C#事件委托、观察者模式、消息中心、消息转发

using System;

namespace EventDelegation
{
    /// <summary>
    /// 事件参数类
    /// </summary>
    public class EventDate : EventArgs
    {
        public int eventID;
        public int a;
        public int b;
    }
    /// <summary>
    /// 事件类，用于事件触发，消息转发，本质是消息中心，要使用单例模式
    /// </summary>
    public class EventProgram
    {
        private static EventProgram _instance;
        public  static EventProgram Instance
        {
            get
            {
                if(_instance == null)
                {
                    _instance = new EventProgram();
                }
                return _instance;
            }
        }
        public event EventHandler<EventDate> OnEvent;
        //事件触发函数
        public void CallEvent(int eventID,int a,int b)
        {
            EventDate e = new EventDate();  //初始化事件参数
            e.eventID = eventID;
            e.a = a;
            e.b = b;

            Console.WriteLine("CallEvent");
            OnEvent(this, e);   //触发调用
        }
    }
   
    /// <summary>
    /// 事件处理类，观察者
    /// </summary>
    class Observer
    {
        int _Id;
        public Observer(int id)
        {
            _Id = id;
            EventProgram.Instance.OnEvent += DoEvent; //订阅事件
        }
        void DoEvent(System.Object sender, EventArgs e)
        {
            char f;
            int c = 0;
            EventDate ad = (EventDate)e;
            if(ad.eventID == 1)
            {
                 c = ad.a + ad.b;
                f = ‘+‘;
            }
            else
            {
                c = ad.a - ad.b;
                f = ‘-‘;
            }
            
            Console.WriteLine("ID:"+_Id+ ",Observer触发事件DoEvent, a{1}b={0}", c,f);
        }
    }
    /// <summary>
    /// 事件处理类，观察者2
    /// </summary>
    class Observer2
    {
        int _Id;
        public Observer2(int id)
        {
            _Id = id;
            EventProgram.Instance.OnEvent += DoEvent2; //订阅事件
        }
        void DoEvent2(System.Object sender, EventArgs e)
        {
            char f;
            int c = 0;
            EventDate ad = (EventDate)e;
            if (ad.eventID == 1)
            {
                c = ad.a * ad.b;
                f = ‘*‘;
            }
            else
            {
                c = ad.a / ad.b;
                f = ‘/‘;
            }
            Console.WriteLine("ID:" + _Id + ",Observer2触发事件DoEvent, a{1}b={0}", c, f);
          
        }
    }

    /// <summary>
    /// 事件触发者,被观察的对象
    /// </summary>
    class EventTrigger
    {
        public void DoSomething()
        {
            EventProgram.Instance.CallEvent(1, 2, 3); //触发事件，通知消息中心
        }
    }


    /// <summary>
    /// 测试
    /// </summary>
    class Program
    {

        static void Main(string[] args)
        {
            //初始化各种观察者
            Observer ob1 = new Observer(1);
            Observer ob2 = new Observer(2);

            Observer2 ob3 = new Observer2(1);
            Observer2 ob4 = new Observer2(2);

            //初始化事件触发者
            EventTrigger et = new EventTrigger();
            et.DoSomething();

            Console.WriteLine("Hello World!");
        }

    }
}