Should a ViewModel in MVVM reference the View?

Question

In the MVVM (Model-View-ViewModel) pattern should the ViewModel reference the view. I would think that it should not. But how should the following scenario be handeled? I ha

Answer 1

In "pure" MVVM, the ViewModel shouldn't really reference the View. It's often convenient, however, to provide some form of interface in the View whereby the ViewModel can interact with it.

However, I've found that I almost never do that anymore. The alternative approach is to use some form of attached property or blend behavior within your View, and bind it to your ViewModel properties. This allows you to keep the View logic 100% within the View. In addition, by creating a behavior for this, you create a reusable type that can be used to handle this in every ViewModel->View interaction. I strongly prefer this approach over having any View logic within the ViewModel.

In order to demonstrate this technique, I wrote a sample for the Expression Code Gallery called WindowCloseBehavior. It demonstrates how you can use a Behavior within the View bound to properties in the ViewModel to handle controlling a Window's life-cycle, including preventing it from being closed, etc.