// Callback for activating first instance of the application.
        /// </summary>
        /// <param name="arg">Callback argument.</param>
        /// <returns>Always null.</returns>
        private static object ActivateFirstInstanceCallback(object arg)
        {
            // Get command line args to be passed to first instance
            IList<string> args = arg as IList<string>;
            ActivateFirstInstance(args);
            return null;
        }

        /// <summary>
        /// Activates the first instance of the application with arguments from a second instance.
        /// </summary>
        /// <param name="args">List of arguments to supply the first instance of the application.</param>
        private static void ActivateFirstInstance(IList<string> args)
        {
            // Set main window state and process command line args
            if (Application.Current == null)
            {
                return;
            }

            ((TApplication)Application.Current).SignalExternalCommandLineArgs(args);
        }

        #endregion

        #region Private Classes

        /// <summary>
        /// Remoting service class which is exposed by the server i.e the first instance and called by the second instance
        /// to pass on the command line arguments to the first instance and cause it to activate itself.
        /// </summary>
        private class IPCRemoteService : MarshalByRefObject
        {
            /// <summary>
            /// Activates the first instance of the application.
            /// </summary>
            /// <param name="args">List of arguments to pass to the first instance.</param>
            public void InvokeFirstInstance(IList<string> args)
            {
                if (Application.Current != null)
                {
                    // Do an asynchronous call to ActivateFirstInstance function
                    Application.Current.Dispatcher.BeginInvoke(
                        DispatcherPriority.Normal, new DispatcherOperationCallback(SingleInstance<TApplication>.ActivateFirstInstanceCallback), args);
                }
            }

            /// <summary>
            /// Remoting Object‘s ease expires after every 5 minutes by default. We need to override the InitializeLifetimeService class
            /// to ensure that lease never expires.
            /// </summary>
            /// <returns>Always null.</returns>
            public override object InitializeLifetimeService()
            {
                return null;
            }
        }

        #endregion
    }
}

第三步：在App.xml.cs中操作：

1：實現接口：ISingleInstanceApp

2：添加以下代碼

 // TODO: Make this unique!
        private const string Unique = "Change this to something that uniquely identifies your program.";

        [STAThread]
        public static void Main()
        {
            if (SingleInstance<App>.InitializeAsFirstInstance(Unique))
            {
                var application = new App();
                application.InitializeComponent();
                application.Run();

                // Allow single instance code to perform cleanup operations
                SingleInstance<App>.Cleanup();
            }
        }

        #region ISingleInstanceApp Members
        public bool SignalExternalCommandLineArgs(IList<string> args)
        {
            // Bring window to foreground
            if (this.MainWindow.WindowState == WindowState.Minimized)
            {
                this.MainWindow.WindowState = WindowState.Normal;
            }

            this.MainWindow.Activate();
            return true;
        }
        #endregion

註：如果只是打開一個窗口沒有其他的操作，實現

SignalExternalCommandLineArgs方法為：

public bool SignalExternalCommandLineArgs(IList<string> args)
        {
            
            return true;
        }

如果是打開一個窗口，重復打開置頂窗口，實現方法為：

public bool SignalExternalCommandLineArgs(IList<string> args)
        {
            // Bring window to foreground
            if (this.MainWindow.WindowState == WindowState.Minimized)
            {
                this.MainWindow.WindowState = WindowState.Normal;
            }

            this.MainWindow.Activate();
            return true;
        }

第四步：將App.xaml的生成方式修改為Page

第五步：將項目的屬性->應用程序->啟動對象，選擇為自己項目名稱.App

WPF實現只打開一個窗口，並且重復打開時已經打開的窗口置頂