NullPointerException 尽管 fx:id 和 fx:controller 是正确的
NullPointerException despite the fx:id and fx:controller are correct
我正在为我的局域网应用创建 table 日志。当我尝试 运行 这个应用程序时，它抛出 NullPointerException，但是 fx:id 和 fx:controller 是正确的。我正在使用 JavaFX 12。
我尝试用 Intellij 重构 fx:id 和 fx:controller，Intellij 在 logPane.fxml 和 LogPaneController.class 中也正确地更改了这一点，但它仍然无法正常工作。如果我注释掉异常所在的行，则所有应用程序都可以正常工作。我用谷歌搜索短语 "FXML component returns NUllPointerException"，但结果始终是 "your fx:id or fx:controller name is not the same in controller"。
logPane.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<AnchorPane HBox.hgrow="ALWAYS" xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http://javafx.com/fxml/1"
fx:controller="com.lanssmaker.controller.LogPaneController">
<children>
<TableView fx:id="logTable" prefHeight="574.0" prefWidth="382.0" AnchorPane.bottomAnchor="0.0"
AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
<columns>
<TableColumn maxWidth="140.0" minWidth="70" prefWidth="70.0" text="Time"/>
<TableColumn text="Content"/>
<TableColumn maxWidth="140.0" minWidth="70" prefWidth="70.0" text="Category"/>
</columns>
<columnResizePolicy>
<TableView fx:constant="CONSTRAINED_RESIZE_POLICY"/>
</columnResizePolicy>
</TableView>
</children>
</AnchorPane>
LogPaneController.class
public class LogPaneController {
@FXML
private TableView<Log> logTable; //it's null
public TableView<Log> getLogTableView() {
return logTable;
}
public void initialize() {
//example ussage calling NullPointerException
logTable.isHover();
}
}
异常日志
Exception in Application start method
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:567)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:464)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363)
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:567)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051)
Caused by: java.lang.RuntimeException: Exception in Application start method
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:900)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication(LauncherImpl.java:195)
at java.base/java.lang.Thread.run(Thread.java:835)
Caused by: javafx.fxml.LoadException:
/D:/Programming/Java/javastart/ssmaker/target/classes/fxml/buttonsPane.fxml
/D:/Programming/Java/javastart/ssmaker/target/classes/fxml/mainPane.fxml:17
at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2625)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2595)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2466)
at javafx.fxml/javafx.fxml.FXMLLoader$IncludeElement.constructValue(FXMLLoader.java:1154)
at javafx.fxml/javafx.fxml.FXMLLoader$ValueElement.processStartElement(FXMLLoader.java:754)
at javafx.fxml/javafx.fxml.FXMLLoader.processStartElement(FXMLLoader.java:2722)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2552)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2466)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3237)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3194)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3163)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3136)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3113)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3106)
at ssmaker/com.lanssmaker.main.Main.start(Main.java:16)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:846)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:455)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:428)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:427)
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(WinApplication.java:174)
... 1 more
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:567)
at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
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:567)
at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:273)
at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2591)
... 22 more
Caused by: java.lang.NullPointerException
at ssmaker/com.lanssmaker.controller.LogPaneController.initialize(LogPaneController.java:25)
... 33 more
package com.lanssmaker.main;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;
public class Main extends Application {
public static void main(String[] args) {
launch(args);
}
@Override
public void start(Stage stage) throws Exception {
Pane mainPane = FXMLLoader.load(getClass().getResource("/fxml/mainPane.fxml"));
Scene scene = new Scene(mainPane);
stage.setScene(scene);
stage.setTitle("LAN ScreenShots Maker");
stage.show();
}
}
mainPane.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.*?>
<AnchorPane maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" minHeight="-Infinity"
minWidth="-Infinity" prefHeight="624.0" prefWidth="813.0" xmlns="http://javafx.com/javafx/11.0.1"
xmlns:fx="http://javafx.com/fxml/1" fx:controller="com.lanssmaker.controller.MainController">
<children>
<HBox layoutX="158.0" layoutY="143.0" prefHeight="624.0" prefWidth="813.0" AnchorPane.bottomAnchor="25.0"
AnchorPane.leftAnchor="25.0" AnchorPane.rightAnchor="25.0" AnchorPane.topAnchor="25.0">
<children>
<AnchorPane HBox.hgrow="NEVER">
<children>
<VBox prefHeight="574.0" prefWidth="389.0" AnchorPane.bottomAnchor="0.0"
AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="15.0" AnchorPane.topAnchor="0.0">
<children>
<fx:include source="connectionPane.fxml"/>
<fx:include source="buttonsPane.fxml"/>
</children>
</VBox>
</children>
</AnchorPane>
<fx:include source="logPane.fxml"/>
</children>
</HBox>
</children>
</AnchorPane>
这里是Project structure
您有 getter class 用于私有 logTable，因此您可以获得一个值，但我没有看到值初始化或 setter class（这将初始化值）。
仔细查看堆栈跟踪：
...
Caused by: javafx.fxml.LoadException:
/D:/Programming/Java/javastart/ssmaker/target/classes/fxml/buttonsPane.fxml
/D:/Programming/Java/javastart/ssmaker/target/classes/fxml/mainPane.fxml:17
...
Caused by: java.lang.NullPointerException
at ssmaker/com.lanssmaker.controller.LogPaneController.initialize(LogPaneController.java:25)
这意味着当您加载 buttonsPane.fxml 而 FXMLLoader 处理
时会发生异常
<fx:include source="buttonsPane.fxml"/>
元素。
此外，它告诉我您不仅将 LogPaneController 用于 logPane.fxml，而且还用于 buttonsPane.fxml。每次加载 fxml 时都会创建单独的控制器实例；使用 <fx:include> 会创建一个单独的 FXMLLoader 实例来加载包含的 fxml。 logTable 字段仅为其中之一注入；对于另一个控制器实例，它仍然是 null。 （这甚至忽略了加载 buttonsPane.fxml 发生在加载 logPane.fxml 之前的事实，所以即使在加载 buttonsPane.fxml 完成时使用了相同的控制器实例， TableView 也没有基于 logPane.fxml.)
创建
为 buttonsPane.fxml 和 logPane.fxml 使用单独的控制器 classes。您不会通过简单地使用相同的控制器 class 来获得两个 fxml "to communicate"。我会建议一个替代方案，但你在那里做的事情没有任何意义（除非你试图挑起 NPE）：isHover 只是重新调整 hover [=44= 的值] 对于尚未成为 Scene.
一部分的节点，它始终是 false
我正在为我的局域网应用创建 table 日志。当我尝试 运行 这个应用程序时，它抛出 NullPointerException，但是 fx:id 和 fx:controller 是正确的。我正在使用 JavaFX 12。
我尝试用 Intellij 重构 fx:id 和 fx:controller，Intellij 在 logPane.fxml 和 LogPaneController.class 中也正确地更改了这一点，但它仍然无法正常工作。如果我注释掉异常所在的行，则所有应用程序都可以正常工作。我用谷歌搜索短语 "FXML component returns NUllPointerException"，但结果始终是 "your fx:id or fx:controller name is not the same in controller"。
logPane.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<AnchorPane HBox.hgrow="ALWAYS" xmlns="http://javafx.com/javafx/11.0.1" xmlns:fx="http://javafx.com/fxml/1"
fx:controller="com.lanssmaker.controller.LogPaneController">
<children>
<TableView fx:id="logTable" prefHeight="574.0" prefWidth="382.0" AnchorPane.bottomAnchor="0.0"
AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0">
<columns>
<TableColumn maxWidth="140.0" minWidth="70" prefWidth="70.0" text="Time"/>
<TableColumn text="Content"/>
<TableColumn maxWidth="140.0" minWidth="70" prefWidth="70.0" text="Category"/>
</columns>
<columnResizePolicy>
<TableView fx:constant="CONSTRAINED_RESIZE_POLICY"/>
</columnResizePolicy>
</TableView>
</children>
</AnchorPane>
LogPaneController.class
public class LogPaneController {
@FXML
private TableView<Log> logTable; //it's null
public TableView<Log> getLogTableView() {
return logTable;
}
public void initialize() {
//example ussage calling NullPointerException
logTable.isHover();
}
}
异常日志
Exception in Application start method
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:567)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:464)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363)
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:567)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051)
Caused by: java.lang.RuntimeException: Exception in Application start method
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication1(LauncherImpl.java:900)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication(LauncherImpl.java:195)
at java.base/java.lang.Thread.run(Thread.java:835)
Caused by: javafx.fxml.LoadException:
/D:/Programming/Java/javastart/ssmaker/target/classes/fxml/buttonsPane.fxml
/D:/Programming/Java/javastart/ssmaker/target/classes/fxml/mainPane.fxml:17
at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2625)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2595)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2466)
at javafx.fxml/javafx.fxml.FXMLLoader$IncludeElement.constructValue(FXMLLoader.java:1154)
at javafx.fxml/javafx.fxml.FXMLLoader$ValueElement.processStartElement(FXMLLoader.java:754)
at javafx.fxml/javafx.fxml.FXMLLoader.processStartElement(FXMLLoader.java:2722)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2552)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2466)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3237)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3194)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3163)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3136)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3113)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3106)
at ssmaker/com.lanssmaker.main.Main.start(Main.java:16)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1(LauncherImpl.java:846)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait(PlatformImpl.java:455)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:428)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:389)
at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater(PlatformImpl.java:427)
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(WinApplication.java:174)
... 1 more
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:567)
at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:76)
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:567)
at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:273)
at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:83)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2591)
... 22 more
Caused by: java.lang.NullPointerException
at ssmaker/com.lanssmaker.controller.LogPaneController.initialize(LogPaneController.java:25)
... 33 more
package com.lanssmaker.main;
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Scene;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;
public class Main extends Application {
public static void main(String[] args) {
launch(args);
}
@Override
public void start(Stage stage) throws Exception {
Pane mainPane = FXMLLoader.load(getClass().getResource("/fxml/mainPane.fxml"));
Scene scene = new Scene(mainPane);
stage.setScene(scene);
stage.setTitle("LAN ScreenShots Maker");
stage.show();
}
}
mainPane.fxml
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.layout.*?>
<AnchorPane maxHeight="1.7976931348623157E308" maxWidth="1.7976931348623157E308" minHeight="-Infinity"
minWidth="-Infinity" prefHeight="624.0" prefWidth="813.0" xmlns="http://javafx.com/javafx/11.0.1"
xmlns:fx="http://javafx.com/fxml/1" fx:controller="com.lanssmaker.controller.MainController">
<children>
<HBox layoutX="158.0" layoutY="143.0" prefHeight="624.0" prefWidth="813.0" AnchorPane.bottomAnchor="25.0"
AnchorPane.leftAnchor="25.0" AnchorPane.rightAnchor="25.0" AnchorPane.topAnchor="25.0">
<children>
<AnchorPane HBox.hgrow="NEVER">
<children>
<VBox prefHeight="574.0" prefWidth="389.0" AnchorPane.bottomAnchor="0.0"
AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="15.0" AnchorPane.topAnchor="0.0">
<children>
<fx:include source="connectionPane.fxml"/>
<fx:include source="buttonsPane.fxml"/>
</children>
</VBox>
</children>
</AnchorPane>
<fx:include source="logPane.fxml"/>
</children>
</HBox>
</children>
</AnchorPane>
这里是Project structure
您有 getter class 用于私有 logTable，因此您可以获得一个值，但我没有看到值初始化或 setter class（这将初始化值）。
仔细查看堆栈跟踪：
...
Caused by: javafx.fxml.LoadException:
/D:/Programming/Java/javastart/ssmaker/target/classes/fxml/buttonsPane.fxml
/D:/Programming/Java/javastart/ssmaker/target/classes/fxml/mainPane.fxml:17
...
Caused by: java.lang.NullPointerException
at ssmaker/com.lanssmaker.controller.LogPaneController.initialize(LogPaneController.java:25)
这意味着当您加载 buttonsPane.fxml 而 FXMLLoader 处理
<fx:include source="buttonsPane.fxml"/>
元素。
此外，它告诉我您不仅将 LogPaneController 用于 logPane.fxml，而且还用于 buttonsPane.fxml。每次加载 fxml 时都会创建单独的控制器实例；使用 <fx:include> 会创建一个单独的 FXMLLoader 实例来加载包含的 fxml。 logTable 字段仅为其中之一注入；对于另一个控制器实例，它仍然是 null。 （这甚至忽略了加载 buttonsPane.fxml 发生在加载 logPane.fxml 之前的事实，所以即使在加载 buttonsPane.fxml 完成时使用了相同的控制器实例， TableView 也没有基于 logPane.fxml.)
为 buttonsPane.fxml 和 logPane.fxml 使用单独的控制器 classes。您不会通过简单地使用相同的控制器 class 来获得两个 fxml "to communicate"。我会建议一个替代方案，但你在那里做的事情没有任何意义（除非你试图挑起 NPE）：isHover 只是重新调整 hover [=44= 的值] 对于尚未成为 Scene.
false