JavaFX 2.0 + FXML - strange lookup behaviour

Question

I want to find a VBox node in a scene loaded with FXMLoader thanks to Node#lookup() but I get the following exception :

java.lang.ClassCastException: com.sun.javafx.scene.control.skin.SplitPaneSkin$Content cannot be cast to javafx.scene.layout.VBox

The code :

public class Main extends Application {  
    public static void main(String[] args) {
        Application.launch(Main.class, (java.lang.String[]) null);
    }
    @Override
    public void start(Stage stage) throws Exception {
        AnchorPane page = (AnchorPane) FXMLLoader.load(Main.class.getResource("test.fxml"));
        Scene scene = new Scene(page);
        stage.setScene(scene);
        stage.show();

        VBox myvbox = (VBox) page.lookup("#myvbox");
        myvbox.getChildren().add(new Button("Hello world !!!"));
    }
}

The fxml file:

<AnchorPane id="AnchorPane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns:fx="http://javafx.com/fxml" >
  <children>
    <SplitPane dividerPositions="0.5" focusTraversable="true" prefHeight="400.0" prefWidth="600.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
      <items>
        <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="160.0" prefWidth="100.0" />
        <VBox fx:id="myvbox" prefHeight="398.0" prefWidth="421.0" />
      </items>
    </SplitPane>
  </children>
</AnchorPane>

I would like to know :
1. Why lookup method return a SplitPaneSkin$Content and not a VBox ?
2. How I can get the VBox in another manner ?

Thanks in advance

Answer 1

The easiest way to get a reference to the VBox is by calling FXMLLoader#getNamespace(). For example:

VBox myvbox = (VBox)fxmlLoader.getNamespace().get("myvbox");

Note that you'll need to create an instance of FXMLLoader and call the non-static version of load() in order for this to work:

FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("test.fxml"));
AnchorPane page = (AnchorPane) fxmlLoader.load();

Answer 2

1. SplitPane puts all items in separate stack panes (fancied as SplitPaneSkin$Content). For unknown reason FXMLLoader assign them the same id as root child. You can get VBox you need by next utility method:

   public <T> T lookup(Node parent, String id, Class<T> clazz) {
       for (Node node : parent.lookupAll(id)) {
           if (node.getClass().isAssignableFrom(clazz)) {
               return (T)node;
           }
       }
       throw new IllegalArgumentException("Parent " + parent + " doesn't contain node with id " + id);
   }
   

   and use it next way:

   VBox myvbox = lookup(page, "#myvbox", VBox.class);
   myvbox.getChildren().add(new Button("Hello world !!!"));
   

2. you can use Controller and add autopopulated field:

   @FXML
   VBox myvbox;