选择/取消选择具有多个子代的CheckBoxTreeItem（Javafx8）时如何显示进度消息？

Question

我正在使用CheckBoxTreeItem项目创建文件系统的Treeview。因为对于某些目录（例如c：\ windows），树结构可能非常大，所以加载树视图可能会花费很长时间。因此，我实现了Java文档https://docs.oracle.com/javase/8/javafx/api/javafx/scene/control/TreeItem.html中所述的延迟加载方法。

这解决了树视图的缓慢初始加载问题。但是，使用这种方法时，单击具有许多子项的项目旁边的CheckBox会在选择/取消选择所有子项时导致很长的暂停/延迟。

在我的情况下，延迟可以接受，只要我可以通知用户它正在工作。有没有一种方法可以在选中的checkboxtreeitem旁边显示“正在加载...”消息或不确定的进度栏？

我使用的代码是：

    @FXML
    private TreeView<File> treeview_treeview;

    treeview_treeview.setCellFactory(CheckBoxTreeCell.<File>forTreeView());
    TreeItem<File> root = createNode(new File("c:\\"));
    treeview_treeview.setRoot(root);

    private CheckBoxTreeItem<File> createNode(final File f) {
      return new CheckBoxTreeItem<File>(f) {
          // We cache whether the File is a leaf or not. A File is a leaf if
          // it is not a directory and does not have any files contained within
          // it. We cache this as isLeaf() is called often, and doing the 
          // actual check on File is expensive.
          private boolean isLeaf;

          // We do the children and leaf testing only once, and then set these
          // booleans to false so that we do not check again during this
          // run. A more complete implementation may need to handle more 
          // dynamic file system situations (such as where a folder has files
          // added after the TreeView is shown). Again, this is left as an
          // exercise for the reader.
          private boolean isFirstTimeChildren = true;
          private boolean isFirstTimeLeaf = true;

          @Override public ObservableList<TreeItem<File>> getChildren() {
              if (isFirstTimeChildren) {
                  isFirstTimeChildren = false;

                  // First getChildren() call, so we actually go off and 
                  // determine the children of the File contained in this TreeItem.
                  super.getChildren().setAll(buildChildren(this));
              }
              return super.getChildren();
          }

          @Override public boolean isLeaf() {
              if (isFirstTimeLeaf) {
                  isFirstTimeLeaf = false;
                  File f = (File) getValue();
                  isLeaf = f.isFile();
              }

              return isLeaf;
          }

          private ObservableList<TreeItem<File>> buildChildren(TreeItem<File> TreeItem) {
              //TreeItem.setGraphic(new ImageView(new Image(getClass().getResourceAsStream("/images/cancel.png"))));
              File f = TreeItem.getValue();
              if (f != null && f.isDirectory()) {
                  File[] files = f.listFiles();
                  if (files != null) {
                      ObservableList<TreeItem<File>> children = FXCollections.observableArrayList();

                      for (File childFile : files) {
                          if (childFile.isDirectory()){
                            children.add(createNode(childFile));
                          }
                      }

                      return children;
                  }
              }

              return FXCollections.emptyObservableList();
          }
      };
  }