How can I make a TextArea stretch to fill the content, expanding the parent in the process?

Question

So I have a TextArea and as the user pastes paragraphs into it, or just writes in it, I want it to expand vertically to reveal all the available text. I.e. not to use a scrollbar in the text field itself... much like what happens on many web pages. Many users, myself included, don't like to be forced to edit in a small window. Exactly how Facebook status updates box works.

I've tried

myTextArea.autoSize()

wrapped in an

myTextArea.textProperty().addListener(new ChangeListener()....);

but that doesn't work. I think it's happy autosizing to its current size.

The left, right & top anchors are set to it's parent AnchorPane. I've tried it with the bottom attached and not attached. Ideally I'd like to grow the anchor pane as the textarea grows.

I don't mind reading the TextProperty and calculating a trigger size which I set myself... but this seems a hacky approach IF there is already a best practise. The number of properties and sub objects of javafx is sufficiently daunting that it seems like a good point to ask the question here, rather than trying to figure out how many pixels the font/paragraphs etc are taking up.

Update:

So I thought maybe I was overthinking it, and all I needed to do was to switch the scrollbars off and the rest would happen. Alas, looking for available fields and methods for "scroll", "vertical", "vbar" comes up with nothing I can use. ScrollTopProperty looks like it's for something else.

Answer 1

The problem; the height of textArea is wanted to be grown or shrunk while its text is changing by either user's typing or copy-pasting. Here is another approach:

public class TextAreaDemo extends Application {

    private Text textHolder = new Text();
    private double oldHeight = 0;

    @Override
    public void start(Stage primaryStage) {
        final TextArea textArea = new TextArea();
        textArea.setPrefSize(200, 40);
        textArea.setWrapText(true);

        textHolder.textProperty().bind(textArea.textProperty());
        textHolder.layoutBoundsProperty().addListener(new ChangeListener<Bounds>() {
            @Override
            public void changed(ObservableValue<? extends Bounds> observable, Bounds oldValue, Bounds newValue) {
                if (oldHeight != newValue.getHeight()) {
                    System.out.println("newValue = " + newValue.getHeight());
                    oldHeight = newValue.getHeight();
                    textArea.setPrefHeight(textHolder.getLayoutBounds().getHeight() + 20); // +20 is for paddings
                }
            }
        });

        Group root = new Group(textArea);
        Scene scene = new Scene(root, 300, 250);
        primaryStage.setScene(scene);
        primaryStage.show();

        //  See the explanation below of the following line. 
        //  textHolder.setWrappingWidth(textArea.getWidth() - 10);  // -10 for left-right padding. Exact value can be obtained from caspian.css
    }

    public static void main(String[] args) {
        launch(args);
    }
}

But it has a drawback; the textarea's height is changing only if there are line breaks (ie Enter keys) between multiple lines, if the user types long enough the text gets wrapped to multiple line but the height is not changing.

To workaround this drawback I added this line

textHolder.setWrappingWidth(textArea.getWidth() - 10);

after primaryStage.show();. It works well for long typings where user does not linebreaks. However this generates another problem. This problem occurs when the user is deleting the text by hitting "backspace". The problem occurs exactly when the textHolder height is changed and where the textArea's height is set to new value. IMO it maybe a bug, didn't observe deeper.

In both case the copy-pasting is handling properly.