javafx TextArea 抛出 NullPointerException

Question

我总是收到 NullPointerException。有什么想法我做错了吗？我查了一下是TextArea引起的。但我给出了 ID 并识别了 Controller 。我不知道为什么它还没有看到它？!

public class YoutubeController extends Application{

@FXML
 TextArea area;


public static void main(String[] args) throws Exception { launch(args); }

@Override
public void start(Stage primaryStage) throws Exception {


    Parent root= FXMLLoader.load(getClass().getResource("/youtube.fxml"));
    Scene scene = new Scene(root);
    primaryStage.setScene(scene);
    primaryStage.setResizable(false);
    primaryStage.setTitle("A.I.T YOUTUBE SEARCH");
    primaryStage.show();

}

@FXML
public void lyricsClicked(){
    Parent root;
    try {

        root = FXMLLoader.load(getClass().getResource("/lyrics.fxml"));
        Scene scene = new Scene(root);
        Stage stage = new Stage();
        stage.setScene(scene);
        stage.setResizable(false);
        stage.setTitle("Lyrics");
        area.setText(lyrics); // i checked lyrics and it is full of data
        stage.show();


    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

这是 fxml 文件。

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

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

<AnchorPane prefHeight="474.0" prefWidth="610.0" xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1" fx:controller="youtube.YoutubeController" >
   <children>
      <TextArea fx:id="area" editable="false" layoutX="194.0" layoutY="64.0" prefHeight="474.0" prefWidth="610.0" AnchorPane.bottomAnchor="0.0" AnchorPane.leftAnchor="0.0" AnchorPane.rightAnchor="0.0" AnchorPane.topAnchor="0.0" />
   </children>
</AnchorPane>

堆栈跟踪:

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:8216)
    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$MouseHandler.process(Scene.java:3724)
    at javafx.scene.Scene$MouseHandler.access$1500(Scene.java:3452)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1728)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2461)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:348)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:273)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:382)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:553)
    at com.sun.glass.ui.View.notifyMouse(View.java:925)
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:483)
    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:483)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1759)
    ... 43 more
Caused by: java.lang.NullPointerException
    at youtube.YoutubeController.lyricsClicked(YoutubeController.java:273)
    ... 53 more

Answer 1

空指针是由区域中的空值引起的，而不是由歌词中的空值引起的。与歌词.fxml 相关的组件与 youtube.fxml 是同一类，但它有不同的实例!所以你不能将 setText() 中的值传递给它。

您应该从它的实例中获取歌词组件和访问区域:

public void setAreaText(String text) {
    area.setText(text);
}

@FXML
public void lyricsClicked() {
    Parent root;
    try {

        //root = FXMLLoader.load(getClass().getResource("/lyrics.fxml"));
        URL location = getClass().getResource("/lyrics.fxml");
        FXMLLoader fxmlLoader = new FXMLLoader();
        fxmlLoader.setLocation(location);
        fxmlLoader.setBuilderFactory(new JavaFXBuilderFactory());
        root = fxmlLoader.load(location.openStream());
        YoutubeController contr = fxmlLoader.getController();
        contr.setAreaText(lyrics);

        Scene scene = new Scene(root);
        Stage stage = new Stage();
        stage.setScene(scene);
        stage.setResizable(false);
        stage.setTitle("Lyrics");
        stage.show();

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}