Drag & drop lines between list fields

[Keith Clarke]

Hi folks,
To help with some XML file analysis, I've created a pair of list fields that display the current node's children. The 'left' field is filled with all the child nodes and I filter this list down to just the nodes I will investigate further, by dragging into the 'right' list the nodes I will ignore. 

I thought I'd use this opportunity to learn about drag & drop, so the script below sits in each field and allows me to move fields back and forth between 'monitor' and 'ignore' lists - well, nearly! It's working but in an overall 'copy' mode - not 'move'. 

My problem is with the 'line -3' which should check that the drop was successful and then delete the line from the source field.

Any clues as to what I'm doing wrong?

/*
Drag and drop control for managing parameters between 'Monitor' and 'Ignore' lists
*/
on dragStart
   ---Start dragging a Parameter 
   put the hilitedLine of me into tLine --a line number reference and not the text
   put the line tLine of me into tParameter --gets the text from the referenced line number
   set the allowableDragActions to "move"
   set the dragAction to "move"
   set the dragData["text"] to tParameter --creates the 'payload' for the drag & drop action
   pass dragStart
end dragStart

on dragEnter
   --Enable as a receiving field 
   set the dragAction to "copy"
   pass dragEnter
end dragEnter

on dragDrop
   --Put some dragsource logic in here - exit if dragSource is not the expected field or the dragData payload is empty 
   --Deposit the drag 'payload'
   put the dragData["text"] into tDraggedArray
   if me is not empty then put return after me --adds a return after the last item when the destination list is not empty 
   put line 1 of tDraggedArray after me --adds the Parameter to the list
   sort lines of me --sorts a-z
   if the dragDestination contains tParameter then delete line tLine of me
   pass dragDrop
end dragDrop

Oh, and a minor point - dragAction is set to 'move' but I get the OSX 'plus' icon attached to the drag action, which implies copy?!?
Best,
Keith..