Adding the INavigation interface to the ViewModel class

To be able to access the navigator we extend the ViewModel base class, making it available to all ViewModels. Proceed as follows:

1. In the News project, open the ViewModels folder, and then open the ViewModel.cs file.
2. Add the following code marked in bold to the class:

public abstract class ViewModel : INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    public INavigate Navigation { get; set; } = new Navigator();
}

The ViewModel now exposes the Navigator property through the INavigate interface, and we are ready to wire up the navigation to our Article view.