using System;

// The delegate indicates what type methods can be notified of an event.
// The method(s) must have the same signature as the delegate. 
public delegate void NewsDelegate(News news);

public class News 
{
  public string news;
  public News(string news) {this.news=news;} 
}

// This class notifies subscribers when the specified event occurs.
// In this case the event is that newNews() is called.
public class NewsService
{
  // Must have the format: public event delegateName anyName
  public event NewsDelegate NewsEventSubscribers;

  public void newNews(string news)
  {
    Console.WriteLine("An event! New news.");
    // first check if there are subscribers to this event
    if (NewsEventSubscribers !=null)
    {
      // This will send an instance of News to each subscriber of local news
      NewsEventSubscribers(new News(news));
    }
  }
  public NewsService(){}
}

public class Subscriber
{ 
  public string name; 
  NewsDelegate delNews;

  public void SubscribeNewsService(NewsService ns)
  {
    // Create a new NewsDelegate. Its parameter is the method to notify
    // when the event occurs. This method may also be in another class,
    // in which case the parameter is InstanceOfSomeOtherClass.method
    delNews=new NewsDelegate(WriteNews); 
    // Register the delegate with the NewsService
    ns.NewsEventSubscribers +=delNews;
    Console.WriteLine(name + " subscribed to news."); 
  }

  public void UnsubscribeNewsService(NewsService ns)
  {
    // unsubscribing
    ns.NewsEventSubscribers -=delNews;
    Console.WriteLine(name + " unsubscribed to news.");
  }

  // This method must have the same signature as
  // the delegate NewsDelegate declared above. 
  public void WriteNews(News e)
  { 
    Console.WriteLine(name + " received news: " + e.news);
   } 

  public Subscriber(string name) {this.name=name;}
} 

class MakeNews
{
  static void Main(string[] args)
  {
    NewsService ns=new NewsService();
    Subscriber julie=new Subscriber("Julie");
    julie.SubscribeNewsService(ns);
    Subscriber matthew=new Subscriber("Matthew");
    matthew.SubscribeNewsService(ns);
    ns.newNews("More money for schools.");
    julie.UnsubscribeNewsService(ns);
    ns.newNews("New mayor.");
   }
}