using System;

using System.Collections.Generic;

​

public interface IObserver

{

    void Notify();

}

​

public class SpreadSheet : IObserver

{

    public void Notify()

    {

        Console.WriteLine("Spreadsheet got notified");

    }

}

​

public class Chart: IObserver

{

    public void Notify()

    {

        Console.WriteLine("Chart got notified");

    }

}

​

public interface ISubject

{

    void AddObserver(IObserver observer);

    void RemoveObserver(IObserver observer);

    void NotifyObservers();

}

​

public class DataSource : ISubject

{

    List<IObserver> observers = new List<IObserver>();

    private int value;

​

    public int Value { 

        get => value; 

        set {

            this.value = value;

            NotifyObservers();

        } 

    }

​

    public void AddObserver(IObserver observer)

    {

        observers.Add(observer);

    }

​

    public void NotifyObservers()

    {

        foreach (IObserver observer in observers)

        {

            observer.Notify();

        }

    }

​

    public void RemoveObserver(IObserver observer)

    {

        observers.Remove(observer);

    }

}

public class Program

{

    public static void Main()

    {

        var spreadSheet = new SpreadSheet();

        Chart chart = new Chart();

        DataSource dataSource = new DataSource();

        dataSource.AddObserver(spreadSheet);

        dataSource.AddObserver(chart);

​

        dataSource.Value = 10;

    }

}