C#中Delegate

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Ch1
{

    public delegate void GreetingDelegate(string name);//委托

    public class FirstDelegate
    {
        public static void GreetingChinese(string name)
        {
            Console.WriteLine("早上好：" + name);
        }

        public static void GreetingEnglish(string name)
        {
            Console.WriteLine("Good morning：" + name);
        }
    }

    public class GreetingManager
    {
        public static GreetingDelegate MakeLanguageByDelegate;
        public static void GreetingPeople(string name)
        {
            if (MakeLanguageByDelegate != null)
            {
                MakeLanguageByDelegate(name);
            }
        }

        public static event GreetingDelegate MakeLanguageByEvent;//事件,不管是不是声明为public，它总是被声明为private

        public static void GreetingPeopleEvent(string name)
        {
            if (MakeLanguageByEvent != null)
            {
                MakeLanguageByEvent(name);
            }
        }

    }

    public class FirstDelegate1
    {
        public void GreetingChinese(string name)
        {
            Console.WriteLine("早上好：" + name);
        }

        public void GreetingEnglish(string name)
        {
            Console.WriteLine("Good morning：" + name);
        }
    }

    public class GreetingManager1
    {
        public GreetingDelegate MakeLanguageByDelegate;
        public void GreetingPeople(string name)
        {
            if (MakeLanguageByDelegate != null)
            {
                MakeLanguageByDelegate(name);
            }
        }

        public event GreetingDelegate MakeLanguageByEvent;

        public void GreetingPeopleEvent(string name)
        {
            if (MakeLanguageByEvent != null)
            {
                MakeLanguageByEvent(name);
            }
        }

    }

}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Ch1
{
    /**
     * Observer模式定义对象间的一对多的依赖关系,当一个对象的状态发生改变时, 所有依赖于它的对象都得到通知并被自动更新。
     * 水烧开的时候通知报警器和显示器
     * */
    public class WaterDelegate
    {
        private int temperature = 0;
        public delegate void BoilHandler(int param);//声明委托
        public event BoilHandler BoilEvent;//声明事件

        public void BoilWater()
        {
            for (int i = 0; i <= 100; i++)
            {
                temperature = i;
                if (temperature >= 95) //温度大于95警告并且显示温度
                {
                    if (BoilEvent != null) //如果有对象注册
                    {
                        BoilEvent(temperature); //调用所有注册方法
                        Console.WriteLine("-----------------");
                    }
                }
            }
        }
    }

    //报警
    public class Alarm
    {
        public void MakeAlert(int temperature)
        {
            Console.WriteLine("Alarm：嘀嘀嘀，水已经 {0} 度了：", temperature);
        }

        /**
         * .Net Framework中的委托与事件
         * 委托声明原型中的Object类型的参数代表了Object，也就是监视对象，在本例中是 Heater(热水器)。回调函数(比如Alarm的MakeAlert)可以通过它访问触发事件的对象(Heater)。
         * EventArgs 对象包含了Observer所感兴趣的数据，在本例中是temperature。
         * */
        public void MakeAlert(Object sender, BoiledEventArgs e)
        {
            Heater heater = (Heater)sender;
            Console.WriteLine("Alarm：{0} - {1}, 嘀嘀嘀，水已经 {2} 度了 ", heater.area, heater.type, e.temperature);
        }
    }

    //显示
    public class Display
    {
        public static void ShowMessage(int temperature)
        {
            Console.WriteLine("Display：水快烧开了，当前温度：{0}度。", temperature);
        }

        public static void ShowMessage(Object sender, BoiledEventArgs e)
        {
            Console.WriteLine("Display：水快烧开了，当前温度：{0}度。", e.temperature);
            Console.WriteLine();
        }
    }

    public class Heater
    {
        private int temperature;

        public string area { get; set; }    //添加地区
        public string type { get; set; }   //添加类型

        public delegate void BoiledEventHandler(Object sender, BoiledEventArgs e);//委托
        public event BoiledEventHandler Boiled;//事件

        // 可以供继承自 Heater 的类重写，以便继承类拒绝其他对象对它的监视
        protected virtual void OnBoild(BoiledEventArgs e)
        {
            if (Boiled != null) //如果有对象注册
            {
                Boiled(this, e); //调用所有注册方法
            }
        }

        public void BoilWater()
        {
            for (int i = 0; i <= 100; i++)
            {
                temperature = i;
                if (temperature >= 95) //温度大于95警告并且显示温度
                {
                    BoiledEventArgs e = new BoiledEventArgs(temperature);
                    OnBoild(e);
                }
            }
        }
    }

    // 定义BoiledEventArgs类，传递给Observer所感兴趣的信息
    public class BoiledEventArgs : EventArgs
    {
        public readonly int temperature;

        public BoiledEventArgs(int temperature)
        {
            this.temperature = temperature;
        }
    }
}

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading.Tasks;

namespace Ch1
{
    class Program
    {
        static void Main(string[] args)
        {
            //------------------------静态处理方法------------------------
            //GreetingManager.MakeLanguageByDelegate = FirstDelegate.GreetingEnglish;
            //GreetingManager.GreetingPeople("jason hua");

            //GreetingManager.MakeLanguageByDelegate = FirstDelegate.GreetingChinese;
            //GreetingManager.GreetingPeople("杰");

            //GreetingManager.MakeLanguageByEvent += FirstDelegate.GreetingEnglish;
            //GreetingManager.GreetingPeopleEvent("Jason Hua");

            //GreetingManager.MakeLanguageByEvent += FirstDelegate.GreetingChinese;
            //GreetingManager.GreetingPeopleEvent("杰");

            //-----------------------普通处理方法-------------------------------
            //FirstDelegate1 fd = new FirstDelegate1();
            //GreetingManager1 gm = new GreetingManager1();
            //gm.MakeLanguageByDelegate = fd.GreetingEnglish;//注册对象
            //gm.GreetingPeople("jason hua");

            //gm.MakeLanguageByDelegate = fd.GreetingChinese;//注册对象
            //gm.GreetingPeople("杰");
            //Console.WriteLine();
            //gm.MakeLanguageByEvent += fd.GreetingEnglish;//注册对象
            //gm.GreetingPeopleEvent("jason hua");

            //gm.MakeLanguageByEvent += fd.GreetingChinese;//注册对象
            //gm.GreetingPeopleEvent("杰");

            //普通的项目中的例子
            //WaterDelegate wd = new WaterDelegate();
            //Alarm alarm = new Alarm();

            //wd.BoilEvent += alarm.MakeAlert;//注册对象
            //wd.BoilEvent += Display.ShowMessage;//注册静态对象

            //wd.BoilWater();

            //仿微软的事件与委托，项目中的小例子
            Heater heater = new Heater();
            Alarm alarm = new Alarm();

            heater.area = "河南";
            heater.type = "九阳";
            heater.Boiled += alarm.MakeAlert;
            heater.Boiled += Display.ShowMessage;

            heater.BoilWater();

            Console.ReadLine();
        }
    }
}

引言委托 和 事件在 .Net Framework中的应用非常广泛，然而，较好地理解委托和事件对很多接触C#时间不长的人来说并不容易。它们就像是一道槛儿，过了这个槛的人，觉得真是太容易了，而没有过去的人每次见到委托和事件就觉得心里别（biè）得慌，混身不自在。本文中，我将通过两个范例由浅入深地讲述什么是委托、为什么要使用委托、事件的由来、.Net Framework中的委托和事件、委托和事件对Observer设计模式的意义，对它们的中间代码也做了讨论。

参看网址：http://www.tracefact.net/CSharp-Programming/Delegates-and-Events-in-CSharp.aspx