Delegate

using System;
public class EventTest
{
// 步骤1，定义delegate对象
public delegate void MyEventHandler(object sender, System.EventArgs e);
// 步骤2省略
public class MyEventCls
{
// 步骤3，定义事件处理方法，它与delegate对象具有相同的参数和返回值类// 型
public void MyEventFunc(object sender, System.EventArgs e)
{
Console.WriteLine("My event is ok!");
}
}
// 步骤4，用event关键字定义事件对象
private event MyEventHandler myevent;
private MyEventCls myecls;
public EventTest()
{
myecls = new MyEventCls();
// 步骤5，用+=操作符将事件添加到队列中
this.myevent += new MyEventHandler(myecls.MyEventFunc);
}
// 步骤6，以调用delegate的方式写事件触发函数
protected void OnMyEvent(System.EventArgs e)
{
if(myevent != null)
myevent(this, e);
}
public void RaiseEvent()
{
EventArgs e = new EventArgs();
// 步骤7，触发事件
OnMyEvent(e);
}
public static void Main()
{
EventTest et = new EventTest();
Console.Write("Please input ‘‘a‘‘:");
string s = Console.ReadLine();
if(s == "a")
{
et.RaiseEvent();
}
else
{
Console.WriteLine("Error");
}
}
}

using System;
using System.Text;
using System.Data;

namespace Class1
{    
    //定义事件引发时，需要传的参数
    class NewMailEventArgs:EventArgs
    {
        private readonly string m_from;
        private readonly string m_to;
        private readonly string m_subject;
        public NewMailEventArgs(string from, string to, string subject)
        {
            m_from = from;
            m_to = to;
            m_subject = subject;
        }
        public string From
        {
            get{return m_from;}
        }
        public string To
        {
            get{return m_to;}
        }
        public string Subject
        {
            get{return m_subject;}
        }

    }

    //事件所用的委托(链表)
    delegate void NewMailEventHandler(object sender, NewMailEventArgs e);

    //提供事件的类
    class MailManager
    {
        public event NewMailEventHandler NewMail;
        //通知已订阅事件的对象
        protected virtual void OnNewMail(NewMailEventArgs e)
        {
            NewMailEventHandler temp = NewMail; //MulticastDelegate一个委托链表
            //通知所有已订阅事件的对象
            if(temp != null)
                temp(this,e); //通过事件NewMail(一种特殊的委托)逐一回调客户端的方法

        }
        //提供一个方法，引发事件
        public void SimulateNewMail(string from, string to, string subject)
        {
            NewMailEventArgs e = new NewMailEventArgs(from,to,subject);
            OnNewMail(e);
        }
    }


    //使用事件
    class Fax
    {
        public Fax(MailManager mm)
        {
            //Subscribe 
            mm.NewMail += new NewMailEventHandler(Fax_NewMail);
        }
        private void Fax_NewMail(object sender, NewMailEventArgs e)
        {
            Console.WriteLine("Message arrived at Fax...");
            Console.WriteLine("From={0}, To={1}, Subject=‘{2}‘",e.From,e.To,e.Subject);
        }
        public void Unregister(MailManager mm)
        {
            mm.NewMail -= new NewMailEventHandler(Fax_NewMail);
        }
    }
    class Print
    {
        public Print(MailManager mm)
        {
            //Subscribe ,在mm.NewMail的委托链表中加入Print_NewMail方法
            mm.NewMail += new NewMailEventHandler(Print_NewMail);
        }
        private void Print_NewMail(object sender, NewMailEventArgs e)
        {
            Console.WriteLine("Message arrived at Print...");
            Console.WriteLine("From={0}, To={1}, Subject=‘{2}‘",e.From,e.To,e.Subject);
        }
        public void Unregister(MailManager mm)
        {
            mm.NewMail -= new NewMailEventHandler(Print_NewMail);
        }
    }

    class ExcelProgram
    {
        [STAThread]
        static void Main(string[] args)
        {    
            MailManager mm = new MailManager();
            if(true)
            {
                Fax fax = new Fax(mm);
                Print prt = new Print(mm);
            }

            mm.SimulateNewMail("Anco","Jerry","Event test");
            Console.ReadLine();
        }
    }
}