using System;
using System.Linq;

namespace ConsoleTest
{
public class NewMailEventArgs : EventArgs
{
private readonly string from, to, subject;

public NewMailEventArgs(string from, string to, string subject)
{
this.from = from;
this.to = to;
this.subject = subject;
}

public string Subject
{
get
{
return this.subject;
}
}

public string To
{
get
{
return this.to;
}
}

public string From
{
get
{
return this.from;
}
}
}
}

public delegate void NewMailHandler(object e, NewMailEventArgs args);

public class MailManager
{
public event NewMailHandler NewMail;
}

public class MailManager
{
public event EventHandler<NewMailEventArgs> NewMail;
}

namespace System
{
// 摘要:
// 表示将处理事件的方法。
//
// 参数:
// sender:
// 事件源。
//
// e:
// 一个包含事件数据的 System.EventArgs。
//
// 类型参数:
// TEventArgs:
// 由该事件生成的事件数据的类型。
[Serializable]
public delegate void EventHandler<TEventArgs>(object sender, TEventArgs e);
}

public class MailManager
{
public event EventHandler<NewMailEventArgs> NewMail;

protected virtual void OnNewMail(NewMailEventArgs e)
{
//处于线程安全的考虑，现在将对委托字段的引用复制到一个临时字段中
EventHandler<NewMailEventArgs> temp = System.Threading.Interlocked.CompareExchange
(ref NewMail, null, null);

//如果有事件订阅者对象的存在，则通知他们，事件已触发
if (temp != null)
temp(this, e);
}
}

public class MailManager
{
public event EventHandler<NewMailEventArgs> NewMail;

protected virtual void OnNewMail(NewMailEventArgs e)
{
//处于线程安全的考虑，现在将对委托字段的引用复制到一个临时字段中
EventHandler<NewMailEventArgs> temp = System.Threading.Interlocked.CompareExchange
(ref NewMail, null, null);

//如果有事件订阅者对象的存在，则通知他们，事件已触发
if (temp != null)
temp(this, e);
}

public void SimulateNewMail(string from, string to, string subject)
{
//构造一个对象来封装向传给事件订阅者的信息
NewMailEventArgs e = new NewMailEventArgs(from, to, subject);

//触发事件引发的入口方法
OnNewMail(e);
}
}

internal sealed class Fax
{
private MailManager mailManager;

public Fax(MailManager mm)
{
this.mailManager = mm;
}

public void Register()
{
mailManager.NewMail += new EventHandler<NewMailEventArgs>(FaxMsg);
}

void FaxMsg(object sender, NewMailEventArgs e)
{
Console.WriteLine("Fax mail message");
Console.WriteLine("From = {0}, To = {1}, Subject = {2}", e.From, e.To, e.Subject);
}

public void Unregister()
{
mailManager.NewMail -= FaxMsg;
}
}