using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        WheatherData data = new WheatherData();

        StatisticScreen sScreen = new StatisticScreen(data);

        ForecastScreen fScreen = new ForecastScreen(data);

​

        data.SetValue(5);

        data.UnregisterObserver(fScreen);

        data.SetValue(10);

    }

}

​

public interface ISubject

{

    void RegisterObserver(IObserver observer);

    void UnregisterObserver(IObserver observer);

}

​

public interface IObserver

{

    void Update(int newValue);

}

​

public class WheatherData : ISubject

{

    int _valueToPass = 0;

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

    public void RegisterObserver(IObserver observer)

    {

        observers.Add(observer);

    }

    public void UnregisterObserver(IObserver observer)

    {

        if(observers.Contains(observer))

            observers.Remove(observer);

    }

    public void SetValue(int newValue)

    {

        this._valueToPass = newValue;

        observers.ForEach(o => o.Update(_valueToPass));

    }

}

​

public class StatisticScreen : IObserver

{

    private ISubject _subject;

    public StatisticScreen(ISubject subject)

    {

        this._subject = subject;

        _subject.RegisterObserver(this);

    }

    public void Update(int newValue)

    {

        Console.WriteLine("Statistic screen updated, new value: " + newValue.ToString());

    }

}

​

public class ForecastScreen : IObserver

{

    private ISubject _subject;

    public ForecastScreen(ISubject subject)

    {

        this._subject = subject;

        _subject.RegisterObserver(this);

    }

    public void Update(int newValue)

    {

        Console.WriteLine("Forecast screen updated, new value: " + newValue.ToString());

    }

}

​

​