How can I set the unit increment for a scroll pane in JavaFX?

Question

The ScrollBar class in JavaFX contains a property for setting the unit increment, which is what I'm after - however I can't find how to get at this ScrollBar, or set the unit increment some other way from the ScrollPane class! I presume I must be missing something obvious - how do I achieve this?

Answer 1

you can setup a ScrollEventListener to the ScrollPane and thus override the original behavior. This way, for example, I implemented a ScrollPane that scrolls horizontally instead of vertically. This is what the relevant part of my code looks like:

public class Overview extends ScrollPane {

...



  private void setupHorizontalScrolling() {
    this.setOnScroll(new EventHandler<ScrollEvent>() {
      @Override
      public void handle(ScrollEvent scrollEvent) {
        double deltaY = scrollEvent.getDeltaY()*2; // *2 to make the scrolling a bit faster
        double width = Overview.this.getContent().getBoundsInLocal().getWidth();
        double hvalue = Overview.this.getHvalue();
        Overview.this.setHvalue(hvalue + -deltaY/width); // deltaY/width to make the scrolling equally fast regardless of the actual width of the component
      }
    });
  }

...

}

To meet your requirement, you can just change the line where the get/setHvalue is called to get/setVvalue and then you can adjust the scrolling like you want.

Answer 2

Technically, you should be able to get to it using the .lookup("scrollbar") method after the skin is initialized (if the scrollbar is visible). I don't like that answer though.

I don't think you're missing anything according to this bug ticket:

• How to access to ScrollBar component in ScrollPane control ?
  https://bugs.openjdk.java.net/browse/JDK-8091864

I'd encourage you to jump on that, present your use case, vote, and see if you can get some sort of response in the future.

Answer 3

What I ended up using is:

  @FXML
  private ScrollPane scrollPane;

  @FXML
  public void initialize() {
    Platform.runLater(() -> setFasterScroller(scrollPane));
  }

  private static void setFasterScroller(ScrollPane scrollPane) {
    ScrollBar verticalScrollbar = (ScrollBar) scrollPane.lookup(".scroll-bar:vertical");
    double defaultUnitIncrement = verticalScrollbar.getUnitIncrement();
    verticalScrollbar.setUnitIncrement(defaultUnitIncrement * 3);
  }

This one modifies the speed of the vertical scroller, what you would want to do more often, but it could be changed to .scrollbar:horizontal as well. 3 is used as modifier to accelerate the movement.