public interface IObserver

{

    void Update();  

}

​

public class Observer: IObserver

{

    public string Name { get; private set; }

    public Observer(string name)

    {

        Name = name;    

    }

    public void Update()

    {

        Console.WriteLine($"{Name} has been updated");

    }

}

​

public interface ISubject

{

    void Subscribe(Observer observer);

    void Unsubscribe(Observer observer);

    void Notify();  

}

​

public class Subject : ISubject

{

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

​

    public void Subscribe(Observer observer)

    {

        observers.Add(observer);    

    }

    public void Unsubscribe(Observer observer)

    {

        observers.Remove(observer); 

    }

    public void Notify()

    {

        observers.ForEach(x => x.Update()); 

    }

    public void DoSomething()

    {

        Notify();   

    }

}

​

static void Main(string[] args)

{

    var subject = new Subject();

    var observerOne = new Observer("One");

    subject.Subscribe(observerOne);

    var observerTwo = new Observer("Two");

    subject.Subscribe(observerTwo);

    subject.DoSomething();

    subject.Unsubscribe(observerOne);

    subject.Unsubscribe(observerTwo);

}