Question

我最近开始使用JavaFX，我遇到了一个控制器问题。

我的问题是这样的： 1）我在project.startup中有fxml文件，它的名字是loginTab.fxml 2）这个窗口的控制器在project.startup.controllers中，它被称为LoginTabController

当我想在我的控制器的initialize方法中在Button上设置disable属性（或向Toggle Group添加一个监听器）时，我有空指针异常。堆栈跟踪显示初始化（）的开始是空指针。

下面我将介绍导致这种可怕情况的代码。事实上我正在寻找一些解决方案，但我找不到任何东西。

我也检查了名字是否拼写正确但不幸的是它是正确的。

1）第一个代码示例是我加载页面的方式：

 try{
     FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("/project/startup/loginTab.fxml"));
     Parent root = fxmlLoader.load();
     Stage stage = new Stage();
     stage.initModality(Modality.APPLICATION_MODAL);
     stage.initStyle(StageStyle.DECORATED);
     stage.setTitle("System Main Menu");
     stage.setScene(new Scene(root));  
     stage.show();
 } catch(Exception ex){
     ex.printStackTrace();
 }

2）我的页面元素

 <GridPane xmlns:fx="http://javafx.com/fxml/1" fx:controller="projectgotham.startup.controllers.LoginTabController" prefHeight="200" prefWidth="500" alignment="center" hgap="20" vgap="20">
    <fx:define>
        <ToggleGroup fx:id = "typeOfLogin"/>
    </fx:define>
    <VBox spacing="5" GridPane.columnIndex="0" GridPane.rowIndex="0">
        <children>
            <Label>Choose type of login</Label>
            <RadioButton text="Face" toggleGroup="$typeOfLogin" selected = "true" userData = "Face"/>
            <RadioButton text="Fingerprint" toggleGroup="$typeOfLogin" userData = "Fingerprint"/>
            <RadioButton text="Face and Fingerprint" toggleGroup="$typeOfLogin" userData = "Face and Fingerprint"/> 
            <RadioButton text="Admin" toggleGroup="$typeOfLogin" userData = "Admin"/>
        </children>
    </VBox>
    <VBox spacing="15" GridPane.columnIndex="0" GridPane.rowIndex="1">
        <children>
            <Label>Current login progress</Label>
            <ProgressBar fx:id = "loginProgressBar" progress="0.30"/>
        </children>
    </VBox> 
    <VBox spacing="20" GridPane.columnIndex="0" GridPane.rowIndex="2">
        <children>
            <Button text="Invoke Login Action" onAction="#handleLoginAction"/>
            <Button fx:id="closeSystemBtn" text="Close System" onAction="#closeSystem"/>
        </children>
    </VBox>
    <VBox spacing="5" GridPane.columnIndex="10" GridPane.rowIndex="0">
        <children>
            <Label>Last loaded image</Label>
            <ImageView fx:id="currentImageViewer" fitHeight="150" fitWidth="200" pickOnBounds="true" preserveRatio="true" visible="true">
            </ImageView>
        </children>
    </VBox>
    <VBox spacing="15" GridPane.columnIndex="10" GridPane.rowIndex="1">
        <children>
            <Button fx:id = "testButton" text="Took a photo" onAction="#testThing"/>
            <Button text="Load a fingerprint image"/>
        </children>
    </VBox>
</GridPane>

3）我的控制器类

public class LoginTabController implements Initializable {

    /**
     * Initializes the controller class.
     */

    @FXML
    private ToggleGroup typeOfLogin;

    @FXML
    private Button closeSystemBtn;

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        closeSystemBtn.setDisable(true);
    }   


    @FXML
    protected void handleLoginAction(ActionEvent event){

        try{
            FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("/projectgotham/startup/LoginIdentification.fxml"));
            Parent root = fxmlLoader.load();
            Stage stage = new Stage();
            stage.initModality(Modality.APPLICATION_MODAL);
            stage.initStyle(StageStyle.DECORATED);
            stage.setTitle("Finish login action");
            stage.setScene(new Scene(root));  
            stage.show();
        } catch(Exception ex){
            ex.printStackTrace();
            Logger.getRootLogger().error("Can't handle action connected with login : " + ex.getMessage());
        }
    }

    @FXML
    protected void closeSystem(ActionEvent event){
        Stage closeStage = (Stage) closeSystemBtn.getScene().getWindow();
        closeStage.close();
    }

    @FXML
    protected void testThing(ActionEvent event){
        typeOfLogin.selectedToggleProperty().addListener(new ChangeListener<Toggle>(){
            @Override
            public void changed(ObservableValue<? extends Toggle> observable, Toggle oldValue, Toggle newValue) {
                System.out.println(typeOfLogin.getSelectedToggle().getUserData().toString());
            }

        });

    }

}

如果你能帮助我解决这个空指针异常，我会很高兴...

编辑：

堆栈追踪：

at javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2601)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2579)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
at javafx.fxml.FXMLLoader.access$2700(FXMLLoader.java:103)
at javafx.fxml.FXMLLoader$IncludeElement.constructValue(FXMLLoader.java:1143)
at javafx.fxml.FXMLLoader$ValueElement.processStartElement(FXMLLoader.java:746)
at javafx.fxml.FXMLLoader.processStartElement(FXMLLoader.java:2707)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2527)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2441)
at javafx.fxml.FXMLLoader.load(FXMLLoader.java:2409)
at projectgotham.startup.Startup$2.handle(Startup.java:60)
at projectgotham.startup.Startup$2.handle(Startup.java:55)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8413)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Scene$MouseHandler.process(Scene.java:3757)
at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:380)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:294)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:416)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:415)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.NullPointerException
at projectgotham.startup.controllers.LoginTabController.initialize(LoginTabController.java:45)
at javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
... 57 more

Answer 1

如果您使用Eclipse，我会添加此答案。使用Eclipse 使用SceneBuilder保存的文件的差异不是同步。

所以每次使用SceneBuilder保存fxml文件时，你需要做的就是在Tab中重新打开它。我的意思是：

1）

例如，您在当前正在使用的项目中打开了4个选项卡。如果其中一个选项卡是对fxml文件的引用，则每次从{{保存fxml文件时1}}选择另一个选项卡，然后再次选择引用FXML文件的选项卡。

或

2）

如果项目中没有打开引用FXML文件的标签，则进入项目并将FXML文件打开到新标签并执行1.


示例图片


Finnally

每次保存FXML时，你都会做1或2-> 1。那个Eclipse：）

JavaFX - controller initialize方法给出了空指针异常

1 个答案: