Как правильно в рамках MVVM открыть новое окно

public class HandleDoubleClickOnRowBehavior : Behavior<DataGrid>
{
    #region Properties
 
    #region Command
 
    public static readonly DependencyProperty CommandProperty =
        DependencyProperty.Register("Command", typeof(ICommand), typeof(HandleDoubleClickOnRowBehavior));
 
    public ICommand Command
    {
        get { return (ICommand) GetValue(CommandProperty); }
        set { SetValue(CommandProperty, value); }
    }
 
    #endregion
 
    #endregion
 
    #region Overridden members
 
    protected override void OnAttached()
    {
        AssociatedObject.MouseDoubleClick += AssociatedObject_MouseDoubleClick;
    }
 
    protected override void OnDetaching()
    {
        AssociatedObject.MouseDoubleClick -= AssociatedObject_MouseDoubleClick;
    }
    
    #endregion
 
    private void AssociatedObject_MouseDoubleClick(object sender, MouseButtonEventArgs e)
    {
        if (Command == null)
            return;
 
        var selectedItem = AssociatedObject.SelectedItem;
        if (selectedItem == null)
            return;
 
        if (!Command.CanExecute(selectedItem))
            return;
 
        Command.Execute(selectedItem);
    }
}