public static void SendMessage(string destProcessName, int msgID, string strMsg);

SendMessage(hwnd, WM_COPYDATA, wParam, lParam);

typedef  struct  tagCOPYDATASTRUCT
{   DWORD  dwData;  //用户定义数据   DWORD  cbData;  //数据大小   PVOID  lpData;  //指向数据的指针
} COPYDATASTRUCT;

protected override void DefWndProc(ref  System.Windows.Forms.Message m)
{switch (m.Msg){case WinMessageUtil.WM_COPYDATA:string str = WinMessageUtil.ReceiveMessage(ref m);break;default:break;}base.DefWndProc(ref  m);
}

using System;
using System.Runtime.InteropServices;
using System.Diagnostics;namespace Speeding.Util
{//WM_COPYDATA消息所要求的数据结构public struct CopyDataStruct{public IntPtr dwData;public int cbData;[MarshalAs(UnmanagedType.LPStr)]public string lpData;}/// <summary>/// 本类封装了一些进程间通讯的细节/// </summary>public class WinMessageUtil{public const int WM_COPYDATA = 0x004A;//通过窗口的标题来查找窗口的句柄[DllImport("User32.dll", EntryPoint = "FindWindow")]private static extern int FindWindow(string lpClassName, string lpWindowName);//在DLL库中的发送消息函数[DllImport("User32.dll", EntryPoint = "SendMessage")]private static extern int SendMessage(int hWnd,                        // 目标窗口的句柄  int Msg,                        // 在这里是WM_COPYDATAint wParam,                    // 第一个消息参数ref  CopyDataStruct lParam        // 第二个消息参数
            );/// <summary>/// 发送消息，只能传递一个自定义的消息ID和消息字符串，想传一个结构，但没成功/// </summary>/// <param name="destProcessName">目标进程名称，如果有多个，则给每个都发送</param>/// <param name="msgID">自定义数据，可以通过这个来决定如何解析下面的strMsg</param>/// <param name="strMsg">传递的消息，是一个字符串</param>public static void SendMessage(string destProcessName, int msgID, string strMsg){if (strMsg == null)return;//按进程名称查找，同名称的进程可能有许多，所以返回的是一个数组Process[] foundProcess = Process.GetProcessesByName(destProcessName);foreach (Process p in foundProcess){int toWindowHandler = p.MainWindowHandle.ToInt32();if (toWindowHandler != 0){CopyDataStruct cds;cds.dwData = (IntPtr) msgID;   //这里可以传入一些自定义的数据，但只能是4字节整数      cds.lpData = strMsg;            //消息字符串cds.cbData = System.Text.Encoding.Default.GetBytes(strMsg).Length + 1;  //注意，这里的长度是按字节来算的//发送方的窗口的句柄, 由于本系统中的接收方不关心是该消息是从哪个窗口发出的，所以就直接填0了int fromWindowHandler = 0;SendMessage(toWindowHandler, WM_COPYDATA, fromWindowHandler, ref  cds);}}}/// <summary>/// 接收消息，得到消息字符串/// </summary>/// <param name="m">System.Windows.Forms.Message m</param>/// <returns>接收到的消息字符串</returns>public static string ReceiveMessage(ref  System.Windows.Forms.Message m){CopyDataStruct cds = (CopyDataStruct) m.GetLParam(typeof(CopyDataStruct));return cds.lpData;}}
}