absolute position(x,y) of ListBoxItem - Binding self , IValueConverter and TransformToVisual - is it possible?

Question

Hi,


I'm trying something like this:
 
....
<DataTemplate...> 
....
        <TextBlock Text="{Binding RelativeSource={RelativeSource Self}, Converter={StaticResource PositionConverter}}" />


and


class Position : IValueConverter
{

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
  GeneralTransform generalTransform = value.TransformToVisual(null);     // here I get error
Point point = generalTransform.Transform(new Point());

return "X="+Point.X+"Y="+Point.Y;
  }
....


and the result is following error:  'object' does not contain a definition for 'TransformToVisual' and no extension method 'TransformToVisual' accepting a first argument of type 'object' could be found 


Any ideas how to solve this, or maybe some one know different approach to get absolute position of listbox elements?

Regards,
Tadek.