public static void Main(string[] args) { var fbObservable = new NotificationProvider("Facebook"); var githubObservable = new NotificationProvider("GitHub"); var observer = new NotificationSubscriber("Florin"); observer.Subscribe(fbObservable); //observer.Unsubscribe(); observer.Subscribe(githubObservable); //observer.Unsubscribe(); var observer2 = new NotificationSubscriber("Piagio"); observer2.Subscribe(fbObservable); fbObservable.EventNotification("Event notification 1 !"); githubObservable.EventNotification("Event notification!"); }