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Java FXML：空指針異常

[英]Java FXML : Nullpointerexception

 原文  2020-07-03 11:39:35  4   1    java/ javafx

問題描述

代碼應打開待辦事項 window，其中可以在文本字段中指定任務。 這些作為復選框存儲在 VBox 中。 如果 CheckBox 被標記為“已選中”，它們將從列表中刪除。 但是，這些應該在新的 window 中可用，使用“完成”按鈕。 Done window 可以打開，但程序無法訪問 VBox doneBox。 NPE 是由：doneBox.getChildren().add(l); 在控制器 1

這個問題有什么解決方案嗎？

錯誤信息：

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1774)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
    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:8411)
    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$MouseEventNotification.run(GlassViewEventHandler.java:394)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:432)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:410)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:431)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$4(WinApplication.java:186)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.Trampoline.invoke(Unknown Source)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    at sun.reflect.misc.MethodUtil.invoke(Unknown Source)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
    ... 48 more
Caused by: java.lang.NullPointerException
    at Controller1.initialize(Controller1.java:93)
    at Controller1.handleDoneButton(Controller1.java:79)
    ... 58 more

主要的：

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class ToDo extends Application {

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

    @Override
    public void start(Stage primaryStage) throws Exception {

        Parent root = FXMLLoader.load(getClass().getResource("Layout1.fxml"));
        
        Scene scene = new Scene(root);
        primaryStage.setTitle("ToDo List");
        primaryStage.setScene(scene);
        primaryStage.setResizable(false);
        primaryStage.show();
        
    }

}

控制器1：

import java.io.IOException;
import java.util.ArrayList;

import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.CheckBox;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Controller1 {
    
    ArrayList<CheckBox> list = new ArrayList();
    ArrayList<CheckBox> donelist = new ArrayList();
    String[] part;
    
    @FXML
    VBox taskBox;
    @FXML
    TextField task;
    @FXML
    CheckBox c;
    @FXML
    Button done;
    @FXML 
    VBox doneBox;
    
    @FXML
    private void handleAddButton(ActionEvent event) {
        String text = task.getText();
        c = new CheckBox(text);
        list.add(c);
        task.clear();

        c.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            @FXML
            public void handle(ActionEvent e) {
                for (int i = 0; i < list.size(); i++) {
                    if (list.get(i).isSelected() == true) {
                        taskBox.getChildren().remove(list.get(i));
                        donelist.add(list.get(i));
                        list.remove(i);
                    }
                }

            }
        });
        taskBox.getChildren().add(c);
    }

    @FXML
    private void handleDoneButton(ActionEvent event) {
        Parent root;
        try {
            root = FXMLLoader.load(getClass().getClassLoader().getResource("Layout2.fxml"));
            
            // new window
            Stage stage1 = new Stage();
            stage1.setTitle("Done Tasks");
            stage1.setScene(new Scene(root, 190, 190));
            stage1.setResizable(false);
            stage1.show();
            
            initialize();
            
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    // Error in this method:
    @FXML
    private void initialize() {
         
        for (int i = 0; i < donelist.size(); i++) {
            part = donelist.get(i).toString().split("'");
            String text = part[1];
            
            Label l = new Label(text);
// Caused by: java.lang.NullPointerException
   // at Controller1.initialize(Controller1.java:93):
            doneBox.getChildren().add(l);
        }
    }
}

布局1：

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

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.ScrollPane?>
<?import javafx.scene.control.TextField?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.layout.HBox?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.text.Font?>

<BorderPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="303.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="Controller1">
   <center>
      <ScrollPane prefHeight="328.0" prefWidth="587.0" BorderPane.alignment="CENTER">
         <content>
            <VBox fx:id="taskBox" prefHeight="309.0" prefWidth="303.0" />
         </content>
      </ScrollPane>
   </center>
   <bottom>
      <HBox prefHeight="27.0" prefWidth="600.0" BorderPane.alignment="CENTER">
         <children>
            <TextField fx:id="task" prefHeight="25.0" prefWidth="213.0" promptText="Aufgabe hier eingeben" HBox.hgrow="ALWAYS" />
            <Button mnemonicParsing="false" onAction="#handleAddButton" prefHeight="25.0" prefWidth="81.0" text="Hinzufügen" />
         </children>
      </HBox>
   </bottom>
   <top>
      <AnchorPane prefHeight="45.0" prefWidth="600.0" style="-fx-background-color: #2A2C2E;" BorderPane.alignment="CENTER">
         <children>
            <Label alignment="CENTER" layoutX="118.0" layoutY="4.0" text="ToDo" textFill="#e5e7e9" textOverrun="CLIP">
               <font>
                  <Font name="System Bold" size="26.0" />
               </font>
            </Label>
            <Button fx:id="done" layoutX="252.0" layoutY="11.0" mnemonicParsing="false" onAction="#handleDoneButton" text="Done" />
         </children>
      </AnchorPane>
   </top>
</BorderPane>

布局2：

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

<?import javafx.scene.control.Label?>
<?import javafx.scene.control.ScrollPane?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.BorderPane?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.text.Font?>

<BorderPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="292.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="Controller1">
   <top>
      <AnchorPane prefHeight="44.0" prefWidth="292.0" style="-fx-background-color: #2A2C2E;" BorderPane.alignment="CENTER">
         <children>
            <Label layoutX="14.0" layoutY="5.0" text="Done Tasks" textFill="WHITE">
               <font>
                  <Font size="23.0" />
               </font>
            </Label>
         </children>
      </AnchorPane>
   </top>
   <center>
      <ScrollPane prefHeight="362.0" prefWidth="292.0" BorderPane.alignment="CENTER">
         <content>
            <VBox fx:id="doneBox" prefHeight="349.0" prefWidth="283.0" />
         </content>
      </ScrollPane>
   </center>
</BorderPane>

1 個解決方案

解決方案1
 0 已采納  2020-07-03 12:14:20

您有兩個不同的 Controller1 實例。 我強烈建議制作兩個控制器以使其更清晰。

如果你必須這可能是一種解決方法，你可以創建一個FXMLLoader object 來獲取對創建的Controller1的引用。

    Parent root;
    try {
        FXMLLoader loader = new FXMLLoader(getClass().getClassLoader().getResource("Layout2.fxml") );
        root = loader.load();
        Controller1 controller2 = loader.getController();
        // new window
        Stage stage1 = new Stage();
        stage1.setTitle("Done Tasks");
        stage1.setScene(new Scene(root, 190, 190));
        stage1.setResizable(false);
        stage1.show();
        
        //don't call initialize.
        //initialize();  
        for (int i = 0; i < donelist.size(); i++) {
            part = donelist.get(i).toString().split("'");
            String text = part[1];
        
            Label l = new Label(text);
            controller2.doneBox.getChildren().add(l);
        }
    } catch (IOException e) {
        e.printStackTrace();
    }

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