JavaFX: Bind to nested position - javafx

Question

I have a Pane that contains some VBoxs and Lines. I want to bind the endpoints of the Lines to the "anchors" inside the VBoxs (basically I want to bind to the position of a Node nested arbitrarily deep in the VBox), but I can't figure out what value represents the Nodes position relative to the top Pane. I've tried layout properties, translate properties, as well as bounds in local and bounds in parent, and none of them seem to work. What am I missing?
(I can provide a code sample if needed, but I don't think it helps explain my problem any better since I can't get it to work.)
EDIT: I forgot to mention the VBox can be moved around the pane freely, which is why I need to bind the lines.
EDIT: Here's some source showing my progress. I can get the correct location, but it's not binding
public class Graph extends Application {
private double startX;
private double startY;
private ObjectBinding<Bounds> bounds;
private DoubleBinding tx;
private DoubleBinding ty;
#Override
public void start(Stage primaryStage) throws Exception {
Pane pane = new Pane();
Circle target = new Circle(5, Color.RED);
VBox node = wrap(target);
Line connector = new Line();
bounds = Bindings.createObjectBinding(() -> {
Bounds nodeLocal = target.getBoundsInLocal();
Bounds nodeScene = target.localToScene(nodeLocal);
Bounds nodePane = pane.sceneToLocal(nodeScene);
return nodePane;
},
target.boundsInLocalProperty(),
target.localToSceneTransformProperty(),
pane.localToSceneTransformProperty()
);
connector.setStartX(0);
connector.setStartY(0);
tx = Bindings.createDoubleBinding(() -> bounds.get().getMinX(), bounds);
ty = Bindings.createDoubleBinding(() -> bounds.get().getMinY(), bounds);
connector.endXProperty().bind(tx);
connector.endYProperty().bind(ty);
connector.setStroke(Color.BLACK);
pane.getChildren().add(node);
pane.getChildren().add(connector);
node.relocate(100, 100);
primaryStage.setScene(new Scene(pane, 300, 300));
primaryStage.show();
}
private VBox wrap(Circle target) {
VBox node = new VBox(new Label("Node"), new StackPane(new Rectangle(50, 50, Color.GRAY), target));
node.setOnMousePressed(event -> {
Node source = (Node) event.getSource();
startX = source.getBoundsInParent().getMinX() - event.getScreenX();
startY = source.getBoundsInParent().getMinY() - event.getScreenY();
});
node.setOnMouseDragged(event -> {
Node source = (Node) event.getSource();
double offsetX = event.getScreenX() + startX;
double offsetY = event.getScreenY() + startY;
source.relocate(offsetX, offsetY);
});
return node;
}
}

Answer 1

Given any Node node in a (meaning it has a parent or indirect ancestor) Pane pane, the basic idea is to do
ObjectBinding<Bounds> boundsInPaneBinding = Bindings.createObjectBinding(() -> {
Bounds nodeLocal = node.getBoundsInLocal();
Bounds nodeScene = node.localToScene(nodeLocal);
Bounds nodePane = pane.sceneToLocal(nodeScene);
return nodePane ;
}, node.boundsInLocalProperty(), node.localToSceneTransformProperty(),
pane.localToSceneTransformProperty());
Then boundsInPaneBinding is an ObservableValue<Bounds> that always contains the bounds of the Node in the Pane's coordinate system. So you can then do things like
line.startXProperty().bind(Bindings.createDoubleBinding(
() -> boundsInPaneBinding.get().getMinX(),
boundsInPaneBinding));
The tricky part here is making sure that the bindings don't get garbage collected prematurely. (See here for a discussion.) First, you need to retain a reference to the binding:
private ObjectBinding<Bounds> boundsInPaneBinding ;
and then (for reasons I can't quite figure out), the binding must actually evaluate the bound property directly:
boundsInPaneBinding = Bindings.createObjectBinding(() -> {
Bounds nodeLocal = node.getBoundsInLocal();
// note how this actually gets the value of localToSceneTransformProperty():
Bounds nodeScene = node.getLocalToSceneTransform().apply(nodeLocal);
Bounds nodePane = pane.sceneToLocal(nodeScene);
return nodePane ;
}, node.boundsInLocalProperty(), node.localToSceneTransformProperty(),
pane.localToSceneTransformProperty());