The mediator pattern promotes loose coupling by defining an object that encapsulates how a set of objects interact. It defines an intermediary object that manages interactions between peers. This allows objects to interact without having explicit knowledge of each other. The mediator pattern identifies objects that would benefit from decoupling, encapsulates their interactions in a mediator class, and has peer objects interact through the mediator instead of directly with each other.

2. Motivations
 lots of classes in the design of framework
 If certain principles are not applied the final
framework will end in a total mess
 to avoid tight coupled frameworks, we need a
mechanism to facilitate the interaction between
objects in a manner in that objects are not aware of the
existence of other objects.

3. Mediator
Mediator promotes loose coupling by keeping objects
from referring to each other explicitly

4. Intent
 Define an object that encapsulates how a set of objects
interact.
 Design an intermediary to decouple many peers
 Promote the many-to-many relationships between
interacting peers to “full object status”.

5. Unmediated

6. Mediated

7. Mediator

8. Check list
 Identify a collection of interacting objects that would
benefit from mutual decoupling.
 Encapsulate those interactions in the abstraction of a
new class.
 Create an instance of that new class and rework all
“peer” objects to interact with the Mediator only.

9.  Balance the principle of decoupling with the principle
of distributing responsibility evenly.
 Be careful not to create a “controller” or “god” object.

10. Mediator design example
 Let us consider design of a class in which one object
send messages to other objects by means of if then if
condition explicitly

11. public class WorkerObject
{
private string _message;
public WorkerObject(string message)
{
_message = message;
}
public string Message
{
get{return _message;}
set{_message = value;}
}
public SendMessage(string message)
{
Console.WriteLine(quot;Message sent : quot; + message);
}
}

12. WorkerObject senderObject = new WorkerObject(quot;message0quot;);
WorkerObject workerObject1 = new WorkerObject(quot;message1quot;);
WorkerObject workerObject2 = new WorkerObject(quot;message2quot;);
WorkerObject workerObject3 = new WorkerObject(quot;message3quot;);
if(!workerObject1.Message.Equals(senderObject.Message))
{
workerObject1.SendMessage(senderObject.Message);
}
if(!workerObject2.Message.Equals(senderObject.Message))
{
workerObject2.SendMessage(senderObject.Message);
}
if(!workerObject3.Message.Equals(senderObject.Message))
{
workerObject3.SendMessage(senderObject.Message);
}

13. Mediator
 we create a mediator class, DoSomeMediation.
 This class contains two methods Register and
SendMessage
 The Register method catalogs all the classes we want
to mediate between.
 The SendMessage method is where the functional
code actually exists

14. public class DoSomeMediation
{
private static ArrayList _workerObjects = new ArrayList();
public static int Register(WorkerObject workerObject)
{
return _workerObjects.Add(workerObject);
}
public static void SendMessage(WorkerObject senderObject)
{
if(senderObject == null) return;
string messageToSend = senderObject.Message;
foreach(WorkerObject workerObject in _workerObjects)
{
//send message to all other objects registered
if(!workerObject.Message.Equals(senderObject.Message))
workerObject.SendMessage(messageToSend);
}
}
}

15. WorkerObject senderObject = new WorkerObject(quot;message0quot;);
WorkerObject workerObject1 = new WorkerObject(quot;message1quot;);
WorkerObject workerObject2 = new WorkerObject(quot;message2quot;);
WorkerObject workerObject3 = new WorkerObject(quot;message3quot;);
DoSomeMediation.Register(senderObject);
DoSomeMediation.Register(workerObject1);
DoSomeMediation.Register(workerObject2);
DoSomeMediation.Register(workerObject3);
DoSomeMediation.SendMessage(senderObject);

16. Flow diagram
WorkerObj1
Mediator
SenderObj
Worker
Obj2

17. CCS Model
 SenderObject(reg,sendmedmsg,sendobjmsg,printmsg)=
reg.sendmedmsg’.SenderObject<reg,sendmedmsg,sendobjmsg,printms
g>
 Mediator(sendmedmsg,sendobj1msg,sendobj2msg)=
sendmedmsg.sendobj1msg’.Mediator<sendmedmsg,sendobj1msg,sendo
bj2msg> +
sendmedmsg.sendobj2msg’.Mediator<sendmedmsg,sendobj1msg,send
obj2msg>
 Workerobj1(reg,sendmedmsg,sendobjmsg,printmsg)=sendobjmsg.prin
tmsg’.Workerobj1<reg,sendmedmsg,sendobjmsg,printmsg>
 Workerobj2(reg,sendmedmsg,sendobjmsg,printmsg)=sendobjmsg.prin
tmsg’.Workerobj2<reg,sendmedmsg,sendobjmsg,printmsg>

18. Simulation on MWB