更新ListView会导致NullPointerException

时间：2017-11-28 19:42:15

标签： java listview javafx nullpointerexception updating

我正在尝试更新ListView，当list.setItems（newObList）被执行时，这会导致java.lang.NullPointerException，尝试将ObservableList引用更改为新的更新列表，并且没有做任何事情。首先清除列表，然后重置项目也会导致NullPointerException。还尝试将项设置为null，然后重置它们，也是NullPointerException。我很困惑，我不知道如何解决这个问题。请指导我。

异常发生在refreshData()语句的list.setItems(obList);方法中。当按下第二阶段中的关闭按钮（＆＃34;插入新单词＆＃34;阶段＆＃34;）时，会发生这种情况，该按钮调用closeInsertWord()方法，该方法调用refreshData()方法。我只使用一个名为MainController.java的控制器类。

public class MainController implements Initializable{

@FXML
private ListView<String> list;


@FXML
TextField iWord, iMeanings, iSyn, iAnt;


public AVLTree dictTree;
public ArrayList<String> aList;
ObservableList<String> obList;

@Override
public void initialize(URL location, ResourceBundle resources)
{
    dictTree = readData();
}

public void fillList()
{

    aList = new ArrayList<>();

    aList.add("Word: meaning1, meaning2, ... , meaningN / a synonym * an antonym");
    dictTree.inOrder(aList);

    obList = FXCollections.observableArrayList(aList);
    list.setItems(obList);
}

//这里有一些重要的代码

public void openInsertWord() throws Exception
{
    Stage primaryStage2 = new Stage();

    Parent root = FXMLLoader.load(getClass().getResource("InsertUI.fxml"));
    primaryStage2.setTitle("Insert a word");
    primaryStage2.getIcons().add(new Image("file:icon.png"));
    primaryStage2.setScene(new Scene(root));
    primaryStage2.setResizable(false);
    primaryStage2.initStyle(StageStyle.UNDECORATED);
    primaryStage2.show();
}

public void insertWord()
{
    String word = iWord.getText();

    String synonym = iSyn.getText();
    String antonym = iAnt.getText();

    String[] meanings = iMeanings.getText().split("[, ]+");

    dictTree.insert(word, meanings, synonym, antonym);
}

public void refreshData()
{
    aList = new ArrayList<>();

    aList.add("Word: meaning1, meaning2, ... , meaningN / a synonym * an antonym");
    dictTree.inOrder(aList);

    obList = FXCollections.observableArrayList(aList);

    list.setItems(obList); // The exception happens here
}

public void closeInsertWord()
{
    (iWord).getScene().getWindow().hide();
    refreshData();
}

主要类别：

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

public class Main extends Application
{

    @Override
    public void start(Stage primaryStage) throws Exception
    {
        Parent root = FXMLLoader.load(getClass().getResource("MainUI.fxml"));
        primaryStage.setTitle("dict");
        primaryStage.getIcons().add(new Image("file:icon.png"));
        primaryStage.setScene(new Scene(root));
        primaryStage.setResizable(false);
        primaryStage.show();
    }

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

堆栈跟踪：

    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: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.EventDispatchChainImp`enter code here`l.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$MouseEventNotification.run(GlassViewEventHandler.java:381)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:417)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$148(WinApplication.java:191)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
    ... 48 more
Caused by: java.lang.NullPointerException
    at MainController.refreshData(MainController.java:155)
    at MainController.closeInsertWord(MainController.java:161)
    ... 58 more

主阶段FXML文件的内容（MainUI.fxml）：

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

<?import javafx.scene.control.Label?>
<?import javafx.scene.control.ListView?>
<?import javafx.scene.control.Menu?>
<?import javafx.scene.control.MenuBar?>
<?import javafx.scene.control.MenuItem?>
<?import javafx.scene.effect.InnerShadow?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.text.Font?>

<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="698.0" prefWidth="582.0" xmlns="http://javafx.com/javafx/8.0.111" xmlns:fx="http://javafx.com/fxml/1" fx:controller="MainController">
   <children>
      <Label layoutX="257.0" layoutY="42.0" text="Dictionary" textFill="#720000">
         <font>
            <Font name="System Bold" size="14.0" />
         </font>
      </Label>
      <ListView fx:id="list" layoutX="22.0" layoutY="72.0" prefHeight="148.0" prefWidth="541.0">
         <effect>
            <InnerShadow blurType="TWO_PASS_BOX" />
         </effect></ListView>
      <MenuBar prefHeight="20.0" prefWidth="582.0">
        <menus>
          <Menu mnemonicParsing="false" text="File">
            <items>
              <MenuItem fx:id="load" mnemonicParsing="false" onAction="#fillList" text="Load Data" />
                  <MenuItem fx:id="export" mnemonicParsing="false" onAction="#export" text="Export to a file" />
                  <MenuItem fx:id="close" mnemonicParsing="false" onAction="#close" text="Close" />
            </items>
          </Menu>
          <Menu mnemonicParsing="false" text="Available Operations">
            <items>
              <MenuItem fx:id="InsertNew" mnemonicParsing="false" onAction="#openInsertWord" text="Insert new word" />
                  <MenuItem fx:id="showPost" mnemonicParsing="false" text="Show Postfix Expressions" />
                  <MenuItem fx:id="evPost" mnemonicParsing="false" text="Evaluate Postfix Expressions" />
            </items>
          </Menu>
        </menus>
      </MenuBar>
   </children>
</AnchorPane>

第二阶段的FXML文件（InsertUI.fxml）：

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

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


<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="297.0" prefWidth="503.0" style="-fx-border-color: #720000; -fx-border-width: 3;" xmlns="http://javafx.com/javafx/8.0.111" xmlns:fx="http://javafx.com/fxml/1" fx:controller="MainController">
   <children>
      <Label layoutX="176.0" layoutY="23.0" text="Insert a new word" textFill="#720000">
         <font>
            <Font name="System Bold" size="18.0" />
         </font>
      </Label>
      <Label layoutX="32.0" layoutY="74.0" text="Word">
         <font>
            <Font name="System Bold" size="13.0" />
         </font>
      </Label>
      <Label layoutX="32.0" layoutY="116.0" text="Meaning(s)">
         <font>
            <Font name="System Bold" size="13.0" />
         </font>
      </Label>
      <Label layoutX="32.0" layoutY="159.0" text="Synonym">
         <font>
            <Font name="System Bold" size="13.0" />
         </font>
      </Label>
      <Label layoutX="32.0" layoutY="204.0" text="Antonym">
         <font>
            <Font name="System Bold" size="13.0" />
         </font>
      </Label>
      <TextField fx:id="iWord" layoutX="134.0" layoutY="71.0" />
      <TextField fx:id="iMeanings" layoutX="134.0" layoutY="113.0" prefHeight="25.0" prefWidth="355.0" />
      <TextField fx:id="iSyn" layoutX="134.0" layoutY="156.0" />
      <TextField fx:id="iAnt" layoutX="134.0" layoutY="201.0" />
      <Button layoutX="355.0" layoutY="245.0" mnemonicParsing="false" onAction="#insertWord" text="Insert" textFill="#720000">
         <font>
            <Font name="System Bold" size="16.0" />
         </font>
      </Button>
      <Button layoutX="444.0" layoutY="263.0" mnemonicParsing="false" onAction="#closeInsertWord" text="close" />
   </children>
</AnchorPane>

The GUI screenshot here

1 个答案:

答案 0 :(得分：0)

在控制器上为第二个FXML文件调用

closeInsertWord()，作为该文件中定义的按钮的处理程序。该FXML文件中没有fx:id="list"的元素，因此该控制器中的列表为空。因此，当您调用list.setItems()时，您会收到空指针异常。

对于与两个不同FXML文件关联的控制器使用相同的类通常是一个坏主意，因为很难跟踪哪些字段已初始化，哪些字段在每个不同的控制器实例中都为空。

为每个FXML文件创建不同的控制器类。将数据传递到加载该文件时所需的第二个控制器。

类似的东西：

public class MainController implements Initializable{

    @FXML
    private ListView<String> list;

    private AVLTree dictTree;

    @Override
    public void initialize(URL location, ResourceBundle resources)
    {
        dictTree = readData();
    }

    public void fillList()
    {

        List<String> aList = new ArrayList<>();
        String data = "Word: meaning1, meaning2, ... , meaningN / a synonym * an antonym";
        aList.add(data);
        dictTree.inOrder(aList);

        list.getItems.add(data);
    }

    public void openInsertWord() throws Exception
    {
        Stage primaryStage2 = new Stage();

        FXMLLoader loader = new FXMLLoader(getClass().getResource("InsertUI.fxml"));
        Parent root = FXMLLoader.load();

        InsertWordController controller = loader.getController();
        // seems like these two things really contain the same information...
        // I don't think you need both of them?
        controller.setDictTree(dictTree);
        controller.setItemsList(list.getItems());

        primaryStage2.setTitle("Insert a word");
        primaryStage2.getIcons().add(new Image("file:icon.png"));
        primaryStage2.setScene(new Scene(root));
        primaryStage2.setResizable(false);
        primaryStage2.initStyle(StageStyle.UNDECORATED);
        primaryStage2.show();
    }
}

然后是第二个FXML文件的控制器：

public class InsertWordController {

    @FXML
    private TextField iWord;
    @FXML
    private TextField iMeanings ;
    @FXML
    private TextField iSyn ;
    @FXML
    private TextField iAnt ;

    private AVLTree dictTree ;
    private List<String> itemsList ;

    public void setDictTree(AVLTree dictTree) {
        this.dictTree = dictTree ;
    }

    public void setItemsList(List<String> itemsList) {
        this.itemsList = itemsList ;
    }

    public void closeInsertWord()
    {
        iWord.getScene().getWindow().hide();
        String data = "Word: meaning1, meaning2, ... , meaningN / a synonym * an antonym" ;
        List<String> aList = new ArrayList<>();
        aList.add(data);
        dictTree.inOrder(aList);
        itemsList.add(data);
    }
}

当然，更改第二个FXML文件中的fx:controller属性。

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