
 
        Returns the column index where a dropped item should be placed in the
 table. Interpretation of the value depends on the return of
 
isInsertColumn(). If that method returns
 
true this value indicates the index where a new
 column should be inserted. Otherwise, it represents the value
 of an existing column on which the data was dropped. This index is
 in terms of the view.
 
 -1 indicates that the drop occurred over empty space,
 and no column could be calculated.
        
        
Returns:
    the drop row