The Mediator design pattern 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.
C# code examples of the Mediator design pattern is provided in 3 forms:
A visualization of the classes and objects participating in this pattern.
The classes and objects participating in this pattern include:
IChatroom)
Chatroom)
Participant)
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.
copyusing System;
namespace Mediator.Structural
{
/// <summary>
/// Mediator Design Pattern
/// </summary>
public class Program
{
public static void Main(string[] args)
{
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.ReadKey();
}
}
/// <summary>
/// The 'Mediator' abstract class
/// </summary>
public abstract class Mediator
{
public abstract void Send(string message,
Colleague colleague);
}
/// <summary>
/// The 'ConcreteMediator' class
/// </summary>
public class ConcreteMediator : Mediator
{
ConcreteColleague1 colleague1;
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);
}
}
}
/// <summary>
/// The 'Colleague' abstract class
/// </summary>
public abstract class Colleague
{
protected Mediator mediator;
// Constructor
public Colleague(Mediator mediator)
{
this.mediator = mediator;
}
}
/// <summary>
/// A 'ConcreteColleague' class
/// </summary>
public 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);
}
}
/// <summary>
/// A 'ConcreteColleague' class
/// </summary>
public 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);
}
}
}
This real-world code demonstrates the Mediator pattern facilitating loosely coupled communication between different Participants registering with a Chatroom. The Chatroom is the central hub through which all communication takes place. At this point only one-to-one communication is implemented in the Chatroom, but would be trivial to change to one-to-many.
using System;
using System.Collections.Generic;
namespace Mediator.RealWorld
{
/// <summary>
/// Mediator Design Pattern
/// </summary>
public class Program
{
public static void Main(string[] args)
{
// Create chatroom
Chatroom chatroom = new Chatroom();
// Create participants and register them
Participant George = new Beatle("George");
Participant Paul = new Beatle("Paul");
Participant Ringo = new Beatle("Ringo");
Participant John = new Beatle("John");
Participant Yoko = new NonBeatle("Yoko");
chatroom.Register(George);
chatroom.Register(Paul);
chatroom.Register(Ringo);
chatroom.Register(John);
chatroom.Register(Yoko);
// Chatting participants
Yoko.Send("John", "Hi John!");
Paul.Send("Ringo", "All you need is love");
Ringo.Send("George", "My sweet Lord");
Paul.Send("John", "Can't buy me love");
John.Send("Yoko", "My sweet love");
// Wait for user
Console.ReadKey();
}
}
/// <summary>
/// The 'Mediator' abstract class
/// </summary>
public abstract class AbstractChatroom
{
public abstract void Register(Participant participant);
public abstract void Send(
string from, string to, string message);
}
/// <summary>
/// The 'ConcreteMediator' class
/// </summary>
public class Chatroom : AbstractChatroom
{
private Dictionary<string, Participant> participants = new Dictionary<string, Participant>();
public override void Register(Participant participant)
{
if (!participants.ContainsValue(participant))
{
participants[participant.Name] = participant;
}
participant.Chatroom = this;
}
public override void Send(string from, string to, string message)
{
Participant participant = participants[to];
if (participant != null)
{
participant.Receive(from, message);
}
}
}
/// <summary>
/// The 'AbstractColleague' class
/// </summary>
public class Participant
{
Chatroom chatroom;
string name;
// Constructor
public Participant(string name)
{
this.name = name;
}
// Gets participant name
public string Name
{
get { return name; }
}
// Gets chatroom
public Chatroom Chatroom
{
set { chatroom = value; }
get { return chatroom; }
}
// Sends message to given participant
public void Send(string to, string message)
{
chatroom.Send(name, to, message);
}
// Receives message from given participant
public virtual void Receive(
string from, string message)
{
Console.WriteLine("{0} to {1}: '{2}'",
from, Name, message);
}
}
/// <summary>
/// A 'ConcreteColleague' class
/// </summary>
public class Beatle : Participant
{
// Constructor
public Beatle(string name)
: base(name)
{
}
public override void Receive(string from, string message)
{
Console.Write("To a Beatle: ");
base.Receive(from, message);
}
}
/// <summary>
/// A 'ConcreteColleague' class
/// </summary>
public class NonBeatle : Participant
{
// Constructor
public NonBeatle(string name)
: base(name)
{
}
public override void Receive(string from, string message)
{
Console.Write("To a non-Beatle: ");
base.Receive(from, message);
}
}
}
The .NET optimized code demonstrates the same code as above but uses
more modern C# and .NET features.
Here is an elegant C# Mediator solution.
namespace Mediator.NetOptimized;
using static System.Console;
using System.Collections.Generic;
/// <summary>
/// Mediator Design Pattern
/// </summary>
public class Program
{
public static void Main()
{
// Create chatroom participants
var George = new Beatle { Name = "George" };
var Paul = new Beatle { Name = "Paul" };
var Ringo = new Beatle { Name = "Ringo" };
var John = new Beatle { Name = "John" };
var Yoko = new NonBeatle { Name = "Yoko" };
// Create chatroom and register participants
var chatroom = new Chatroom();
chatroom.Register(George);
chatroom.Register(Paul);
chatroom.Register(Ringo);
chatroom.Register(John);
chatroom.Register(Yoko);
// Chatting participants
Yoko.Send("John", "Hi John!");
Paul.Send("Ringo", "All you need is love");
Ringo.Send("George", "My sweet Lord");
Paul.Send("John", "Can't buy me love");
John.Send("Yoko", "My sweet love");
// Wait for user
ReadKey();
}
}
/// <summary>
/// The 'Mediator' interface
/// </summary>
public interface IChatroom
{
void Register(Participant participant);
void Send(string from, string to, string message);
}
/// <summary>
/// The 'ConcreteMediator' class
/// </summary>
public class Chatroom : IChatroom
{
private readonly Dictionary<string, Participant> participants = [];
public void Register(Participant participant)
{
participants.TryAdd(participant.Name, participant);
participant.Chatroom = this;
}
public void Send(string from, string to, string message)
{
var participant = participants[to];
if (participant != null)
{
participant.Receive(from, message);
}
}
}
/// <summary>
/// The 'AbstractColleague' class
/// </summary>
public class Participant
{
// Gets or sets participant name
public string Name { get; set; } = null!;
// Gets or sets chatroom
public Chatroom Chatroom { get; set; } = null!;
// Send a message to given participant
public void Send(string to, string message)
{
Chatroom.Send(Name, to, message);
}
// Receive message from participant
public virtual void Receive(string from, string message)
{
WriteLine($"{from} to {Name}: '{message}'");
}
}
/// <summary>
/// A 'ConcreteColleague' class
/// </summary>
public class Beatle : Participant
{
public override void Receive(string from, string message)
{
Write("To a Beatle: ");
base.Receive(from, message);
}
}
/// <summary>
/// A 'ConcreteColleague' class
/// </summary>
public class NonBeatle : Participant
{
public override void Receive(string from, string message)
{
Write("To a non-Beatle: ");
base.Receive(from, message);
}
}
