Design Patterns: Mediator

The Mediator Pattern allows objects to communicate with each other through a common instance of a mediator class. It promotes loose coupling and prevents objects from referring to each other directly.

Figure 1: Subscribed instances

1. public abstract class Mediator
2. {
3. public IList<AirCraft> AirCrafts { get; private set; }
5. public Mediator()
6. {
7. AirCrafts = new List<AirCraft>();
8. }
10. public abstract void Send(AirCraft sender, string message);
11. }
13. public class CommunicationTower : Mediator
14. {
15. public override void Send(AirCraft sender, string message)
16. {
17. foreach (var airCraft in AirCrafts)
18. {
19. if (airCraft != sender)
20. {
21. airCraft.Receive(sender, message);
22. }
23. }
24. }
25. }
27. public abstract class AirCraftCollegue
28. {
29. public abstract void Receive(AirCraft sender, string message);
30. }
32. public class AirCraft : AirCraftCollegue
33. {
34. public AirCraft(CommunicationTower mediator)
35. {
36. mediator.AirCrafts.Add(this);
37. }
39. public string Name { get; set; }
41. public override void Receive(AirCraft sender, string message)
42. {
43. Console.WriteLine("{0}: Received message '{1}' from '{2}'", Name, message, sender.Name);
44. }
45. }

In the preceding example the mediator tells the subscribed aircrafts (except the sender) that one of them is saying something.

Output:

One actual example is the EventAggreagator that we see in WPF. It allows the communication between view models that don't know about the existence of each other.