Question

I’m working on a new WPF application and I’m trying to stay as close to the MVVM pattern as I can. My XAML files right now have no codebehinds, and all my interactivity is achieved using Josh Smith’s RelayCommand class and commands in my ViewModel classes.

This worked great until I started working on the housekeeping tasks, such as an about box and a system preferences page. I want to have these as modal dialogs, but if I create a RelayCommand to open these pages, I’ll be creating a dependency on the view within my view model.

This strikes me as against the grain of the MVVM pattern.

Is there an established method for creating new windows (modal and/or modeless) within the MVVM pattern without creating a dependency? It seems the only way I can keep the ViewModel clean is to create a Click event handler in the XAML codebehind file and create the new view within the old view.

Any recommendations?

Answer 1

One way to handle this is to implement a service that provides Views to ViewModels. Views register with the service and ViewModels can request dialogs from the service. This is an example of the Gang of Four mediator pattern.