一个演示自定义事件(event)的完整例子。

类Car中包含车的制造厂商CarMake，型号CarModel，日期CarYear，车主CarOwner。在这个类中，我们想自定义一个OwnerChanged事件，每当车主CarOwner改变的时候，自动发生这个车主变更事件。COSTOM_PARAM是个预定义开关，演示了两种实现模式，主要是是否用EventHandler这个系统定义好的的代理(delegate)还是自定义代理事件的区别。两种情况编译执行后都会在屏幕上输出：lin-lei这个字符串。

#undef  COSTOM_PARAM  //
using System;
namespace CustomEvents
{
    

    public class Car
    {
#if COSTOM_PARAM
        public delegate void OwnerChangedEventHandler(string newOwner);
        public event OwnerChangedEventHandler OwnerChanged;
#else

        public event EventHandler OwnerChanged;
#endif

        private string make;
        private string model;
        private int year;
        private string owner;

        public string CarMake
        {
            get { return this.make; }
            set { this.make = value; }
        }

        public string CarModel
        {
            get { return this.model; }
            set { this.model = value; }
        }

        public int CarYear
        {
            get { return this.year; }
            set { this.year = value; }
        }

        public string CarOwner
        {
            get { return this.owner; }
            set
            {
                this.owner = value;
                if (this.OwnerChanged != null)
#if COSTOM_PARAM
                    this.OwnerChanged(value);
#else
                    this.OwnerChanged(this, new EventArgs());
#endif
            }
        }

        public Car()
        {
        }
    }

    public class Test
    {
#if COSTOM_PARAM
        public static void car_OwnerChanged(string v)
        {
            //the CarOwner property has been modified
            Console.WriteLine(v);
        }
#else
        public static void car_OwnerChanged(object sender, EventArgs e)
        {
            //the CarOwner property has been modified
            Console.WriteLine(((Car)sender).CarOwner);
        }
#endif

        public static void Main()
        {
            Car car = new Car();

            //adds an event handler to the OwnerChanged event
#if COSTOM_PARAM
            car.OwnerChanged += new Car.OwnerChangedEventHandler(car_OwnerChanged);
#else
            car.OwnerChanged += new EventHandler(car_OwnerChanged);
#endif
            //setting this will fire the OwnerChanged event
            car.CarOwner = "lin-lei";
        }  
    }
}