更新 ListView 导致 NullPointerException
Updating ListView causes NullPointerException
我正在尝试更新 ListView，这导致 java.lang.NullPointerException 当执行 list.setItems(newObList) 时，尝试将 ObservableList 引用更改为新的更新列表，但没有任何作用.先清除列表，然后重置项目也会导致 NullPointerException。还尝试将项目设置为 null，然后重置它们，还有 NullPointerException。我只是很困惑，我不知道如何解决这个问题。请指导我。
异常发生在list.setItems(obList); 语句的refreshData() 方法中。当按下二级阶段的关闭按钮时（"insert new word" 阶段”），该按钮会调用 closeInsertWord() 方法，后者调用 refreshData() 方法。我只使用一个控制器class，称为MainController.java。
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);
}
// 这里有一些不重要的代码
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Class:
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.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.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$MouseHandler.access00(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$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$handleMouseEvent4(GlassViewEventHandler.java:417)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null8(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
主舞台 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
closeInsertWord() 在控制器上为第二个 FXML 文件调用，作为该文件中定义的按钮的处理程序。该 FXML 文件中没有包含 fx:id="list" 的元素，因此该控制器中的列表为空。所以当你调用 list.setItems().
时你会得到一个空指针异常
对与两个不同 FXML 文件关联的控制器使用相同的 class 通常不是一个好主意，因为很难跟踪每个字段中哪些字段已初始化以及哪些字段为空不同的控制器实例。
为每个 FXML 文件创建不同的控制器 class。将数据传递给加载该文件时需要的第二个控制器。
类似于：
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);
}
}
当然还要更改第二个 FXML 文件中的 fx:controller 属性。
我正在尝试更新 ListView，这导致 java.lang.NullPointerException 当执行 list.setItems(newObList) 时，尝试将 ObservableList 引用更改为新的更新列表，但没有任何作用.先清除列表，然后重置项目也会导致 NullPointerException。还尝试将项目设置为 null，然后重置它们，还有 NullPointerException。我只是很困惑，我不知道如何解决这个问题。请指导我。
异常发生在list.setItems(obList); 语句的refreshData() 方法中。当按下二级阶段的关闭按钮时（"insert new word" 阶段”），该按钮会调用 closeInsertWord() 方法，后者调用 refreshData() 方法。我只使用一个控制器class，称为MainController.java。
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);
}
// 这里有一些不重要的代码
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Class:
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$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8413)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$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.access00(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$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent4(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$null8(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$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
主舞台 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
closeInsertWord() 在控制器上为第二个 FXML 文件调用，作为该文件中定义的按钮的处理程序。该 FXML 文件中没有包含 fx:id="list" 的元素，因此该控制器中的列表为空。所以当你调用 list.setItems().
对与两个不同 FXML 文件关联的控制器使用相同的 class 通常不是一个好主意，因为很难跟踪每个字段中哪些字段已初始化以及哪些字段为空不同的控制器实例。
为每个 FXML 文件创建不同的控制器 class。将数据传递给加载该文件时需要的第二个控制器。
类似于：
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);
}
}
当然还要更改第二个 FXML 文件中的 fx:controller 属性。