这也是今天讨论到的一个话题，其实还是比较简单的。因为事件处理程序都是在主线程被执行的，所以主线程肯定是依次执行他们。那么究竟是什么决定了这个顺序呢？

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;using System.Threading;
namespace ConsoleApplication1
{class Program{static void Main(string[] args){///这个例子解释了如果为一个事件绑定了多个事件处理程序，那么他们处理的顺序与绑定顺序是一致的Console.WriteLine("主线程号是:{0}", Thread.CurrentThread.ManagedThreadId);Employee e = new Employee();e.NameChanged += new EventHandler(e_NameChanged);e.NameChanged += new EventHandler(e_NameChanged2);e.Name = "ares chen";Console.Read();}static void e_NameChanged2(object sender, EventArgs e){Console.WriteLine("第2个事件处理程序触发的时间是:{0}", DateTime.Now);Console.WriteLine("当前线程号是:{0}", Thread.CurrentThread.ManagedThreadId);}static void e_NameChanged(object sender, EventArgs e){Console.WriteLine("第1个事件处理程序触发的时间是:{0}", DateTime.Now);Console.WriteLine("当前线程号是:{0}", Thread.CurrentThread.ManagedThreadId);            }}class Employee{public event EventHandler NameChanged;private string name;public string Name{get{return name;}set{name = value;if (NameChanged != null)NameChanged(this, null);}}}
}

其实要深入看的话，这是因为事件的处理程序是通过一个列表来管理的，就是EventHandlerList

[HostProtection(SecurityAction.LinkDemand, SharedState=true)]
public sealed class EventHandlerList : IDisposable
{// Fieldsprivate ListEntry head;private Component parent;// Methodspublic EventHandlerList(){}internal EventHandlerList(Component parent){this.parent = parent;}public void AddHandler(object key, Delegate value){ListEntry entry = this.Find(key);if (entry != null){entry.handler = (entry.handler, value);//这里的关键在于Delegate.Combine，所以根据注册顺序不一样，是一个顺序型的组合}else{this.head = new ListEntry(key, value, this.head);}}public void AddHandlers(EventHandlerList listToAddFrom){for (ListEntry entry = listToAddFrom.head; entry != null; entry = entry.next){this.AddHandler(entry.key, entry.handler);}}public void Dispose(){this.head = null;}private ListEntry Find(object key){ListEntry head = this.head;while (head != null){if (head.key == key){return head;}head = head.next;}return head;}public void RemoveHandler(object key, Delegate value){ListEntry entry = this.Find(key);if (entry != null){entry.handler = Delegate.Remove(entry.handler, value);}}// Propertiespublic Delegate this[object key]{get{ListEntry entry = null;if ((this.parent == null) || this.parent.CanRaiseEventsInternal){entry = this.Find(key);}if (entry != null){return entry.handler;}return null;}set{ListEntry entry = this.Find(key);if (entry != null){entry.handler = value;}else{this.head = new ListEntry(key, value, this.head);}}}// Nested Typesprivate sealed class ListEntry{// Fieldsinternal Delegate handler;internal object key;internal EventHandlerList.ListEntry next;// Methodspublic ListEntry(object key, Delegate handler, EventHandlerList.ListEntry next){this.next = next;this.key = key;this.handler = handler;}}
}所以,既然是通过线性表来保存的，那么就有一个先后顺序的情况。其实，一个更好的写法是下面这样的

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Reflection;using System.Threading;
using System.ComponentModel;
namespace ConsoleApplication1
{class Program{static void Main(string[] args){///这个例子解释了如果为一个事件绑定了多个事件处理程序，那么他们处理的顺序与绑定顺序是一致的Console.WriteLine("主线程号是:{0}", Thread.CurrentThread.ManagedThreadId);Employee e = new Employee();e.NameChanged += new EventHandler(e_NameChanged);e.NameChanged += new EventHandler(e_NameChanged2);e.Name = "ares chen";Console.Read();}static void e_NameChanged2(object sender, EventArgs e){Console.WriteLine("第2个事件处理程序触发的时间是:{0}", DateTime.Now);Console.WriteLine("当前线程号是:{0}", Thread.CurrentThread.ManagedThreadId);}static void e_NameChanged(object sender, EventArgs e){Console.WriteLine("第1个事件处理程序触发的时间是:{0}", DateTime.Now);Console.WriteLine("当前线程号是:{0}", Thread.CurrentThread.ManagedThreadId);            }}class Employee{//public event EventHandler NameChanged;private string name;public string Name{get{return name;}set{name = value;}}}
}

为什么使用EventHandlerList？ 这个问题之前就谈论过，默认情况下，客户端程序每为事件绑定一个处理程序，就需要在类型中产生一个delegate的引用，如此一来，如果事件很多的话，不利于较好地控制内存。但如果用EventHandlerList的话，则有利于统一管理所有的delegate