C#事件访问器详解

}

    class MyClass
    {
        //声明一个成员变量来保存事件句柄（事件被激发时被调用的delegate）
        private EventHandler m_Handler = null;

        //激发事件
        public void FireAEvent()
        {
            if (m_Handler != null)
            {
                m_Handler();
            }
        }

        //声明事件
        public event EventHandler AEvent
        {
            //添加访问器
            add
            {
                //注意,访问器中实际包含了一个名为value的隐含参数
                //该参数的值即为客户程序调用+=时传递过来的delegate
                Console.WriteLine("AEvent add被调用,value的HashCode为:" + value.GetHashCode());
                if (value != null)
                {
                    //设置m_Handler域保存新的handler
                    m_Handler = value;
                }
            }

            //删除访问器
            remove
            {
                Console.WriteLine("AEvent remove被调用,value的HashCode为:" + value.GetHashCode());
                if (value == m_Handler)
                {
                    //设置m_Handler为null,该事件将不再被激发
                    m_Handler = null;
                }
            }

        }

    }

    class Program
    {
        static void Main(string[] args)
        {
            MyClass obj = new MyClass();
            //创建委托
            EventHandler MyHandler = new EventHandler(MyEventHandler);
            MyHandler += MyEventHandle2;
            //将委托注册到事件
            obj.AEvent += MyHandler;
            //激发事件
            obj.FireAEvent();
            //将委托从事件中撤销
            obj.AEvent -= MyHandler;
            //再次激发事件
            obj.FireAEvent();

            Console.ReadKey();
        }

        //事件处理程序
        static void MyEventHandler()
        {
            Console.WriteLine("This is a Event!");
        }

        //事件处理程序
        static void MyEventHandle2()
        {
            Console.WriteLine("This is a Event2!");
        }
    }