How to reffer XML data to IValue Converter?

Question

I am trying to build navigation model where pages are loaded into frame by selection listbox items of the ListBox and also by clicking 'back' / 'forward' buttons. Listboxitems with UriSource associated are generated from XML. While cliking 'back' / 'forward' buttons, I need to make the selected item in the ListBox be the current with the page loaded in the ContentFrame. As a result, I need to pass two values in the Convert method, one is the current source of the frame, another is the items collection of the ListBox, so that I can return the selected index of the item in the ListBox according to these two values. The Value Converter I provide is good for listboxitems defined in the C# code. I need to reffer data from XML to Value Converter. Any ideas are highly appreciated.

XML:

<XmlDataProvider x:Key="PagesData" XPath="Pages"> 
        <x:XData> 
            <Pages xmlns=""> 
                <page id="page01"> 
                    <name>Page 1</name> 
                    <source>Pages/Page1.xaml</source> 
                </page> 
                <page id="page02"> 
                    <name>Page 2</name> 
                    <source>Pages/Page2.xaml</source> 
                </page> 
            </Pages> 
        </x:XData> 
    </XmlDataProvider> 

XAML:

<Window.Resources>

     <DataTemplate x:Key="pageTemplate" > 
        <StackPanel Orientation="Horizontal" > 
            <TextBlock Text="{Binding XPath=name}" FontSize="14" VerticalAlignment="Center" Margin="4" /> 
        </StackPanel> 
    </DataTemplate> 

    <XmlDataProvider x:Key="PagesData" XPath="Pages"> 
        <x:XData> 
            <Pages xmlns=""> 
                <page id="page01"> 
                    <name>Page 1</name> 
                    <source>Pages/Page1.xaml</source> 
                </page> 
                <page id="page02"> 
                    <name>Page 2</name> 
                    <source>pages/Page2.xaml</source> 
                </page> 
            </Pages> 
        </x:XData> 
    </XmlDataProvider> 

    <local:IndexUriSourceConverter  x:Key="indexConverter" />

</Window.Resources>
<StackPanel>

    <ListBox Name="listbox" 
    ItemsSource="{Binding}" 
    SelectedIndex="{Binding ElementName=frame, Path=., Converter={StaticResource indexConverter}}">       
    </ListBox>

    <Frame Name="frame" Source="http://www.google.com/" Tag="{Binding ElementName=listbox, Path=Items}" Navigating="frame_Navigating"></Frame>
    <Button Click="Button_Click">Go</Button>
</StackPanel>

Code behind:

 private void Button_Click(object sender, RoutedEventArgs e)
    {
        frame.Source = new Uri("pages/Page3.xaml", UriKind.RelativeOrAbsolute);

    }

    private void frame_Navigating(object sender, System.Windows.Navigation.NavigatingCancelEventArgs e)
    {
        BindingExpression be = listbox.GetBindingExpression(ListBox.SelectedIndexProperty);
        be.UpdateTarget();
    }

Code for Value Converter:

 public class IndexUriSourceConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        { XmlElement element = value as XmlElement; 

    if (element != null) 
    { 
        string uriSource = element.SelectSingleNode("source").InnerText; 
        return new Uri(uriSource, UriKind.Relative); 
    } 
            var frame = value as Frame;
            if (frame != null)
            {
                var uris = frame.Tag as ItemCollection;
                if (uris != null)
                {
                    return uris.IndexOf(frame.Source.ToString());
                }
            }
            return null;
        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new Exception("The method or operation is not implemented.");
        }
    }