title: Notification from ViewModel to View
body: <p>I need to send notification from ViewModel to View in MVVM WPF application. In most cases it will be simple MessageBox on View side. Is it unacceptable violation of MVVM pattern to use types like System.Windows.MessageBoxResult or System.Windows.MessageBoxImage in ViewModel (in this case VM must reference UI-specific libraries)?  </p>
  
  <p>I need to pass title, message and notification type from VM and by creating custom enumerations I am in fact copying existing functionality from .NET Framework.</p>