MVVM in WPF - How to alert ViewModel of changes in Model… or should I?

Question

I am going through some MVVM articles, primarily this and this.

My specific question is: How do I communicate Model changes from the Model to the ViewModel?<

Answer 1

I have been advocating the directional Model -> View Model -> View flow of changes for a long time now, as you can see in the Flow of Changes section of my MVVM article from 2008. This requires implementing INotifyPropertyChanged on the model. As far as I can tell, it's since become common practice.

Because you mentioned Josh Smith, take a look at his PropertyChanged class. It's a helper class for subscribing to the model's INotifyPropertyChanged.PropertyChanged event.

You can actually take this approach much further, as I have recenty by creating my PropertiesUpdater class. Properties on the view-model are computed as complex expressions that include one or more properties on the model.