How to use a 3rd party control inside the viewmodel?

Question

I have a 3rd party control which among other things performs loading of some data. I want my viewmodel to keep track of this load operation and adjust its own state accordingly.

If it were up to me, I'd do the data loading far away from the view, but it is not. So, I seem to be in the situation where my viewmodel depends on my view. How do I best handle this? I feel rather dirty making the view publish events to the viewmodel but I don't see any other reasonable way to get this info into the viewmodel.

A similar situation might crop up with standard controls, too - imagine if your viewmodel depends on the events coming from a MediaElement - how do you properly model this? Do you put the MediaElement into the viewmodel? That doesn't sound right.

If publishing the events to the viewmodel is indeed the most reasonable way, is there some common pattern used for this? How do you do it?

Answer 1

Generally, you would not allow your ViewModel to know details or even the type of your view controls. Having it respond to events is the cleaner way to go. There are a number of libraries that contain behaviors to map control events to ICommands on your ViewModel.

Caliburn is one such library. You can map control events to methods on your ViewModel.