Design Patterns: Observer Example

CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;
					
public class Program
{
	public static void Main()
	{
		BasketballPlayer damianLillard = new BasketballPlayer("Damian Lillard");
		BasketballFan basketballFan1 = new BasketballFan(damianLillard);
		damianLillard.Attach(basketballFan1);
		damianLillard.Score(3);
		BasketballFan basketballFan2 = new BasketballFan(damianLillard);
		damianLillard.Attach(basketballFan2);
		damianLillard.Score(2);
	}
	
	abstract class Player
	{
		List<Fan> fans = new List<Fan>();
		
		public void Attach(Fan f)
		{
			fans.Add(f);
		}
		
		public void Detach(Fan f)
		{
			fans.Remove(f);
		}
		
		public void Notify()
		{
			foreach(Fan f in fans)
			{
				f.Update();
			}
		}
	}
	
	class BasketballPlayer : Player
	{
		public string Name;
		public int Points = 0;
		
		public BasketballPlayer(string name)
		{
			this.Name = name;
		}
		
		public void Score(int points)
		{
			this.Points += points;
			this.Notify();
		}
	}
	
	abstract class Fan
	{
		public abstract void Update();
	}
	
	class BasketballFan : Fan
	{
		BasketballPlayer FavoritePlayer;
		int FavoritePlayerPoints;
		
		public BasketballFan(BasketballPlayer player)
		{
			this.FavoritePlayer = player;
			this.FavoritePlayerPoints = this.FavoritePlayer.Points;
		}
		
		public override void Update()
		{
			this.FavoritePlayerPoints = this.FavoritePlayer.Points;
			Console.WriteLine(this.FavoritePlayer.Name + " has " + this.FavoritePlayerPoints + " points!");
		}
	}
}