Mediator Design Pattern
 definition UML diagram participants | sample code in C# |
medium low
UML class diagram
participants
The classes and/or objects participating in this pattern are:
- Mediator (IChatroom)
- defines an interface for communicating with Colleague objects
- ConcreteMediator (Chatroom)
- implements cooperative behavior by coordinating Colleague objects
- knows and maintains its colleagues
- Colleague classes (Participant)
- each Colleague class knows its Mediator object
- each colleague communicates with its mediator whenever it would have otherwise communicated with another colleague
sample code in C#
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.
Hide code
// Mediator pattern -- Structural example
|
using System;
namespace DoFactory.GangOfFour.Mediator.Structural
{
/// <summary>
/// MainApp startup class for Structural
/// Mediator Design Pattern.
/// </summary>
class MainApp
{
/// <summary>
/// Entry point into console application.
/// </summary>
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.ReadKey();
}
}
/// <summary>
/// The 'Mediator' abstract class
/// </summary>
abstract class Mediator
{
public abstract void Send(string message,
Colleague colleague);
}
/// <summary>
/// The 'ConcreteMediator' class
/// </summary>
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);
}
}
}
/// <summary>
/// The 'Colleague' abstract class
/// </summary>
abstract class Colleague
{
protected Mediator mediator;
// Constructor
public Colleague(Mediator mediator)
{
this.mediator = mediator;
}
}
/// <summary>
/// A 'ConcreteColleague' class
/// </summary>
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>
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);
}
}
}
|
Output
Colleague2 gets message: How are you?
Colleague1 gets message: Fine, thanks |
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.
Hide code
// Mediator pattern -- Real World example
|
using System;
using System.Collections.Generic;
namespace DoFactory.GangOfFour.Mediator.RealWorld
{
/// <summary>
/// MainApp startup class for Real-World
/// Mediator Design Pattern.
/// </summary>
class MainApp
{
/// <summary>
/// Entry point into console application.
/// </summary>
static void Main()
{
// 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>
abstract class AbstractChatroom
{
public abstract void Register(Participant participant);
public abstract void Send(
string from, string to, string message);
}
/// <summary>
/// The 'ConcreteMediator' class
/// </summary>
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>
class Participant
{
private Chatroom _chatroom;
private 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>
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>
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);
}
}
}
|
Output
To a Beatle: Yoko to John: 'Hi John!'
To a Beatle: Paul to Ringo: 'All you need is love' To a Beatle: Ringo to George: 'My sweet Lord' To a Beatle: Paul to John: 'Can't buy me love' To a non-Beatle: John to Yoko: 'My sweet love' |
This .NET optimized code demonstrates the same real-world situation as above but uses modern, built-in .NET features, such as, generics, reflection, object initializers, automatic properties, etc.
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