Getting data from a view in MVVM?

Question

I have a silverlight bing map application. I am using the MVVM pattern with PRISM. The bing map has a "BoundingRectangle" property that is not available in XAML, but it is available via code behind. Of course this does me no good since I need the data in my viewmodel which doesn't have access to the View's code behind (nor do I want to add it, since I'd really like to try to not use the view's code behind if possible).

Normally, you would do a two way bind to a viewmodel property. The Bing map will surface BoundingRectangle for layers, but not for the base map (that I can find).

I'm not looking for a hack here, just wondering what the best practices or convention for getting data out of a view to a viewmodel that isn't "bindable".

Thanks!

Answer 1

Databinding in Silverlight is just a framework feature that automatically synchronizes data between your view and your view model (if you are following the MVVM pattern). However, there is nothing wrong with doing this yourself!

The two main advantages of the MVVM pattern (other than the usual separation of concerns that most UI patterns provide) are:

1. It aids unit testing, the View Model can be exercised from your unit test code without a view present.
2. It helps the developer / designer workflow, reducing the files shared between the designer and developer.

In my experience, having a small amount of code-behind that 'assists' the binding framework does no hard at all!

You can use techniques such as attached behaviours to wrap this code up, but often this just results in a cosmetic improvement.

Answer 2

CraigF, you can use Mediator pattern, if you use Galasoft Light toolkit then use messenger to send message from view to your viewmodel. Viewmodel register to that message and if recive one set your property in viewmodel and do some logic..