委托，改写客户端传递的参数。好了最终代码如下，好累

using System;
class MyEventArgs:EventArgs
{
 private char keyChar;
 public MyEventArgs(char keyChar)
 {
  this.keyChar=keyChar;
 }
 public char KeyChar
 {
  get
  {
   return keyChar;
  }
 }
}
  

class UserInputMonitor
{
 public delegate void UserRequest(object sender,MyEventArgs e);
 //定义委托
 public event UserRequest OnUserRequest;
 //此委托类型类型的事件
 public void Run()
 {
  bool finished=false;
  do
  {
   string inputString= Console.ReadLine();
   if (inputString!="") 
    OnUserRequest(this,new MyEventArgs(inputString[0]));
  }while(!finished);
 }
}

  

public class Client
{
 public static void Main()
 {
  UserInputMonitor monitor=new UserInputMonitor();
  new Client(monitor);
  monitor.Run();
 }
 private void ShowMessage(object sender,MyEventArgs e)
 {
  Console.WriteLine("捕捉到：{0}",e.KeyChar);
 }
 Client(UserInputMonitor m)
 {
  m.OnUserRequest+=new UserInputMonitor.UserRequest(this.ShowMessage);
  //m.OnUserRequest+=new m.UserRequest(this.ShowMessage);
  //注意这种写法是错误的，因为委托是静态的
 }
}