Adding Custom Dialog to Javafx with Spring DI

I have a gui built with javafx the controllers are loaded from fxml and created as Beans with spring so I can access my model. But that is predefined in fxml and loaded at start. Now I would like to load components, defined in fxml at runtime, but I could not yet find a working example, and no matter how I try it doesn't work.

So my question:

• How can I create a custom Dialog (or any custom component) in runtime , that is loaded from .fxml and is aware of (Spring application) context?

Edit

So it loads but some fields are not initialized. This is my custom DialogPane,

@Controller
@Scope("prototype")
public class NewProgramDialogPane extends DialogPane implements Initializable {
public static final ButtonType buttonTypeOk = new ButtonType("Create", ButtonBar.ButtonData.OK_DONE);
public static final ButtonType buttonTypeCancel = new ButtonType("Cancel", ButtonBar.ButtonData.CANCEL_CLOSE);

public TextField nameField;
public TextField data1Field;
public TextField data2Field;
public RegexValidator requiredField1;
public RequiredField requiredField2;
public RequiredField requiredField3;
public ErrorLabel duplicateProjectErrorLabel;

private SimpleBooleanProperty match = new SimpleBooleanProperty(false);

@Autowired
MainService mainService;

public NewProgramDialogPane() {
    URL url = getClass().getClassLoader().getResource("com/akos/fxml/NewProgramDialog.fxml");
    FXMLLoader loader = new FXMLLoader();
    loader.setLocation(url);
    loader.setRoot(this);
    try {
        loader.load();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

@Override
public void initialize(URL location, ResourceBundle resources) {
    this.lookupButton(buttonTypeOk).addEventHandler(ActionEvent.ACTION, event -> {
        if (!validate()) {
            event.consume();
        }
    });
    duplicateProjectErrorLabel.visibleProperty().bind(match);
}

public boolean validate() {
    requiredField1.eval();
    requiredField2.eval();
    requiredField3.eval();

    match.set(mainService.getPrograms().stream().anyMatch(
            program -> program != null && program.getName().equals(nameField.getText())));

    return !match.get() &&
            !requiredField1.getHasErrors() &&
            !requiredField2.getHasErrors() &&
            !requiredField3.getHasErrors();
}
}

And when I try to read the nameField, it is null.

public class NewProgramDialog extends Dialog<Program> {

public NewProgramDialog() {
    this.setDialogPane(new NewProgramDialogPane());
    this.setTitle("New program");
    this.initModality(Modality.APPLICATION_MODAL);
    this.initStyle(StageStyle.DECORATED);

    this.setResultConverter(param -> {
        if (param == NewProgramDialogPane.buttonTypeOk) {
            int x = 0;
            return new Program(((NewProgramDialogPane) getDialogPane()).nameField.getText());
        }
        return null;
    });
}
}