Question

我将逐步解释这个问题：

我正在尝试从TextArea（在First.fxml中）读取文本，然后将相同的文本写入另一个TextArea（在Second.fxml中）。两个.fxml文件未嵌套。

First.fxml有一个名为“textArea1”的TextArea和一个名为“openStage2”的按钮。
“openStage2”按钮将Second.fxml加载到舞台中并显示它。
Second.fxml有一个名为“textArea2”的TextArea，以及一个名为“showText”的按钮。

我想，“showText”按钮应该从“textArea2”复制文本（无论我写什么）并在“textArea1”中显示它。但我得到NullPointerException（如下所示），我想这意味着目标“textField1”没有初始化。即使已经加载了“textField1”（或First.fxml）。我希望了解为什么会这样。我感谢您的努力。谢谢！

First.java（此类加载主fxml文件）

public class First extends Application {
    @Override
    public void start(Stage stage) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("First.fxml"));
        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }
    public static void main(String[] args) {launch(args);}
}

FirstController.java

public class FirstController implements Initializable {
    private Stage Stage2;
    public TextArea getTextArea1(){
        return textArea1;
    }

    @FXML
    private Button openStage2;
    @FXML
    private TextArea textArea1;

    @Override
    public void initialize(URL url, ResourceBundle rb) {}    

    @FXML
    private void openStage2Action(ActionEvent event) throws IOException {
        Stage2 = new Stage();
        FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("Second.fxml"));
        Object root = fxmlLoader.load();
        Scene scene = new Scene((Parent) root);
        Stage2.setScene(scene);
        SecondController secondController = (SecondController)fxmlLoader.getController();
        secondController.setStage2(Stage2); 
        Stage2.showAndWait(); // Stack Trace: at first.FirstController.openStage2Action(FirstController.java:55)
    }

}

SecondController.java

public class SecondController implements Initializable {
    private Stage stage2;
    private FirstController firstControllerClass;
//    private First firstClass;

    @FXML
    private TextArea textArea2;
    @FXML
    private Button showText;


    public void setStage2(Stage stage2){
        this.stage2 = stage2;
    }

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        // TODO
    }    

    @FXML
    private void showTextAction(ActionEvent event) {
        System.out.println(textArea2.getText()); // this line prints whatever text is typed in textArea2 
        firstControllerClass.getTextArea1().appendText(textArea2.getText()); // this line gives this Exception in Stack Trace: at first.SecondController.showTextAction(SecondController.java:46) 

        //I have also tried to access the TextArea1 by setting up a FXMLLoader and its controller, like this:
//        FirstController firstController = (FirstController)firstClass.getFxmlLoader().getController();
//        firstController.getTextArea1().appendText("\n"+textArea2.getText());

    }

}

堆栈追踪：

Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1449)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:69)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:28)
    at javafx.event.Event.fireEvent(Event.java:171)
    at javafx.scene.Node.fireEvent(Node.java:6867)
    at javafx.scene.control.Button.fire(Button.java:179)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:193)
    at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:336)
    at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:329)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:64)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:28)
    at javafx.event.Event.fireEvent(Event.java:171)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3311)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3151)
    at javafx.scene.Scene$MouseHandler.access$1900(Scene.java:3106)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1563)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2248)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:250)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:173)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:292)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:530)
    at com.sun.glass.ui.View.notifyMouse(View.java:924)
    at com.sun.glass.ui.gtk.GtkApplication.enterNestedEventLoopImpl(Native Method)
    at com.sun.glass.ui.gtk.GtkApplication._enterNestedEventLoop(GtkApplication.java:144)
    at com.sun.glass.ui.Application.enterNestedEventLoop(Application.java:384)
    at com.sun.glass.ui.EventLoop.enter(EventLoop.java:83)
    at com.sun.javafx.tk.quantum.QuantumToolkit.enterNestedEventLoop(QuantumToolkit.java:523)
    at javafx.stage.Stage.showAndWait(Stage.java:397)
    at first.FirstController.openStage2Action(FirstController.java:55)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:75)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:279)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1444)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:69)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:28)
    at javafx.event.Event.fireEvent(Event.java:171)
    at javafx.scene.Node.fireEvent(Node.java:6867)
    at javafx.scene.control.Button.fire(Button.java:179)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:193)
    at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:336)
    at com.sun.javafx.scene.control.skin.SkinBase$4.handle(SkinBase.java:329)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:64)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:217)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:170)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:38)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:37)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:33)
    at javafx.event.Event.fireEvent(Event.java:171)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3311)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3151)
    at javafx.scene.Scene$MouseHandler.access$1900(Scene.java:3106)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1563)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2248)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:250)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:173)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:292)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:530)
    at com.sun.glass.ui.View.notifyMouse(View.java:924)
    at com.sun.glass.ui.gtk.GtkApplication._runLoop(Native Method)
    at com.sun.glass.ui.gtk.GtkApplication$3$1.run(GtkApplication.java:89)
    at java.lang.Thread.run(Thread.java:744)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:75)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:279)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1444)
    ... 101 more
Caused by: java.lang.NullPointerException
    at first.SecondController.showTextAction(SecondController.java:46)
    ... 111 more

Answer 1

不要在控制器中公开UI组件;必要时公开数据。换句话说，从FirstController中删除getTextArea（）方法，并在SecondController中执行以下操作：

public class SecondController {
  private StringProperty text  = new SimpleStringProperty(this, "text", "");;
  @FXML
  private TextArea textArea2 ;
  public StringProperty textProperty() {
    return text ;
  }
  public final String getText() {
    return text.get();
  }
  public final void setText(String text) {
    this.text.set(text);
  }

  // ...

  @FXML 
  private void showTextAction(ActionEvent event) {
    text.set(textArea2.getText());
  }
}

现在在FirstController中只需观察textProperty：

public class FirstController {

  // ...

    @FXML
    private void openStage2Action(ActionEvent event) throws IOException {
        Stage2 = new Stage();
        FXMLLoader fxmlLoader = new FXMLLoader(getClass().getResource("Second.fxml"));
        Object root = fxmlLoader.load();
        Scene scene = new Scene((Parent) root);
        Stage2.setScene(scene);
        SecondController secondController = (SecondController)fxmlLoader.getController();
        secondController.textProperty().addListener(new ChangeListener<String>() {
            @Override
            public void changed(ObservableValue<? extends String> obs, String oldValue, String newValue) {
                textArea1.appendText(newValue);
            }
        });
        Stage2.show();  
    }
}

从一个TextArea（在一个.fxml中）读取并写入另一个TextArea（在另一个.fxml中）。不是嵌套控制器

1 个答案: