JavaFX - 尝试导航回上一个视图时出现问题

Question

我是JavaFX和FXML的新手，我遇到了一个我似乎无法理解的问题，所以希望你们中的一些人能够启发我。

问题似乎发生在我的MainApp.java和我的控制器之间。

public class MainApp extends Application {
    private Stage primaryStage;
    private AnchorPane overviewPage;

    @Override
    public void start(Stage primaryStage) {
        this.primaryStage = primaryStage;
        this.primaryStage.setTitle("");
        initStartupLayout();
    }

    public void initStartupLayout() {
        try {
            FXMLLoader FXMLLoader = new FXMLLoader();
            FXMLLoader.setLocation(getClass().getResource("/view/StandardView.fxml"));
            overviewPage = (AnchorPane) FXMLLoader.load();
            Scene scene = new Scene(overviewPage);
            primaryStage.setScene(scene);
            primaryStage.setResizable(false);
            primaryStage.sizeToScene();
            primaryStage.show();
            RootController controller = FXMLLoader.getController();
            controller.setMainApp(this);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void loadCreateNewRent() {
        try {
            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(MainApp.class.getResource("/view/CreateNewRentView.fxml"));
            AnchorPane page = (AnchorPane) loader.load();
            // Create the dialog Stage.
            Stage dialogStage = new Stage();
            dialogStage.setTitle("Opret udlejning");
            dialogStage.initModality(Modality.WINDOW_MODAL);
            dialogStage.initOwner(primaryStage);
            Scene scene = new Scene(page);
            dialogStage.setScene(scene);        

            // Gets the controller and attaches the stage to display
            CreateNewRentController controller = loader.getController();
            controller.setDialogStage(dialogStage);

            // Show the dialog and wait until the user closes it
            dialogStage.showAndWait();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public void loadAdministrateRentals() {
            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(getClass().getResource("/view/AdministrateRentalsView.fxml"));
            loader.load();
            overviewPage.getChildren().set(1, FXMLLoader.load(getClass().getResource("/view/AdministrateRentalsView.fxml")));
            AdministrateRentalsController controller = (AdministrateRentalsController) loader.getController();
            controller.setMainApp(this);               
 } catch (IOException e) {

                e.printStackTrace();
            }
    }

    public void backToInitView() {
    try {
        FXMLLoader loader = new FXMLLoader();
        loader.setLocation(getClass().getResource("/view/AdministrateRentalsView.fxml"));
        loader.load();
        overviewPage.getChildren().set(1, FXMLLoader.load(getClass().getResource("/view/AdministrateRentalsView.fxml")));
    } catch (IOException e) {
        e.printStackTrace();
    }
}       
    public void createNewProduct() {
        try {
            FXMLLoader loader = new FXMLLoader();
            loader.setLocation(MainApp.class.getResource("/view/AdministrateRentalsView.fxml"));
            overviewPage.getChildren().set(1, FXMLLoader.load(MainApp.class.getResource("/view/C.fxml")));

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

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


public class RootController implements Initializable {
    private Stage primaryStage;
    private MainApp mainApp;

    @FXML
    public void createLease(ActionEvent event) {
        mainApp.loadCreateNewRent();
    }
    @FXML
    public void administrateLease(ActionEvent event) {
        mainApp.loadAdministrateRentals();
    }

    @Override
    public void initialize(URL arg0, ResourceBundle arg1) {
        // TODO Auto-generated method stub  
    }

    public void setMainApp(MainApp mainApp) {
        this.mainApp = mainApp;
    }

}



public class AdministrateRentalsController implements Initializable {
    private Stage primaryStage;
    private MainApp mainApp;

    @FXML
    public void backToInitScreen(ActionEvent event) {
        mainApp.initStartupLayout();
    }

    @FXML 
    public void backToStartup(ActionEvent event) {
        mainApp.backToInitView();
    }

    @FXML
    public void createNewProduct(ActionEvent event) {
        mainApp.createNewProduct();
    }

    @Override
    public void initialize(URL location, ResourceBundle resources) {
        // TODO Auto-generated method stub
    }

    public void setMainApp(MainApp mainApp) {
        this.mainApp = mainApp;
    }
}

当我在调用administrateLease方法时从StandardView转到AdministrateRentView时，它工作得很好。但是当我试图通过调用backToStartUp方法回到上一个视图时，它会给我一个NullPointerException，我似乎无法弄清楚，堆栈跟踪：

    Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(Unknown Source)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
    at javafx.event.Event.fireEvent(Unknown Source)
    at javafx.scene.Node.fireEvent(Unknown Source)
    at javafx.scene.control.Button.fire(Unknown Source)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(Unknown Source)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEventImpl(Unknown Source)
    at com.sun.javafx.event.EventUtil.fireEvent(Unknown Source)
    at javafx.event.Event.fireEvent(Unknown Source)
    at javafx.scene.Scene$MouseHandler.process(Unknown Source)
    at javafx.scene.Scene$MouseHandler.access$1500(Unknown Source)
    at javafx.scene.Scene.impl_processMouseEvent(Unknown Source)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(Unknown Source)
    at com.sun.glass.ui.View.handleMouseEvent(Unknown Source)
    at com.sun.glass.ui.View.notifyMouse(Unknown Source)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$141(Unknown Source)
    at com.sun.glass.ui.win.WinApplication$$Lambda$37/1109371569.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.Trampoline.invoke(Unknown Source)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.MethodUtil.invoke(Unknown Source)
    ... 52 more
        Caused by: java.lang.NullPointerException
    at Controller.AdministrateRentalsController.backToStartup      
        (AdministrateRentalsController.java:23)
    ... 61 more