Prism NotificationRequest vs Xceed MessageBox

Question

When we use MVVM we are told to avoid using System.Windows.MessageBox in our ViewModel, and I guess it is because it would not be good for our tests. Is it true?

With Prism NotificationRequest, we can comunicate with our users, but it is a little more complicated than a simple MessageBox.

Another way is to use Xceed Wpf Toolkit MessageBox, which is simplier than Prism NotificationRequest.

My question is: are both of them equivalent? Can we use any of them in a MVVM way? If NO, when do we need to use NotificationRequest and when can we use Xceed MessageBox?

Thank you

Answer 1

If you call MessageBox.Show() from a service that can be replaced with a mock when testing, you're fine.

After all, what you do not want is a message box popping up when running your view models unit tests...

Example:

public interface IMessageBoxService
{
    ClickedButten ShowMessageBox( string message, Buttons buttons );
}

internal class SomeViewModel
{
    public SomeViewModel( IMessageBoxService messageBoxService )
    {
        _messageBoxService = messageBoxService;
    }

    public void SomeMethodThatNeedsAMessageBox()
    {
        var theClickedButton = _messageBoxService.ShowMessageBox( "Click me!", Buttons.Ok | Buttons.Cancel );
        // react to the click...
    }
}

internal class SystemMessageBoxService : IMessageBoxService
{
    public ClickedButten ShowMessageBox( string message, Buttons buttons )
    {
        // adapt parameters...
        MessageBox.Show(...);
        // adapt result...
    }
}

internal class XceedMessageBoxService : IMessageBoxService
{
    public ClickedButten ShowMessageBox( string message, Buttons buttons )
    {
        // adapt parameters...
        Xceed.ShowMessageBox(...);
        // adapt result...
    }
}

Now just bind the service that you want to use (could even be decided at runtime), and inject a mock when testing.