See Also Example
Combo box, list box.
Specifies the index Not available at design time; read-only at run time. of the item most recently added to a combo box or list box.
This property is useful with sorted lists when you need a list of values that correspond to each item in the ItemData As you add an item in a sorted list, Visual Basic inserts the item in the list alphabetically. This property tells you where the item was inserted so that you can insert a corresponding value in the ItemData property at the same index. property array.
NewIndex will return -1 if there are no items in the list or if an item has been deleted since the last item was added.
Chapter 3, "Creating and Using Controls"