import javafx.application.Platform;
import javafx.embed.swing.JFXPanel;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.layout.HBox;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import com.sun.javafx.application.PlatformImpl;

import java.awt.FlowLayout;

public class PreferredSize
{

Label l;
JFXPanel fxPanel;
HBox g;
Scene scene;

    private PreferredSize()
    {
        final JFrame f = new JFrame("Test JFXPanel pref size");
        f.setSize(800, 600);
        f.setLocationRelativeTo(null);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        f.setLayout(new FlowLayout());
        f.add(new JButton("Button 1"));
        fxPanel = new JFXPanel();
        f.add(fxPanel);
        f.add(new JLabel("Label1"));

        PlatformImpl.startup(new Runnable()
        {
            @Override
            public void run()
            {
                g = new HBox();
                l = new Label("bla");
                g.getChildren().add(l);
                scene = new Scene(g);

                fxPanel.setScene(scene);
                deblockThread();
            }
        });
        
        blockThread();
        
        f.pack();
        f.setVisible(true);
    }
    
    public void setText(String text)
    {
     final String s = text;
     Platform.runLater(new Runnable(){

@Override
public void run() {
l.setText(s);
deblockThread();
}
    
     });
     blockThread();
     System.out.println(g.getPrefWidth(0.0));
     System.out.println(g.getPrefHeight(0.0));
     System.out.println(g.getBoundsInParent());
    }

    private synchronized void blockThread()
{
try {
this.wait();
} catch (InterruptedException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}

private synchronized void deblockThread()
{
this.notify();
}

    
    public static void main(String[] args)
    {
        PreferredSize p = new PreferredSize();
        p.setText("huhuhuhu");
    }
}

I start a JavaFX-Label in Swing and it gets autosized to the right size. Then i set a new Text with Platform.runLater();. Although the PrefSize-Methods of the label show the right values, the bounds of the label are not updated.
I tried with adding the group to the dirtylayout list, i tried to revalidate it, i tried to repaint the jfxPanel, nothing updated the bounds of the label (control) / jfxPanel.