JavaFX中多个FXML/Controller的Root不能为null异常

Question

workoutsmain.fxml：

<AnchorPane id="AnchorPane" fx:id="anchorPane" prefHeight="900.0" prefWidth="1600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="workouts.WorkoutsMainController">
    <children>
        <SplitPane fx:id="splitPane" dividerPositions="0.15" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
            <items>
                <AnchorPane>
                    <children>
                        <StackPane fx:id="menuPane" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0"/>
                    </children>
                </AnchorPane>
                <AnchorPane>
                    <children>
                        <Pane fx:id="statisticsPane" visible="false" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="130.0"/>
                        <Pane fx:id="workoutsPane" visible="false" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="130.0">
                        //... other FX elements
                        </Pane>
                        <Pane fx:id="calendarPane" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="130.0"/>
                        <StackPane fx:id="logoPane" onMouseClicked="#setLogo" AnchorPane.bottomAnchor="778.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0"/>
                    </children>
                </AnchorPane>
            </items>
        </SplitPane>
    </children>
</AnchorPane>

WorkoutsMainController.java：

public class WorkoutsMainController implements Initializable, SplitPaneDividerController {
    private final DataBase dataBase = new DataBase();
    private boolean first = true;
    private String logoName;
    @FXML
    private StackPane logoPane, menuPane;
    private final List<Pane> panes = new ArrayList<>();
    @FXML
    private Pane calendarPane, workoutsPane, statisticsPane;
    @FXML
    private SplitPane splitPane;
    @FXML
    private AnchorPane anchorPane;
    // methods and functions
    @Override
    public void initialize(URL url, ResourceBundle rb) {
        setLogo();
        disableSplitPaneDivider(splitPane, 0.1525);
        setUpMainMenu();
    }
}

java：

public class MainClass extends Application {
    private Parent anchorPane;
    private final String fxml = "WorkoutsMain.fxml";
    @Override
    public void start(Stage stage) {       
        try {
            anchorPane = FXMLLoader.load(getClass().getResource(fxml));
        } catch (IOException ex) {
            System.out.println("Error when trying to load " + fxml);
          }
        Scene scene = new Scene(anchorPane);
        stage.setScene(scene);
        stage.getIcons().add(new Image(getClass().getResourceAsStream("/calendarIconWhite.png")));
        stage.setTitle("THE WORKOUT CALENDAR 1.7.0 by hazazs®");
        stage.setResizable(false);
        stage.show();
    }
    public static void main(String[] args) {
        launch(args);
    }
}

<Pane fx:id="workoutsPane" visible="false" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="130.0">
    //... other FX elements
</Pane>

<fx:include source="Workouts.fxml" fx:id="workoutsPane"/>

<Pane fx:id="workoutsPane" visible="false" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="130.0" xmlns:fx="http://javafx.com/fxml/1" fx:controller="workouts.WorkoutsController">
// other FX elements
</Pane>

public class WorkoutsMainController implements Initializable, SplitPaneDividerController {
    protected static final DataBase dataBase = new DataBase();
    private final WorkoutsController workoutsController = new WorkoutsController();
    private boolean first = true;
    private String logoName;
    @FXML
    private StackPane logoPane, menuPane;
    private final List<Pane> panes = new ArrayList<>();
    @FXML
    private Pane calendarPane, workoutsPane, statisticsPane;
    @FXML
    protected static SplitPane splitPane;
    @FXML
    protected static AnchorPane anchorPane;
    // and so on..

Exception in Application start method
java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:389)
    at com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:328)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:767)
Caused by: java.lang.RuntimeException: Exception in Application start method
    at com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:917)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication$159(LauncherImpl.java:182)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NullPointerException: Root cannot be null
    at javafx.scene.Scene.<init>(Scene.java:336)
    at javafx.scene.Scene.<init>(Scene.java:194)
    at workouts.MainClass.start(MainClass.java:23)
    at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$166(LauncherImpl.java:863)
    at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$179(PlatformImpl.java:326)
    at com.sun.javafx.application.PlatformImpl.lambda$null$177(PlatformImpl.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.application.PlatformImpl.lambda$runLater$178(PlatformImpl.java:294)
    at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:95)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$152(WinApplication.java:177)
    ... 1 more

有什么建议吗，伙计们，我应该做什么让这再次工作？有了一个。fxml和一个控制器，它工作得很好。
谢谢

Answer 1

您正在WorkoutsMainController中创建一个新的WorkoutsController实例，而不是使用FXMLLoader为您创建的实例。您创建的实例中的@fxml-notnated字段将全部为null，因此您可能会在某个地方得到一个null指针异常。（您应该在控制台中看到“尝试加载workoutsmain.fxml时出错”消息。）因此，start()方法中的anchorpane从未初始化，并且当将空的anchorpane引用传递给scene构造函数时，会出现异常。

注意：您已经（出于某种未知的原因）将splitpane和anchorpane:这样做没有意义，FXMLLoader不会初始化静态字段。所以这些字段在控制器中也是null。

如果不压缩通过加载FXML引发的异常，您将能够看到底层异常的实际堆栈跟踪。

修复措施有：

>

不要使@fxml-带注释的字段静态化。参见JavaFX8兼容性问题--FXML静态字段

要为包含的由FXMLLoader创建的FXML注入实际的控制器实例，请参见文档中的嵌套控制器。简而言之，由于fx:include具有fx:id=“workoutspane”，因此应该替换

 private final WorkoutsController workoutsController = new WorkoutsController();

 @FXML private WorkoutsController workoutsPaneController ;