当您按下按钮时，我想在JavaFx中的两个场景之间切换：
mainPlayButton.setOnmouseclicked(new EventHandler<MouseEvent>() {
@Override
public void handle(MouseEvent mouseEvent) {
Stage stage = (Stage) ((Node) mouseEvent.getsource()).getScene().getWindow();
stage.close();
try {
FXMLLoader loader = new FXMLLoader(getclass().getResource("spiel.fxml"));
BorderPane root = loader.load();
stage.setTitle("Kartenspiel");
Scene sc = new Scene(root,500,400);
stage.setScene(sc);
loader.getcontroller();
stage.show();
} catch (IOException e) {
e.printStackTrace();
}
}
});
但是当我按下按钮时，我在新的Controller中得到了NullPointerException：
public class SpielController{
@FXML
BorderPane mainBorderPane;
@FXML
HBox centerHbox;
@FXML
public void initialize() {
System.out.println(mainBorderPane);
ImageView iv = new ImageView();
iv.setImage(new Image(Objects.requireNonNull(getclass().getclassLoader().getResource("KarteBeispiel.png")).toString(),true));
centerHbox.getchildren().add(iv);
}
}
我的fxml文件：
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<BorderPane id="mainBorderPane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/10.0.2-internal" xmlns:fx="http://javafx.com/fxml/1" fx:controller="GUI.SpielController">
<top>
<MenuBar BorderPane.alignment="CENTER">
<Menu mnemonicParsing="false" text="Allgemein">
<items>
<MenuItem mnemonicParsing="false" text="Zurück ins Menü" />
<MenuItem mnemonicParsing="false" text="Spiel neustarten" />
<MenuItem mnemonicParsing="false" text="Spiel beenden" />
</items>
</Menu>
<Menu mnemonicParsing="false" text="Zug">
<items>
<MenuItem mnemonicParsing="false" text="Delete" />
</items>
</Menu>
<Menu mnemonicParsing="false" text="Hilfe">
<items>
<MenuItem mnemonicParsing="false" text="Es gibt keine Hilfe..." />
</items>
</Menu>
</MenuBar>
</top>
<center>
<HBox id="centerHbox" prefHeight="100.0" prefWidth="200.0" />
</center>
<bottom>
<GridPane BorderPane.alignment="CENTER">
<columnConstraints>
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
<ColumnConstraints hgrow="SOMETIMES" minWidth="10.0" prefWidth="100.0" />
</columnConstraints>
<rowConstraints>
<RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
</rowConstraints>
</GridPane>
</bottom>
</BorderPane>
错误消息：
javafx.fxml.LoadException:
/I:/LUCA/Programming/InformatikProjekt/out/production/InformatikProjekt/GUI/spiel.fxml
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.load(FXMLLoader.java:2435)
at GUI.MenuController$3.handle(MenuController.java:55)
at GUI.MenuController$3.handle(MenuController.java:48)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3564)
at javafx.graphics/javafx.scene.Scene$ClickGenerator.access$8200(Scene.java:3492)
at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3860)
at javafx.graphics/javafx.scene.Scene$MouseHandler.access$1200(Scene.java:3579)
at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2588)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:397)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.base/java.security.accessController.doPrivileged(accessController.java:391)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:434)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:390)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:433)
at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
at java.base/java.lang.Thread.run(Thread.java:832)
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 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:564)
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)
... 32 more
java.lang.NullPointerException
at GUI.SpielController.initialize(SpielController.java:31)
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 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:564)
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)
at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2466)
at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:2435)
at GUI.MenuController$3.handle(MenuController.java:55)
at GUI.MenuController$3.handle(MenuController.java:48)
at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
at javafx.graphics/javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3564)
at javafx.graphics/javafx.scene.Scene$ClickGenerator.access$8200(Scene.java:3492)
at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3860)
at javafx.graphics/javafx.scene.Scene$MouseHandler.access$1200(Scene.java:3579)
at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1849)
at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2588)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:397)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
at java.base/java.security.accessController.doPrivileged(accessController.java:391)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:434)
at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:390)
at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:433)
at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
at java.base/java.lang.Thread.run(Thread.java:832)
CenterHBox为空（也为mainBorderPane）。但为什么？在其他类中，@ FXML注释已足够。为什么在此类中会出现NullPointerException？