InvocationTargetException 和 NullPointerException JavaFX

Question

我正在使用 SceneBuilder 创建一个 GUI，以通过文本字段从用户那里获取信息。当我单击 calcPremiumButton 按钮时，我得到了这个 InvocationTargetException 和堆栈跟踪。

> 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:54)
    at javafx.event.Event.fireEvent(Event.java:198)
    at javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3470)
    at javafx.scene.Scene$ClickGenerator.access$8100(Scene.java:3398)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3766)
    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$MouseEventNotification.run(GlassViewEventHandler.java:352)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:275)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$355(GlassViewEventHandler.java:388)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:387)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.lambda$null$149(WinApplication.java:191)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1771)
    ... 31 more
Caused by: java.lang.NullPointerException
    at PremiumCalculator.calculatePremiumAction(PremiumCalculator.java:52)
    ... 41 more

我已经将NullPointerException 追溯到setOnMouseClicked 方法。

    import java.lang.*;
    import java.util.*;
    import java.awt.*;
    import javafx.event.Event;
    import javafx.event.EventHandler;
    import javafx.scene.input.MouseEvent;
    import javafx.fxml.FXML;
    import javafx.scene.control.Button;
    import javafx.scene.control.Label;
    import javafx.scene.control.TextField;

    /*** PremiumCalculator ***/
    public class PremiumCalculator extends LifeInsurancePolicy
    {   
       @FXML
       private static TextField coverage;

      @FXML
      private static TextField number;

      @FXML
      private static TextField lName;

      @FXML
      private static TextField a;

      @FXML
      private static TextField fName;

      @FXML
      private static TextField s;

      @FXML
      private static TextField pName;

      @FXML
      private static Label outputLabel;

      @FXML
      private static Button calcPremiumButton;

      @FXML
      private static TextField w;

      @FXML
      private static TextField h;

      @FXML
      private void calculatePremiumAction()
      {
          /*** setOnMouseClicked ***/     
          PremiumCalculator.calcPremiumButton.setOnMouseClicked(new EventHandler<MouseEvent>()
          {
             /*** handle ***/
             public void handle(MouseEvent mouseEvent)
             {
                /*** Get information from the GUI text boxes ***/
                String number = PremiumCalculator.number.getText();
                String pName = PremiumCalculator.pName.getText();
                String fName = PremiumCalculator.fName.getText();
                String lName = PremiumCalculator.lName.getText();
                String a = PremiumCalculator.a.getText();
                String s = PremiumCalculator.s.getText();
                String h = PremiumCalculator.h.getText();
                String w = PremiumCalculator.w.getText();
                String coverage = PremiumCalculator.coverage.getText();

                /*** Convert Strings ***/
                int num = Integer.parseInt(number);
                int ag = Integer.parseInt(a);
                double he = Double.parseDouble(h);
                double we = Double.parseDouble(w);
                double c = Double.parseDouble(coverage);
                double lifeInsurance = Double.parseDouble(lifeInsurancePolicyString);

                /*** Instantiate a new LifeInsurancePolicy object ***/
                LifeInsurancePolicy customer = new LifeInsurancePolicy(num, pName, fName, lName, ag, s, he, we);

                /*** Call an instance of the LifeInsurancePolicy object to get the life insurance cost ***/
                double lifeInsuranceAmount = customer.calculateLifeInsurance(s, bmi);

                /*** Display the life insurance cost ***/
                outputLabel.setText("Life Insurance Cost: " + lifeInsuranceAmount);
             }   
             /*** End handle ***/
          });
          /*** End setOnMouseClicked ***/        
       }                
    }
    /*** End PremiumCalculator ***/

我不确定我收到异常是因为setOnMouseClicked 方法还是由其他原因引起的。任何帮助将不胜感激！

Answer 1

SceneBuilder 允许某人编辑 FXML 文件。这些文件描述了一个视图、一个界面，就像 HTML 文件对网页所做的那样。

问题是您试图在函数private void calculatePremiumAction() 内的按钮上放置一个事件。 但是这个函数已经是一个事件函数（因为它上面有@FXML），你只需要将它与你在SceneBuilder中的按钮绑定。

Here 一个你应该怎么做的例子。

Answer 2

首先使用SceneBuilder 让您的生活更轻松。它将为您创建 FXML。

其次在代码部分使用SceneBuilder的'On Action'字段直接在控制器中命名按钮的处理方法，而不用匿名类作为参数的笨拙的setOnMouseClicked()调用。在 FXML 中应该是这样的：

<Button onAction="#onBtnClicked" text="Text on button" />

在控制器中：

@FXML
void onBtnClicked(ActionEvent event) {
   // your handling code goes here
}

然后FXMLLoader 可用于从 *.fxml 加载您的 javaFx Node 并将所有 @FXML 注释字段注入您的 UI 控制器实例。

URL fxmlLocation = new URL("url to your fxml");
FXMLLoader loader = new FXMLLoader(fxmlLocation);
PremiumCalculator controller = new PremiumCalculator();
loader.setController(controller);
// now load and inject  
Node javafxNode = loader.load();

将javafxNode 添加到您的场景中，使其成为可见场景图的一部分。这应该可以解决问题。另外，您在控制器中的代码将更加简单易懂。