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Friday, 31 January 2014

Draggable and detachable tabs in JavaFX 2

JavaFX currently doesn't have the built in ability to change the order of tabs by dragging them, neither does it have the ability to detach tabs into separate windows (like a lot of browsers do these days.) There is a general issue for improving TabPanes filed here, so if you'd like to see this sort of behaviour added in the main JavaFX libraries then go ahead and cast your vote, it would be a very welcome addition!

However, as nice as this would be in the future, it's not here at the moment and it looks highly unlikely it'll be here for Java 8 either. I've seen a few brief attempts at reordering tabs in JavaFX, but very few examples on dragging them and nothing to do with detaching / reattaching them from the pane.

Given this, I've decided to create a reusable class that should hopefully be as easy as possible to integrate into existing applciations - it extends from Tab, and for the most part you create it and use it like a normal tab (you can just add it to a normal TabPane for instance.) It works pretty well for me as you can see in this simple example:

There's a few things to be aware of however before you rush out and use it!
  • To set the text, make sure you use setLabelText() rather than setText(), otherwise you'll get odd results. Sadly the latter is final so I can't override it.
  • You can't have DraggableTabs and normal Tabs on the same TabPane, otherwise you'll see all sorts of errors pop up. If you don't want a particular tab to be detachable, just call setDetachable(false). Tab 1 (the black tab) is set this way in the example program below.
  • This seems to work well for me, but it's far from bulletproof - use at your own risk! It should be pretty easy to work out what's going on though so if you want to change it, modify or otherwise extend it then redistribute it, feel free.

If you don't want to copy / paste from here, just grab the raw files.

 * Just a very simple sample application that uses the class below.
public class FXTabs extends Application {

    public void start(final Stage primaryStage) {

        DraggableTab tab1 = new DraggableTab("Tab 1");
        tab1.setContent(new Rectangle(500, 500, Color.BLACK));
        DraggableTab tab2 = new DraggableTab("Tab 2");
        tab2.setContent(new Rectangle(500, 500, Color.RED));
        DraggableTab tab3 = new DraggableTab("Tab 3");
        tab3.setContent(new Rectangle(500, 500, Color.BLUE));
        DraggableTab tab4 = new DraggableTab("Tab 4");
        tab4.setContent(new Rectangle(500, 500, Color.ORANGE));
        TabPane tabs = new TabPane();

        StackPane root = new StackPane();

        Scene scene = new Scene(root);



All the real work happens in this class - it's not the neatest thing in the world by a long stretch, but I've kept it all in one place to make it easier to just copy across and experiment with:

import java.util.HashSet;
import java.util.Set;
import javafx.collections.ListChangeListener;
import javafx.event.EventHandler;
import javafx.geometry.Point2D;
import javafx.geometry.Pos;
import javafx.geometry.Rectangle2D;
import javafx.scene.Scene;
import javafx.scene.control.Control;
import javafx.scene.control.Label;
import javafx.scene.control.Tab;
import javafx.scene.control.TabPane;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.StackPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.scene.text.Text;
import javafx.stage.Stage;
import javafx.stage.StageStyle;
import javafx.stage.WindowEvent;

 * A draggable tab that can optionally be detached from its tab pane and shown
 * in a separate window. This can be added to any normal TabPane, however a
 * TabPane with draggable tabs must *only* have DraggableTabs, normal tabs and
 * DrragableTabs mixed will cause issues!
 * <p>
 * @author Michael Berry
public class DraggableTab extends Tab {

    private static final Set<TabPane> tabPanes = new HashSet<>();
    private Label nameLabel;
    private Text dragText;
    private static final Stage markerStage;
    private Stage dragStage;
    private boolean detachable;

    static {
        markerStage = new Stage();
        Rectangle dummy = new Rectangle(3, 10, Color.web("#555555"));
        StackPane markerStack = new StackPane();
        markerStage.setScene(new Scene(markerStack));

     * Create a new draggable tab. This can be added to any normal TabPane,
     * however a TabPane with draggable tabs must *only* have DraggableTabs,
     * normal tabs and DrragableTabs mixed will cause issues!
     * <p>
     * @param text the text to appear on the tag label.
    public DraggableTab(String text) {
        nameLabel = new Label(text);
        detachable = true;
        dragStage = new Stage();
        StackPane dragStagePane = new StackPane();
        dragText = new Text(text);
        StackPane.setAlignment(dragText, Pos.CENTER);
        dragStage.setScene(new Scene(dragStagePane));
        nameLabel.setOnMouseDragged(new EventHandler<MouseEvent>() {

            public void handle(MouseEvent t) {
                dragStage.setWidth(nameLabel.getWidth() + 10);
                dragStage.setHeight(nameLabel.getHeight() + 10);
                Point2D screenPoint = new Point2D(t.getScreenX(), t.getScreenY());
                InsertData data = getInsertData(screenPoint);
                if(data == null || data.getInsertPane().getTabs().isEmpty()) {
                else {
                    int index = data.getIndex();
                    boolean end = false;
                    if(index == data.getInsertPane().getTabs().size()) {
                        end = true;
                    Rectangle2D rect = getAbsoluteRect(data.getInsertPane().getTabs().get(index));
                    if(end) {
                        markerStage.setX(rect.getMaxX() + 13);
                    else {
                    markerStage.setY(rect.getMaxY() + 10);
        nameLabel.setOnMouseReleased(new EventHandler<MouseEvent>() {

            public void handle(MouseEvent t) {
                if(!t.isStillSincePress()) {
                    Point2D screenPoint = new Point2D(t.getScreenX(), t.getScreenY());
                    TabPane oldTabPane = getTabPane();
                    int oldIndex = oldTabPane.getTabs().indexOf(DraggableTab.this);
                    InsertData insertData = getInsertData(screenPoint);
                    if(insertData != null) {
                        int addIndex = insertData.getIndex();
                        if(oldTabPane == insertData.getInsertPane() && oldTabPane.getTabs().size() == 1) {
                        if(oldIndex < addIndex && oldTabPane == insertData.getInsertPane()) {
                        if(addIndex > insertData.getInsertPane().getTabs().size()) {
                            addIndex = insertData.getInsertPane().getTabs().size();
                        insertData.getInsertPane().getTabs().add(addIndex, DraggableTab.this);
                    if(!detachable) {
                    final Stage newStage = new Stage();
                    final TabPane pane = new TabPane();
                    newStage.setOnHiding(new EventHandler<WindowEvent>() {

                        public void handle(WindowEvent t) {
                    pane.getTabs().addListener(new ListChangeListener<Tab>() {

                        public void onChanged(ListChangeListener.Change<? extends Tab> change) {
                            if(pane.getTabs().isEmpty()) {
                    newStage.setScene(new Scene(pane));


     * Set whether it's possible to detach the tab from its pane and move it to
     * another pane or another window. Defaults to true.
     * <p>
     * @param detachable true if the tab should be detachable, false otherwise.
    public void setDetachable(boolean detachable) {
        this.detachable = detachable;

     * Set the label text on this draggable tab. This must be used instead of
     * setText() to set the label, otherwise weird side effects will result!
     * <p>
     * @param text the label text for this tab.
    public void setLabelText(String text) {

    private InsertData getInsertData(Point2D screenPoint) {
        for(TabPane tabPane : tabPanes) {
            Rectangle2D tabAbsolute = getAbsoluteRect(tabPane);
            if(tabAbsolute.contains(screenPoint)) {
                int tabInsertIndex = 0;
                if(!tabPane.getTabs().isEmpty()) {
                    Rectangle2D firstTabRect = getAbsoluteRect(tabPane.getTabs().get(0));
                    if(firstTabRect.getMaxY()+60 < screenPoint.getY() || firstTabRect.getMinY() > screenPoint.getY()) {
                        return null;
                    Rectangle2D lastTabRect = getAbsoluteRect(tabPane.getTabs().get(tabPane.getTabs().size() - 1));
                    if(screenPoint.getX() < (firstTabRect.getMinX() + firstTabRect.getWidth() / 2)) {
                        tabInsertIndex = 0;
                    else if(screenPoint.getX() > (lastTabRect.getMaxX() - lastTabRect.getWidth() / 2)) {
                        tabInsertIndex = tabPane.getTabs().size();
                    else {
                        for(int i = 0; i < tabPane.getTabs().size() - 1; i++) {
                            Tab leftTab = tabPane.getTabs().get(i);
                            Tab rightTab = tabPane.getTabs().get(i + 1);
                            if(leftTab instanceof DraggableTab && rightTab instanceof DraggableTab) {
                                Rectangle2D leftTabRect = getAbsoluteRect(leftTab);
                                Rectangle2D rightTabRect = getAbsoluteRect(rightTab);
                                if(betweenX(leftTabRect, rightTabRect, screenPoint.getX())) {
                                    tabInsertIndex = i + 1;
                return new InsertData(tabInsertIndex, tabPane);
        return null;

    private Rectangle2D getAbsoluteRect(Control node) {
        return new Rectangle2D(node.localToScene(node.getLayoutBounds().getMinX(), node.getLayoutBounds().getMinY()).getX() + node.getScene().getWindow().getX(),
                node.localToScene(node.getLayoutBounds().getMinX(), node.getLayoutBounds().getMinY()).getY() + node.getScene().getWindow().getY(),

    private Rectangle2D getAbsoluteRect(Tab tab) {
        Control node = ((DraggableTab) tab).getLabel();
        return getAbsoluteRect(node);

    private Label getLabel() {
        return nameLabel;

    private boolean betweenX(Rectangle2D r1, Rectangle2D r2, double xPoint) {
        double lowerBound = r1.getMinX() + r1.getWidth() / 2;
        double upperBound = r2.getMaxX() - r2.getWidth() / 2;
        return xPoint >= lowerBound && xPoint <= upperBound;

    private static class InsertData {

        private final int index;
        private final TabPane insertPane;

        public InsertData(int index, TabPane insertPane) {
            this.index = index;
            this.insertPane = insertPane;

        public int getIndex() {
            return index;

        public TabPane getInsertPane() {
            return insertPane;