Mediator Design Pattern in C#

Defines an object that encapsulates how a set of objects interact. Mediator promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently.

This structural code demonstrates the Mediator pattern facilitating loosely coupled communication between different objects and object types. The mediator is a central hub through which all interaction must take place.

using System;
using System.Collections;

  class MainApp
  {
    static void Main()
    {
      ConcreteMediator m = new ConcreteMediator();

      ConcreteColleague1 c1 = new ConcreteColleague1(m);
      ConcreteColleague2 c2 = new ConcreteColleague2(m);

      m.Colleague1 = c1;
      m.Colleague2 = c2;

      c1.Send("How are you?");
      c2.Send("Fine, thanks");

      // Wait for user 
      Console.Read();
    }
  }

  // "Mediator" 
  abstract class Mediator
  {
    public abstract void Send(string message, 
      Colleague colleague);
  }

  // "ConcreteMediator" 
  class ConcreteMediator : Mediator
  {
    private ConcreteColleague1 colleague1;
    private ConcreteColleague2 colleague2;

    public ConcreteColleague1 Colleague1
    {
      set{ colleague1 = value; }
    }

    public ConcreteColleague2 Colleague2
    {
      set{ colleague2 = value; }
    }

    public override void Send(string message, 
      Colleague colleague)
    {
      if (colleague == colleague1)
      {
        colleague2.Notify(message);
      }
      else
      {
        colleague1.Notify(message);
      }
    }
  }

  // "Colleague" 
  abstract class Colleague
  {
    protected Mediator mediator;

    // Constructor 
    public Colleague(Mediator mediator)
    {
      this.mediator = mediator;
    }
  }

  // "ConcreteColleague1" 
  class ConcreteColleague1 : Colleague
  {
    // Constructor 
    public ConcreteColleague1(Mediator mediator) 
      : base(mediator) 
    { 
    }

    public void Send(string message)
    {
      mediator.Send(message, this);
    }

    public void Notify(string message)
    {
      Console.WriteLine("Colleague1 gets message: " 
        + message);
    }
  }

  // "ConcreteColleague2" 
  class ConcreteColleague2 : Colleague
  {
    // Constructor 
    public ConcreteColleague2(Mediator mediator) 
      : base(mediator) 
    { 
    }

    public void Send(string message)
    {
      mediator.Send(message, this);
    }

    public void Notify(string message)
    {
      Console.WriteLine("Colleague2 gets message: " 
        + message);
    }
  }