观察模式：定义对象间的一种一对多的依赖关系,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;

以下的列子含义：当车站要求指定的列车发车，所有在站内的列表均得到发车通知！

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace PatternProject{    public interface ITrain    {        string From        { get; set; }        string To        { get; set; }        DateTime StartingDateTime        { get; set; }        void Start(ITrain train);    }    public interface IStation    {        void AddTrain(ITrain train);        void CancelTrain(ITrain train);        void StartNotify(ITrain train);    }    public class Station : IStation    {        List
     
       _trainList = new List
      
       ();        public void AddTrain(ITrain train)        {            _trainList.Add(train);        }        public void CancelTrain(ITrain train)        {            _trainList.Remove(train);        }        public void StartNotify(ITrain train)        {            foreach (ITrain t in _trainList)            {                t.Start(train);            }        }    }    public class Train : ITrain    {       public string From        { get; set; }       public string To        { get; set; }       public DateTime StartingDateTime        { get; set; }       public Train(string from, string to, DateTime startingDateTime)       {           this.From = from;           this.To = to;           this.StartingDateTime = startingDateTime;       }       public bool IsCurrent(ITrain train)       {           if (train.From == this.From && train.To == this.To && train.StartingDateTime == this.StartingDateTime)           {               return true;           }           else           {               return false;           }       }       public void Start(ITrain train)       {           Console.WriteLine("{0}开往{1}列车收到通知：",this.From,this.To);           if (IsCurrent(train))           {               Console.WriteLine("从{0}开往{1}的列车,于{2}开车，敬请注意！", this.From, this.To, this.StartingDateTime);           }           else           {               Console.WriteLine("还未到开车时间，敬请稍候！");           }       }    }}
      
     

　

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace PatternProject{    class Program    {        static void Main(string[] args)        {            Station station = new Station();                        station.AddTrain(new Train("北京", "上海", new DateTime(2014, 5, 1)));            station.AddTrain(new Train("北京", "武汉", new DateTime(2014, 3, 1)));            station.AddTrain(new Train("武汉", "上海", new DateTime(2014, 2, 1)));            station.AddTrain(new Train("上海", "南京", new DateTime(2014, 8, 1)));            Train t = new Train("北京", "武汉", new DateTime(2014, 3, 1));            station.StartNotify(t);            Console.ReadKey();        }    }}