public ListCellX() {
        setOnDragDetected(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                is_draggable.set(true);
                event.consume();
            }
        });
    }

        final ChangeListener<Boolean> draggable_listener = new ChangeListener<Boolean>() {
            EventHandler<? super DragEvent> onDragOver;
            EventHandler<? super DragEvent> onDragDropped;
            EventHandler<? super MouseEvent> onDragDetected;

            @Override
            public void changed(final ObservableValue<? extends Boolean> ov, Boolean t, Boolean t1) {
                if (t1) {
                    Callback<TreeView<Position>, TreeCell<Position>> cellFactory = tree.getTree().getCellFactory();
                    final TreeCell<Position> call = cellFactory.call(tree.getTree());
                    onDragOver= call.getOnDragOver();
                    onDragDropped=call.getOnDragDropped();
                    onDragDetected = call.getOnDragDetected();
                  
                    tree.getTree().setCellFactory(new Callback<TreeView<Position>, TreeCell<Position>>() {

                        @Override
                        public TreeCell<Position> call(TreeView<Position> p) {
                            final TreeCellImpl<Position> tci = new TreeCellImpl();
                            tci.setOnDragOver(new EventHandler<DragEvent>() {

                                @Override
                                public void handle(DragEvent t) {
                                    t.acceptTransferModes(TransferMode.MOVE);
                                }
                            });
                            tci.setOnDragDropped(new EventHandler<DragEvent>() {

                                @Override
                                public void handle(DragEvent t) {
                                    SimpleBooleanProperty sbp=(SimpleBooleanProperty)ov;
                                    sbp.set(false);
                                }
                            });
                            return tci;
                        }

                    });

                } else {
                    tree.getTree().setCellFactory(new Callback<TreeView<Position>, TreeCell<Position>>() {

                        @Override
                        public TreeCell<Position> call(TreeView<Position> p) {
                            final TreeCellImpl<Position> tci = new TreeCellImpl();
                            tci.setOnDragOver(onDragOver);
                            tci.setOnDragDropped(onDragDropped);
                            tci.setOnDragDetected(onDragDetected);
//это все отрабатывает, Event'ы не null. Но они не выполняются.
                            return tci;
                        }

                    });
                }
            }
        };