using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        ConcreteSubject subject = new ConcreteSubject();

        ConcreteObserver observer = new ConcreteObserver(subject);

        subject.Attach(observer);

        subject.SomeState = 100;

        subject.Notify();

    }

}

​

abstract class Subject

{

    List<Observer> observers = new List<Observer>();

    public void Attach(Observer observer)

    {

        observers.Add(observer);

    }

​

    public void Detach(Observer observer)

    {

        observers.Remove(observer);

    }

​

    public void Notify()

    {

        foreach (var observer in this.observers)

        {

            observer.Update();

        }

    }

}

​

class ConcreteSubject : Subject

{

    public int SomeState { get; set; }

}

​

abstract class Observer

{

    public abstract void Update();

}

​

class ConcreteObserver : Observer

{

    public int ObserverState { get; set; }

​

    ConcreteSubject MySubject { get; set; }

​

    public ConcreteObserver(ConcreteSubject subject)

    {

        this.MySubject = subject;

    }

​

    public override void Update()

    {

        this.ObserverState = MySubject.SomeState;

        Console.WriteLine("My state has been updated: " + this.ObserverState);

    }

}