如何从ViewModel访问MetroWindow的ShowMessageAsync方法

I am using MahApps.metro WPF library with MVVM. I have a ViewModel from which I need to display a Dialog. The MetroWindow has ShowMessageAsync. But what is the proper way to access it from the ViewModel? As I understand I need a View instance but passing that into the ViewModel doesn't seem like a good approach.I am using MahApps.metro WPF library with MVVM.