如何从另一个控制器中访问JavaFX FXML控制器方法

Question

我试图从一个单独的控制器内的一个控制器类访问一个方法。我正在尝试访问的方法setPiece()用于将图像绘制到窗格上，并位于控制器GoBoardController中。我试图从Tutorial_selectController访问此方法的控制器。

在Tutorial_selectController中，我在StonePlaceTutorial（）方法中调用setPiece()方法。我认为通过GoBoardController对象调用setPiece()方法会起作用，但只要在控制器内调用RuntimeException方法，我就会得到InvocationTargetException和setPiece()。

GoBoardController.java

public class GoBoardController implements Initializable {
    @FXML
    private ImageView goBoardImageView;
    @FXML
    private Button boardBackButton;
    @FXML
    private Button boardBackTutorial;
    @FXML
    private AnchorPane boardPane;

    private GoBoard goBoard;

    FXMLLoader loader;

    /**
     * Initializes the controller class.
     */
    @Override
    public void initialize(URL url, ResourceBundle rb) {
        //Creating a new GoBoard object on initilization of the controller
        goBoard = new GoBoard(boardPane);
    }    

    //Method I'm trying to access
    public void setPiece(double x, double y, String p){
        if(p == "b"){
            goBoard.setStoneBlack(x, y);
        }
        else if(p == "w"){
            goBoard.setStoneWhite(x, y);
        }
    }
}

Tutorial_selectController.java

public class Tutorial_selectController implements Initializable {
    @FXML
    private Button quitButton;
    @FXML
    private Button mainMenuButton;
    @FXML
    private Button stonePlaceButton;

    private Go_Tutorial_Lessons lessons;
    private Stage lessonStage;
    private Parent root;
    private Scene lessonScene;

    private GoBoardController goBoardController;

     //x and y values will be used to pre-set the board for specific tutorials
    private final int x1 = 349;

    private final int y1 = 99;

    /**
     * Initializes the controller class.
     */
    @Override
    public void initialize(URL url, ResourceBundle rb) {
        lessons = new Go_Tutorial_Lessons();
        try{
           root = FXMLLoader.load(Go.class.getResource("/GoFXML/GoBoard.fxml"));
        }catch(Exception e){
            e.printStackTrace();
        } 
        lessonScene = new Scene(root);      
    }    

    //Where I'm attempting to access the setPiece() method
    @FXML
    private void StonePlaceTutorial(ActionEvent event) throws IOException  {
        lessonStage = (Stage)mainMenuButton.getScene().getWindow();

        lessonStage.setScene(lessonScene);

        goBoardController.setPiece(x1, y1, "b"); //doesn't work, why.
        lessons.L1_Stone_Placement();
    }
}

如何正确访问setPiece()方法，以便在屏幕上绘制所需内容？