static void Main(string[] args) { var subject = new ConcreteSubject(); var observer1 = new ConcreteObserver1(); subject.Attach(observer1); var observer2 = new ConcreteObserver2(); subject.Attach(observer2); var observer3 = new ConcreteObserver3(); subject.Attach(observer3); subject.BusinessLogic(); subject.BusinessLogic(); subject.Detach(observer3); subject.BusinessLogic(); }