Question

I’m using WPF with the WAF framework.

I have a piece of UI (let’s say it collects the user credentials) that gets presented on multiple views (see image).

I figured, hey, this is reusable, let’s put it in its own user control.

I can get everything working fine if I ignore the inner user control and just “flatten” it if you will, but trying to encapsulate it is making me wonder what the best approach is. Should this “credentials” user control have its own dedicated view model? Should it be exposing its data through dependency properties instead? What’s the best approach?

I will need to expose the data collected from the credentials control to the view model of the outer user control.

Answer 1

Should this “credentials” user control have its own dedicated view model? Should it be exposing its data through dependency properties instead? What’s the best approach?

A UserControl can serve two purposes –

If you want to use it as a “Control” – which is often the case in a situation like this, I would treat it as 100% view. As such, I would not make the UserControl have a ViewModel at all (at least not publically), and expose it’s properties via Dependency Properties. This provides the most flexibility in terms of reuse, as the UserControl acts like any other FrameworkElement, and can be dropped in and bound to your own properties in your other location like any other control.

When a UserControl acts as a View for a ViewModel, however, things are different. Here, the goal isn’t reuse, but separation of concerns between your View and VM.

This situation sounds more like the first – you want to have a control that can be reused in multiple locations. In this case, this basically becomes a view element.