Mediators

Mediators are the implementation of Gang of Four's Mediator pattern. In MVVM-based applications, they can be used to connect different disconnected parts of the application. Mediators aren't available directly in WPF or Silverlight but most of the MVVM toolkits have provided a mediator implementation. PRISM and MVVM Light have the EventAggregator and Messenger respectively as mediators. They are implemented based on Publisher/Subscriber model. One party publishes a message and if any other part of the application has subscribed to that message then the mediator hands message over to them. If, however, there are no subscribers then the message is ignored. Mediators generally have no limitations on the number of subscriber for a particular message so it could also be used for broadcasting certain information like Disconnected from Server or Logging off. Messages are generally received by a subscriber on the same thread that it was published on. Some MVVM toolkits allow publishing...