using System;

using System.Collections.Generic;

​

public class WeatherStation

{

    public static void Main(String[] args)

    {

        WeatherData weatherData = new WeatherData();

        CurrentConditionsDisplay currentDisplay = new CurrentConditionsDisplay(weatherData);

        //StatisticsDisplay statisticsDisplay = new StatisticsDisplay(weatherData);

        //ForecastDisplay forecastDisplay = new ForecastDisplay(weatherData);

        weatherData.SetMeasurements(80, 65, 30.4f);

        weatherData.SetMeasurements(82, 70, 29.2f);

        weatherData.SetMeasurements(78, 90, 29.2f);

    }

}

​

//---------------------------------------------------------------

//interface

​

public interface ISubject

{

    public void RegisterObserver(IObserver o);

    public void RemoveObserver(IObserver o);

    //both methods above take an observer as an argument; that is, the observer to be registered or removed. 

    public void NotifyObservers();

    //this method is called to notify all observers when the subjects state is changed.

}

​

public interface IObserver

{

    public void Update(double temp, double humidity, double pressure);

    //the state values the observers get from the subject when a weather measurement changes.

    //the observer interface is implemented by all observers so they all have to implemnent the update() method. 

    //here were passing measurements to the observer.

}

​

public interface IDisplayElement

{

    public void Display();

    //will be called when an element needs to be displayed.

}

​

//---------------------------------------------------------------

//WeatherData

​

public class WeatherData : ISubject

{

    //weatherData now implements the subject interface

    //ab array list holds the observers registered the the subject and also is instatiated in the constructor below.

    private List<IObserver> observers;

    private double temperature;

    private double humidity;

    private double pressure;

    public WeatherData()

    {

        observers = new List<IObserver>();

    }

    public void RegisterObserver(IObserver o)

    {

        //when an observer registers we just add it to the end of the list

        observers.Add(o);

    }

    public void RemoveObserver(IObserver o)

    {

        //likewise when we want to remove an observer we find its index and take it off the list

        int i = observers.IndexOf(o);

        if(i >= 0)

            observers.Remove(o);        

    }

    public void NotifyObservers()

    {

        //here's the fun part; this is where we tell all the observers about the state.

        // because they are all observers we know they all implement update() so we know how to notify them.

        foreach(IObserver observer in observers)

            observer.Update(temperature, humidity, pressure);

    }

    public void MeasurementsChanged()

    {

        //notify the observers when we get updated measurements from the weather station.

        NotifyObservers();

    }

    public void SetMeasurements(double temperature, double humidity, double pressure)

    {

        //this is boilerplate that allows us to provide data instead of reading from actual sources.

        this.temperature = temperature;

        this.humidity = humidity;

        this.pressure = pressure;

        MeasurementsChanged();

    }

    //other WeatherData Methods here

}

​

//---------------------------------------------------------------

//Display

​

public class CurrentConditionsDisplay : IObserver, IDisplayElement

{

    //this display implements IObserver so it can get changes from the WeatherData object.

    //it also implements DisplayedElement because our API is going to require all display elements to implement this interface.

    private double temperature;

    private double humidity;

    private ISubject weatherData;

    //the constructor is passed the weatherData object (the subject) and we use it to register the display as an observer.

    public CurrentConditionsDisplay(ISubject weatherData)

    {

        this.weatherData = weatherData;

        weatherData.RegisterObserver(this);

    }

    //when update() is called we save the temp and humidity and call Display();

    public void Update(double temperature, double humidity, double pressure)

    {

        this.temperature = temperature;

        this.humidity = humidity;

        Display();

    }

    //the Display() method just prints out the most recent temp and humidity.

    public void Display()

    {

        Console.WriteLine("Current Conditions: {0}F degrees and {1}% humidity", temperature, humidity);

    }

}