如何更改JavaFX场景中标签的值？我试图想办法在按钮点击时更改标签的文本值，但它不起作用。 我为按钮和标签设置了 fx：id 并设置了它们的控制器（ CPCS305_JAVAFX_FXML ，类本身。该按钮也链接到 handleButtonAction2 （）功能。
public class CPCS305_JAVAFX_FXML extends Application {
@FXML
Scene scene;
Stage stage;
Label main_label
Button login_button;
AnchorPane root;
@Override
public void start(Stage stage) throws Exception {
root = FXMLLoader.load(getClass().getResource("FXMLDocument.fxml"));
scene = new Scene(root);
stage.setScene(scene);
stage.show();
@FXML
private void handleButtonAction2(ActionEvent event) throws IOException, Exception {
main_label.setText("Hello World");
}
public static void main(String[] args) {
launch(args);
}}
错误报告是：
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$354(GlassViewEventHandler.java:417)
at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:416)
at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
at com.sun.glass.ui.View.notifyMouse(View.java:937)Caused by: java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
... 45 moreCaused by: java.lang.NullPointerException
at cpcs305_javafx_fxml.CPCS305_JAVAFX_FXML.handleButtonAction2(CPCS305_JAVAFX_FXML.java:64)
... 55 more
我有2个其他FXML文件及其控制器，功能，但我将其留待以后使用。我想解决一个场景中无法通信的问题，然后转到多个场景。
对新学员的任何想法？
编辑：此课程的FXML文件 here
EDIT2：已修复。问题是错误的进口。很抱歉给大家带来麻烦，但感谢您的支持。
答案 0 :(得分：0)
@FXML注释应该只在FXML文件中定义的元素之上，例如标签，按钮和锚定窗格。
尝试一下，让我们看看。
答案 1 :(得分：0)
您需要使用@FXML注释每个实例字段，以便由FXML Loader分配。如果不这样做，值将保持null。此外，FXML加载程序需要知道哪个对象是控制器。您已在fx:controller="cpcs305_javafx_fxml.CPCS305_JAVAFX_FXML"中在FXML中指定了这一点，但这意味着FXMLLoader将创建您的类的第二个实例，因为它确实有一种方法可以将它连接到您当前的类。您可以通过指定具有setController的控制器，通过setControllerFactory指定控制器工厂，或者通过将参数传递给采用静态函数的更多参数来执行此操作。
由于您已在FXML中定义了类，因此需要使用控制器工厂。 FXML加载器将要求控制器工厂实例化它作为参数提供的类的对象。如果您想使用已经实例化的类，只需忽略类参数并返回this。
public class CPCS305_JAVAFX_FXML extends Application {
@FXML // because there is a fx:id="main_label" in the FXML
private Label main_label; // Java naming convention would be mainLabel
@FXML // because there is a fx:id="login_button" in the FXML
private Button login_button; // Java naming convention would be loginButton
@Override
public void start(Stage stage) throws Exception {
FXMLLoader loader = new FXMLLoader(getClass().getResource("FXMLDocument.fxml"));
loader.setControllerFactory(controllerClass -> this); // 'this' object will be the controller.
Parent root = loader.load();
Scene scene = new Scene(root);
stage.setScene(scene);
stage.show();
}
@FXML // because there is a onAction="#handleButtonAction" in the FXML
private void handleButtonAction() { // parameter is optional
main_label.setText("Hello World");
}
}
答案 2 :(得分：0)
我在Scene Builder上使用的按钮/标签上使用了错误的导入。我修复了那些进口，一切正常。