static void Main(string[] args) { var observerA = new ConcreteObserverA(); var observerB = new ConcreteObserverB(); var subject = new Subject(); subject.RegisterObserver(observerA); subject.RegisterObserver(observerB); subject.NotifyObservers(); Console.WriteLine("--------------------"); subject.UnregisterObserver(observerA); subject.NotifyObservers(); }