private void textBox1_KeyPress(object sender, KeyPressEventArgs e)
{
    MessageBox.Show(((int)(e.KeyChar)).ToString());
}

------解决方案--------------------
IntPtr hwnd = FindWindow(null, "a.txt");  
if (hwnd.ToInt32() != 0)
{
   if (SetForegroundWindow(hwnd))
       SendKeys.SendWait(Keys.A.ToString());  
}
else { MessageBox.Show("记事本没有运行 "); }  
Process myProcess = System.Diagnostics.Process.Start(@"D:\WINDOWS\notepad.exe");
  myProcess.StartInfo.WindowStyle = ProcessWindowStyle.Normal;
  myProcess.WaitForInputIdle(1000);
  if (myProcess.Responding)
  {
 SendKeys.SendWait("文字！");
 SendKeys.SendWait("{ENTER}");
 SendKeys.SendWait("%EA");
 SendKeys.SendWait("^C");
 SendKeys.SendWait("^V");
 SendKeys.SendWait("%FS");
 SendKeys.SendWait(@"C:\Test.txt");
 SendKeys.SendWait("%S");
  }
private void Form1_KeyUp ( object sender , KeyEventArgs e )  
{  
MessageBox.Show(e.KeyCode.ToString ( )) ;  
}  
句柄是一个32位的整数，是Windows在内存中维护的一个对象(窗口等)内存物理地址列表的整数索引