C#使用SendMessage进行进程间通讯

最近公司有个需求是，拖动文件到桌面图标上，自动打开文件。那么只需在OnStartup事件中通过StartupEventArgs获取文件名然后进行操作即可。操作之后发现当软件已经启动了（单例运行），那么将无法将参数传给业务层。原因是因为跨进程了，那么我们可以通过窗口句柄的方式来进行通讯。

 public partial class App : Application
 {
     private static Mutex AppMutex;
     public App()
     {

     }

     protected override void OnStartup(StartupEventArgs e)
     {
         //获取启动参数
         var param = string.Empty;
         if (e.Args.Length > 0)
         {
             param = e.Args[0].ToString();
         }

         //WpfApp8 = 你的项目名称
         AppMutex = new Mutex(true, "WpfApp8", out var createdNew);

         if (!createdNew)
         {
             var current = Process.GetCurrentProcess();

             foreach (var process in Process.GetProcessesByName(current.ProcessName))
             {
                 if (process.Id != current.Id)
                 { 
                     Win32Helper.SetForegroundWindow(process.MainWindowHandle);
                     Win32Helper.SendMessageString(process.MainWindowHandle, param);
                     break;
                 }
             }
             Environment.Exit(0);
         }
         else
         {
             base.OnStartup(e);
         }
     }
 }

 public class Win32Helper
 {
     [DllImport("user32.dll", ExactSpelling = true, CharSet = CharSet.Auto)]
     public static extern bool SetForegroundWindow(IntPtr hWnd);

     /// <summary>
     /// 发送消息
     /// </summary>
     /// <param name="hWnd"></param>
     /// <param name="Msg"></param>
     /// <param name="wParam"></param>
     /// <param name="lParam"></param>
     /// <returns></returns>
     [DllImport("user32.dll")]
     public static extern IntPtr SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, ref COPYDATASTRUCT lParam);

     // 声明常量
     public const int WM_COPYDATA = 0x004A; 

     // 定义 COPYDATASTRUCT 结构
     [StructLayout(LayoutKind.Sequential)]
     public struct COPYDATASTRUCT
     {
         public IntPtr dwData;
         public int cbData;
         public IntPtr lpData;
     }

     /// <summary>
     /// 发送字符串消息
     /// </summary>
     /// <param name="hWnd"></param>
     /// <param name="message"></param>
     public static void SendMessageString(IntPtr hWnd, string message)
     {
         if (string.IsNullOrEmpty(message)) return;

         byte[] messageBytes = Encoding.Unicode.GetBytes(message + '\0'); // 添加终止符

         COPYDATASTRUCT cds = new COPYDATASTRUCT();
         cds.dwData = IntPtr.Zero;
         cds.cbData = messageBytes.Length;
         cds.lpData = Marshal.AllocHGlobal(cds.cbData);
         Marshal.Copy(messageBytes, 0, cds.lpData, cds.cbData);
         try
         {
             SendMessage(hWnd, WM_COPYDATA, IntPtr.Zero, ref cds);
         }
         finally
         {
             //释放分配的内存，即使发生异常也不会泄漏资源
             Marshal.FreeHGlobal(cds.lpData);
         }
     } 
 }

 public partial class MainWindow : Window
 {
     public MainWindow()
     {
         InitializeComponent();
     }

     protected override void OnSourceInitialized(EventArgs e)
     {
         base.OnSourceInitialized(e);

         HwndSource hwndSource = PresentationSource.FromVisual(this) as HwndSource;
         hwndSource.AddHook(WndProc);
     }

     private IntPtr WndProc(IntPtr hwnd, int msg, IntPtr wParam, IntPtr lParam, ref bool handled)
     {
         if (msg == WM_COPYDATA)
         {
             COPYDATASTRUCT cds = (COPYDATASTRUCT)Marshal.PtrToStructure(lParam, typeof(COPYDATASTRUCT));
             string receivedMessage = Marshal.PtrToStringUni(cds.lpData);

             Console.WriteLine("收到消息：" + receivedMessage);

             //TODO:业务处理
             MessageBox.Show(receivedMessage);

             handled = true;
         }

         return IntPtr.Zero;
     }
 }