Dragging Function does not work correctly! JavaFX VBox Dragging

Question

I create a new Stage in the Code and it's needed, that the Stage is undecorated! In this case the new created Stage loses the Drag-Function.

I created the following code, now i can drag the Stage, but the handling is incorrect and the Stage follows not in a correct way the Mouse.

I hope you can tell me my mistake and fix my error.

Thanks for your help.

EXAMPLE - CODE:

import javafx.application.Application;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.event.EventHandler;
import javafx.geometry.Insets;
import javafx.geometry.Point2D;
import javafx.scene.Cursor;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.MenuBar;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.layout.Priority;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javafx.stage.StageStyle;


public class DragStuff  extends Application{

    VBox mainContainer;
    Stage mainSt;

    @Override
    public void start(Stage mainStage) throws Exception {
        // TODO Auto-generated method stub
        mainStage.initStyle(StageStyle.UNDECORATED);
        mainSt = mainStage;
        mainContainer = new VBox();
        mainContainer.setStyle("-fx-background-color:red");


        Label headlineInformation = new Label("Testing");
        headlineInformation.getStyleClass().addAll("popup-label-name");
        headlineInformation.setMaxWidth(Double.MAX_VALUE);

        Button closeButton = new Button("X");
        closeButton.setVisible(true);
        closeButton.getStyleClass().addAll("popup-button",
            "popup-button-color");

        HBox headContainer = new HBox();
        HBox.setHgrow(headlineInformation, Priority.ALWAYS);
        headContainer.setPadding(new Insets(5, 5, 5, 5));
        headContainer.getChildren().addAll(headlineInformation, closeButton);



        Pane pane = new Pane();
        pane.getChildren().addAll(new Label("Text                                                                                      Stuff"));

        mainContainer.getChildren().addAll(headContainer,pane);

        Scene sc = new Scene(mainContainer);
        mainStage.setScene(sc);
        mainStage.show();

        dragHandling();

    }

    public void dragHandling()
    {
        final ObjectProperty<Point2D> mouseKoordinates = new SimpleObjectProperty<>();
        mainContainer.setOnMousePressed(new EventHandler<MouseEvent>()
        {
            @Override
            public void handle(MouseEvent event)
            {
                mouseKoordinates.set(new Point2D(event.getSceneX(), event.getSceneY()));
                mainContainer.getScene().setCursor(Cursor.HAND);
            };
        });

        mainContainer.setOnMouseReleased(new EventHandler<MouseEvent>()
        {
            @Override
            public void handle(final MouseEvent arg0)
            {
                mouseKoordinates.set(null);
                mainContainer.getScene().setCursor(Cursor.DEFAULT);
            }
        });

        mainContainer.setOnMouseDragged(new EventHandler<MouseEvent>()
        {
            @Override
            public void handle(MouseEvent event)
            {
                if (mouseKoordinates.get() != null)
                {
                    double x = event.getScreenX();
                    double deltaX = x - mouseKoordinates.get().getX();
                    double y = event.getScreenY();
                    double deltaY = y - mouseKoordinates.get().getY();
                    mainSt.setX(mainSt.getX() + deltaX);
                    mainSt.setY(mainSt.getY() + deltaY);
                    mouseKoordinates.set(new Point2D(x, y));
                }
            }
        });
    }

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

Answer 1

You must not use getScreenX() and getScreenY() in your code as they return the absolute positions. In place of them try using getX() and getY().

Moreover, I don't understand why are you using mouseKoordinates.set(new Point2D(x, y)); as well.

Try using the following code

mainContainer.setOnMouseDragged(new EventHandler<MouseEvent>()
{
    @Override
    public void handle(MouseEvent event)
    {
        if (mouseKoordinates.get() != null)
        {
            double x = event.getX();
            double deltaX = x - mouseKoordinates.get().getX();
            double y = event.getY();
            double deltaY = y - mouseKoordinates.get().getY();
            mainSt.setX(mainSt.getX() + deltaX);
            mainSt.setY(mainSt.getY() + deltaY);
        }
    }
});