问一个SendMessage的问题（C#）

//方法声明

[DllImport("user32.dll")]

        static extern int SendMessage(IntPtr Handle, int WParam, int LParam);



        [DllImport("User32.dll", EntryPoint = "FindWindow")]

        private static extern IntPtr FindWindow(string lpClassName, string lpWindowName);



        [DllImport("user32.dll", EntryPoint = "FindWindowEx")]

        private static extern IntPtr FindWindowEx(IntPtr hwndParent, IntPtr hwndChildAfter, string lpszClass, string lpszWindow);



        [DllImport("User32.dll", EntryPoint = "SendMessage")]

        private static extern int SendMessage(IntPtr hWnd, int Msg, IntPtr wParam, string lParam);

        [DllImport("user32.dll", EntryPoint = "SetForegroundWindow", SetLastError = true)]

        private static extern void SetForegroundWindow(IntPtr hwnd);



        //单击事件

        private void btn_msg_start_Click(object sender, EventArgs e)

        {

            try

            {//启动旺旺客户端程序

                System.Diagnostics.Process txt = System.Diagnostics.Process.Start("C:\\Program Files\\Alisoft\\WangWang\\AliIM.exe", @"d:\text_test.txt");

                txt.StartInfo.WindowStyle = ProcessWindowStyle.Normal;

                //等待一秒，以便目标程序notepad.exe输入状态就绪

                txt.WaitForInputIdle(1000);

                //如果目标程序 notepad.exe 没有停止响应，则继续

                if (txt.Responding)

                {

                    SearchWindow();

                }

            }

            catch { }

        }

        

       





        const int WM_GETTEXT = 0x000D;

        const int WM_SETTEXT = 0x000C;

        const int WM_CLICK = 0x00F5; 

        

        

         private int SearchWindow() 

        { 

            int retval = 0; //增加一个返回值用来判断操作是否成功 

     

            //下面的这些参数都可以用Spy++查到 

            string lpszParentClass = "StandardWindow"; //整个窗口的类名 

            string lpszParentWindow = "登录窗口"; //窗口标题 

            string lpszClass = "EditComponent"; //需要查找的子窗口的类名，也就是用户名输入框 

            string lppassword = "ATL:Edit";//密码输入框

            string lpszClass_Submit = "StandardButton"; //需要查找的Button的类名 

            string lpszName_Submit = "登  录"; ///需要查找的Button的标题 

           

     

            IntPtr ParenthWnd = new IntPtr(0); 

            IntPtr EdithWnd = new IntPtr(0); 

     

            //查到窗体，得到整个窗体 

            ParenthWnd = FindWindow(lpszParentClass,lpszParentWindow); 

     

            //判断这个窗体是否有效 

            if (!ParenthWnd.Equals(IntPtr.Zero)) 

            { 

                //得到User Name这个子窗体，并设置其内容 

                EdithWnd = FindWindowEx(ParenthWnd,EdithWnd,lpszClass,""); 

                if (!EdithWnd.Equals(IntPtr.Zero)) 

                { 

                   

                    //调用SendMessage方法设置其内容 

                    SendMessage(EdithWnd, WM_SETTEXT, (IntPtr)0, "sdfsdfd"); 

                  retval ++; 

                } 

            //得到Password这个子窗体，并设置其内容 



                EdithWnd = FindWindowEx(ParenthWnd, EdithWnd,lppassword, ""); 

                if (!EdithWnd.Equals(IntPtr.Zero)) 

                { 

                    

                    SendMessage(EdithWnd, WM_SETTEXT, (IntPtr)0, "sdfsdsdfsdasdfd"); 

                    retval ++; 

                } 

     

               

     

                //得到Button这个子窗体，并触发它的Click事件 

                EdithWnd = FindWindowEx(ParenthWnd,EdithWnd, lpszClass_Submit, lpszName_Submit);

                if (!EdithWnd.Equals(IntPtr.Zero))

                {

                    SendMessage(EdithWnd, WM_CLICK, (IntPtr)0, "0");

                    retval++;

                }

           }



            return retval;

        }