How to Find the Equivalent of FocusEvent.getOppositeComponent in JavaFX

Question

What is the equivalent method of FocusEvent.getOppositeComponent in JavaFX?

// Getting focus traversal in JavaFX
Node newFocusedNode = event.getTarget(); // Current focused node
Node oppositeNode = ... // Find the opposite node based on your criteria

Answer

In JavaFX, unlike Swing, there isn't a direct one-to-one equivalent of the `FocusEvent.getOppositeComponent` method. However, you can achieve similar functionality through a combination of event handling and the focus traversal policy.

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.StackPane;
import javafx.scene.input.FocusEvent;
import javafx.stage.Stage;

public class FocusExample extends Application {
    private Node previousFocusedNode;

    @Override
    public void start(Stage primaryStage) {
        Button button1 = new Button("Button 1");
        Button button2 = new Button("Button 2");

        button1.setOnFocusGained(e -> handleFocusChange(e));
        button2.setOnFocusGained(e -> handleFocusChange(e));

        StackPane root = new StackPane();
        root.getChildren().addAll(button1, button2);
        Scene scene = new Scene(root, 300, 250);

        primaryStage.setTitle("Focus Example");
        primaryStage.setScene(scene);
        primaryStage.show();
    }

    private void handleFocusChange(FocusEvent event) {
        Node currentNode = event.getTarget();
        if (previousFocusedNode != null) {
            System.out.println("Opposite component: " + previousFocusedNode.toString());
        }
        previousFocusedNode = currentNode;
        System.out.println("Current focused: " + currentNode.toString());
    }

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

Causes

JavaFX handles focus differently compared to Swing or AWT, hence some methods like getOppositeComponent do not exist.
Focus handling is managed through focus listeners and traverse methods in JavaFX.

Solutions

Implement a focus listener using `Node.focusedProperty()` to detect when a node gains or loses focus.
Use the `FocusEvent` class to listen for focus changes and determine the previously focused node by maintaining a reference.

Common Mistakes

Mistake: Not resetting the previous focused node after losing focus.

Solution: Ensure to update or reset the previous focused node in the focus change handler.

Mistake: Failing to check if a node is null before processing focus events.

Solution: Always check for null by using if-condition before accessing properties or calling methods on nodes.

Helpers

JavaFX focus event
FocusEvent.getOppositeComponent
JavaFX handling focus
JavaFX focus traversal
JavaFX equivalent methods