Dynamically Add to List Box (image included)

When I click the "Add Affiliation" button, I would like it to add the item number associated with that particular subform row added to the listbox below it. I calculate the item number from the index (the text field is called "txtCalcItemNumber").

This is what is in my click event for btnAddAffiliations:

Page1.Affiliations.Details.instanceManager.addInstance();

(i tried the code below to add items to listbox but doesn't work)

var values = xfa.resolveNode("Page1.Affiliations.Details[" + this.parent.index + "]").txtCalcItemNumber.rawValue;

ListBox1.addItem(values);

THANKS FOR YOUR HELP!!