observertheory.cs

  using System;
  using System.Collections;
  using System.Threading;

  class ObserverPattern {
   
    //Observer Pattern            Judith Bishop Jan 2007
   
    // The Subject runs in a thread and changes its state
    // independently. At each change, it notifies its Observers.
   
    class Subject {
      public delegate void Callback (string s);
     
      public event Callback Notify;

      Simulator simulator = new Simulator();
      const int speed = 200;
      public string SubjectState {get; set;}
     
      public void Go() {
        new Thread(new ThreadStart(Run)).Start();
      }
     
      void Run () {
        foreach (string s in simulator) {
          Console.WriteLine("Subject: "+s);
          SubjectState = s;
          Notify(s);
          Thread.Sleep(speed); //millisconds
        }
      }
    }

    interface IObserver {
     void Update(string state);
    }

    class Observer : IObserver {
      string name;
      Subject subject;
      string state;
      string gap;
   
      public Observer (Subject subject, string name,string gap) {
        this.subject = subject;
        this.name = name;
        this.gap = gap;
        subject.Notify += Update;
      }
     
      public void Update(string subjectState) {
        state = subjectState;
        Console.WriteLine(gap+name+": "+state);
      }
    }
 
    static void Main () {
      Subject subject = new Subject();
      Observer Observer =  new Observer(subject,"Center","\t\t");
      Observer observer2 = new Observer(subject,"Right","\t\t\t\t");
      subject.Go();
    }
   
    class Simulator : IEnumerable {
 
    string [] moves = {"5","3","1","6","7"};

    public IEnumerator GetEnumerator () {
      foreach( string element in moves )
        yield return element;
      }
    }
  }
/*Output
Subject: 5
    Center: 5
        Right: 5
Subject: 3
    Center: 3
        Right: 3
Subject: 1
    Center: 1
        Right: 1
Subject: 6
    Center: 6
        Right: 6

*/