In the early days of WPF (they are over now, today is Silverlight), there was an app called Microsoft MAX
that combined photo-gallery with an RSS reader and looked pretty neat.
Dan Crevier, a member of the team at Microsoft, who build MAX, then went and described the underlying
design pattern, which he called the DataModel-ViewModel-View pattern.
You can read all about it here.
It took a while until I realized that this is an incarnation of what Martin Fowler describes as PresentationModel.
What's special about DM-VM-M is that View and ViewModel are glued together using DataBinding quite heavily.
DataBinding is a very powerful concept in WPF and this is a nice way to do it.
Basically what DM-VM-M gives you is something that is very close to the view, but separated and testable:
a model of the view. The VM also contains the logic that talks to the data-model and that's why I would not
choose to implement it for more complex types of apps.
Instead, what I favor is a variation of the Supervising Controller Pattern, which Martin Fowler describes here.
A Supervising Controller type Model-View-Presenter architecture fits very well with the powerful databinding
machinerie of WPF and allows very good testability of the behavior of an application.
Basically what you do it set the DataContext of the Window or the current view (UserControl) to the object
model, so you can bind your data against it. You add Commands in XAML and expose the CanExecute
and Executed events in the view interface. It makes sense to add a little bit of translation logic there
that removes the Routed- aspect and casts the command parameter to type that's actually data-bound.
e.g.
interface IView
{
event EventHandler<CommandExecutedArgs<Item>>
EditExecuted;
event EventHandler<CommandCanExecuteArgs<Item>>
CanExecuteEdit;
void ShowEditDialog();
}
class SupervisingController
{
private IView _view;
private IDataModel _model;
}
DM-M-VM does have its place, but it's not the only way to design WPF apps.
In fact I would use DM-M-VM for simple apps where you want to maximize testing on the view.
If there's a bit more logic involved, I'd go for a Supervising controller approach, where the view basically
manages itself and the presenter encapsulates the logical behavior.
cheers,
Florian