User prompts (MessageBox) with MVVM

March 12, 2010 · 1 min read

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!(https://geekswithblogs.net/Providers/BlogEntryEditor/FCKeditor/editor/images/smiley/msn/wink_smile.gif)

- Design my own dialog, then what to do from there!(https://geekswithblogs.net/Providers/BlogEntryEditor/FCKeditor/editor/images/smiley/msn/devil_smile.gif)

- 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... !(https://geekswithblogs.net/Providers/BlogEntryEditor/FCKeditor/editor/images/smiley/msn/whatchutalkingabout_smile.gif)

- 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.

!(/images/mukapu/user-prompts-messagebox-with-mvvm/70b54ed8-UserPrompt1.png)

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

!(/images/mukapu/user-prompts-messagebox-with-mvvm/504a2e6d-UserPrompt2.png)

!(/images/mukapu/user-prompts-messagebox-with-mvvm/30006bbb-UserPrompt3.png)

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

!(/images/mukapu/user-prompts-messagebox-with-mvvm/5853efb6-UserPrompt4.png)

How do I Use?

- Just place the necessary XAML tag in the view

!(/images/mukapu/user-prompts-messagebox-with-mvvm/998c0712-UserPrompt5.png)

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

!(/images/mukapu/user-prompts-messagebox-with-mvvm/1c8c410e-UserPrompt6.png)

- Run unit tests on the commands

!(/images/mukapu/user-prompts-messagebox-with-mvvm/b4af0bc2-UserPrompt7.png)

I am also attaching the code for the MessageBox control and a demo application.

Hope this is useful to somebody out there... Comments are welcome....

!(file:///C:/DOCUME1/706015/LOCALS1/Temp/moz-screenshot-1.png)

This article is part of the GWB Archives. Original Author: mukapu

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