"MVVM - It's Not Kool-Aid" by Jesse Liberty
Jesse Liberty's blog post titled "MVVM - It's Not Kool-Aid" illustrates succinctly a key refrain in the MVVM mantra.
There is intentionally/explicitly NOT a red arrow from the View all the way down to the Model . Also of note is the fact that the arrows are not bidirectional-this underscores the fact that the View knows about the ViewModel and that the ViewModel knows about the Model, but NOT any combination ofthe reverse. When a field in the ViewModel has been bound to something in the View, the ViewModel is not specifically telling that particular View that the field has changed; instead, generically, the ViewModel's field is changed and the ViewModel notifies subscribers of the change.