DesignPattern_Behavioral_Observer

void Main()
{
    Subject s = new Subject();
    s.Add(new ObserverA(s));
    s.Add(new ObserverB(s));
    s.Notify();
}

class Subject
{
    List<Observer> observers = new List<Observer>();
    public void Add(Observer o){ observers.Add(o);}
    public void Remove(Observer o){ observers.Remove(o);}
    public void Notify(){
        foreach (var observer in observers)
        {
            observer.Show();
        }
    }
}
abstract class Observer{
    protected Subject subject;
    public Observer(Subject s){ subject = s; }
    public abstract void Show();
}
class ObserverA:Observer{
    public ObserverA(Subject s):base(s){}
    public override void Show(){}
}
class ObserverB:Observer{
    public ObserverB(Subject s):base(s){}
    public override void Show(){}
}