切换场景时JavaFX选择框空指针异常

Posted 2023-02-19

技术标签:

【中文标题】切换场景时JavaFX选择框空指针异常【英文标题】：JavaFX choice box null pointer exception while switching scene 【发布时间】：2022-01-04 03:21:54 【问题描述】：

该程序基本上显示选择框和一个按钮，无论用户选择什么，它都会在场景 2 的标签中打印出来。但是这个错误不断出现。

当我从选择框菜单中选择一个项目时会发生错误，而当我按下按钮时会发生另一个错误。

注意：我对两个 fxml 文件使用相同的 Controller 类。

错误：


javafx.fxml.LoadException: 
/C:/Users/yasse/eclipse-workspace/FinalProject/bin/application/exscene2.fxml

   at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2685)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3331)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3287)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3255)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3227)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3203)
   at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3196)
   at application.BookController.switchscene(BookController.java:57)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   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.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:49)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8792)
   at javafx.controls/javafx.scene.control.ChoiceBox$4.invalidated(ChoiceBox.java:333)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:147)
   at javafx.controls/javafx.scene.control.ChoiceBox.setValue(ChoiceBox.java:342)
   at javafx.controls/javafx.scene.control.ChoiceBox.lambda$new$1(ChoiceBox.java:194)
   at javafx.base/com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(ExpressionHelper.java:181)
   at javafx.base/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
   at javafx.base/javafx.beans.property.ReadOnlyObjectPropertyBase.fireValueChangedEvent(ReadOnlyObjectPropertyBase.java:80)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
   at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:557)
   at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:943)
   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:184)
   at java.base/java.lang.Thread.run(Thread.java:831)
Caused by: java.lang.NullPointerException: Cannot invoke "javafx.scene.control.ChoiceBox.getItems()" because "this.box" is null
   at application.BookController.initialize(BookController.java:44)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
   ... 79 more
Exception in thread "JavaFX Application Thread" java.lang.NullPointerException: Cannot invoke "javafx.scene.control.Label.setText(String)" because "this.label" is null
   at application.BookController.switchscene(BookController.java:66)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   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.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:49)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8792)
   at javafx.controls/javafx.scene.control.ChoiceBox$4.invalidated(ChoiceBox.java:333)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:112)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:147)
   at javafx.controls/javafx.scene.control.ChoiceBox.setValue(ChoiceBox.java:342)
   at javafx.controls/javafx.scene.control.ChoiceBox.lambda$new$1(ChoiceBox.java:194)
   at javafx.base/com.sun.javafx.binding.ExpressionHelper$SingleChange.fireValueChangedEvent(ExpressionHelper.java:181)
   at javafx.base/com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(ExpressionHelper.java:80)
   at javafx.base/javafx.beans.property.ReadOnlyObjectPropertyBase.fireValueChangedEvent(ReadOnlyObjectPropertyBase.java:80)
   at javafx.base/javafx.beans.property.ReadOnlyObjectWrapper.fireValueChangedEvent(ReadOnlyObjectWrapper.java:102)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.markInvalid(ObjectPropertyBase.java:113)
   at javafx.base/javafx.beans.property.ObjectPropertyBase.set(ObjectPropertyBase.java:147)
   at javafx.controls/javafx.scene.control.SelectionModel.setSelectedItem(SelectionModel.java:105)
   at javafx.controls/javafx.scene.control.SingleSelectionModel.updateSelectedIndex(SingleSelectionModel.java:223)
   at javafx.controls/javafx.scene.control.SingleSelectionModel.select(SingleSelectionModel.java:149)
   at javafx.controls/javafx.scene.control.ChoiceBox$ChoiceBoxSelectionModel.select(ChoiceBox.java:586)
   at javafx.controls/javafx.scene.control.skin.ChoiceBoxSkin.lambda$addPopupItem$7(ChoiceBoxSkin.java:390)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.controls/javafx.scene.control.MenuItem.fire(MenuItem.java:459)
   at javafx.controls/com.sun.javafx.scene.control.ContextMenuContent$MenuItemContainer.doSelect(ContextMenuContent.java:1385)
   at javafx.controls/com.sun.javafx.scene.control.ContextMenuContent$MenuItemContainer.lambda$createChildren$12(ContextMenuContent.java:1338)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   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.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   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$MouseHandler.process(Scene.java:3897)
   at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1878)
   at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2623)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
   at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
   at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
   at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:557)
   at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:943)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
   at java.base/java.lang.Thread.run(Thread.java:831)
javafx.fxml.LoadException: 
/C:/Users/yasse/eclipse-workspace/FinalProject/bin/application/exscene2.fxml

   at javafx.fxml/javafx.fxml.FXMLLoader.constructLoadException(FXMLLoader.java:2707)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2685)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2548)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3331)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3287)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3255)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3227)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:3203)
   at javafx.fxml/javafx.fxml.FXMLLoader.load(FXMLLoader.java:3196)
   at application.BookController.switchscene(BookController.java:57)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
   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:77)
   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:275)
   at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:84)
   at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1852)
   at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1724)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   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.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:49)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8792)
   at javafx.controls/javafx.scene.control.Button.fire(Button.java:203)
   at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:208)
   at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3897)
   at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1878)
   at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2623)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
   at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
   at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
   at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:557)
   at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:943)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
   at java.base/java.lang.Thread.run(Thread.java:831)
Caused by: java.lang.NullPointerException: Cannot invoke "javafx.scene.control.ChoiceBox.getItems()" because "this.box" is null
   at application.BookController.initialize(BookController.java:44)
   at javafx.fxml/javafx.fxml.FXMLLoader.loadImpl(FXMLLoader.java:2655)
   ... 65 more
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
   at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1857)
   at javafx.fxml/javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1724)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
   at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
   at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
   at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
   at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
   at javafx.graphics/javafx.scene.Node.fireEvent(Node.java:8792)
   at javafx.controls/javafx.scene.control.Button.fire(Button.java:203)
   at javafx.controls/com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:208)
   at javafx.controls/com.sun.javafx.scene.control.inputmap.InputMap.handle(InputMap.java:274)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:247)
   at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
   at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:234)
   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.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$MouseHandler.process(Scene.java:3897)
   at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1878)
   at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2623)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:411)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:301)
   at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:450)
   at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:424)
   at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:449)
   at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:557)
   at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:943)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
   at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:184)
   at java.base/java.lang.Thread.run(Thread.java:831)
Caused by: java.lang.reflect.InvocationTargetException
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:78)
   at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.base/java.lang.reflect.Method.invoke(Method.java:567)
   at com.sun.javafx.reflect.Trampoline.invoke(MethodUtil.java:77)
   at jdk.internal.reflect.GeneratedMethodAccessor2.invoke(Unknown Source)
   at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.base/java.lang.reflect.Method.invoke(Method.java:567)
   at javafx.base/com.sun.javafx.reflect.MethodUtil.invoke(MethodUtil.java:275)
   at javafx.fxml/com.sun.javafx.fxml.MethodHelper.invoke(MethodHelper.java:84)
   at javafx.fxml/javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1852)
   ... 46 more
Caused by: java.lang.NullPointerException: Cannot invoke "javafx.scene.control.Label.setText(String)" because "this.label" is null
   at application.BookController.switchscene(BookController.java:66)
   ... 57 more

我的主要：

package application;    
import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Scene;
import javafx.scene.layout.AnchorPane;



public class Main extends Application 
    //@Override
    public void start( Stage primaryStage) throws Exception 
        // TODO Auto-generated method stub
        
        AnchorPane mainpane= (AnchorPane) FXMLLoader.load(Main.class.getResource("exscene1.fxml"));
        primaryStage.setScene(new Scene(mainpane));
        
        primaryStage.show();
        
        
        
    
    
    public static void main(String[] args) 
        Application.launch(args);

我的控制器类：

package application;

import java.io.IOException;
import java.net.URL;
import java.util.ResourceBundle;
import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.fxml.Initializable;
import javafx.scene.control.Button;
import javafx.scene.control.ChoiceBox;
import javafx.scene.control.Label;
import javafx.scene.layout.AnchorPane;

public class BookController implements Initializable 

    @FXML
    private Button button;

    @FXML
    private AnchorPane scene1pane;

    @FXML
    private ChoiceBox<String> box;

    @FXML
    private AnchorPane scene2pane;

    @FXML
    private Label label;
    
    @FXML
    private Label label1;
    
    
    
    ObservableList<String> test = FXCollections.observableArrayList("AAA","BBB","CCC"); 
    
  
    public void initialize(URL arg0, ResourceBundle arg1) 
        // TODO Auto-generated method stub
        box.getItems().addAll(test);
        box.setOnAction(this::switchscene);
        
        
    
    
    
    
  public  void switchscene(ActionEvent event)  
        
        
        AnchorPane pane;
        try 
            pane = FXMLLoader.load(getClass().getResource("exscene2.fxml"));
            scene1pane.getChildren().setAll(pane);
            
         catch (IOException e) 
            // TODO Auto-generated catch block
            e.printStackTrace();
    
        
        String str = box.getValue();
        label.setText(str);

我的第一个场景 fxml 文件：

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.text.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>

<AnchorPane fx:id="scene1pane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.BookController">
   <children>
      <Button fx:id="button" layoutX="223.0" layoutY="162.0" mnemonicParsing="false" onAction="#switchscene" text="Button">
         <font>
            <Font size="36.0" />
         </font>
      </Button>
      <Label fx:id="label1" layoutX="139.0" layoutY="50.0" prefHeight="27.0" prefWidth="148.0" text="Scene 1">
         <font>
            <Font size="42.0" />
         </font>
      </Label>
      <ChoiceBox fx:id="box" layoutX="303.0" layoutY="31.0" prefWidth="150.0" />
   </children>
</AnchorPane>

我的第二个场景 fxml 文件：

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.text.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>

<AnchorPane fx:id="scene2pane" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="application.BookController">
   <children>
      <Label fx:id="label" layoutX="262.0" layoutY="92.0" text="Welcome">
         <font>
            <Font size="33.0" />
         </font>
      </Label>
   </children>
</AnchorPane>

【问题讨论】：

fxml : 控制器必须是 1:1 - 控制器不能在 fxmls 之间共享第一个场景 FXML 没有带有 fx:id=“label” 的元素，因此在加载该 FXML 时创建的控制器中 label 为空（如堆栈跟踪所述）。当我起草答案时，这两个错误都已在 cmets 中得到解决：) 【参考方案1】：

在这个例子中有很多事情需要考虑。首先，让我解释一下您面临的错误。

首先，单击按钮或选择选择框，您将得到constructLoadException。这是因为您对两个 fxml 使用相同的 Controller 类。而且您期望两个 fxml 共享同一个 Controller 实例。情况不会如此。使用您的代码，每个 fxml 都将拥有自己的 BookController 实例。所以在fxml1控制器中，所有与fxml2相关的实例变量都会为null，反之亦然。

所以当你启动 fxml2 时，会创建一个新的 BookController 实例并调用 initialize 方法。由于 fxml2 中没有“box”节点，因此该变量将为 null，显然会抛出 NPE，从而导致加载 fxml 的异常。

NPE的第二个错误也一样，这次你期待的是fxml1控制器中的fxml2实例变量“label”。

解决方案：

有两种方法可以解决此问题。这取决于您是否要共享相同的控制器类，或者您是否可以为每个 fxml 使用单独的控制器类。

#1。使用相同的控制器类

这样，你需要做以下两个更改。

删除 exscene2 fxml 中的控制器声明。如下更改初始化和 switchScene 方法。主要变化是我们正在将相同的控制器实例手动设置为 fxml2 装载机。并在初始化方法中进行一些检查，以不重新添加再次项目。

public void initialize(URL arg0, ResourceBundle arg1) 
    if(box.getItems().isEmpty()) 
        box.getItems().addAll(test);
        box.setOnAction(this::switchscene);
    


public void switchscene(ActionEvent event) 
    AnchorPane pane;
    try 
        // Initiate a loader for the fxml 2
        final FXMLLoader loader = new FXMLLoader(getClass().getResource("exscene2.fxml"));
        // Set this controller instance to fxml 2
        loader.setController(this);
        // And load the fxml 2.
        pane = loader.load();
        // By this line, both fxmls use same instance of controller
        scene1pane.getChildren().setAll(pane);
     catch (IOException e) 
        e.printStackTrace();
    

    String str = box.getValue();
    if(str!=null && !str.isEmpty()) 
        label.setText(str);

#2。使用单独的控制器类

这样，你需要做以下两个更改。

使用仅与 fxml 2 相关的实例变量为 fxml 2（比如说 BookController2.java）创建一个新的 Controller 类。

import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Label;
import javafx.scene.layout.AnchorPane;

import java.net.URL;
import java.util.ResourceBundle;

public class BookController2 implements Initializable 

    @FXML
    private AnchorPane scene2pane;

    @FXML
    private Label label;


    @Override
    public void initialize(URL url, ResourceBundle resourceBundle) 
        // Empty
    

    public final Label getLabel()
        return label;

将此 BookController2 设置为 fxml 2 中的控制器。

fx:controller="application.BookController2"

在 BookController.java 中删除 fxml 2 的所有实例变量并更改 switchScene 方法如下。

public void switchscene(ActionEvent event) 
    AnchorPane pane;
    try 
        // Initiate the loader for fxml 2. Using this loader, you can get the controller instance of fxml 2
        final FXMLLoader loader = new FXMLLoader(getClass().getResource("exscene2.fxml"));
        pane = loader.load();
        scene1pane.getChildren().setAll(pane);

        String str = box.getValue();
        if (str != null && !str.isEmpty()) 
            // Get the label from the controller and set the text.
            ((BookController2) loader.getController()).getLabel().setText(str);
        
     catch (IOException e) 
        e.printStackTrace();

【讨论】：

第一个解决方案（我不太推荐）远不止“共享同一个控制器class”。它实际上共享同一个控制器（即实际的控制器实例）。 @James_D 感谢您的更正。我的实际意图也是一样的..共享同一个控制器实例。

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