
 
        Returns the index where dropped data should be placed in the
 list. Interpretation of the value depends on the drop mode set on
 the associated component. If the drop mode is either
 
DropMode.USE_SELECTION or 
DropMode.ON,
 the return value is an index of a row in the list. If the drop mode is
 
DropMode.INSERT, the return value refers to the index
 where the data should be inserted. If the drop mode is
 
DropMode.ON_OR_INSERT, the value of
 
isInsert() indicates whether the index is an index
 of a row, or an insert index.
 
 -1 indicates that the drop occurred over empty space,
 and no index could be calculated.
        
        
Returns:
    the drop index