JavaFX FXML 场景切换不起作用 [NullPointerException]
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【中文标题】JavaFX FXML 场景切换不起作用 [NullPointerException]【英文标题】：JavaFX FXML scene switching is not working [NullPointerException] 【发布时间】：2017-07-09 10:48:06 【问题描述】：当我按下按钮时，我正在尝试切换布局。我尝试了很多东西，也在这里在 *** 上进行了搜索，但给出的答案似乎不适合我。
我的 FrontendView.class：
/* FrontendView Class by @Aebian */
package org.aebian.umFrontend.view;
import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.image.Image;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.GridPane;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;
import javafx.stage.StageStyle;
import java.io.IOException;
public class FrontendView extends Application
@FXML
protected static Button btnLogin, btnSave, btnDiscard, btnRefresh, btnEdit;
@FXML
private Stage primaryStage;
@FXML
private Scene scene;
@FXML
private VBox vDefault;
@FXML
protected BorderPane rootLayout;
private double xOffset = 0;
private double yOffset = 0;
@Override
public void start(Stage primaryStage)
GridPane root = new GridPane();
primaryStage.setMinWidth(800);
primaryStage.initStyle(StageStyle.UNDECORATED);
primaryStage.setMinHeight(600);
primaryStage.setResizable(false);
primaryStage.getIcons().add(new Image("file:res/images/uMgmt.png"));
primaryStage.setTitle("User Management");
Scene scene = new Scene(root, 800, 600);
primaryStage.setScene(scene);
this.primaryStage = primaryStage;
root.setAlignment(Pos.CENTER);
showRoot();
showLogin();
public void showRoot() // Load root layout
try
FXMLLoader loader = new FXMLLoader();
loader.setLocation(FrontendView.class.getResource("UI/umFrontendRoot.fxml"));
rootLayout = loader.load();
rootLayout.setId("umFrontend");
//Let the root Layout be able to moved around.
rootLayout.getTop().setOnMousePressed(new EventHandler<MouseEvent>()
@Override
public void handle(MouseEvent event)
xOffset = event.getSceneX();
yOffset = event.getSceneY();
);
rootLayout.getTop().setOnMouseDragged(new EventHandler<MouseEvent>()
@Override
public void handle(MouseEvent event)
primaryStage.setX(event.getScreenX() - xOffset);
primaryStage.setY(event.getScreenY() - yOffset);
);
// Show the scene containing the root layout.
Scene scene = new Scene(rootLayout);
primaryStage.setScene(scene);
String css = FrontendView.class.getResource("UI/umFrontendStyles.css").toExternalForm();
scene.getStylesheets().clear();
scene.getStylesheets().add(css);
primaryStage.show();
catch (IOException e)
public void showLogin() // Load the login page.
try
FXMLLoader loader = new FXMLLoader();
loader.setLocation(FrontendView.class.getResource("UI/umFrontendLogin.fxml"));
vDefault = loader.load();
// Set login to center of root layout.
rootLayout.setCenter(vDefault);
catch (IOException e)
public void showAbout() // Load the about page.
try
FXMLLoader loader = new FXMLLoader();
loader.setLocation(FrontendView.class.getResource("UI/umFrontendAbout.fxml"));
vDefault = loader.load();
// Set about page to center of root layout.
this.rootLayout.setCenter(vDefault);
catch (IOException e)
public void showAdminOverview() // Load the admin overview / edit page.
try
FXMLLoader loader = new FXMLLoader();
loader.setLocation(FrontendView.class.getResource("UI/umFrontendAdminOverview.fxml"));
VBox showAdminOverview = loader.load();
// Set admin overview page to center of root layout.
rootLayout.setCenter(showAdminOverview);
catch (IOException e)
public void showUserOverview() // Load the user overview / edit page.
try
FXMLLoader loader = new FXMLLoader();
loader.setLocation(FrontendView.class.getResource("UI/umFrontendUserOverview.fxml"));
VBox showUserOverview = loader.load();
// Set admin overview page to center of root layout.
rootLayout.setCenter(showUserOverview);
catch (IOException e)
/**
* Getter and setter.
*
* @return
*/
public BorderPane getBorderPane()
return rootLayout;
在第 62 行我打电话给showLogin()，它工作正常。如果我尝试通过按钮运行它，它将失败。同样适用于showAbout()。如果我用它替换第 62 行上的showLogin()，它将起作用。在按钮上它不会。
我的 FrontendViewController.class：
package org.aebian.umFrontend.view;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.Parent;
import javafx.scene.control.Alert;
import javafx.scene.control.Button;
import javafx.scene.control.ButtonType;
import javafx.scene.control.MenuItem;
import java.io.IOException;
import java.util.Optional;
public class FrontendViewController
FrontendView FView = new FrontendView();
Boolean admin = false;
@FXML
MenuItem appClose;
@FXML
MenuItem appAbout;
@FXML
Button buttonLogin;
@FXML
Parent root;
/* Button Events */
@FXML
private void handleButtonAction(ActionEvent e) throws IOException
if (e.getSource() == appClose) // Exit application when user clicks on Edit > Close
System.exit(0);
else if (e.getSource() == appAbout) // Show About page when user clicks on Help > About
FView.showAbout();
else if (e.getSource() == buttonLogin) // Function that gets triggered when the user presses the Login Button
if (admin == true)
FView.showAdminOverview();
else
FView.showUserOverview();
/* Frontend Dialogs */
public void delUserConfirmDialog()
Alert alert = new Alert(Alert.AlertType.CONFIRMATION);
alert.setTitle("Delete User Dialog");
alert.setHeaderText("Delete User $ss");
alert.setContentText("Are you sure you want to delete the selected action?");
Optional<ButtonType> result = alert.showAndWait();
if (result.get() == ButtonType.OK)
FView.showAdminOverview();
else
// ... user chose CANCEL or closed the dialog
我也尝试动态设置控制器，但这并没有改变任何东西。 我从编译器得到的错误是这个：
"C:\Program Files\Java\jdk1.8.0_121\bin\java" -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:6660,suspend=y,server=n -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_121\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_121\jre\lib\rt.jar;C:\Users\agoebbel\Tempo Box\Development & PS\Eclipse-Workspaces\userMan\out\production\userMan;C:\Program Files (x86)\JetBrains\IntelliJ IDEA 2016.3.4\lib\idea_rt.jar" org.aebian.umFrontend.Frontend
Connected to the target VM, address: '127.0.0.1:6660', transport: 'socket'
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$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.control.MenuItem.fire(MenuItem.java:462)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1405)
at com.sun.javafx.scene.control.skin.ContextMenuContent$MenuItemContainer.lambda$createChildren$343(ContextMenuContent.java:1358)
at com.sun.javafx.event.CompositeEventHandler$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.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$148(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
... 43 more
Caused by: java.lang.NullPointerException
at org.aebian.umFrontend.view.FrontendView.showAbout(FrontendView.java:115)
at org.aebian.umFrontend.view.FrontendViewController.handleButtonAction(FrontendViewController.java:39)
... 53 more
所以我可以直接运行 showLogin()、showAbout() 等方法，这不是输入流的错误。 如果您需要我的 FXML 文件之一：
umFrontendAbout.fxml：
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.paint.*?>
<?import javafx.scene.text.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.AnchorPane?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.paint.Color?>
<?import javafx.scene.text.Font?>
<VBox alignment="CENTER" prefHeight="600.0" prefWidth="900.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="org.aebian.umFrontend.view.FrontendView">
<children>
<SplitPane focusTraversable="true" orientation="VERTICAL" prefHeight="-1.0" prefWidth="-1.0" VBox.vgrow="ALWAYS">
<items>
<AnchorPane prefHeight="576.0" prefWidth="328.0">
<children>
<Label layoutX="272.0" layoutY="121.0" text="Java User Managment">
<font>
<Font size="24.0" />
</font>
</Label>
<Label layoutX="228.0" layoutY="164.0" text="A java written user management solution with mysql support" />
<Label layoutX="251.0" layoutY="181.0" text="© 2017 by Adrian (Simmarith) & Alexander (Aebian)" />
<Label alignment="CENTER" layoutX="38.0" layoutY="14.0" minWidth="60.0" prefWidth="-1.0" style=" " text="User Management \ About" textAlignment="CENTER" wrapText="false">
<font>
<Font size="18.0" fx:id="x1" />
</font>
<textFill>
<Color blue="0.624" green="0.624" red="0.624" fx:id="x2" />
</textFill>
</Label>
<Label layoutX="338.0" layoutY="220.0" text="aebian@aebian.org" />
</children>
</AnchorPane>
</items>
</SplitPane>
</children>
</VBox>
我该如何解决这个问题？
我尝试过但对我不起作用的事情：
通过动态设置控制器在控制器中创建了一个 setPrimaryStage 方法( (控制器) loader.getController() ).setPrimaryStage(primaryStage);
【问题讨论】：
为什么您希望rootLayout 在您在FrontendViewController 中创建的FrontendView 实例中被初始化？它由start 方法初始化（有效），该方法在您启动应用程序时在为您创建的实例上调用。这只是结构不正确：您永远不应该自己创建 Application 类的实例，而 Application 类应该只启动应用程序。您需要重构代码，使其适合 FX 应用程序生命周期。
【参考方案1】：
我在调试和尝试后自己解决了这个问题。 问题是控制器没有获得初始化值。只有在方法启动运行时才存在。因此，我要么需要在我的控制器中有“应用程序”，要么因为 JavaFX 已经基于 MVC，所以我可以将我的控制器与 View 类本身合并。
我做了第二个选项，它现在可以工作了。 感谢您的帮助。
Aebian 出来了。
【讨论】：
【参考方案2】：你在调用handleButtonAction()方法之前初始化rootLayout了吗？
据我了解，您在 showRoot() 上加载了 rootLayout，但是当应用程序到达方法 handleButtonAction() 时，rootLayout 没有被初始化。
尝试保存您在 showRoot() 上初始化的 rootLayout，以便您可以通过 handleButtonAction() 在 showAbout 上使用它；
【讨论】：
我该怎么做呢？我试过 showRoot();方法与 this.rootLayout = rootLayout;并尝试为此创建一个吸气剂。 对不起，我没有很好地阅读代码。您是否尝试在 FrontendViewController.class 上将BorderPane bPane = FView.getBorderPane(); 重命名为 BorderPane rootLayout = FView.getBorderPane(); 并使用以下命令编辑 showAbout() 方法：this.rootLayout.setCenter(vDefault);
我做了并相应地更新了代码堆栈跟踪也保持不变。嗯，我的猜测是 showAbout() 在 showRoot() 之前加载，但我不知道那是不是真的
其他方法FView.showAdminOverview(); 和FView.showUserOverview(); 是否有效？如果不是，我的猜测是您在 Controller 上初始化的对象 FView 要么与您之前创建的不同，要么不执行 start(); 方法。此外，您可以尝试使用 IDE 的调试器并检查在方法 FView.showAbout(); 之前是否已初始化 rootLayout。
其他方法产生相同的错误。 !Debug 这是我断点的输出。以上是关于JavaFX FXML 场景切换不起作用 [NullPointerException]的主要内容，如果未能解决你的问题，请参考以下文章
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