Before coming to this question WPF interviewer would first like to know What is MVVM architecture pattern. So in case you are new to MVVM start from this WPF MVVM interview question http://dotnetinter.livejournal.com/88971.html written by www.questpond.com
Below are the benefits of MVVM pattern:-
Separation of concern: – As the project is divided in to layers, every layer handles its own responsibility. This leads to better maintenance because when we change one layer the other layer does not get affected.
Increased UI Reusability: – The whole point of MVVM is to remove behind code i.e. XAML.CS code. The problem with behind code is that it is tied up with a UI technology for example ASPX.CS code is tied up with the ASP page class, XAML.CS file is tied with WPF UI technology and so on. So we cannot use ASPX.CS behind code with WPF XAML UI.
By moving the behind code to the view model class we can now use this with any UI technology.
Automated UI Unit testing: – View model class represents your UI. The properties of the class represent UI text boxes, combo boxes and the methods of the class represent action. Now as the UI is represented by the view model class, we can do automated UI testing using unit testing by creating the objects of view model class and doing the necessary asserts.
If you want to learn WPF step by step ,start from this video which talks WPF and how WPF differs from winforms