什么时候Vbox / Hbox为它的孩子分配坐标？

Question

我在点击时将矩形放在vbox上，然后打印矩形的坐标。按下键时我只打印坐标。请看这个示例代码示例：

@FXML
private VBox vbox;

@FXML
private AnchorPane anchorpane;

private List<Rectangle> rectangles = new ArrayList<>();

@Override
public void initialize(URL location, ResourceBundle resources) {
    System.out.println("init");

}

@FXML
private void onMouseClick(MouseEvent e) {
    System.out.println("click");
    vbox.getChildren().clear();

    for(int i = 0; i < 3 ; i++){
        Rectangle r = new Rectangle(100.0, 10.0, Color.BLACK);
        r.addEventHandler(KeyEvent.ANY, this::onKeyTyped);
        rectangles.add(r);
        vbox.getChildren().add(r);

        System.out.println(" r Yposition :" + r.getLayoutY() + " or " + r.getBoundsInParent().getMinY() + " or " + r.getBoundsInLocal().getMinY());
        System.out.println("Vbox height : " + vbox.getBoundsInLocal().getHeight());

    }

}

@FXML
private void onKeyTyped(KeyEvent e) {
    System.out.println("Key pressed");
    for (Rectangle r : rectangles){         
        System.out.println(" r Yposition :" + r.getLayoutY() + " or " + r.getBoundsInParent().getMinY() + " or " + r.getBoundsInLocal().getMinY());
        }
    System.out.println("Vbox height : " + vbox.getBoundsInLocal().getHeight());
}

这给我以下输出：

click
r Yposition :0.0 or 0.0 or 0.0
Vbox height : 10.0
r Yposition :0.0 or 0.0 or 0.0
Vbox height : 10.0
 r Yposition :0.0 or 0.0 or 0.0
Vbox height : 10.0

Key pressed
 r Yposition :0.0 or 0.0 or 0.0
 r Yposition :10.0 or 10.0 or 0.0
 r Yposition :20.0 or 20.0 or 0.0
Vbox height : 30.0

所以我想JavaFX在屏幕上打印时会分配形状的坐标。但是当我刷新它时，如何在Vbox中获得形状的坐标？