Drag into TreeView

Question

Hello everyone,
I want to make an easy application where you have a tree and on the other side three images. In this example I used three rectangles each one with a different color.
The user should be able to drag one of the rectangles to a tree item in order to add a new subitem.
Everything is working, the only problem I have is that I also be able to drop anywhere in the whole tree "frame". I want that the user is only allowed to release over
a tree item, not anywhere in the treeframe.
My second question is, can I also drag the whole image / rectangle instead of this small windows standard box when a user tries to drag something? I read that this
would be possible in JavaFX 8, there you are able to pass a whole image to the dragboard. My goal was to set the opacity of the draged rectangle to 20% and then stick
the rectangle to the mouse and if the user release the mouse, the rectangle should go back to its orignal position with the full opacity. That would be a "nice to have", but
the first problem is kind of important.
This example should work out of the box:
package de.hauke.edi;
import java.io.IOException;
import de.cargosoft.edi.eservicemanager.Main3.ModuleTreeItem;
import javafx.animation.TranslateTransition;
import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.TreeCell;
import javafx.scene.control.TreeItem;
import javafx.scene.control.TreeView;
import javafx.scene.image.ImageView;
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.BorderPane;
import javafx.scene.layout.VBox;
import javafx.scene.paint.Color;
import javafx.scene.shape.Rectangle;
import javafx.stage.Stage;
import javafx.util.Callback;
import javafx.util.Duration;
public class Main4 extends Application {
    @Override
    public void start(Stage primaryStage) throws IOException {
        BorderPane border = new BorderPane();
        Scene scene = new Scene(border, 700, 700);
        // setup tree
        TreeView<String> tree = new TreeView<String>();
        TreeItem<String> rootItem = new TreeItem<String>("Root");
        rootItem.setExpanded(true);
        for (int i = 1; i < 6; i++) {
            TreeItem<String> item = new TreeItem<String>("Node" + i);
            rootItem.getChildren().add(item);
        tree.setRoot(rootItem);
        // setup boxes
        final Rectangle red = new Rectangle(100, 100);
        red.setFill(Color.RED);
        final Rectangle green = new Rectangle(100, 100);
        green.setFill(Color.GREEN);
        final Rectangle blue = new Rectangle(100, 100);
        blue.setFill(Color.BLUE);
        addDragFunction(red, "red");
        addDragFunction(green, "green");
        addDragFunction(blue, "blue");
        tree.setCellFactory(new Callback<TreeView<String>, TreeCell<String>>() {
            public TreeCell<String> call(TreeView<String> arg0) {
                final TreeCell<String> treeCell = new TreeCell<String>() {
                    protected void updateItem(String item, boolean empty) {
                        super.updateItem(item, empty);
                        if (item != null) {
                            setText(item);
                treeCell.setOnDragOver(new EventHandler<DragEvent>() {
                    public void handle(DragEvent event) {
                        event.acceptTransferModes(TransferMode.COPY_OR_MOVE);
                        event.consume();
                treeCell.setOnDragDropped(new EventHandler<DragEvent>() {
                    public void handle(DragEvent event) {
                        Dragboard db = event.getDragboard();
                        if (db.hasString()) {
                            TreeItem<String> item = new TreeItem<String>("New "+db.getString() + " colored element dropped");
                            treeCell.getTreeItem().getChildren().add(item);
                            treeCell.getTreeItem().setExpanded(true);
                        event.consume();
                return treeCell;
        // add elements to stage
        VBox vbox = new VBox();
        vbox.getChildren().add(red);
        vbox.getChildren().add(green);
        vbox.getChildren().add(blue);
        border.setLeft(tree);
        border.setRight(vbox);
        primaryStage.setScene(scene);
        primaryStage.show();
    private void addDragFunction(final Rectangle control, final String code) {
        control.setOnDragDetected(new EventHandler<MouseEvent>() {
            public void handle(MouseEvent event) {
                Dragboard db = control.startDragAndDrop(TransferMode.ANY);
                /* put a string on dragboard */
                ClipboardContent content = new ClipboardContent();
                content.putString(code);
                db.setContent(content);
                event.consume();
        control.setOnDragDone(new EventHandler<DragEvent>() {
            public void handle(DragEvent event) {
                event.consume();
    public static void main(String[] args) {
        launch(args);
Thanks for any help!

Answer 1

Everything is working, the only problem I have is that I also be able to drop anywhere in the whole tree "frame". I want that the user is only allowed to release over
a tree item, not anywhere in the treeframe.
Just surround the code in the handle methods for your setOnDragOver and setOnDragDropped handlers with
if ( ! treeCell.isEmpty() ) { ... }
You could add further logic here if you needed, e.g. to prevent the user dropping on the root or to limit the number of children dropped onto a single node.
For the JavaFX 8 image functionality with the drag, in your setOnDragDetected handler, change the opacity, create an image from the control by calling snapshot(), and pass the image to the Dragboard's setDragView(...) method. In the setOnDragDone handler, revert the opacity.