JavaFX: How to change the focus traversal policy?

Question

Is it possible in JavaFX to change the focus traversal policy, like in AWT?

Because the traversal order for two of my HBoxes is wrong.

Solution 1

In common case the navigation is done in a container order, in order of children, or according to arrow keys pressing. You can change order of nodes - it will be the optimal solution for you in this situation.

There is a back door in JFX about traversal engine strategy substitution :

you can subclass the internal class com.sun.javafx.scene.traversal.TraversalEngine

engine = new TraversalEngine(this, false) {
            @Override public void trav(Node owner, Direction dir) {
                // do whatever you want
            }
        };

And use

setImpl_traversalEngine(engine); 

call to apply that engine.

You can observe the code of OpenJFX, to understand, how it works, and what you can do.

Be very careful : it is an internal API, and it is likely to change, possibly, in the nearest future. So don't rely on this (you cannot rely on this officialy, anyway).

Sample implementation :

public void start(Stage stage) throws Exception {
    final VBox vb = new VBox();

    final Button button1 = new Button("Button 1");
    final Button button2 = new Button("Button 2");
    final Button button3 = new Button("Button 3");

    TraversalEngine engine = new TraversalEngine(vb, false) {
        @Override
        public void trav(Node node, Direction drctn) {
            int index = vb.getChildren().indexOf(node);

            switch (drctn) {
                case DOWN:
                case RIGHT:
                case NEXT:
                    index++;
                    break;
                case LEFT:
                case PREVIOUS:
                case UP:
                    index--;
            }

            if (index < 0) {
                index = vb.getChildren().size() - 1;
            }
            index %= vb.getChildren().size();

            System.out.println("Select <" + index + ">");

            vb.getChildren().get(index).requestFocus();
        }
    };

    vb.setImpl_traversalEngine(engine);

    vb.getChildren().addAll(button1, button2, button3);
    Scene scene = new Scene(vb);
    stage.setScene(scene);
    stage.show();
}

It will require strong analitical skills for common case ;)

Solution 2

The simplest solution is to edit the FXML file and reorder the containers appropriately. As an example, my current application has a registration dialog in which a serial number can be entered. There are 5 text fields for this purpose. For the focus to pass from one text field to the other correctly, I had to list them in this way:

<TextField fx:id="tfSerial1" layoutX="180.0" layoutY="166.0" prefWidth="55.0" />
<TextField fx:id="tfSerial2" layoutX="257.0" layoutY="166.0" prefWidth="55.0" />
<TextField fx:id="tfSerial3" layoutX="335.0" layoutY="166.0" prefWidth="55.0" />
<TextField fx:id="tfSerial4" layoutX="412.0" layoutY="166.0" prefWidth="55.0" />
<TextField fx:id="tfSerial5" layoutX="488.0" layoutY="166.0" prefWidth="55.0" />

Solution 3

Bluehair's answer is right, but you can do this even in JavaFX Scene Builder.

You have Hierarchy panel in left column. There are all your components from scene. Their order represents focus traversal order and it responds to their order in FXML file.

I found this tip on this webpage:www.wobblycogs.co.uk

Solution 4

We're using JavaFX event filters for this, e.g.:

cancelButton.addEventFilter(KeyEvent.KEY_PRESSED, new EventHandler<KeyEvent>() {
    @Override
    public void handle(KeyEvent event) {
        if (event.getCode() == KeyCode.TAB && event.isShiftDown()) {
            event.consume();
            getDetailsPane().requestFocus();
        }
    }
});

The event.consume() suppresses the default focus traversal, which otherwise causes trouble when calling requestFocus().

Solution 5

This is the accepted answer adapted to change of internal api (happened at some point of fx-8, my current version is 8u60b5). Obviously the original disclaimer still applies: it's internal api, open to change without notice at any time!

The changes (compared to the accepted answer)

• Parent needs a TraversalEngine of type ParentTraversalEngine
• nav is no longer a method of TraversalEngine (nor ParentTE) but only of TopLevelTraversalEngine
• the navigation implementation is delegated to strategy called Algorithm
• actual focus transfer is (seems to be?) handled by TopLevelTE, Algorithm only finds and returns the new target

The plain translation of the example code:

/**
 * Requirement: configure focus traversal
 * old question with old hack (using internal api):
 * http://stackoverflow.com/q/15238928/203657
 * 
 * New question (closed as duplicate by ... me ..)
 * http://stackoverflow.com/q/30094080/203657
 * Old hack doesn't work, change of internal api
 * rewritten to new internal (sic!) api
 * 
 */
public class FocusTraversal extends Application {

    private Parent getContent() {
        final VBox vb = new VBox();

        final Button button1 = new Button("Button 1");
        final Button button2 = new Button("Button 2");
        final Button button3 = new Button("Button 3");

        Algorithm algo = new Algorithm() {

            @Override
            public Node select(Node node, Direction dir,
                    TraversalContext context) {
                Node next = trav(node, dir);
                return next;
            }

            /**
             * Just for fun: implemented to invers reaction
             */
            private Node trav(Node node, Direction drctn) {
                int index = vb.getChildren().indexOf(node);

                switch (drctn) {
                    case DOWN:
                    case RIGHT:
                    case NEXT:
                    case NEXT_IN_LINE:    
                        index--;
                        break;
                    case LEFT:
                    case PREVIOUS:
                    case UP:
                        index++;
                }

                if (index < 0) {
                    index = vb.getChildren().size() - 1;
                }
                index %= vb.getChildren().size();

                System.out.println("Select <" + index + ">");

                return vb.getChildren().get(index);
            }

            @Override
            public Node selectFirst(TraversalContext context) {
                return vb.getChildren().get(0);
            }

            @Override
            public Node selectLast(TraversalContext context) {
                return vb.getChildren().get(vb.getChildren().size() - 1);
            }

        };
        ParentTraversalEngine engine = new ParentTraversalEngine(vb, algo);
        // internal api in fx8
        // vb.setImpl_traversalEngine(engine);
        // internal api since fx9
        ParentHelper.setTraversalEngine(vb, engine);
        vb.getChildren().addAll(button1, button2, button3);
        return vb;
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
        primaryStage.setScene(new Scene(getContent()));
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

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