Programmatic Binding speed

string myCode="AAA"; 
Binding bdd = new Binding() { Converter = new CodeToName(), Source = myCode};

myTextBlock.SetBinding(TextBlock.TextProperty, bdd);

Say my code is like this and I have a giant listbox that has a lot of myTextBlock.

The Converter 'CodeToName' runs a linq query that effects the performance.  I only want this to run when these items are scrolled into view of the listbox.  I'm guess this would do it, and the converter would only run when the UI tells it to display.

Am I correct?

dan