I am a bit OT here, but I was able to attach a Picture (drag.Picture = MyTmpPict): very nice !
The Picture holds the data from selected Rows you are currently dragging. This is a simple user interface, I do not save the image.
For dragging a Row from a Listbox… last time I checked, it created as many Clipping text files as you have Rows. I worked a bit more on that (drag image above), but I do not recall my results. Sorry, I do not have that project handly.
I forgot to mention that sometimes, when the Finder target window is in list display, the drag does not occured (.Clipping files). Changing that to View as Icons makes the drag working again. I am not sure this is a Xojo bug.