using System;

using System.Collections.Generic;

public class MainApp

{

    public static void Main()

    {

        var s = new ConcreteSubject();

        s.Attach(new ConcreteObserver(s, "x"));

        s.Attach(new ConcreteObserver(s, "y"));

        s.Attach(new ConcreteObserver(s, "z"));

        s.SubjectState = "ABC";

        s.Notify();

    }

}

​

abstract class Observer

{

    public abstract void Update();

}

​

abstract class Subject

{

    public Subject() 

    {

        Observers = new List<Observer>();

    }

    public List<Observer> Observers { get; set; }

    public void Attach(Observer observer)

    {

        Observers.Add(observer);

    }

    public void Detach(Observer observer)

    {

        Observers.Remove(observer);

    }

    public void Notify()

    {

        foreach(var o in Observers)

        {

            o.Update();

        }

    }

}

​

class ConcreteSubject : Subject

{

    public string SubjectState {get;set;}

}

​

​

class ConcreteObserver : Observer

{

    private ConcreteSubject _subject;

    private string _name;

    public string ObserverState {get;set;}

    public ConcreteObserver(ConcreteSubject subject, string name)

    {

        this._subject = subject;

        this._name = name;

    }

    public override void Update()

    {

        ObserverState = _subject.SubjectState;

        Console.WriteLine("Observer {0}'s new state is {1}",_name, ObserverState);

    }

    public ConcreteSubject Subject {get;set;}

}