在运行时运行case 0时，我一直收到java.lang.NullPointerException。该问题似乎与设置TextField的提示文本有关。但是，切换选项卡时问题不会返回。 GUI是在Scene Builder中构建的。如何将TextField初始化为非空值。
public class BackEndController implements Initializable{
@FXML
private TabPane tabPane;
@FXML
private Tab bookingTab;
@FXML
private Tab waitListTab;
@FXML
private Tab excursionsTab;
@FXML
private TextField searchEntry;
@Override
public void initialize(URL location, ResourceBundle resources) {
searchEntry.setPromptText("");
}
@FXML
public void switchTabs() {
int selectedTab = tabPane.getSelectionModel().getSelectedIndex();
switch (selectedTab){
case 0:
searchEntry.setPromptText("Enter booking ID");
break;
case 1:
searchEntry.setPromptText("Enter event name");
break;
case 2:
searchEntry.setPromptText("Enter list ID");
break;
}
}
这是确切的错误代码
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1787)
at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1670)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.controls/javafx.scene.control.Tab$1.invalidated(Tab.java:215)
at javafx.base/javafx.beans.property.BooleanPropertyBase.markInvalid(BooleanPropertyBase.java:110)
at javafx.base/javafx.beans.property.BooleanPropertyBase.set(BooleanPropertyBase.java:145)
at javafx.controls/javafx.scene.control.Tab.setSelected(Tab.java:189)
at javafx.controls/javafx.scene.control.TabPane$TabPaneSelectionModel.select(TabPane.java:738)
at javafx.controls/javafx.scene.control.TabPane$TabPaneSelectionModel.select(TabPane.java:751)
at javafx.controls/javafx.scene.control.TabPane$TabPaneSelectionModel.findNearestAvailableTab(TabPane.java:810)
at javafx.controls/javafx.scene.control.TabPane$TabPaneSelectionModel.lambda$new$0(TabPane.java:707)
at javafx.base/com.sun.javafx.collections.ListListenerHelper$Generic.fireValueChangedEvent(ListListenerHelper.java:329)
at javafx.base/com.sun.javafx.collections.ListListenerHelper.fireValueChangedEvent(ListListenerHelper.java:73)
at javafx.base/javafx.collections.ObservableListBase.fireChange(ObservableListBase.java:233)
at javafx.base/javafx.collections.ListChangeBuilder.commit(ListChangeBuilder.java:482)
at javafx.base/javafx.collections.ListChangeBuilder.endChange(ListChangeBuilder.java:541)
at javafx.base/javafx.collections.ObservableListBase.endChange(ObservableListBase.java:205)
at javafx.base/javafx.collections.ModifiableObservableListBase.add(ModifiableObservableListBase.java:155)
at java.base/java.util.AbstractList.add(AbstractList.java:111)
at javafx.fxml/javafx.fxml.FXMLLoader$Element.add(FXMLLoader.java:175)
at javafx.fxml/javafx.fxml.FXMLLoader$PropertyElement.add(FXMLLoader.java:1415)
at javafx.fxml/javafx.fxml.FXMLLoader$ValueElement.processEndElement(FXMLLoader.java:796)
at javafx.fxml/javafx.fxml.FXMLLoader.processEndElement(FXMLLoader.java:2838)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2557)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2466)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3253)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3210)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3179)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3152)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3129)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3122)
at com.main.backend.BackEnd.start(BackEnd.java:18)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(LauncherImpl.java:919)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$11(PlatformImpl.java:449)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$9(PlatformImpl.java:418)
at java.base/java.security.AccessController.doPrivileged(Native Method)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:417)
at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:175)
at java.base/java.lang.Thread.run(Thread.java:844)
Caused by: java.lang.reflect.InvocationTargetException
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1784)
... 47 more
Caused by: java.lang.NullPointerException
at com.main.backend.BackEndController.switchTabs(BackEndController.java:58)
... 59 more
我的FXML文件
<?xml version="1.0" encoding="UTF-8"?>
<?import com.jfoenix.controls.JFXButton?>
<?import com.jfoenix.controls.JFXListView?>
<?import com.jfoenix.controls.JFXTabPane?>
<?import com.jfoenix.controls.JFXTextField?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.Separator?>
<?import javafx.scene.control.Tab?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.text.Font?>
<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="810.0" prefWidth="1250.0" style="-fx-background-color: #FFFFFF;" xmlns="http://javafx.com/javafx/9.0.1" xmlns:fx="http://javafx.com/fxml/1" fx:controller="com.main.backend.BackEndController">
<children>
<JFXTabPane fx:id="tabPane" layoutY="67.0" prefHeight="743.0" prefWidth="1250.0" stylesheets="@dark-theme.css">
<tabs>
<Tab fx:id="bookingTab" onSelectionChanged="#switchTabs" text="Bookings">
<content>
<AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="180.0" prefWidth="200.0" style="-fx-background-color: #F7F7F9;" />
</content>
</Tab>
<Tab fx:id="excursionsTab" onSelectionChanged="#switchTabs" text="Excursions">
<content>
<AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="180.0" prefWidth="200.0" style="-fx-background-color: #F7F7F9;">
<children>
<AnchorPane layoutX="736.0" layoutY="16.0" prefHeight="672.0" prefWidth="501.0" style="-fx-background-color: #FFFFFF; -fx-border-color: #D4D6D8;">
<children>
<JFXTextField alignment="CENTER" layoutX="17.0" layoutY="85.0" prefHeight="33.0" prefWidth="135.0" promptText="Port ID" styleClass="main-text" stylesheets="@dark-theme.css">
<font>
<Font name="System Bold" size="15.0" />
</font>
</JFXTextField>
<Label alignment="CENTER" layoutX="12.0" layoutY="33.0" prefHeight="33.0" prefWidth="478.0" text="Label" textFill="#9f9f9f">
<font>
<Font name="System Bold" size="15.0" />
</font>
</Label>
<JFXButton layoutX="265.0" layoutY="178.0" prefHeight="33.0" prefWidth="174.0" style="-fx-background-color: #FA597A; -fx-border-color: #FA597A; -fx-border-radius: 30; -fx-background-radius: 30;" text="Delete Event" textFill="WHITE">
<font>
<Font name="System Bold" size="15.0" />
</font>
</JFXButton>
<JFXButton layoutX="17.0" layoutY="178.0" prefHeight="33.0" prefWidth="185.0" style="-fx-background-color: #FFFFFF; -fx-border-color: #214099; -fx-border-radius: 30; -fx-background-radius: 30;" text="Update Event" textFill="#214099">
<font>
<Font name="System Bold" size="15.0" />
</font>
</JFXButton>
<Separator layoutX="21.0" layoutY="272.0" prefHeight="13.0" prefWidth="460.0" />
<JFXTextField alignment="CENTER" layoutX="17.0" layoutY="321.0" prefHeight="33.0" prefWidth="468.0" promptText="Event Name" styleClass="main-text" stylesheets="@dark-theme.css">
<font>
<Font name="System Bold" size="15.0" />
</font>
</JFXTextField>
<JFXTextField alignment="CENTER" layoutX="19.0" layoutY="396.0" prefHeight="33.0" prefWidth="135.0" promptText="Port ID" styleClass="main-text" stylesheets="@dark-theme.css">
<font>
<Font name="System Bold" size="15.0" />
</font>
</JFXTextField>
<JFXButton layoutX="173.0" layoutY="470.0" prefHeight="33.0" prefWidth="185.0" style="-fx-background-color: #FFFFFF; -fx-border-color: #15d31e; -fx-border-radius: 30; -fx-background-radius: 30;" text="Add Event" textFill="#15d31e">
<font>
<Font name="System Bold" size="15.0" />
</font>
</JFXButton>
</children>
</AnchorPane>
<JFXListView fx:id="excursionsList" layoutX="16.0" layoutY="16.0" prefHeight="672.0" prefWidth="711.0" styleClass="list-cell" stylesheets="@dark-theme.css" />
</children>
</AnchorPane>
</content>
</Tab>
<Tab fx:id="waitListTab" onSelectionChanged="#switchTabs" text="Waiting List">
<content>
<AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="180.0" prefWidth="200.0" style="-fx-background-color: #F7F7F9;" />
</content>
</Tab>
</tabs>
</JFXTabPane>
<JFXButton layoutX="609.0" layoutY="18.0" prefHeight="32.0" prefWidth="110.0" style="-fx-background-color: #214099; -fx-border-color: #214099; -fx-border-radius: 30; -fx-background-radius: 30;" text="Search" textFill="WHITE">
<font>
<Font name="System Bold" size="15.0" />
</font>
</JFXButton>
<JFXButton layoutX="740.0" layoutY="18.0" prefHeight="32.0" prefWidth="99.0" style="-fx-background-color: #FFFFFF; -fx-border-color: #214099; -fx-border-radius: 30; -fx-background-radius: 30;" text="Reset" textFill="#214099">
<font>
<Font name="System Bold" size="15.0" />
</font>
</JFXButton>
<JFXButton layoutX="1113.0" layoutY="18.0" prefHeight="32.0" prefWidth="116.0" style="-fx-background-color: #FA597A; -fx-border-color: #FA597A; -fx-border-radius: 30; -fx-background-radius: 30;" text="Sign Out" textFill="WHITE">
<font>
<Font name="System Bold" size="15.0" />
</font>
</JFXButton>
<JFXTextField fx:id="searchEntry" layoutX="104.0" layoutY="20.0" prefHeight="32.0" prefWidth="449.0" promptText="Enter booking ID" styleClass="search-textfield" stylesheets="@dark-theme.css">
<font>
<Font name="System Bold" size="15.0" />
</font>
</JFXTextField>
</children>
</AnchorPane>
FXML文件确实附带了正确的控制器
答案 0 :(得分：0)
在解析FXML时，FXMLLoader会创建TabPane，并创建Tab并将其添加到TabPane。添加第一个选项卡后，它将被选中，因此其selected状态发生更改并调用其onSelectionChanged处理程序。由于TabPane出现在searchEntry文本字段之前的FXML文件中，因此会在searchEntry初始化之前发生，因此您的switchTabs()方法会抛出空指针异常。
您可以简单地向处理程序方法添加空检查：
@FXML
public void switchTabs() {
if (searchEntry == null) {
return ;
}
int selectedTab = tabPane.getSelectionModel().getSelectedIndex();
switch (selectedTab){
case 0:
searchEntry.setPromptText("Enter booking ID");
break;
case 1:
searchEntry.setPromptText("Enter event name");
break;
case 2:
searchEntry.setPromptText("Enter list ID");
break;
}
}
添加此代码只是为了处理仅在加载过程中出现的特殊情况，这有点难看。我更喜欢在initalize()方法中注册一个处理程序。从FXML文件的标签中删除所有onSelectionChanged处理程序，并将以下内容添加到控制器的initialize()方法中：
@Override
public void initialize(URL location, ResourceBundle resources) {
tabPane.getSelectionModel().selectedIndexProperty().addListener(
(obs, oldIndex, newIndex) -> switchTabs());
// initialize prompt text for initially-selected tab:
switchTabs();
// searchEntry.setPromptText("");
}