JavaFx 13 - TableView 垂直滚动条处理程序返回 NullPointerException

Question

I need to handle JavaFx13 scroll to bottom event, but this code:

   @Override
   public void initialize(URL location, ResourceBundle resources) {
     // ...
     // ScrollBar verticalBar = (ScrollBar) this.emailsTable.lookupAll(".scroll-bar");
        ScrollBar verticalBar = (ScrollBar) this.emailsTable.lookup(".scroll-bar:vertical");
        verticalBar.valueProperty().addListener((obs, oldValue, newValue) -> { // <-- Line 49
             // if (verticalBar.getOrientation() != Orientation.VERTICAL) return;
            if (newValue.doubleValue() >= verticalBar.getMax()) {
                System.out.println("BOTTOM!");
            }
        });
     // ...
   }

...returns that error at FXML load:

Caused by: java.lang.NullPointerException
at it.unito.prog.views.MainView.initialize(MainView.java:49)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2573)
... 19 more

Answer 1

You can scroll using tableView.scrollTo() to scroll to either an index or a specific item.

To be notified that a scroll has occurred, you can use tableView.setOnScrollTo() .

Don't use a lookup for this task

The scroll bar is only shown as needed. It may or may not be there when you look it up.

If you try to lookup() the scroll bar before you add items to the table view, or before you add the table view to a scene, or before the scene has undergone a rendering pass, a scroll bar is almost certain to not be there. If the scroll bar is not there when you try to look it up then the lookup method will return a null value (which is what you are seeing). Even if a scroll bar is there when you first look it up, it may be subsequently removed and a new one added as needed, so your original reference will end up becoming invalid. So I don't recommend your lookup based approach.