designPatternGuru/DesignPatternGuru/Observer/Observers/ConcreteObserverA.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Observer.Observers
{
    internal class ConcreteObserverA : IObserver
    {
        public void Update(ISubject subject)
        {
            if ((subject as Subject).State < 3)
                Console.WriteLine("ConcreteObserverA: Reacted to the event.");
        }
    }
}