JavaFX walk widget tree - widget

Question

Is there a simple (uniform) way to recursively descend a JavaFX widget tree starting from a defined node (possibly from the Scene itself)?
The following code:
static class Visitor {
public void visit(Node node){
...
}
}
protected void walkWidgets(Node n, Visitor cb) {
if (n instanceof Parent) {
Parent p = (Parent) n;
for (Node c : p.getChildrenUnmodifiable()) {
walkWidgets(c, cb);
}
}
cb.visit(n);
}
... does not work because the "children" of some containers (e.g.: SplitPane, BorderPane, etc.) are not listed in their children Property.
To overcome this I should specialize the code to allow for all the quirks of all different widgets. This is particularly annoying when You start using widget libs beyond the "standard" provision.
Am I missing something? (I surely hope so!)

Answer 1

This seems to work fine: it gets all the child nodes in the BorderPane, SplitPane and TabPane.
import java.util.function.Consumer;
import javafx.application.Application;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.ListView;
import javafx.scene.control.SplitPane;
import javafx.scene.control.Tab;
import javafx.scene.control.TabPane;
import javafx.scene.control.TextArea;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
public class WalkComponentTree extends Application {
#Override
public void start(Stage primaryStage) {
BorderPane root = new BorderPane();
root.setTop(new Label("Title"));
SplitPane splitPane = new SplitPane();
root.setCenter(splitPane);
ListView<String> list = new ListView<>();
list.getItems().addAll("One", "Two", "Three");
TabPane tabPane = new TabPane();
Tab tab1 = new Tab();
tab1.setContent(new TextArea());
Tab tab2 = new Tab();
tab2.setContent(new Label("Tab 2"));
tabPane.getTabs().addAll(tab1, tab2);
splitPane.getItems().addAll(tabPane, list);
Button button = new Button("Walk tree");
button.setOnAction(event -> walkTree(root, node ->
System.out.println(node.getClass())));
root.setBottom(button);
Scene scene = new Scene(root, 600, 400);
primaryStage.setScene(scene);
primaryStage.show();
}
private void walkTree(Node node, Consumer<Node> visitor) {
visitor.accept(node);
if (node instanceof Parent) {
((Parent) node).getChildrenUnmodifiable()
.forEach(n -> walkTree(n, visitor));
}
}
public static void main(String[] args) {
launch(args);
}
}
Note you can also use node.lookupAll("*");, though this is less robust as it only works once css has been applied to the node.

Answer 2

In my opinion you are correct to say that there is no "standard" way to walk through the JavaFX scene graph.
One reason is, that Tab is not derived from Node, so you will not get a List of Tabs from Parent.getChildrenUnmodifiable(). Another reason is, that ScrollPane and TitledPane do not publish their content node in Parent.getChildrenUnmodifiable(). Some other Panes like Accordion, SplitPane and Toolbar also don't publish their children with Parent.getChildrenUnmodifiable(). So you need to handle this yourself.
For more Information please see:
Walking the JavaFX Scene Graph