Nice quote there from Josh Smith. But yeah,why not allocate the steroids to the parts that can make best use of them, including reusable View parts that aren’t coupled to business objects, like the author’s PhoneNumberControl?

In my shop, I think developers will buy into the separation of concerns argument and the ease of automated unit testing argument for MVVM. But I don’t think anybody’s going to favor walking through and maintaining extra code for ViewModel objects that aren’t clearly necessary or that do work that can more easily be done with built-in types accessible from the View or reusable View objects that are not coupled to business objects.

As for unit testing, i.e, ensuring 100% test coverage of all statements or all branches or all basis paths or some other criteria, you have to do that either way, whether you extend the ViewModel or the View. Surely the guys who make controls for a living aren’t cutting corners on unit testing or on automating as many tests as possible.

Sorry – I don’t have time to solve individual problems. Please try the WPF forums:

social.msdn.microsoft.com/forums/en/wpf/threads/

Colin E.

I am passing CheckListBox ( for multiple selection) , However its not raising SelectionChangeEvent of list, any workaround ?

Glad you found this article interesting. I have also found myself transferring WPF patterns to WinForms, as you know we use MVVM for our grid controls. (However, MVVM is really just a new and sexy name for the Martin Fowler’s presentation-model pattern!)

Regarding unit testing, I had this same discussion with Gergely yesterday, I don’t believe in unit testing UI code.

With the example I use in this blog post, the ViewModel is being used as a means to format a phone number, something that is hard to achieve with the tools available in the WPF framework. The important point to me is that this is ‘formatting’, i.e. pure presentation.

Sure, you could try and unit test it, however, what if someone screws up the positioning of the controls, or the font? your tests would pass, but the UI would be all wrong! In my opinion UIs should be tested by humans.

(Having said that, I probably would unit test the parts of the code which manipulate the phone number and extract its component parts – however, I would make this a separate, non UI-centric unit!)

Regards, Colin E.

I tried applying this pattern directly to WinForms (given the projects I work with currently are WinForms) and it comes up quite nicely.

I do share Brian Genisio’s concern about unit testing, but its an interesting point about not coupling the View and ViewModel to any business objects – "decompose it into a number of re-usable controls, each containing mini-ViewModels". I guess you could introduce an interface for business objects to use, but that adds complexity and defeats the purpose of your article.

Think miniViewModel is something I’ll add toolbox. Thanks Colin.