> You mentioned Supervising Controller by Martin Fowler; > did you know he has another variant of that same idea > called Presentation Model? http://martinfowler.com/eaaDev/PresentationModel.html
Fowler describes four different patterns which he regards as different ways of implementing the MVC or MVP patterns in his GUI architectures article http://martinfowler.com/eaaDev/uiArchs.html and supporting articles (Separated Presentation http://martinfowler.com/eaaDev/SeparatedPresentation.html, Presentation Model, Supervising Controller http://martinfowler.com/eaaDev/SupervisingPresenter.html, and Passive view http://martinfowler.com/eaaDev/PassiveScreen.html. My interpretation is that he sees the Separated Presentation as being at the heart of the MVC concept. He has retired the MVC pattern in his thinking since he sees different forms of implementation. He sees this pattern as separating the common functionality from the view specific functionality. The Presentation Model he argues is the beginning of the shift from MVC to MVP although he contends that the boundary is unclear. He says that the presentation model is a class that contains "all the data of the UI window, but without any of the controls used to render that UI on the screen." In effect, it separates the view from the data needed to build the view. Fowler talks about problems in synchronising the presentation model and the view. The Passive View sees the manipulates the view as well as being a presentation model. This approach sees the view having no built in functionality and the controller or presenter manipulating the view to make changes. The controller pushes data back into the view. The Supervising Controller is similar to the passive view except that the controller doesn't push data back into the view. This is left to data binding mechanisms. The model in this pattern may be closer to a presentation model rather than a domain model. The controller handles all user gestures. One of the things with this pattern is that because the controller and model have no knowledge of the view, it is easier to implement in a test driven fashion. I believe one of the points of difference between the patterns is the degree of relationship between the view and the controller. In MVC, the controller focused on handling user gestures and manipulating the model. The view was left to look after itself. The presentation model was an attempt to recognise that the view actually had model elements that could be used with alternative views. The passive view proves difficult to test as you have to mock out the view. The supervising controller removes all links back to the view making it easier to build tests. --------------------------------- Errol Thompson Kiwi-ET Computing Education Research Wellington, New Zealand Phone: +64 21 210 1662 E-Mail: kiwiet (at) acm.org kiwiet (at) computer.org Web: www.teach.thompsonz.net ---------------------------------
