尝试在 JavaFX 中切换场景时出现 NullPointerException
NullPointerException when trying to switch scenes in JavaFX
我试图在我的 GUI 中单击一个按钮并切换到同一阶段中的一个单独场景。这看起来很简单，除了当我单击按钮时我在控制器 class 中得到一个 NullPointerException。该按钮用 fx:id="settings" 和 onAction="#handleSettings" 编写在 FXML 中。 handleSettings 方法位于控制器中。
我试图通过在顶部写入 [=17=] 将 primaryStage 从 Main.java 导入到 Controller.java，但我显然遗漏了一些东西。 GUI 启动正常，但在单击“设置”按钮时发生错误。下面是完整的代码以及错误。错误指向这一行：primaryStage.setScene(sceneSettings);
我是否需要以某种方式对 primaryStage 使用 get/set？显然，我的技能处于 1 级。有什么帮助，谢谢。
Main.java
import ...
public class Main extends Application {
public static void main(String[] args) {
launch(args);
}
@Override
public void start(Stage primaryStage) throws Exception{
Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
Scene scene = new Scene(root, 450, 580);
scene.getStylesheets().add("styleMain.css");
primaryStage.initStyle(StageStyle.UTILITY);
primaryStage.setTitle("Scene 1");
primaryStage.setScene(scene);
primaryStage.show();
}
}
Controller.java
import ...
public class Controller{
Scene sceneSettings;
public Stage primaryStage;
public void handleFieldData(){
System.out.println("field data");
}
public void handleComments(){
System.out.println("comments");
}
@FXML
public void handleSettings() throws IOException {
Button button2 = new Button("settings");
StackPane layout = new StackPane();
layout.getChildren().add(button2);
sceneSettings = new Scene(layout, 450, 580);
primaryStage.setScene(sceneSettings);
primaryStage.setTitle("Settings Menu");
primaryStage.show();
}
}
sample.fxml
<GridPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.40" xmlns:fx="http://javafx.com/fxml/1"
fx:controller="Controller">
<columnConstraints>
<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="20.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="20.0" vgrow="SOMETIMES" />
</rowConstraints>
<padding>
<Insets bottom="10.0" left="70.0" right="70.0" top="10.0" />
</padding>
<children>
<Button fx:id="comments" mnemonicParsing="false" onAction="#handleComments" GridPane.columnIndex="1" GridPane.halignment="CENTER" GridPane.valignment="CENTER">
<padding>
<Insets bottom="15.0" left="50.0" right="50.0" top="90.0" />
</padding>
</Button>
<Button fx:id="settings" mnemonicParsing="false" onAction="#handleSettings" text="Settings" GridPane.columnIndex="1" GridPane.halignment="CENTER" GridPane.rowIndex="1" GridPane.valignment="CENTER">
<padding>
<Insets bottom="15.0" left="30.0" right="30.0" top="15.0" />
</padding>
</Button>
<Label text="Comments" GridPane.columnIndex="1" GridPane.halignment="CENTER" GridPane.valignment="TOP" />
</children>
</GridPane>
错误：
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:8411)
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.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.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$MouseHandler.access00(Scene.java:3485)
at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1762)
at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2494)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:352)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent5(GlassViewEventHandler.java:388)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null9(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:497)
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:497)
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 Controller.handleSettings(Controller.java:38)
... 58 more
加载控制器时，您需要将其传递给初级阶段。
public class Controller{
Scene sceneSettings;
public Stage primaryStage;
...
public void setPrimaryStage(Stage stage) {
this.primaryStage = stage;
}
...
主要
@Override
public void start(Stage primaryStage) throws Exception{
FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("sample.fxml"));
Parent root = loader.load();
loader.getController().setPrimaryStage(primaryStage);
Scene scene = new Scene(root, 450, 580);
scene.getStylesheets().add("styleMain.css");
primaryStage.initStyle(StageStyle.UTILITY);
primaryStage.setTitle("Scene 1");
primaryStage.setScene(scene);
primaryStage.show();
...
我试图在我的 GUI 中单击一个按钮并切换到同一阶段中的一个单独场景。这看起来很简单，除了当我单击按钮时我在控制器 class 中得到一个 NullPointerException。该按钮用 fx:id="settings" 和 onAction="#handleSettings" 编写在 FXML 中。 handleSettings 方法位于控制器中。
我试图通过在顶部写入 [=17=] 将 primaryStage 从 Main.java 导入到 Controller.java，但我显然遗漏了一些东西。 GUI 启动正常，但在单击“设置”按钮时发生错误。下面是完整的代码以及错误。错误指向这一行：primaryStage.setScene(sceneSettings);
我是否需要以某种方式对 primaryStage 使用 get/set？显然，我的技能处于 1 级。有什么帮助，谢谢。
Main.java
import ...
public class Main extends Application {
public static void main(String[] args) {
launch(args);
}
@Override
public void start(Stage primaryStage) throws Exception{
Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
Scene scene = new Scene(root, 450, 580);
scene.getStylesheets().add("styleMain.css");
primaryStage.initStyle(StageStyle.UTILITY);
primaryStage.setTitle("Scene 1");
primaryStage.setScene(scene);
primaryStage.show();
}
}
Controller.java
import ...
public class Controller{
Scene sceneSettings;
public Stage primaryStage;
public void handleFieldData(){
System.out.println("field data");
}
public void handleComments(){
System.out.println("comments");
}
@FXML
public void handleSettings() throws IOException {
Button button2 = new Button("settings");
StackPane layout = new StackPane();
layout.getChildren().add(button2);
sceneSettings = new Scene(layout, 450, 580);
primaryStage.setScene(sceneSettings);
primaryStage.setTitle("Settings Menu");
primaryStage.show();
}
}
sample.fxml
<GridPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8.0.40" xmlns:fx="http://javafx.com/fxml/1"
fx:controller="Controller">
<columnConstraints>
<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="20.0" vgrow="SOMETIMES" />
<RowConstraints minHeight="10.0" prefHeight="20.0" vgrow="SOMETIMES" />
</rowConstraints>
<padding>
<Insets bottom="10.0" left="70.0" right="70.0" top="10.0" />
</padding>
<children>
<Button fx:id="comments" mnemonicParsing="false" onAction="#handleComments" GridPane.columnIndex="1" GridPane.halignment="CENTER" GridPane.valignment="CENTER">
<padding>
<Insets bottom="15.0" left="50.0" right="50.0" top="90.0" />
</padding>
</Button>
<Button fx:id="settings" mnemonicParsing="false" onAction="#handleSettings" text="Settings" GridPane.columnIndex="1" GridPane.halignment="CENTER" GridPane.rowIndex="1" GridPane.valignment="CENTER">
<padding>
<Insets bottom="15.0" left="30.0" right="30.0" top="15.0" />
</padding>
</Button>
<Label text="Comments" GridPane.columnIndex="1" GridPane.halignment="CENTER" GridPane.valignment="TOP" />
</children>
</GridPane>
错误：
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$ControllerMethodEventHandler.handle(FXMLLoader.java:1657)
at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
at javafx.event.Event.fireEvent(Event.java:198)
at javafx.scene.Node.fireEvent(Node.java:8411)
at javafx.scene.control.Button.fire(Button.java:185)
at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.handle(BehaviorSkinBase.java:96)
at com.sun.javafx.scene.control.skin.BehaviorSkinBase.handle(BehaviorSkinBase.java:89)
at com.sun.javafx.event.CompositeEventHandler$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.access00(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:352)
at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent5(GlassViewEventHandler.java:388)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
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$null9(WinApplication.java:191)
at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
... 48 more
Caused by: java.lang.NullPointerException
at Controller.handleSettings(Controller.java:38)
... 58 more
加载控制器时，您需要将其传递给初级阶段。
public class Controller{
Scene sceneSettings;
public Stage primaryStage;
...
public void setPrimaryStage(Stage stage) {
this.primaryStage = stage;
}
...
主要
@Override
public void start(Stage primaryStage) throws Exception{
FXMLLoader loader = new FXMLLoader();
loader.setLocation(getClass().getResource("sample.fxml"));
Parent root = loader.load();
loader.getController().setPrimaryStage(primaryStage);
Scene scene = new Scene(root, 450, 580);
scene.getStylesheets().add("styleMain.css");
primaryStage.initStyle(StageStyle.UTILITY);
primaryStage.setTitle("Scene 1");
primaryStage.setScene(scene);
primaryStage.show();
...