我能'；t将JavaFX对象添加到第二个场景中，而不会获得空指针异常

我对Javafx比较陌生，如果这个问题很琐碎，我很抱歉。我目前正在使用IntelliJ与javafx一起工作，因此我使用场景生成器和控制器类来控制场景。我目前有2.fxml文件，我可以通过每个场景上的按钮在它们之间切换。这是正确的。现在，我正在尝试在用户切换到第二个场景后将ImageView添加到该场景

我试过这个：

但它给了我一个空指针异常。我认为这与图像加载不正确有关，所以我尝试只添加一个按钮，但得到了相同的错误。我意识到这与向新场景添加任何对象有关。有没有理由我不能添加任何新元素？我相信“null”对象是我试图添加新元素的窗格，但它不应该为null，因为我已经初始化了它，并且它与.fxml文件中的fx:id相同

这是我的整个控制器类：

import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.scene.Node;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.AnchorPane;
import javafx.scene.layout.GridPane;
import javafx.stage.Stage;

import java.io.IOException;
import java.util.ArrayList;

public class Controller {
    public GridPane panes1;
    public AnchorPane panes2;
    public Button switcher1;
    public Button switcher2;

    private int numplayers;

    ArrayList<Card> player1 = new ArrayList();
    ArrayList<Card> player2 = new ArrayList();
    ArrayList<Card> player3 = new ArrayList();
    ArrayList<Card> player4 = new ArrayList();

    @FXML
    public void toScene2(ActionEvent event) throws IOException {
        Stage s = (Stage) ((Node)event.getSource()).getScene().getWindow();
        Parent gameroot = FXMLLoader.load(getClass().getResource("game.fxml"));
        Scene game = new Scene(gameroot, 900,825);
        s.setScene(game);

        Image c = new Image("/PNG/1C.png");
        ImageView b = new ImageView();
        b.setImage(c);
        panes2.getChildren().add(b);

        //Deck deck = new Deck();
        //deck.initialize();
        //deck.shuffle();

        //for(Card a: deck.cards){
            //panes2.getChildren().add(a.show);
        //}


    }

    @FXML
    public void toScene1(ActionEvent event) throws IOException {
        Stage s = (Stage) ((Node)event.getSource()).getScene().getWindow();
        Parent gameroot = FXMLLoader.load(getClass().getResource("ercmenu.fxml"));
        Scene game = new Scene(gameroot, 900,825);
        s.setScene(game);

    }
}

以下是第一个场景的.fxml：

<?xml version="1.0" encoding="UTF-8"?>

<?import javafx.scene.*?>
<?import javafx.scene.text.*?>
<?import javafx.scene.control.*?>
<?import java.lang.*?>
<?import javafx.scene.layout.*?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.control.Label?>

<?import sample.Card?>
<GridPane fx:id="panes1" alignment="CENTER" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="527.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.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="30.0" vgrow="SOMETIMES" />
    <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
    <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
    <RowConstraints minHeight="10.0" prefHeight="30.0" vgrow="SOMETIMES" />
  </rowConstraints>
   <children>
      <Button fx:id="switcher1" alignment="CENTER" contentDisplay="CENTER" mnemonicParsing="false" onAction="#toScene2" prefHeight="52.0" prefWidth="267.0" text="Switch to 2" GridPane.rowIndex="2">
         <font>
            <Font name="System Bold" size="39.0" />
         </font>
         <cursor>
            <Cursor fx:constant="OPEN_HAND" />
         </cursor>
      </Button>
      <Button mnemonicParsing="false" prefHeight="37.0" prefWidth="264.0" text="Button" GridPane.rowIndex="1" />
      <Button mnemonicParsing="false" prefHeight="38.0" prefWidth="264.0" text="Play" />
      <Button mnemonicParsing="false" text="Button" GridPane.rowIndex="3" />
   </children>
</GridPane>

<?xml version="1.0" encoding="UTF-8"?>

<?import java.lang.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.image.*?>
<?import javafx.scene.layout.*?>

<AnchorPane fx:id="panes2" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
      <Button fx:id="switcher2" layoutX="12.0" layoutY="13.0" mnemonicParsing="false" onAction="#toScene1" prefHeight="4.0" prefWidth="60.0" text="Back" />
      <ImageView fitHeight="105.0" fitWidth="239.0" layoutX="403.0" layoutY="47.0" pickOnBounds="true" preserveRatio="true" rotate="45.0" AnchorPane.rightAnchor="-20.192703247070312" AnchorPane.topAnchor="47.0">
         <image>
            <Image url="@../PNG/back_cards-07.png" />
         </image>
      </ImageView>
   </children>
</AnchorPane>

---

谢谢大家!

第一步是找出哪个对象为null，如中所述。第二个是分析，为什么那个特定的字段是空的。为了得到帮助，你必须提供一个-应用程序，控制器，fxml，stacktrace-来演示这个问题。我添加了所有内容以使其可复制，并且AnchorPane是空的。我只是不知道为什么它是空的。你不能在不同的fxml中使用同一个控制器-加载会创建一个新实例，它只注入在该fxml中声明的字段，而将其他字段保留为空“我添加了所有要重现的内容”执行它所需的所有资源（例如图像）都应该可用。如果必须使用图像来演示问题的使用。否则，请移除它们。

<?xml version="1.0" encoding="UTF-8"?>

<?import java.lang.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.image.*?>
<?import javafx.scene.layout.*?>

<AnchorPane fx:id="panes2" maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="sample.Controller">
   <children>
      <Button fx:id="switcher2" layoutX="12.0" layoutY="13.0" mnemonicParsing="false" onAction="#toScene1" prefHeight="4.0" prefWidth="60.0" text="Back" />
      <ImageView fitHeight="105.0" fitWidth="239.0" layoutX="403.0" layoutY="47.0" pickOnBounds="true" preserveRatio="true" rotate="45.0" AnchorPane.rightAnchor="-20.192703247070312" AnchorPane.topAnchor="47.0">
         <image>
            <Image url="@../PNG/back_cards-07.png" />
         </image>
      </ImageView>
   </children>
</AnchorPane>

/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/bin/java "-javaagent:/Users/nicholaskoran/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.6015.11/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=50423:/Users/nicholaskoran/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.6015.11/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/lib/tools.jar:/Users/nicholaskoran/IdeaProjects/Q2ERC/out/production/Q2ERC sample.Main
objc[13364]: Class JavaLaunchHelper is implemented in both /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/bin/java (0x10c3f64c0) and /Library/Java/JavaVirtualMachines/jdk1.8.0_111.jdk/Contents/Home/jre/lib/libinstrument.dylib (0x10c4704e0). One of the two will be used. Which one is undefined.
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$MouseEventNotification.run(GlassViewEventHandler.java:380)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:294)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$354(GlassViewEventHandler.java:416)
    at com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:415)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:555)
    at com.sun.glass.ui.View.notifyMouse(View.java:937)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1769)
    ... 45 more
Caused by: java.lang.NullPointerException
    at sample.Controller.toScene2(Controller.java:39)
    ... 55 more