JavaFx TableView how to tell if ScrollBar is visible

Question

Based on this example (Option #1) I am creating a fixed column by using 2 TableViews in a SplitPane. The TableView that shows the other columns (not the fixed one) may get so wide that a ScrollBar is displayed, for which I have to compensate with -fx-padding: 0 0 13px 0; in order to keep the TableRows of both TableViews aligned.

So I have to figure out now whether a ScrollBar is being displayed or not or find a completely different way to ensure the TableRow alignment. The obvious way unfortunately doesn't seem to be working. (The ScrollBar is not null, I just didn't post the code to ensure that)

ScrollBar horizontalScrollBar = (ScrollBar) lookup(".scroll-bar:horizontal");
horizontalScrollBar.visibleProperty().addListener((observable, oldValue, newValue) -> {
    System.out.println(newValueobservableScrollBar);
});

For some reason the Listener is not fired when the ScrollBar appears or disappears.

I guess the `ScrollBar` is completely removed from the scene instead of just made invisible. (Which would be the more efficient approach for layout performance anyways... You could listen to this by adding a listener to the `scene` property and checking for `null`, but the exact way the `ScrollBar` is displayed/hidden is an implementation detail and the code could break any time the java runtime is updated...). — fabian, Jun 28 '18 at 09:23
So you mean basically just replacing the ```visibleProperty()``` with ```sceneProperty()```? — Samarek, Jun 28 '18 at 09:32

score 1 · Accepted Answer · answered Jul 02 '18 at 08:32

So in order to figure out whether a particular scrollbar is visibile I first had to find it, so I looked up all the scrollbars on that particular table.

Set<Node> scrollBars = itemsTableView.lookupAll(".scroll-bar");

Then filter the set in order to retrieve the specific scrollbar I was looking for (horizontal in my case)

Optional<Node> horizontalScrollBar = scrollBars.stream()
          .filter(node ->
            ((ScrollBar) node).getOrientation().equals(Orientation.HORIZONTAL))
          .findAny();

And then attach the listener to the visibility-property of the scrollbar

horizontalScrollBar.ifPresent(node ->
          node.visibleProperty().addListener((observable, oldValue, newValue) -> {
                    if(newValue)
                    {
                        columnTableView.setStyle("-fx-padding: 0 0 13px 0;");
                    } else
                    {
                        columnTableView.setStyle("-fx-padding: 0 0 0 0;");
                    }
              })
        );

Almost looks kinda simply right? Well, it is, as soon as you have figured out that

lookup(".scroll-bar:horizontal");

does NOT return the horizontal scrollbar but the first (vertical) one. And unless you realize that, your Application will behave kinda mysteriously.

JavaFx TableView how to tell if ScrollBar is visible

1 Answers1