I am working in a JavaFX project. There I have fxml included in other fxml files. Now I need to send data from the outer controller to the inner controller. I’ve tried it, but the combobox looses its items as soon as the transferMethod finished.

Outer Controller:

public class AbfragenController {

    private EFController efControllerModul;

    private ArrayList<KQ> kqList;
    private ArrayList<DLS> dlsList;
    private ArrayList<PDI> pdiList;
    private ArrayList<Hauptbeschwerden> hauptbeschwerdenList;
    private ArrayList<DlsProtocols> dlsProtocolsList;

public void initialize() {
        try {
            FXMLLoader loader = new FXMLLoader(getClass().getResource("/at/palberon/miniproqa/miniproqa/moduls/abfragenUImoduls/EF.fxml"));
            Node efNode = loader.load(); // This loads the FXML and initializes the controller
            efControllerModul = loader.getController(); // This retrieves the controller instance

            // Setzen der Ereignisbehandler für Änderungen im inneren Controller
            setInnerControllerEventHandlers();;

            //<editor-fold defaultstate="collapsed" desc="Imports">
            Import importData = new Import();
            kqList = importData.getKqList();
            dlsList = importData.getDlsList();
            pdiList = importData.getPdiList();
            hauptbeschwerdenList = importData.getHauptbeschwerdenList();
            dlsProtocolsList = importData.getDlsProtocolsList();
            //</editor-fold>

            // Setzen der Daten für die inneren Controller
            System.out.println("Setting data for EFController");
            for (Hauptbeschwerden hauptbeschwerden : hauptbeschwerdenList) {
                System.out.println(hauptbeschwerden.getHauptbeschwerdeName());
            }

            efControllerModul.setListHBComboBox(hauptbeschwerdenList);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

Inner Controller:

public class EFController {
@FXML
    private Text efTextBreathing;

    @FXML
    private ChoiceBox<String> efChoiceBoxBreathing;

 private ObservableList<String> hbObservableList;

public void initialize() {
        breathingPatInputChanged();

        hbObservableList = FXCollections.observableArrayList();

        System.out.println("EFController initialized");
    }

 public void breathingPatInputChanged() {
        efChoiceBoxBreathing.valueProperty().addListener((observable, oldValue, newValue) -> {
            System.out.println(efComboBoxHB.getItems());
            System.out.println(hbObservableList);
            efComboBoxHB.setItems(hbObservableList);
            efComboBoxHB.setDisable(false);
            efComboBoxHB.requestFocus();
            efComboBoxHB.show();
            System.out.println(efComboBoxHB.getItems());
        });
    }


    public void setListHBComboBox(ArrayList<Hauptbeschwerden> hauptbeschwerdenList) {
        List<String> hbStringList = hauptbeschwerdenList.stream()
                .map(Hauptbeschwerden::getHauptbeschwerdeName)
                .collect(Collectors.toList());

        hbObservableList.setAll(hbStringList); // Using setAll to directly replace the content

        System.out.println("hbStringList: " + hbStringList);
        System.out.println("hbObservableList: " + hbObservableList);

        efComboBoxHB.setItems(hbObservableList);

        System.out.println("efComboBoxHB items: " + efComboBoxHB.getItems());

        if (hbObservableList.isEmpty()) {
            System.out.println("ObservableList for ComboBox is empty.");
        } else {
            System.out.println("ComboBox items set successfully.");
        }
    }
}

Console Output when running:

EFController initialized
EFController initialized
Setting data for EFController
01 - Bauchschmerzen/-beschwerden
31 - Bewusstlosigkeit/Ohnmacht (Beinahe-)
hbStringList: [01 - Bauchschmerzen/-beschwerden, 31 - Bewusstlosigkeit/Ohnmacht (Beinahe-)]
hbObservableList: [01 - Bauchschmerzen/-beschwerden, 31 - Bewusstlosigkeit/Ohnmacht (Beinahe-)]
efComboBoxHB items: [01 - Bauchschmerzen/-beschwerden, 31 - Bewusstlosigkeit/Ohnmacht (Beinahe-)]
ComboBox items set successfully.
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Both codes are shortned by me, but there should be everything that ist relvant.