Initialize a javafx scene without the use of a button event

Question

I have created a new scene called quiz_scene and the quiz_scene_controller in a javafx project. This scene simulates a question and answer quiz game. The object of the scenes are the question_label and the answer_text_field or the answer_buttons. In total the number of questions are 7 and after the system directs into the next scene.

I want when I am entering the system to perform a query in an initialize function to a sql database with the questions and answers to fetch the current questions and answers. This procedure needs to be occured once when the system open the quiz_scene (and also every time the answer button is pressed). I tried to add the functionality of the query inside the **@FXML public void initialize()**, however it did not work.

When I tried to add the functionality in a button event the query worked and I am able to change the label and the buttons of the scene using the info from the db. One of the issues I found is the fact that when I am performing the query I am creating a reference to my main class which contains the loader for the quiz_scene. Without event I am not retrieving the current object and I am retrieving a null one. How I can do so without the use of a button? Why my object is null?

The code can be found here: code.

public class quizSceneController{

 private Flow flow;
 public void setMain(Flow flow){ this.flow = flow;}
 @FXML Button answerbutton;
 @FXML Text timeField, scoreField;
 @FXML public Label question, showQuestionCounter, answer, questionId, questionType, questionSpeed;
 NextQuestion nextQuestion;
 public String temp, temp2;
 public GridPane takingTestPane = new GridPane();

 public void chooseNextQuestion(Flow flow){

    try {
        this.flow.nextQ = false;
        this.flow.startTime = System.currentTimeMillis();
        //Choosing the next question
        String sql = "select * from Questions where Subject = ? and Level = ?  and questionId = ?";
        PreparedStatement pst = 
this.flow.connectionQuestions.prepareStatement(sql);
        pst.setString(1, this.flow.textSubjectQTest);
        pst.setString(2, this.flow.user_course_level);
        pst.setString(3, this.flow.list.get(counter));
        ResultSet rs = pst.executeQuery();
        if (rs.next()) {

            temp = rs.getString("Question");
            temp2 = rs.getString("Answer");

            pst.execute();
            pst.close();
        } else {
            System.out.println("No data for this subject");
        }

    } catch (Exception a) {
        System.out.println(a);
    }
 }

 @FXML private void myButton(ActionEvent event){

    chooseNextQuestion(this.flow);
    this.question.setText(temp);
 }
 @FXML public void initialize(){

    chooseNextQuestion(this.flow);
    this.question.setText(temp);
 }
}

Finally the way I am loading the fxml from the main class is the following:

loader = new FXMLLoader();         
loader.setLocation(Flow.class.getResource("/gui/quiz/quiz.fxml"));
quizPane = loader.load();
quizSceneController quiz = loader.getController();

EDIT: How can instead of using the button to initialize the whole scene using the code of chooseNextQuestion?

Answer 1

Your controller needs to implement the Initializable interface

import javafx.fxml.Initializable;

public final class QuizSceneController implements Initializable {

     @Override
     public void initialize(URL location, ResourceBundle resources) {
           // do stuff
     }
}