//引用
using System.Runtime.InteropServices;
using System.Diagnostics;
//在类中声明外部函数
        [DllImport("user32.dll", CharSet = CharSet.Auto, CallingConvention = CallingConvention.Winapi)]
        internal static extern IntPtr GetFocus();
        [DllImport("user32.dll", EntryPoint = "FindWindowEx")]
        internal static extern IntPtr FindWindowEx(IntPtr hWndParent, IntPtr hWndChildAfter, string lpszClass, string lpszWindow);
        [DllImport("user32.dll",EntryPoint="SendMessageA")]
        internal static extern int SendMessage(IntPtr hWnd, int msg, IntPtr wparam, string lparam);

// 声明消息标识
public const int WM_SETTEXT = 0x000C;
//在Button_click事件中添加以下代码
                    Process.Start("Notepad");
                    IntPtr myNotePad = IntPtr.Zero;
                    myNotePad = FindWindowEx(IntPtr.Zero, IntPtr.Zero, "无标题 - 记事本", null);
                    IntPtr myNote = IntPtr.Zero;
                    myNote = FindWindowEx(myNotePad, IntPtr.Zero, "Edit", null);
                    //SendMessage(myNote, WM_SETTEXT, IntPtr.Zero, strData);
                    SendMessage(myNote, WM_SETTEXT, IntPtr.Zero, "display str");

#region [ 启动记事本 ]

                System.Diagnostics.Process Proc;

                try
                {
                    // 启动记事本
                    Proc = new System.Diagnostics.Process();
                    Proc.StartInfo.FileName = "notepad.exe";
                    Proc.StartInfo.UseShellExecute = false;
                    Proc.StartInfo.RedirectStandardInput = true;
                    Proc.StartInfo.RedirectStandardOutput = true;

                    Proc.Start();
                }
                catch
                {
                    Proc = null;
                }

                #endregion

                #region [ 传递数据给记事本 ]

                if (Proc != null)
                {
                    // 调用 API, 传递数据
                    while (Proc.MainWindowHandle == IntPtr.Zero)
                    {
                        Proc.Refresh();
                    }

                    IntPtr vHandle = FindWindowEx(Proc.MainWindowHandle, IntPtr.Zero, "Edit", null);

                    // 传递数据给记事本
                    SendMessage(vHandle, WM_SETTEXT, IntPtr.Zero, "display str");
                }

                #endregion