学步园

模拟主持人发布一个问题，由多个嘉宾来回答这个问题。

分析：从需求中抽出Host (主持人) 类和Guests (嘉宾) 类。

作为问题的发布者，Host不知道问题如何解答。因此它只能发布这个事件，将事件委托给多个嘉宾去处理。因此在Host 类定义事件，在Guests类中定义事件的响应方法。通过多番委托的"+="将响应方法添加到事件列表中，最终 Host 类将触发这个事件。实现过程如下：

代码其实很少下面贴出来所有代码：

QuestionArgs.cs

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

namespace EventDemo
{
    public class QuestionArgs:EventArgs
    {
        public string Message { get; set; }
    }
}

Program.cs

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

namespace EventDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            Host host = new Host();
            host.Name = "主持人";
            host.args.Message = "C#的事件如何实现的？";
            Guests[] gArray = new Guests[3]
            {
                new GuestA(){Name = "张小三"},
                new GuestB(){Name = "李小四"},
                new GuestC(){Name = "王老五"}
            };
            //用+=号，将嘉宾的答题方法加入到委托链
            host.QuestionEvent += new QuestionHandler(gArray[0].answer);
            host.QuestionEvent += new QuestionHandler(gArray[1].answer);
            host.QuestionEvent += new QuestionHandler(gArray[2].answer);

            //触发事件
            host.StartAnswer();
            Console.ReadLine();
        }
    }
}

Host.cs

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

namespace EventDemo
{
    public delegate void QuestionHandler(object sender,QuestionArgs e);
    public class Host
    {
        //定义一个事件
        public event QuestionHandler QuestionEvent;
        public QuestionArgs args { set; get; }
        public Host()
        {
            //初始化事件参数
            args = new QuestionArgs();
        }
        public string Name { get; set; }
        public void StartAnswer()
        {
            Console.WriteLine("开始答题");
            QuestionEvent(this, args);
        }
    }
}

Guests.cs

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

namespace EventDemo
{
    /// <summary>
    /// 父类
    /// </summary>
    public class Guests
    {
        /// <summary>
        /// 嘉宾姓名
        /// </summary>
        public string Name { get; set; }

        public virtual void answer(object sender, QuestionArgs e)
        {
            Console.Write("事件的发出者：" + (sender as Host).Name);
            Console.WriteLine("问题是：" + e.Message);
        }
    }
}

GuestC.cs

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

namespace EventDemo
{
    class GuestC:Guests
    {
        public override void answer(object sender, QuestionArgs e)
        {
            base.answer(sender, e);
            Console.WriteLine("{0}开始答题：我不知道", this.Name);
        }
    }
}

GuestB.cs

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

namespace EventDemo
{
    class GuestB:Guests
    {
        public override void answer(object sender, QuestionArgs e)
        {
            base.answer(sender, e);
            Console.WriteLine("{0}开始答题：我不知道", this.Name);
        }
    }
}

GuestA.cs

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

namespace EventDemo
{
    class GuestA:Guests
    {
        public override void answer(object sender, QuestionArgs e)
        {
            base.answer(sender, e);
            Console.WriteLine("{0}开始答题：我不知道", this.Name);
        }
    }
}

运行结果：