The problem statement:

I am tired of thinking how to show a simple message box or user prompt and act based on the response in Model-View-View-Model (MVVM).

Common approaches:

- It's ok, let's just do this one thing from ViewModel and mock this out for unit testing

- Design my own dialog, then what to do from there

- Can I write something in view code behind, ah yes, that seems to be the only way out, as anyway MVVM is still not matured... 

- and what not?

I am pretty much one among the few frustrated out in this world looking for some convincing answers. I think we can do it a little neater without having the feeling of violating any of our self defined rules!

Solution:

The Control

- Implement a simple control with no designer visibility.

- Allow a property to be bound to tell when to show the MessageBox

- Provide command binding for possible user actions, Yes, No, Cancel...

How do I Use?

- Just place the necessary XAML tags in the view

- Implement the command for all user actions in the View Model

- Run unit tests on the commands