如何为Bank类增加一个BeforeClosed事件？

using System;

namespace ConsoleApplication1

{

    class Program

    {

        static void Main(string[] args)

        {



            Bank b = new Bank();

            b.BeforeClosed +=new Bank.BeforeBankCloseHandler(b_BeforeClosed);

            b.Close();

        }



        static void b_BeforeClosed(object sender, BeforeBankCloseEventArgs e)

        {

            Console.WriteLine("Bank'Name is:"+e.BankName);

            Console.WriteLine("Before bank is closed,I can do something");

        }



    }



    public class Bank

    {

        public delegate void BeforeBankCloseHandler(object sender, BeforeBankCloseEventArgs e);

        public event BeforeBankCloseHandler BeforeClosed;







        public void Close()

        {

            string bName = "China Bank";

            BeforeBankCloseEventArgs arg = new BeforeBankCloseEventArgs(bName);

            BeforeClosed(this, arg);

            Console.WriteLine("Bank Closed");

        }





    }



    public class BeforeBankCloseEventArgs : EventArgs

    {

        public BeforeBankCloseEventArgs(string m)

        {

            _bankName = m;

        }

        private string _bankName;

        public string BankName

        {

            get { return _bankName; }

            set { _bankName = value; }

        }



    }

}

using System;



class Program {

    public static void Main() {

        Console.ReadLine();

        Band b = new Band();

        b.BeforeClosed += new EventHandler(b_Changed);

    }



    static void b_Changed(object sender, EventArgs e) {

        throw new Exception("The method or operation is not implemented.");

    }

}



public class Band {

    public event EventHandler BeforeClosed;



    public void Close() {

        if (BeforeClosed != null) {

            BeforeClosed(this, EventArgs.Empty);

        }

    }

}