按下按钮时javaFX应用程序线程中的InvocationTargetException

我刚刚开始在FXML中开发RPG游戏。基本上，我现在要做的是在创建角色时设置一种改变ui中统计信息的方法。按下按钮时，字符强度（ST）的值应更改为微调器中的值。然后标签的文本应更改为该数字。项目正在运行，但当我单击按钮时，会收到此错误消息

objc[6393]: Class JavaLaunchHelper is implemented in both ``    
/Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/bin/java (0x10a51a4c0) and /Library/Java/JavaVirtualMachines/jdk1.8.0_131.jdk/Contents/Home/jre/lib/libinstrument.dylib (0x10b5854e0). One of the two will be used. Which one is undefined.
method called
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:1771)
    ... 45 more
Caused by: java.lang.NullPointerException
    at sample.Controller.onSTButtonPressed(Controller.java:22)
    ... 55 more

Process finished with exit code 0

控制器

package sample;
import javafx.fxml.FXML;
import javafx.scene.control.Spinner;
import javafx.scene.control.Button;
import javafx.scene.control.Label;

import java.awt.event.ActionEvent;

public class Controller {
    @FXML
    Spinner stSpinner;
    @FXML
    Button stButton;
    @FXML
    Label stCount;
    StatHolder statHolder;

    @FXML
    public void onSTButtonPressed(){
        System.out.println("method called");
        statHolder.setST((Integer) stSpinner.getValue());
        stCount.setText(String.valueOf(statHolder.getST()));
        System.out.print("ST is now " + statHolder.getST());

    }
}

主要

sample.fxml

<?import javafx.geometry.Insets?>
<?import javafx.scene.layout.GridPane?>

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.Spinner?>
<?import javafx.scene.layout.HBox?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.control.SpinnerValueFactory.IntegerSpinnerValueFactory?>
<GridPane fx:controller="sample.Controller"
          xmlns:fx="http://javafx.com/fxml" alignment="TOP_LEFT" hgap="10" vgap="10">
    <HBox>
        <VBox>
            <HBox>
                <Label text="ST: "/>
                <Label text="10" fx:id="stCount"/>
                <Spinner min="0" max="50" initialValue="10" fx:id="stSpinner" />
                <Button text="change" onAction="#onSTButtonPressed" fx:id="stButton"/>


            </HBox>
            <HBox>
                <Label text ="DX"/>


            </HBox>

        </VBox>
        <VBox>

        </VBox>
    </HBox>

---

如果查看stacktrace的底部，您将看到从

onSTButtonPressed

方法中抛出的NullPointerException。下一步是找出此方法中的

null

。看起来statHolder为null。

<?import javafx.geometry.Insets?>
<?import javafx.scene.layout.GridPane?>

<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.control.Spinner?>
<?import javafx.scene.layout.HBox?>
<?import javafx.scene.layout.VBox?>
<?import javafx.scene.control.SpinnerValueFactory.IntegerSpinnerValueFactory?>
<GridPane fx:controller="sample.Controller"
          xmlns:fx="http://javafx.com/fxml" alignment="TOP_LEFT" hgap="10" vgap="10">
    <HBox>
        <VBox>
            <HBox>
                <Label text="ST: "/>
                <Label text="10" fx:id="stCount"/>
                <Spinner min="0" max="50" initialValue="10" fx:id="stSpinner" />
                <Button text="change" onAction="#onSTButtonPressed" fx:id="stButton"/>


            </HBox>
            <HBox>
                <Label text ="DX"/>


            </HBox>

        </VBox>
        <VBox>

        </VBox>
    </HBox>

public class StatHolder {
    private int ST;

    public void setST(int ST) {
        this.ST = ST;
    }

    public int getST() {
        return ST;
    }
    public String getSTString(){
        String output = "" + ST;
        return output;
    }
}