JavaFX 调用异常和 NullPointer 异常-解网

问：

我是 Javafx 的新手，在做一个小项目时遇到了一个问题。这个程序应该是一个小型调度程序，其中用户应该能够在 scene2 和 scene4 中创建事件，并在 scene3.fxml 中查看它们。在创建事件并且用户导航到 scene3.fxml 后，它应该将标签更改为事件列表（我尝试了 listView，但它有其他错误）。出于某种原因，每当我尝试访问“scene3.fxml”时，我都会收到下面的错误堆栈，即使我看到场景，它也没有按预期工作。我已确保所有fxids都是正确的，并且所有其他fxml文件都正常工作。包应用; 场景控制器.java：

package application;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.net.URL;
import java.time.LocalDate;
import java.util.ResourceBundle;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.DatePicker;
import javafx.scene.control.Label;
import javafx.scene.control.ListView;
import javafx.scene.control.TextArea;
import javafx.scene.control.TextField;
import javafx.scene.image.ImageView;
import javafx.scene.layout.AnchorPane;
import javafx.stage.Stage;
import javafx.scene.image.*;
import java.util.ArrayList;


public class SceneController {
    
    
    
    private Stage stage;
    private Scene scene;
    private Parent root;
    
    //Scene2
    @FXML
    private DatePicker myDatePicker;
    @FXML
    private Label dateLabel;
    
    @FXML
    private Label errorDate;
    
    //Scene3
    @FXML
    private Label listLabel;
    @FXML
    private Label ScheduleLabel;
    @FXML
    private Button returnFrom3;
    
    
    //Scene4
    @FXML
    private TextArea description;
    @FXML 
    private TextField name;
    @FXML
    private Button eventSubmitter;
    @FXML
    private Label errorLabel;
    public static ArrayList<String> events = new ArrayList<String>();
    public static ArrayList<String> descriptions = new ArrayList<String>();
    public static ArrayList<LocalDate> dates = new ArrayList<LocalDate>();
    private LocalDate myDate;
    
    
    
    ImageView myImageView;
    String currentEvent;
    Image myImage = new Image(getClass().getResourceAsStream("SchedulerLogo.PNG"));
    
    
    /*
    @Override
    public void initialize(URL arg0, ResourceBundle arg1) {
        
        // TODO Auto-generated method stub
        /*
        listLabel.getItems().addAll(events);
        listLabel.getSelectionModel().selectedItemProperty().addListener(new ChangeListener<String>() {

            @Override
            public void changed(ObservableValue<? extends String> arg0, String arg1, String arg2) {
                // TODO Auto-generated method stub
                currentEvent = listLabel.getSelectionModel().getSelectedItem();
            }
            
        });
        
    }
*/
    
    
    public String getDate() {
        try {
            myDate = myDatePicker.getValue();
            System.out.println(myDate.toString());
            dates.add(myDate);
            return myDate.toString();
        }catch(NullPointerException e) {
            System.out.println("NullPointerException e");
            return "";
        }catch(Exception e) {
            System.out.println("exception e");
            LocalDate myDate = myDatePicker.getValue();
            dates.add(myDate);
            System.out.println(myDate.toString());
            return myDate.toString();
        }
    }
    
    public void switchToScene1(ActionEvent event) throws IOException {
        Parent root = FXMLLoader.load(getClass().getResource("fxml.fxml"));
        stage = (Stage)((Node)event.getSource()).getScene().getWindow();
        scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
        //myImageView.setImage(myImage);
        
    }
    
    public void switchToScene2(ActionEvent event) throws IOException {
        Parent root = FXMLLoader.load(getClass().getResource("scene2.fxml"));
        stage = (Stage)((Node)event.getSource()).getScene().getWindow();
        scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }
    
    public void loadEvents() {
        for(int i =0; i<events.size(); i++) {
            currentEvent = currentEvent + events.get(i);
        }
        listLabel.setText(currentEvent);
    }
    
    public void switchToScene3(ActionEvent event) throws IOException {
        Parent root = FXMLLoader.load(getClass().getResource("scene3.fxml"));
        stage = (Stage)((Node)event.getSource()).getScene().getWindow();
        scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
        loadEvents();
    }
    
    public void submitDate(ActionEvent event) throws IOException {
        
        if (myDate != null) {
            System.out.println(myDate + "numba 2 ");
            //dates.add();
            Parent root = FXMLLoader.load(getClass().getResource("scene4.fxml"));
            stage = (Stage) ((Node) event.getSource()).getScene().getWindow();
            scene = new Scene(root);
            stage.setScene(scene);
            stage.show();
        } else {
            errorDate.setVisible(true);
        }
        printArrays();
    }
    
    public void submitEvent(ActionEvent event) throws IOException{
        String eventName = name.getText();
        String eventDescription = description.getText();
        if(eventName.length()>0) {
            events.add(eventName);
            descriptions.add(eventDescription);
            errorLabel.setVisible(true);
            errorLabel.setText("Your event has been submitted. You may now navigate back to the main menu.");
            
        }else {
            errorLabel.setVisible(true);
        }
        printArrays();
        
    }
    public void printArrays() {
        System.out.println(events);
        System.out.println(descriptions);
        System.out.println(dates);
        
    }

    
    
    

}

Main.java：

package application;

import javafx.application.Application;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.BorderPane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Line;
import javafx.scene.Group;
import javafx.scene.Parent;
import javafx.scene.image.*;
import javafx.scene.input.KeyCombination;
import javafx.scene.text.*;
import java.io.FileInputStream; 
import java.io.FileNotFoundException; 
import javafx.application.Application; 
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;  
import javafx.scene.control.DatePicker;
import java.io.IOException;
import java.net.URL;
import java.time.LocalDate;
import java.util.ResourceBundle;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.DatePicker;
import javafx.scene.control.Label;
import javafx.scene.control.ListView;
import javafx.scene.control.TextArea;
import javafx.scene.control.TextField;
import javafx.scene.image.ImageView;
import javafx.stage.Stage;
import javafx.scene.image.*;
import java.util.ArrayList;




public class Main extends Application {
    
    
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage stage) throws Exception {
        try {
            LocalDate e = LocalDate.now();
            SceneController.events.add(" ");
            SceneController.descriptions.add(" ");
            SceneController.dates.add(e);
        Parent root = FXMLLoader.load(getClass().getResource("fxml.fxml"));
        Scene scene = new Scene(root);
        String css = this.getClass().getResource("application.css").toExternalForm();
        scene.getStylesheets().add(css);
        
        
        Image icon = new Image("SchedulerLogo.PNG");
        stage.getIcons().add(icon);
        stage.setTitle("Scheduler");
        stage.setWidth(1000);
        stage.setHeight(700);
        stage.setFullScreen(false);
        stage.setFullScreenExitHint("press q to escape?");
        stage.setFullScreenExitKeyCombination(KeyCombination.valueOf("q"));
        
        
        
        stage.setScene(scene);
        stage.show();
        }catch(Exception e) {
            e.printStackTrace();
        }
    }
}

scene3.fxml：

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.text.Font?>

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="1255.0" prefWidth="1299.0" style="-fx-background-color: pink;" xmlns="http://javafx.com/javafx/19" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.SceneController">
   <children>
      <Label fx:id="ScheduleLabel" alignment="CENTER" layoutX="-4.0" layoutY="73.0" prefHeight="17.0" prefWidth="1309.0" style="-fx-background-color: pink;" text="Upcoming Events:">
         <font>
            <Font size="75.0" />
         </font>
      </Label>
      <Button fx:id="returnFrom3" layoutX="625.0" layoutY="1136.0" mnemonicParsing="false" onAction="#switchToScene1" prefWidth="94.0" text="Main Menu" />
      <Label fx:id="listLabel" alignment="TOP_LEFT" layoutY="301.0" prefHeight="821.0" prefWidth="1299.0" text="Label" />
   </children>
</AnchorPane>

错误堆栈跟踪：

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at [email protected]/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1858)
    at [email protected]/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1726)
    at [email protected]/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at [email protected]/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:232)
    at [email protected]/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:189)
    at [email protected]/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at [email protected]/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at [email protected]/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at [email protected]/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at [email protected]/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.ba[email protected]/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at [email protected]/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at [email protected]/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at [email protected]/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at [email protected]/javafx.event.Event.fireEvent(Event.java:198)
    at [email protected]/javafx.scene.Node.fireEvent(Node.java:8944)
    at [email protected]/javafx.scene.control.Button.fire(Button.java:203)
    at [email protected]/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:207)
    at [email protected]/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
    at [email protected]/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
    at [email protected]/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at [email protected]/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:232)
    at [email protected]/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:189)
    at [email protected]/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at [email protected]/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at [email protected]/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at [email protected]/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at [email protected]/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at [email protected]/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at [email protected]/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at [email protected]/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at [email protected]/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at [email protected]/javafx.event.Event.fireEvent(Event.java:198)
    at [email protected]/javafx.scene.Scene$MouseHandler.process(Scene.java:3980)
    at [email protected]/javafx.scene.Scene.processMouseEvent(Scene.java:1890)
    at [email protected]/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2704)
    at [email protected]/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
    at [email protected]/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
    at [email protected]/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
    at [email protected]/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
    at [email protected]/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
    at [email protected]/com.sun.glass.ui.View.handleMouseEvent(View.java:551)
    at [email protected]/com.sun.glass.ui.View.notifyMouse(View.java:937)
    at [email protected]/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at [email protected]/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:185)
    at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.lang.reflect.InvocationTargetException
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:72)
    at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:568)
    at [email protected]/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:270)
    at [email protected]/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:84)
    at [email protected]/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1853)
    ... 46 more
Caused by: java.lang.NullPointerException: Cannot invoke "javafx.scene.control.Label.setText(String)" because "this.listLabel" is null
    at hellofx/application.SceneController.loadEvents(SceneController.java:157)
    at hellofx/application.SceneController.switchToScene3(SceneController.java:166)
    ... 57 more

我尝试重新创建fxml文件，我认为所有库和构建路径都井井有条，我不知道发生了什么。请帮忙。

java javafx nullpointerexception 调用目标异常

2赞 James_D 6/6/2023

对每个 FXML 文件使用不同的控制器类。

答： 暂无答案

上一个：NPE：尝试在空对象引用上调用虚拟方法“android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo（）”

下一个：在另一个类中调用 getter 时，Java null 指针超出，即使 getter 的返回值不是 null [duplicate]

JavaFX 调用异常和 NullPointer 异常

javafx invocation exception and nullpointer exception

评论