再谈CLR：事件定义

来源：互联网发布：day one 2 mac 破解版编辑：程序博客网时间：2024/05/16 12:19

这是今天课堂上的一个话题。如何定义事件，这好像并不是问题，我们习惯性直接用下面的代码定义，不是吗？

    class Customer {        public event EventHandler NameChanging;    }

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这样做的话，大致是会怎么编译呢？

其实编译器会帮我们生成两个方法: add_NameChanging和remove_NameChanging

还会有一个字段，是EventHandler这个类型的。

关键就在这里。它每次都会在创建对象的时候准备一个EventHandler，但问题是，并不是每个事件都会被用到。这就意味着，有一部分EventHandler其实是浪费的。

如果类型的事件很多，那么这个问题可能比较明显。

如何改进呢？

请参考下面的代码

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.ComponentModel;namespace ConsoleApplication1{    class Program    {        static void Main(string[] args)        {            Employee e = new Employee();            e.NameEvent += new EventHandler(e_NameEvent);            e.LNameEvent += new EventHandler(e_LNameEvent);            e.Name = "ares";            e.LName = "chen";            Console.Read();        }        static void e_LNameEvent(object sender, EventArgs e)        {            Employee emp = (Employee)sender;            Console.WriteLine(emp.LName);        }        static void e_NameEvent(object sender, EventArgs e)        {            Employee emp = (Employee)sender;            Console.WriteLine(emp.Name);        }    }    class Employee    {        private string name;        public string Name        {            get            {                return name;            }            set            {                name = value;                                if (list[nameEventKey] != null)                    list[nameEventKey].DynamicInvoke(new object[] { this, null });            }        }        private string lname;        public string LName        {            get            {                return lname;            }            set            {                lname = value;                if (list[lnameEventKey] != null)                    list[lnameEventKey].DynamicInvoke(new object[] { this, null });            }        }        private EventHandlerList list = new EventHandlerList();        private object nameEventKey=null;        public event EventHandler NameEvent        {            add            {                if (nameEventKey == null)                    nameEventKey = new object();                list.AddHandler(nameEventKey, value);            }            remove            {                if (nameEventKey == null)                    nameEventKey = new object();                list.RemoveHandler(nameEventKey, value);            }        }        private object lnameEventKey=null;        public event EventHandler LNameEvent        {            add            {                if (lnameEventKey == null)                    lnameEventKey = new object();                list.AddHandler(lnameEventKey, value);            }            remove            {                if (lnameEventKey == null)                    lnameEventKey = new object();                list.RemoveHandler(lnameEventKey, value);            }        }    }}