我有以下代碼：package pl.javastart.youtufy.controller;import java.net.URL;import java.util.ResourceBundle;import javafx.application.Platform;import javafx.event.ActionEvent;import javafx.event.EventHandler;import javafx.fxml.FXML;import javafx.fxml.Initializable;import javafx.scene.Node;import javafx.scene.control.Button;import javafx.scene.control.Label;import javafx.scene.control.ToggleButton;import javafx.scene.web.WebEngine;import javafx.stage.Stage;public class ConnectionErrorController implements Initializable {    @FXML    private Label infoLabel;    @FXML    private Button tryButton;    @FXML    private Button exitButton;    @Override    public void initialize(URL location, ResourceBundle resources) {        MainController mc = new MainController();        infoLabel.setText("Connection lost, please try again");        tryButton.setText("try again");        exitButton.setText("exit");        tryButton.setOnAction(new EventHandler<ActionEvent>() {            @Override            public void handle(ActionEvent event) {                WebEngine webEngine = mc.getContentPaneController().getVideoWebView().getEngine(); // 1                ToggleButton playButton = mc.getControlPaneController().getPlayButton(); // 2                Node source = (Node) event.getSource();                Stage stage = (Stage) source.getScene().getWindow();                if (mc.testInet()) {                    stage.close();                    mc.play(webEngine, playButton);                } else {                    stage.close();                    MainController.exist = false;                }            }        });        exitButton.setOnAction(new EventHandler<ActionEvent>() {            @Override            public void handle(ActionEvent event) {                Platform.exit();            }        });    }}但是它仍然返回NullPointerException。當我嘗試僅對ConnectionErrorController中的控制器進行引用時，我遇到了同樣的問題。如何從ConnectionErrorController中的控制器正確引用ToggleButton i WebEngine對象？