如何在没有按钮的情况下切换 JavaFX 中的场景（倒数计时器）

Question

Java newbie here building a quiz app. I have no trouble switching between scenes from a button, but am trying to switch between scenes at the end of a timer which is controlled by a Timeline. So the event is slightly different. I am having some trouble and keep getting an error. The timer runs through the 'runTimer' method and the 'startQuiz' method should in theory switch the scenes.

Any help would be an absolute lifesaver!

Code posted here excluding imports (but I have included all the ones the IDE suggested).

public class countDownScreenController implements Initializable {
private Stage stage;
private Scene scene;
private Parent root;
private StringProperty timerText;
private int timerTotal;
private Timeline timeLine;

@Override
public void initialize(URL url, ResourceBundle resourceBundle) {
    runTimer();
}

public void runTimer(){
    timerTotal = 3;
    setTimerText(timerTotal);
    timeLine = new Timeline();
    timeLine.setCycleCount(timerTotal);
    timeLine.getKeyFrames().add(new KeyFrame(Duration.seconds(1), e -> {
        timerTotal--;
        setTimerText(timerTotal);
    }));
    timeLine.play();
    timeLine.setOnFinished(e -> {
        startQuiz();
    });
}
public void startQuiz (ActionEvent event) throws IOException {
    Parent root = FXMLLoader.load(getClass().getResource("/fxml/quizScreenScreen.fxml"));
    stage = (Stage) ((Node)event.getSource()).getScene().getWindow();
    stage.setScene(scene);
    stage.show();
}

public countDownScreenController() {
    timerText = new SimpleStringProperty();
}

public String getTimerText() {
    return timerText.get();
}

public StringProperty timerTextProperty() {
    return timerText;
}

public void setTimerText(String timerText) {
    this.timerText.set(timerText);
}

public void setTimerText(int remainingSeconds) {
    int minutes = remainingSeconds / 60;
    int seconds = remainingSeconds % 60;
    setTimerText(String.format("%02d:%02d", minutes, seconds));
}

}

Answer 1

Try in this order, but use your scene.

FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("/fxml/quizScreenScreen.fxml"));
Scene scene = new Scene(fxmlLoader.load());
stage.setScene(scene);
stage.show();

Answer 2

In the end I found it just easier to tie the switch scene event to the Label containing the timer/countdown clock, and then I could switch scenes in the way I know using:

timeLine.setOnFinished(e -> {
        try {
            startQuiz();
        } catch (IOException ioException) {
            ioException.printStackTrace();
        }
    });
}

public void startQuiz() throws IOException {
    FXMLLoader loader = new FXMLLoader(getClass().getResource("/fxml/quizScreen.fxml"));
    Parent root = loader.load();
    countDownClock.getScene().setRoot(root);
}