JavaFX walk widget tree

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.