sendmessage 发信息 ？

Question

发送信息 通过sendmessag发送信息。并传递一个字符串。 能够收到信息 但收到的结构中的字符串为空？？源代码：
  发送方：
       private static readonly int CUSTOM_MESSAGE = 0X400 + 2;
      //api声明 
       [DllImport("user32.dll")]
        public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
        [DllImport("User32.dll", EntryPoint = "SendMessage")]
        private static extern int SendMessage(
        IntPtr hWnd,        // 信息发住的窗口的句柄
        int Msg,            // 消息ID
        int wParam,         // 参数1
        ref messagstring lParam // 参数2   [MarshalAs(UnmanagedType.LPTStr)]StringBuilder lParam
        );
      发送代码：
        IntPtr hwnd_win;
            hwnd_win = FindWindow(null, "reseviceform");  //找到要发送的窗体
            string strtext = "aaa";
            messagstring ms;
            ms.lpData = strtext;
            SendMessage(hwnd_win, CUSTOM_MESSAGE, 0, ref ms);   
接收方：     protected override void WndProc(ref Message m)
        {
            if (m.Msg == CUSTOM_MESSAGE)
            {
                messagstring ms=new messagstring () ;
                Type mytype = ms.GetType();
                ms = (messagstring)m.GetLParam(mytype);               textBox1.Text =Convert.ToString ( ms.lpData);
            }             
            base.WndProc(ref m);
        }发送的数据结构
        namespace copyMessage
  { 
    //要发信息数据结构，作为SendMessage函数的LParam参数
    public struct messagstring
    {
        [MarshalAs(UnmanagedType.LPStr)]
        public string lpData;       //要发送的信息
    }
   }

Answer 1

应该是没有找到窗口句柄   
            IntPtr hwnd_win;
            hwnd_win = FindWindow(null, "reseviceform");  //找到要发送的窗体
            if (hwnd_win.ToInt32() == null)
            {
                string strtext = "aaa";
                messagstring ms;
                ms.lpData = strtext;
                SendMessage(hwnd_win, CUSTOM_MESSAGE, 0, ref ms);
                // 可以使用当前窗口测试
                //SendMessage(this.Handle,CUSTOM_MESSAGE 0, ref ms);
            }
            else
            {
                MessageBox.Show("找不到窗口");
            }

Answer 2

[DllImport("user32.dll")]
        public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
        [DllImport("User32.dll", EntryPoint = "SendMessage")]
        private static extern int SendMessage(
        IntPtr hWnd,        // 信息发住的窗口的句柄
        int Msg,            // 消息ID
        int wParam,         // 参数1
        StringBuilder lParam
        );
用这样的声明可以吗?

Answer 3

如何在C#用WM_COPYDATA消息来实现两个进程之间传递数据
http://www.chenjiliang.com/Article/View.aspx?ArticleID=2277&TypeID=84关于C#中实现两个应用程序消息通讯的问题
http://www.chenjiliang.com/Article/View.aspx?ArticleID=3495&TypeID=79

Answer 4

  
接受方。
      const int WM_COPYDATA = 0x004A;   
        protected override void DefWndProc(ref   System.Windows.Forms.Message m)
        {
            switch (m.Msg)
            {
                case WM_COPYDATA:
                    COPYDATASTRUCT mystr = new COPYDATASTRUCT();
                    Type mytype = mystr.GetType();
                    mystr = (COPYDATASTRUCT)m.GetLParam(mytype);
                    
                    break;
                default:
                    base.DefWndProc(ref   m);
                    break;            }        }        const int WM_COPYDATA = 0x004A;        [DllImport("User32.dll", EntryPoint = "SendMessage")]
        private static extern int SendMessage(
        IntPtr hWnd,   //   handle   to   destination   window   
        int Msg,   //   message   
        int wParam,   //   first   message   parameter   
        ref   COPYDATASTRUCT lParam   //   second   message   parameter   
        );
        const int WM_COPYDATA = 0x004A;
      public struct COPYDATASTRUCT
        {
            public IntPtr dwData;
            public int cbData;
            [MarshalAs(UnmanagedType.LPStr)]
            public string lpData;
        }发送..
        const int WM_CHAR = 0x0102;
            IntPtr hwnd_win;
            IntPtr hwnd_textbox;            hwnd_win = FindWindow(null, "Form4");
            
           
            const int BM_CLICK = 0x00F5;
            COPYDATASTRUCT cds;
            cds.dwData = (IntPtr)100;
            cds.lpData = "Test Message";
            cds.cbData = 14;            //Message msg = Message.Create(hwnd_textbox, BM_CLICK, new IntPtr(0), new IntPtr(0));
            //// PostMessage(msg.HWnd, msg.Msg, msg.WParam, msg.LParam);
            ////SendMessage(hwnd_textbox, BM_CLICK, 0, ref cds);
            SendMessage(hwnd_win, WM_COPYDATA, 0, ref cds);

Answer 5

        [DllImport("user32.dll")]
        public static extern IntPtr FindWindow(string lpClassName, string lpWindowName);        [DllImport("user32.dll")]
        public static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);        [DllImport("user32.dll", CharSet = CharSet.Unicode)]
        public static extern IntPtr PostMessage(IntPtr hwnd, int wMsg, IntPtr wParam, IntPtr lParam);
可以收到。。正确信息...