using System;

using System.Collections.Generic;

abstract class Subject

{

    private List<Observer> _observers = new List<Observer>();

    public void Attach(Observer observer)

    {

      _observers.Add(observer);

    }

    public void Detach(Observer observer)

    {

      _observers.Remove(observer);

    }

    public void Notify()

    {

      foreach (Observer o in _observers)

      {

        o.Update();

      }}

}

​

class State : Subject

{

    private string _subjectState;

    public string SubjectState

    {

      get { return _subjectState; }

      set { _subjectState = value; }

    }

}

abstract class Observer

{

    public abstract void Update();

}

class ConcreteObserver : Observer

  {

    private string _name;

    private string _observerState;

    private State _subject;

    public ConcreteObserver(

      State subject, string name)

    {

      this._subject = subject;

      this._name = name;

    }

    public override void Update()

    {

      _observerState = _subject.SubjectState;

      Console.WriteLine("{0} booked {1}",

        _name, _observerState);

    }

​

    public State Subject

    {

      get { return _subject; }

      set { _subject = value; }

    }

}

​

public class Cab

{

    public static void Main()

    {

        State s = new State();

        Console.WriteLine("--------------------");

        Console.WriteLine("Cab Booking details");

        Console.WriteLine("--------------------");

        s.Attach(new ConcreteObserver(s, "Antaun"));

        s.Attach(new ConcreteObserver(s, "Aswin"));

        s.Attach(new ConcreteObserver(s, "Ivan"));

​

        s.SubjectState = "Premium Cab";

        s.Notify();

        Console.WriteLine("--------------------");

    }

}

​