C# WPF 窗体传递消息

 对于存在窗体的WPF程序（或者说，起码在任务栏上有个图标，即ShowInTaskbar = true），互相传递消息是很容易的。

步骤：

1，寻找窗体的句柄

2，运用windows API: SendMessage或PostMessage

3，目标窗体收到消息

这里的代码，展示了一个APP不希望多开所以在启动时检查是否存在一个已经运行的进程。如果进程已经存在，则给对方发送消息并结束自身。

1.判断/获取已经运行的实例

       /// <summary>
        /// 获取当前exe文件的是否已经在电脑上运行了一个实例，如果是，则返回那个实例的Process；如果否，就返回null；
        /// 如果有窗体，可以通过process.MainWindowHandle获取窗体的句柄，如果没窗体（ShowInTaskbar = false）,则句柄为空
        /// </summary>
        public static Process GetCurrentExeProcess()
        {
            Process targetProcess = null;

            Process currentProcess = Process.GetCurrentProcess();
            string exeName = string.Format("{0}.exe", currentProcess.ProcessName);
            //PTZ.Tracer.AppLog.Info("$$$$$Get Current Process Successfully, current process exe: {0}", exeName);

            try
            {
                Process[] aryProcess = Process.GetProcessesByName(currentProcess.ProcessName);

                //PTZ.Tracer.AppLog.Info("$$$$$Get aryProcess Successfully, aryProcess count: {0}", aryProcess.Count());
                foreach (Process process in aryProcess)
                {
                    if (process.Id != currentProcess.Id && process.ProcessName == currentProcess.ProcessName)
                    {
                        targetProcess = process;
                        //PTZ.Tracer.AppLog.Info("$$$$$Get MainWindowHandle Successfully, hWnd: {0}", hWnd);
                        break;
                    }
                }
            }
            catch (System.PlatformNotSupportedException pEx)
            {
                //PTZ.Tracer.AppLog.Error("$$$$$GetCurrentWindowsInstanceHandle exception:", pEx);
            }
            catch (System.InvalidOperationException iEx)
            {
                //PTZ.Tracer.AppLog.Error("$$$$$GetCurrentWindowsInstanceHandle exception:", iEx);
            }
            catch (System.ComponentModel.Win32Exception win32Ex)
            {
                //PTZ.Tracer.AppLog.Error("$$$$$GetCurrentWindowsInstanceHandle exception:", win32Ex);
            }

            return targetProcess;
        }

但是这个方法在某些奇怪权限设置的电脑上会遭遇UnauthorizedException，所以，如果只是想获取窗体句柄的话，还可以将上述方法的Try & Catch部分换成下面的代码：

            try
            {
                string wmiQueryString = string.Format("SELECT ProcessId, Handle,ExecutablePath,Name FROM Win32_Process WHERE ProcessId != {0} AND Name = '{1}'", currentProcess.Id, exeName);
                using (var searcher = new ManagementObjectSearcher(wmiQueryString))
                {
                    using (var results = searcher.Get())
                    {
                        ManagementObject mo = results.Cast<ManagementObject>().FirstOrDefault();
                        if (mo != null)
                        {
                            string s = (string)mo["ExecutablePath"];
                            string handleStr = (string)mo["Handle"];
                            string sss = (string)mo["Name"];
                            Tracing.Trace.Information("￥*￥ManagementObjectSearcher, name: {0} Handle: {1} Path: {2}", sss, handleStr, s);

                            int handle = int.Parse(handleStr);
                            Process p = Process.GetProcessById(handle);
                            hWnd = p.MainWindowHandle;
                            isRunExist = true;
                            Tracing.Trace.Information("￥*￥ManagementObjectSearcher, hWnd: {0}", hWnd);
                        }
                    }
                }
            }
            catch (Exception e)
            {
                Tracing.Trace.Error("ManagementObjectSearcher exception:", e);
            }

2.注册WindowsAPI

        #region Dll Imports

        [DllImport("user32.dll")]
        static extern IntPtr PostMessage(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam);

        public const uint WM_APP = 0x9112;////0x8001~0xBFFF，随意#endregion Dll Imports

3.修改App.OnStartup方法

当程序启动，就需要检测实例。如已有实例运行，则发送消息；如没有，则继续正常运行。所以我们需要修改Appxaml.cs的OnStartup方法：

protected override void OnStartup(StartupEventArgs e)
        {
            base.OnStartup(e);

            Process targetProcess = SingleExeHelper.GetCurrentExeProcess();

            if (targetProcess!=null)//Software has been running...
            {

//currentHandle通过targetProcess.MainWindowHandle得到

                PostMessage(currentHandle,WM_APP, IntPtr.Zero, IntPtr.Zero);

                Environment.Exit(0);//Software has been running, close this
            }
            else
            {
                //do nothing
            }
        }

4.主窗体监听消息：

       protected override void OnSourceInitialized(EventArgs e)
        {
            base.OnSourceInitialized(e);
            ((HwndSource)PresentationSource.FromVisual(this)).AddHook(myHook);

            //HwndSource source = HwndSource.FromHwnd(new WindowInteropHelper(this).Handle);
            //source.AddHook(new HwndSourceHook(myHook));
        }

        private IntPtr myHook(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
        {
            int m = (int)App.WM_APP;
            if (msg == m)
            {
                System.Windows.MessageBox.Show("haha");
            }
            return IntPtr.Zero;
        }