MVP Javafx

//MAIN PRESENTER CLASS//

public class MainPresenter implements Observer{

    FxmlController mainView;

    private SettingsPresenter settingsPresenter;

    public MainPresenter(){

        try
        {
            FXMLLoader loader = new FXMLLoader();
            loader.load(getClass().getResourceAsStream("main.fxml"));
            mainView = loader.getController();
        }
        catch (IOException e)
        {
            throw new RuntimeException("Unable to load Main.fxml", e);
        }

        mainView.addObserver(this);
    }

    public Parent getView(){
        return mainView.getView();
    }

    public void showSettings(){
        System.out.println("PROVA");
    }

    @Override
    public void update(Observable o, Object arg) {

        String action = arg.toString();

        switch (action){
            case "show_settings_button":
                showSettings();
                break;
        }
    }
}

//FXML CONTROLLER//

public class FxmlController extends Observable{

    @FXML private Parent root;

    public Parent getView(){
        return root;
    }

    @FXML private void handleShowSettingsButton(){

        setChanged();
        notifyObservers("show_settings_button");

    }


}

//main.fxml//

<?xml version="1.0" encoding="UTF-8"?>

<?import java.lang.*?>
<?import javafx.geometry.*?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>

<BorderPane fx:id="root" minWidth="-1.0" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/2.2" fx:controller="cotl.MenuWnd.Main.FxmlController">
  <center>
    <Button mnemonicParsing="false" onMouseClicked="#handleShowSettingsButton" text="Button">
      <BorderPane.margin>
        <Insets bottom="100.0" left="100.0" right="100.0" top="100.0" />
      </BorderPane.margin>
    </Button>
  </center>
</BorderPane>

//APP CLASS//

public class App extends Application {

    @Override
    public void start(Stage stage) throws Exception{

        MainPresenter presenter = new MainPresenter();
        Scene scene = new Scene(presenter.getView(), 800, 600);
        stage.setScene(scene);
        stage.setTitle("PROVA");
        stage.show();
    }

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