Using DragEvents between different JFXPanels

Question

Hi. I'm trying to set up a drag-and-drop function in my application that should transfer some data on a successful drag-and-drop completion. I'm following the examples given here:
Drag-and-Drop Feature in JavaFX Applications | JavaFX 2 Tutorials and Documentation
The event handler code for my source and target objects are exact copies of the source.setOnDragDetected and target.setOnDragOver / target.setOnDragDropped provided in the above example. I am putting a simple String into the DragBoard with a call to putString on the source event handler.
The drag and drop is initiated successfully (source event handler fires and puts the text in the DragBoard as per the example), but upon receving the DragEvent in the target event handler, it is not the same DragBoard - this one is simply empty. A call to DragBoard.getString() on the target DragEvent returns null.
The example works fine, with exactly the same code - line for line. What is different in my application is that both the source and the target nodes exist within separate JFXPanels. I have confirmed that both event handlers fire on the same thread, so it is not a threading issue either.
I'm drawing a blank here and am starting to think that embedding the scene in a JFXPanel somehow screws up the drag and drop data transfer via DragBoard. Can anybody clarify a bit around this issue for me? Thanks.

Answer 1

Just running some simple tests, the different JFXPanels do indeed appear to have different dragboards. One workaround is to use a JavaFX Property (or some other mutable wrapper for your data) to store the value being dragged.
import javafx.application.Platform;
import javafx.beans.property.SimpleStringProperty;
import javafx.beans.property.StringProperty;
import javafx.embed.swing.JFXPanel;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.input.ClipboardContent;
import javafx.scene.input.DragEvent;
import javafx.scene.input.Dragboard;
import javafx.scene.input.MouseEvent;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.VBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class JFXPanelDnD {
    private final StringProperty draggingContent ;
    public JFXPanelDnD() {
        draggingContent = new SimpleStringProperty();
    private void initAndShowGUI() {
        // Execute on EDT thread
        final JFrame frame = new JFrame("DnD Between JFX Panels");
        final JFXPanel leftPanel = new JFXPanel();
        final JFXPanel rightPanel = new JFXPanel();
        final JPanel panel = new JPanel();
        panel.add(leftPanel);
        panel.add(rightPanel);
        frame.add(panel);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(420, 320);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
        Platform.runLater(new Runnable() {
           @Override
           public void run() {
               configureLeftPanel(leftPanel);
               configureRightPanel(rightPanel);
    private void configureLeftPanel(JFXPanel panel) {
        // Execute on JavaFX Application thread
        final TextField textField = new TextField();
        final VBox root = new VBox();
        root.setOnDragDetected(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                System.out.println("Drag detected");
                Dragboard db = root.startDragAndDrop(TransferMode.ANY);
                System.out.println(db);
                ClipboardContent content = new ClipboardContent();
                content.putString(textField.getText());
                db.setContent(content);
                draggingContent.set(textField.getText());
                event.consume();
        root.setOnDragDone(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent event) {
                draggingContent.set(null);
        root.getChildren().add(textField);
        Scene scene = new Scene(root, 200, 300);
        panel.setScene(scene);
    private void configureRightPanel(JFXPanel panel) {
        final Label label = new Label("Text");
        final VBox root = new VBox();
        root.setOnDragOver(new EventHandler<DragEvent>() {
            @Override
            public void handle(DragEvent event) {
                final Dragboard dragboard = event.getDragboard();
                System.out.println(dragboard);
//                if (dragboard.hasString()) {
//                    event.acceptTransferModes(TransferMode.COPY);
//                } else {
//                    System.out.println("No string content");
                if (draggingContent.get() != null) {
                    event.acceptTransferModes(TransferMode.COPY);
        root.setOnDragDropped(new EventHandler<DragEvent>(){
            @Override
            public void handle(DragEvent event) {
//                Dragboard db = event.getDragboard() ;
//                if (db.hasString()) {
//                    label.setText(db.getString());
//                    event.setDropCompleted(true);
//                } else {
//                    event.setDropCompleted(false);
                if (draggingContent.get()==null) {
                    event.setDropCompleted(false);
                } else {
                    label.setText(draggingContent.get());
                    event.setDropCompleted(true);
                event.consume();
        root.getChildren().add(label);
        Scene scene = new Scene(root, 200, 300);
        panel.setScene(scene);
    public static void main(String[] args) {
        final JFXPanelDnD test = new JFXPanelDnD();
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                test.initAndShowGUI();