在Java FX上检测拖放事件？

Question

I got some Circle objects which I want to join with a Line when dragging from the circles.

I started with this code in order to test being and end drag and drop coordinates:

Circle nodo = new Circle(15.0);
nodo.setOnDragDetected(new EventHandler<MouseEvent>() {

    @Override
    public void handle(MouseEvent event) {
        coordenadas[0] = event.getX();
        coordenadas[1] = event.getY();
    }
});

nodo.setOnDragDropped(new EventHandler<DragEvent>() {

    @Override
    public void handle(DragEvent event) {
        coordenadas[2] = event.getX();
        coordenadas[3] = event.getY();
        System.out.println(coordenadas);
    }
});

When I try to drag a Circle nothing is being printed out to console when I drop the mouse. What's the correct approach and how should I being drawing a Line on dragging.

Answer 1

For detecting drag and drop, follow this approach:

        //
        // ON MOUSE PRESSED
        // ----------------------
        nodo.onMousePressedProperty().set(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                event.setDragDetect(true);
                nodo.setEffect(new DropShadow(10.0, Color.BLACK));
            }
        });

        //
        // ON MOUSE DRAGGED
        // ----------------------
        nodo.onMouseDraggedProperty().set(new EventHandler<MouseEvent>() {
            @Override
            public void handle(MouseEvent event) {
                nodo.setEffect(new DropShadow(10.0, Color.BLUEVIOLET));

                /*
                final Circle indicator = new Circle(3);
                indicator.setStroke(Color.BLUEVIOLET);
                indicator.setCenterX(x);
                indicator.setCenterY(y);
                */

            }
        });

Change the commented part for whatever you need. In your case, save the initial event coordinates (X,Y) and, in the "dragged" part, use them as initial coordinates for your line.