MouseDragRelease is not called on Node

public class Example extends Application {
@Override
public void start(Stage stage) throws Exception {
Pane pane = new Pane();
Scene scene = new Scene(pane, 1000, 1000);
Circle circle = new Circle(400, 500, 50);
Rectangle rect = new Rectangle(200, 200, 20, 30);
Line line = new Line();
line.setStroke(Color.RED);
pane.getChildren().add(circle);
pane.getChildren().add(rect);
pane.getChildren().add(line);
Node[] nodes = {circle, rect};
scene.setOnMouseDragReleased(e -> {
System.out.println("Scene: drag released");
});
for (Node node:nodes) {
node.setOnDragDetected(e -> {
System.out.println("drag started");
line.setStartX(node.localToScene(node.getBoundsInLocal()).getCenterX());
line.setStartY(node.localToScene(node.getBoundsInLocal()).getCenterY());
line.setEndX(e.getX());
line.setEndY(e.getX());
node.startFullDrag();
});
node.setOnMouseDragged(e -> {
line.setEndX(e.getX());
line.setEndY(e.getY());
});
node.setOnMouseDragReleased(e -> {
System.out.println("Node: drag released");
line.setEndX((node.localToScene(node.getBoundsInLocal()).getCenterX()));
line.setEndY((node.localToScene(node.getBoundsInLocal()).getCenterX()));
});
stage.setScene(scene);
stage.show();
}
}
}

For some reason, drag release is called only for scene, but not for node. When line update in onMouseDragged for node is commented out, end of line doesn't follow the cursor, but onMouseDragRelease is called for both scene and node.
I want to have smooth line drawing, but also preserve onMouseDragRelease particulary for the node.

From the documentation:

> When you drag a node, it's still under cursor, so it is considered being a potential gesture target during the whole gesture. If you need to drag a node to a different node and let the other node know about it, you need to ensure that the nodes under the dragged node are picked as the potential gesture targets. You can achieve this by calling setMouseTransparent(true) on the dragged node

In your case, the line is immediately under the mouse cursor (because you set the end coordinates of the line to the mouse coordinates during dragging), so the line receives the mouse drag released event.

Call

line.setMouseTransparent(true);

so that the node underneath can receive the event.

If you need the line to be able to receive mouse events at times other than the dragging, call

line.setMouseTransparent(true);

in the onDragDetected handler, and

line.setMouseTransparent(false);

in the onMouseDragReleased handler.

Note also that onDragDetected is only called after the mouse has been dragged a few pixels. From the documentation

> Note that his event is generated based on dragging the mouse over a platform-specific distance threshold.

On the other hand, onMouseDragged events are generated during simple mouse press-drag-release, so onMouseDragged is invoked immediately the mouse is dragged a single pixel. Consequently, during the beginning of the drag gesture, the onMouseDragged handler is invoked before the onDragDetected handler, causing the line's end coordinates to be set while its start coordinates are out of sync.

One solution to this is to use onMouseDragOver (which is only invoked during full mouse press-drag-release gestures, which are initiated by the call to startFullDrag()) in place of onMouseDragged. Since you want to detect drag over anywhere, add this handler to the scene, not to the individual nodes. Since it is only invoked during the full mouse press-drag-release gestures, it will only be invoked after dragging has started on a node. I implement this solution in the code below.

Another option is to force detection of a mouse drag gesture by calling setDragDetect(true) in the onMouseDragged handler.

There are also a couple of copy-paste errors in the original code which I have fixed below.

(Credit to @SedJ601 for spotting a couple of these bugs.)

public class Example extends Application {
@Override
public void start(Stage stage) throws Exception {
Pane pane = new Pane();
Scene scene = new Scene(pane, 1000, 1000);
Circle circle = new Circle(400, 500, 50);
Rectangle rect = new Rectangle(200, 200, 20, 30);
Line line = new Line();
line.setStroke(Color.RED);
pane.getChildren().add(circle);
pane.getChildren().add(rect);
pane.getChildren().add(line);
Node[] nodes = {circle, rect};
scene.setOnMouseDragReleased(e -> {
System.out.println("Scene: drag released");
});
for (Node node:nodes) {
node.setOnDragDetected(e -> {
System.out.println("drag started");
line.setStartX(node.localToScene(node.getBoundsInLocal()).getCenterX());
line.setStartY(node.localToScene(node.getBoundsInLocal()).getCenterY());
line.setEndX(e.getX());
// Copy-paste bug fixed in line below;
line.setEndY(e.getY());
line.setMouseTransparent(true);
node.startFullDrag();
});
node.setOnMouseDragReleased(e -> {
System.out.println("Node: drag released");
line.setEndX((node.localToScene(node.getBoundsInLocal()).getCenterX()));
// Note you had a copy-and-paste error in the next line, which I have fixed:
line.setEndY((node.localToScene(node.getBoundsInLocal()).getCenterY()));
line.setMouseTransparent(false);
});
}
// onMouseDragged replaced by onMouseDragOver:
scene.setOnMouseDragOver(e -> {
line.setEndX(e.getX());
line.setEndY(e.getY());
});
stage.setScene(scene);
stage.show();
}
}