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mediator

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Vivek Mahajan
Vivek Mahajan

The mediator pattern promotes loose coupling between classes by defining an object that encapsulates how groups of classes interact. It defines an intermediary object that manages interactions between peers instead of peers referring to each other directly. The mediator pattern identifies classes that could benefit from loose coupling, encapsulates their interactions in a mediator class, and has peer objects interact with the mediator instead of each other. This allows peer objects to be unaware of changes to other peer objects, reducing coupling between classes.

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mediator
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.
Mediator Mediator promotes loose coupling by keeping objects from referring to each other explicitly
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”.
Unmediated
Mediated
Mediator
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.
 Balance the principle of decoupling with the principle of distributing responsibility evenly.  Be careful not to create a “controller” or “god” object.
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
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); } }
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); }
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
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); } } }
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);
Flow diagram WorkerObj1 Mediator SenderObj Worker Obj2
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>
Simulation on MWB

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mediator

  • 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”.
  • 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>