How to redirect MouseEvent.MOUSE_PRESSED to a different Node? - javafx-2

Question

I have a Region called 'R', and a Node called 'N'. N is the only child on R. Consider this behaviour:
the user presses the left-mouse button on some part of R
N (which is somewhere else on R) moves so that it is centered on the spot where the user pressed
the user releases the left-mouse button, then presses it again without moving the mouse
with the left-mouse button still pressed, the user drags the mouse, and N now follows the mouse cursor around as it is dragged.
I have no problems implementing the behaviour I've just described. I put a MOUSE_PRESSED handler on R that implements step 2. And I put a MOUSE_DRAGGED handler on N that implements step 4. JavaFX automatically directs the MouseEvents to these handlers on R and N for the presses in step 1 and 3 respectively.
The Problem:
I need to do this WITHOUT step 3. That is, the user should not have to press-release-press-drag, but rather should simply press-drag, and N should "jump" to the mouse location on the "press", and then start receiving MOUSE_DRAGGED events immediately.
Unfortunately, this doesn't happen. The release-click that I'm trying to omit seems to be necessary, otherwise the drag events all happen on R instead of N.
I'm thinking the solution will involve redispatching the initial MOUSE_PRESSED, or something along those lines. Does anyone know a way to do this (or a better way to solve my problem?)

Answer 1

Node has api to mark it as the target of drag gestures:
public void startFullDrag()
Starts a full press-drag-release gesture with this node as gesture
source. This method can be called only from a DRAG_DETECTED mouse
event handler. More detail about dragging gestures can be found in the
overview of MouseEvent and MouseDragEvent.
Assuming circle being your currently active node in a pane (borrowing code/names from James's answer), the collaborators are handlers on
mousePressed on pane that snaps the position of circle to the the current location
dragDetected on pane that calls startsFullDrag on circle
dragAny on circle that does the actual moving
In code:
pane.setOnMousePressed(new EventHandler<MouseEvent>() {
#Override
public void handle(MouseEvent event) {
circle.setCenterX(event.getX());
circle.setCenterY(event.getY());
}
});
pane.setOnDragDetected(new EventHandler<MouseEvent>() {
#Override
public void handle(MouseEvent event) {
circle.startFullDrag();
}
});
circle.addEventHandler(MouseDragEvent.ANY, new EventHandler<MouseDragEvent>() {
#Override
public void handle(MouseDragEvent event) {
circle.setCenterX(event.getX());
circle.setCenterY(event.getY());
}
});

Answer 2

I chose the simplest node to work with for this, but I think this would work in general:
import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Circle;
import javafx.stage.Stage;
public class ClickAndDragTest extends Application {
#Override
public void start(Stage primaryStage) {
final Pane pane = new Pane();
final Circle circle = new Circle(100, 100, 50, Color.CORNFLOWERBLUE);
pane.getChildren().add(circle);
pane.setOnMousePressed(new EventHandler<MouseEvent>() {
#Override
public void handle(MouseEvent event) {
circle.setCenterX(event.getX());
circle.setCenterY(event.getY());
}
});
pane.setOnMouseDragged(new EventHandler<MouseEvent>() {
#Override
public void handle(MouseEvent event) {
circle.setCenterX(event.getX());
circle.setCenterY(event.getY());
}
});
final Scene scene = new Scene(pane, 400, 400);
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}