观察者模式 c#

当某一对象发生变化时，所有依赖它的对象都需要得到通知。

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApplication1
{
    class Program
    {

        public class CreditCard
        {
            private float money;
            public event EventHandler<CreditCard> spendMoney;

            public float Money
            {
                get { return money; }
                set
                {
                    money = value;
                    Notify();
                }
            }

            public void Notify()
            {
                if (spendMoney != null)
                {
                    spendMoney(this, this);
                }
            }
        }

        public class Phone
        {
            public void Notify(object sender, CreditCard e)
            {
                Console.WriteLine("phone notify " + e.Money);
            }
        }

        public class Computer
        {
            public void Notify(object sender, CreditCard e)
            {
                Console.WriteLine("computer notify " + e.Money);
            }
        }

        static void Main(string[] args)
        {
            CreditCard creditCard = new CreditCard();
            Phone phone = new Phone();
            Computer computer = new Computer();
            creditCard.spendMoney += phone.Notify;
            creditCard.spendMoney += computer.Notify;

            creditCard.Money = 200;
          
        }
    }
}