WPF实现只打开一个窗口，并且重复打开时已经打开的窗口置顶

内容来自：https://codereview.stackexchange.com/questions/20871/single-instance-wpf-application

第一步：添加system.runtime.remoting引用

第二步：新建一个类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：实现接口：isingleinstanceapp

2：添加以下代码

 // 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

注：如果只是打开一个窗口没有其他的操作，实现

signalexternalcommandlineargs方法为：

public bool signalexternalcommandlineargs(ilist<string> args)
        {
            
            return true;
        }

如果是打开一个窗口，重复打开置顶窗口，实现方法为：

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：将app.xaml的生成方式修改为page

第五步：将项目的属性->应用程序->启动对象，选择为自己项目名称.app