DropHandler (DnDEvent event) { if (event == null) return null; DnDAction action = event.getAction(); if (action == null) return null; int id = action.getActionId(); if (id == DnDConstants.ACTION_COPY) return createCopyHandler(); if (id != DnDConstants.ACTION_COPY_OR_MOVE && id != DnDConstants.ACTION_MOVE) return null; return createMoveHandler(); }