public class BaggageInfo
{
   private int flightNo;
   private string origin;
   private int location;
   internal BaggageInfo(int flight, string from, int carousel)
   {
      this.flightNo = flight;
      this.origin = from;
      this.location = carousel;
   }
   public int FlightNumber {
      get { return this.flightNo; }
   }
   public string From {
      get { return this.origin; }
   }
   public int Carousel {
      get { return this.location; }
   }
}
///
/// 发布者
///
public class BaggageHandler : IObservable<BaggageInfo>
{
   private List<IObserver<BaggageInfo>> observers;
   private List<BaggageInfo> flights;
   public BaggageHandler()
   {
      observers = new List<IObserver<BaggageInfo>>();
      flights = new List<BaggageInfo>();
   }
   public IDisposable Subscribe(IObserver<BaggageInfo> observer)
   {
      // Check whether observer is already registered. If not, add it
      if (! observers.Contains(observer)) {
         observers.Add(observer);
         // Provide observer with existing data.
         foreach (var item in flights)
            observer.OnNext(item);
      }
      return new Unsubscriber<BaggageInfo>(observers, observer);
   }
   // Called to indicate all baggage is now unloaded.
   public void BaggageStatus(int flightNo)
   {
      BaggageStatus(flightNo, String.Empty, 0);
   }
   public void BaggageStatus(int flightNo, string from, int carousel)
   {
      var info = new BaggageInfo(flightNo, from, carousel);
      // Carousel is assigned, so add new info object to list.
      if (carousel > 0 && ! flights.Contains(info)) {
         flights.Add(info);
         foreach (var observer in observers)
            observer.OnNext(info);
      }
      else if (carousel == 0) {
         // Baggage claim for flight is done
         var flightsToRemove = new List<BaggageInfo>();
         foreach (var flight in flights) {
            if (info.FlightNumber == flight.FlightNumber) {
               flightsToRemove.Add(flight);
               foreach (var observer in observers)
                  observer.OnNext(info);
            }
         }
         foreach (var flightToRemove in flightsToRemove)
            flights.Remove(flightToRemove);
         flightsToRemove.Clear();
      }
   }
   public void LastBaggageClaimed()
   {
      foreach (var observer in observers)
         observer.OnCompleted();
      observers.Clear();
   }
}
internal class Unsubscriber<BaggageInfo> : IDisposable
{
   private List<IObserver<BaggageInfo>> _observers;
   private IObserver<BaggageInfo> _observer;
   internal Unsubscriber(List<IObserver<BaggageInfo>> observers, IObserver<BaggageInfo> observer)
   {
      this._observers = observers;
      this._observer = observer;
   }
   public void Dispose() 
   {
      if (_observers.Contains(_observer))
         _observers.Remove(_observer);
   }
}
///
/// 订阅者
///
public class ArrivalsMonitor : IObserver<BaggageInfo>
{
   private string name;
   private List<string> flightInfos = new List<string>();
   private IDisposable cancellation;
   private string fmt = "{0,-20} {1,5}  {2, 3}";
   public ArrivalsMonitor(string name)
   {
      if (String.IsNullOrEmpty(name))
         throw new ArgumentNullException("The observer must be assigned a name.");
      this.name = name;
   }
   public virtual void Subscribe(BaggageHandler provider)
   {
      cancellation = provider.Subscribe(this);
   }
   public virtual void Unsubscribe()
   {
      cancellation.Dispose();
      flightInfos.Clear();
   }
   public virtual void OnCompleted() 
   {
      flightInfos.Clear();
   }
   // No implementation needed: Method is not called by the BaggageHandler class.
   public virtual void OnError(Exception e)
   {
      // No implementation.
   }
   // Update information.
   public virtual void OnNext(BaggageInfo info) 
   {
      bool updated = false;
      // Flight has unloaded its baggage; remove from the monitor.
      if (info.Carousel == 0) {
         var flightsToRemove = new List<string>();
         string flightNo = String.Format("{0,5}", info.FlightNumber);
         
         foreach (var flightInfo in flightInfos) {
            if (flightInfo.Substring(21, 5).Equals(flightNo)) {
               flightsToRemove.Add(flightInfo);
               updated = true;
            }
         }
         foreach (var flightToRemove in flightsToRemove)
            flightInfos.Remove(flightToRemove);
         flightsToRemove.Clear();
      }
      else {
         // Add flight if it does not exist in the collection.
         string flightInfo = String.Format(fmt, info.From, info.FlightNumber, info.Carousel);
         if (! flightInfos.Contains(flightInfo)) {
            flightInfos.Add(flightInfo);
            updated = true;
         }
      }
      if (updated) {
         flightInfos.Sort();
         Console.WriteLine("Arrivals information from {0}", this.name);
         foreach (var flightInfo in flightInfos)
            Console.WriteLine(flightInfo);
         Console.WriteLine();
      }
   }
}
using System;
using System.Collections.Generic;
public class Example
{
    public static void Main()
    {
        //发布者
        BaggageHandler provider = new BaggageHandler();
        // 订阅者
        ArrivalsMonitor observer1 = new ArrivalsMonitor("BaggageClaimMonitor1");
        // 订阅者
        ArrivalsMonitor observer2 = new ArrivalsMonitor("SecurityExit");
        // 发布
        provider.BaggageStatus(712, "Detroit", 3);
        //订阅
        observer1.Subscribe(provider);
        
        provider.BaggageStatus(712, "Kalamazoo", 3);
        provider.BaggageStatus(400, "New York-Kennedy", 1);
        provider.BaggageStatus(712, "Detroit", 3);
        observer2.Subscribe(provider);
        
        provider.BaggageStatus(511, "San Francisco", 2);
        provider.BaggageStatus(712);
        observer2.Unsubscribe();
        
        provider.BaggageStatus(400);
        provider.LastBaggageClaimed();
    }
}