刚开始使用JavaFx（通常也是Java的初学者），几天来，我一直在尝试使其工作，但一直无法解决。我收到一个空指针异常，该异常在这里介绍： 什么是NullPointerException，如何解决它？
因此，我希望这个问题不会因为重复而结束，因为我知道npe是什么，并且（通常）知道如何解决此问题。
我也（大多数时候）知道如何躲避它们和/或修复它们（如果发生），但是在这种情况下，我只是不知道如何解决它。
我还检查了有关fxml的其他问题，但仍然无法解决。 如何从javaFx borderPane中的LeftPane更改CenterPane？ 在javaFX的BorderPane中的窗格之间切换在 同一场景中加载新的fxml
在我的应用程序中，我想以borderpane为根，在左侧，我有三个按钮，根据我按的是哪个按钮，按新的fxml和一个tabpane应该在borderpane的中央加载，当我按下按钮时得到一个我认为是由于我没有引用正确的边框的npe，但我看不到我要去哪里错误。
我想做的是，当我按下按钮custMenuButton时，应该加载fxml并将其设置为borderpane的中心。
主班
import java.io.IOException; import javafx.application.Application; import javafx.fxml.FXML; import javafx.fxml.FXMLLoader; import javafx.scene.Scene; import javafx.scene.layout.BorderPane; import javafx.stage.Stage; public class Main extends Application { @FXML private BorderPane root; Stage window; @Override public void start(Stage primaryStage) throws IOException { window = primaryStage; FXMLLoader loader = new FXMLLoader(Main.class.getResource("MainWindowView.fxml")); this.root = loader.load(); MainWindowController mwc = new MainWindowController(); mwc.setMain(this); Scene scene = new Scene(root); window.setTitle("JavaFX"); window.setScene(scene); window.show(); } public static void main(String[] args) { launch(args); } public BorderPane getBorderPane() { return root; } }
主视窗控制器
import java.io.IOException; import javafx.fxml.FXML; import javafx.fxml.FXMLLoader; import javafx.scene.control.Button; import javafx.scene.control.TabPane; import javafx.scene.layout.BorderPane; import javafx.scene.layout.VBox; public class MainWindowController { private Main main; @FXML private BorderPane root; @FXML private VBox sideBox; @FXML private Button custMenuButton; @FXML private Button accMenuButton; @FXML private Button transMenuButton; public void setMain(Main main) { this.main = main; } public void handleCustMenuButton() throws IOException { FXMLLoader loader = new FXMLLoader(getClass().getResource("CustomerView.fxml")); TabPane pane = (TabPane) loader.load(); CustomerViewController cvc = loader.getController(); cvc.setMain(main); main.getBorderPane().setCenter(pane); } }
客户视图控制器
import java.net.URL; import java.util.ResourceBundle; import javafx.fxml.FXML; import javafx.fxml.Initializable; import javafx.scene.control.Tab; import javafx.scene.control.TabPane; public class CustomerViewController implements Initializable { Main main; @FXML private TabPane custTabPane; @FXML private Tab createTab; @FXML private Tab listAllTab; @FXML private Tab deleteTab; public void setMain(Main main){ this.main = main; } @Override public void initialize(URL url, ResourceBundle rb) { // TODO } }
主窗口视图
<?xml version="1.0" encoding="UTF-8"?> <?import javafx.geometry.Insets?> <?import javafx.scene.control.Button?> <?import javafx.scene.control.Menu?> <?import javafx.scene.control.MenuBar?> <?import javafx.scene.control.MenuItem?> <?import javafx.scene.layout.BorderPane?> <?import javafx.scene.layout.VBox?> <BorderPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="600.0" prefWidth="800.0" xmlns="http://javafx.com/javafx/8.0.141" xmlns:fx="http://javafx.com/fxml/1" fx:controller="firstfx.MainWindowController"> <top> <MenuBar BorderPane.alignment="CENTER"> <menus> <Menu mnemonicParsing="false" text="File"> <items> <MenuItem mnemonicParsing="false" text="Close" /> </items> </Menu> <Menu mnemonicParsing="false" text="Help"> <items> <MenuItem mnemonicParsing="false" text="About" /> </items> </Menu> </menus> </MenuBar> </top> <left> <VBox fx:id="sideBox" prefHeight="200.0" prefWidth="150.0" spacing="2.0" BorderPane.alignment="CENTER"> <children> <Button fx:id="custMenuButton" mnemonicParsing="false" onAction="#handleCustMenuButton" prefHeight="50.0" prefWidth="130.0" text="Kundmeny" /> <Button fx:id="accMenuButton" mnemonicParsing="false" prefHeight="50.0" prefWidth="130.0" text="Kontomeny" /> <Button fx:id="transMenuButton" mnemonicParsing="false" prefHeight="50.0" prefWidth="130.0" text="Transaktioner" /> </children> <padding> <Insets bottom="10.0" left="10.0" right="10.0" top="10.0" /> </padding> </VBox> </left> </BorderPane>
客户视图fxml
<?xml version="1.0" encoding="UTF-8"?> <?import javafx.scene.control.Tab?> <?import javafx.scene.control.TabPane?> <?import javafx.scene.layout.AnchorPane?> <TabPane fx:id="custTabPane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" tabClosingPolicy="UNAVAILABLE" xmlns="http://javafx.com/javafx/8.0.141" xmlns:fx="http://javafx.com/fxml/1" fx:controller="firstfx.CustomerViewController"> <tabs> <Tab fx:id="createTab" text="Skapa kund"> <content> <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="180.0" prefWidth="200.0" /> </content> </Tab> <Tab fx:id="listAllTab" text="Lista alla kunder"> <content> <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="180.0" prefWidth="200.0" /> </content> </Tab> <Tab fx:id="deleteTab" text="Radera kund"> <content> <AnchorPane minHeight="0.0" minWidth="0.0" prefHeight="180.0" prefWidth="200.0" /> </content> </Tab> </tabs> </TabPane>
堆栈跟踪
Executing /home/garnbutik/NetBeansProjects/FirstFX/dist/run1223809748/FirstFX.jar using platform /home/garnbutik/jdk1.8.0_151/jre/bin/java 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.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$353(GlassViewEventHandler.java:417) at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389) at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416) at com.sun.glass.ui.View.handleMouseEvent(View.java:555) at com.sun.glass.ui.View.notifyMouse(View.java:937) at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method) at com.sun.glass.ui.gtk.GtkApplication.lambda$null$48(GtkApplication.java:139) at java.lang.Thread.run(Thread.java:748) Caused by: java.lang.reflect.InvocationTargetException at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71) at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275) at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771) ... 48 more Caused by: java.lang.NullPointerException at firstfx.MainWindowController.handleCustMenuButton(MainWindowController.java:31) ... 58 more BUILD STOPPED (total time: 4 minutes 14 seconds)
setMain(...)加载时不会调用创建的控制器MainWindowView.fxml。因此，MainWindowController当您尝试做
setMain(...)
MainWindowView.fxml
MainWindowController
main.getBorderPane()...
您会得到一个空指针异常。
在您的start()方法中，您需要以与稍后在中相同的方式来获取控制器handleCustMenuButton(...)，即
start()
handleCustMenuButton(...)
FXMLLoader loader = new FXMLLoader(Main.class.getResource("MainWindowView.fxml")); this.root = loader.load(); // MainWindowController mwc = new MainWindowController(); MainWindowController mwc = loader.getController(); mwc.setMain(this);
