c#windows消息循环sendmessage实例

 [DllImport("User32.dll", EntryPoint = "SendMessage")]
        private static extern int SendMessage(
        IntPtr hWnd,        // 信息发往的窗口的句柄  
        int Msg,            // 消息ID  
        int wParam,         // 参数1  
        string lParam
        );
        [DllImport("User32.dll", EntryPoint = "SendMessage")]
        private static extern int SendMessage2(
       IntPtr hWnd,        // 信息发往的窗口的句柄  
       int Msg,            // 消息ID  
       int wParam,         // 参数1  
       IntPtr lParam
       );

        [DllImport("User32.dll", EntryPoint = "FindWindow")]
        private extern static IntPtr FindWindow(string lpClassName, string lpWindowName);

        [DllImport("User32.dll", EntryPoint = "FindWindowEx")]
        private static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpClassName, string lpWindowName);

 private void button4_Click(object sender, EventArgs e)
        {
          IntPtr hwnd=   FindWindow(null, "testForm");
            string info = "my info:ΑΒβδγζηθ";
          IntPtr pinfo= Marshal.StringToHGlobalAnsi(info);
            SendMessage2(hwnd, Form2.USERMESSAGEID, 12, pinfo);
            SendMessage(hwnd, Form2.USERMESSAGEID, 12, info);
        }

public  const int  USERMESSAGEID =0x2021;
        protected override void WndProc(ref Message m)
        {
             switch(m.Msg)
            {
                case USERMESSAGEID:
                   {
                        int wparam= m.WParam.ToInt32();
                        string str = Marshal.PtrToStringAnsi(m.LParam);
                        break;
                    }

            }
            base.WndProc(ref m);
        }

  [DllImport("User32.dll", EntryPoint = "SendMessage")]
        private static extern int SendMessage(
        IntPtr hWnd,        // 信息发往的窗口的句柄  
        int Msg,            // 消息ID  
        int wParam,         // 参数1  
        ref My_lParam lParam
        );

 IntPtr ptr = FindWindow(null, "主界面");
                    SendMessage(ptr, MYMESSAGE, 1, ref m);//发送消息  

  protected override void DefWndProc(ref Message m)
        {
            try
            {
                switch (m.Msg)
                {
                    
                    case MYMESSAGE:
                       {
                        My_lParam ml = new My_lParam();
                        Type t = ml.GetType();
                        ml = (My_lParam)m.GetLParam(t);
                       
                       break;
                        }
                   deafult ：base.DefWndProc(ref m);
               }
            catch()
              {                  }
            }