方法一，详细的声明

namespace HelloWorldConsole
{internal class Program{static void Main(string[] args){Customer customer = new Customer();Waiter waiter = new Waiter();customer.Order += waiter.Action;customer.Action();}}public class OrderEventArgs : EventArgs{public string DishName { get; set; }public string Size { get; set; }}public delegate void OrderEventHandler(Customer customer, OrderEventArgs e);public class Customer{public double Bill { get; set; }private OrderEventHandler orderEventHandler;public event OrderEventHandler Order{add { orderEventHandler += value; }remove { orderEventHandler -= value; }}public void PayTheBill(){Console.WriteLine("i will pay-{0}", Bill);}public void Think(){if (orderEventHandler != null){OrderEventArgs e = new OrderEventArgs();e.DishName = "宫保鸡丁";e.Size = "large";orderEventHandler(this, e);}}public void Action(){Think();PayTheBill();}}public class Waiter{public void Action(Customer customer, OrderEventArgs e){double price = 10;switch (e.Size){case "small": price /= 2; break;case "large": price *= 1.5; break;default: break;}Console.WriteLine("i will serve the dish {0}-{1}", e.DishName, e.Size);customer.Bill += price;}}
}

方法二，简化的声明，也是最常用的写法

namespace HelloWorldConsole
{internal class Program{static void Main(string[] args){Customer customer = new Customer();Waiter waiter = new Waiter();customer.Order += waiter.Action;customer.Action();}}/// <summary>/// 事件参收/// </summary>public class OrderEventArgs : EventArgs{public string DishName { get; set; }public string Size { get; set; }}public class Customer{public double Bill { get; set; }public event EventHandler Order;public void Think(){if (Order != null){OrderEventArgs e = new OrderEventArgs();e.DishName = "宫保鸡丁";e.Size = "large";Order(this, e);}}public void PayTheBill(){Console.WriteLine("i will pay-{0}", Bill);}public void Action(){Think();PayTheBill();}}public class Waiter{public void Action(object sender, EventArgs _e){Customer customer = sender as Customer;OrderEventArgs e = _e as OrderEventArgs;double price = 10;switch (e.Size){case "small": price /= 2; break;case "large": price *= 1.5; break;default: break;}Console.WriteLine("i will serve the dish {0}-{1}", e.DishName, e.Size);customer.Bill += price;}}
}