Question

我遇到NullPointerException问题。

这是我的控制器：

    public class Controller implements Initializable{

    public Label lbTitle;
    public Label lbAuthor;
    public Label lbChapters;
    public TextField tfTitle;
    public TextField tfAuthor;
    public TextArea taChapters;
    public ListView<Book> listView;

    private void OpenNewWindow(Book book1) throws Exception {

        String selected = listView.getSelectionModel().getSelectedItem().toString();

        FXMLLoader fxmlLoader = new FXMLLoader();
        fxmlLoader.setLocation(getClass().getResource("/zli/BooksFX/NewWindow.fxml"));
        Scene scene = new Scene(fxmlLoader.load(), 400, 400);
        Stage stage = new Stage();

        tfTitle.setText(book1.getTitle());
        tfAuthor.setText(book1.getAuthor());
        taChapters.setText(book1.toStringChapters());

        stage.setTitle(selected);
        stage.setScene(scene);
        stage.show();
    }

    @Override
    public void initialize(URL location, ResourceBundle resources) {
        Chapter chapter1Book1 = new Chapter(1, 100, "First Chapter...");
        Chapter chapter2Book1 = new Chapter(2, 400, "Second Chapter...");
        ArrayList<Chapter> book1Chapters = new ArrayList<>();
        book1Chapters.add(chapter1Book1);
        book1Chapters.add(chapter2Book1);
        Book book1 = new Book("IT: Not the one with the clown", "Stephen ITBerg", book1Chapters);

        Chapter chapter1Book2 = new Chapter(1, 100, "First Chapter...");
        Chapter chapter2Book2 = new Chapter(2, 400, "Second Chapter...");
        ArrayList<Chapter> book2Chapters = new ArrayList<>();
        book1Chapters.add(chapter1Book2);
        book1Chapters.add(chapter2Book2);
        Book book2 = new Book("Z Men", "Stan Lee", book2Chapters);

        Chapter chapter1Book3 = new Chapter(1, 100, "First Chapter...");
        Chapter chapter2Book3 = new Chapter(2, 400, "Second Chapter...");
        ArrayList<Chapter> book3Chapters = new ArrayList<>();
        book1Chapters.add(chapter1Book3);
        book1Chapters.add(chapter2Book3);
        Book book3 = new Book("Captain AlivePool", "Undead Zombie", book3Chapters);

        ObservableList<Book> items = FXCollections.observableArrayList (book1, book2, book3);
        listView.setItems(items);
        listView.setOnMouseClicked(e -> {
            try {
                OpenNewWindow(book1);
            } catch (Exception e1) {
                e1.printStackTrace();
            }
        });

    }
}

这是我的.fxml：

<Pane prefHeight="400.0" prefWidth="400.0" style="-fx-background-color: #1ba77f;" xmlns="http://javafx.com/javafx/8.0.121" xmlns:fx="http://javafx.com/fxml/1" fx:controller="zli.BooksFX.Controller">
    <ListView fx:id="listView" disable="true" opacity="0.0" prefHeight="400.0" prefWidth="400.0" />
   <Label fx:id="lbTitle" layoutX="8.0" layoutY="20.0" prefHeight="27.0" prefWidth="57.0" text="Title: " />
   <Label fx:id="lbAuthor" layoutX="8.0" layoutY="90.0" text="Author: " />
   <TextField text="ert" fx:id="tfTitle" editable="false" layoutX="72.0" layoutY="14.0" prefHeight="39.0" prefWidth="316.0" />
   <TextField text="sdf" fx:id="tfAuthor" editable="false" layoutX="72.0" layoutY="84.0" prefHeight="39.0" prefWidth="316.0" />
   <Label fx:id="lbChapters" layoutX="8.0" layoutY="160.0" text="Chapters: " />
   <TextArea text="sdfs" fx:id="taChapters" editable="false" layoutX="7.0" layoutY="187.0" prefHeight="200.0" prefWidth="383.0" />
</Pane>

这是错误消息：

java.lang.NullPointerException
    at zli.BooksFX.Controller.OpenNewWindow(Controller.java:37)
    at zli.BooksFX.Controller.lambda$initialize$0(Controller.java:73)
    at javafx.base/com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at javafx.base/com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at javafx.base/com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at javafx.base/com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at javafx.base/com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.base/javafx.event.Event.fireEvent(Event.java:198)
    at javafx.graphics/javafx.scene.Scene$ClickGenerator.postProcess(Scene.java:3589)
    at javafx.graphics/javafx.scene.Scene$ClickGenerator.access$8300(Scene.java:3517)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.process(Scene.java:3885)
    at javafx.graphics/javafx.scene.Scene$MouseHandler.access$1300(Scene.java:3604)
    at javafx.graphics/javafx.scene.Scene.processMouseEvent(Scene.java:1874)
    at javafx.graphics/javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2613)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:397)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:295)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.lambda$handleMouseEvent$2(GlassViewEventHandler.java:434)
    at javafx.graphics/com.sun.javafx.tk.quantum.QuantumToolkit.runWithoutRenderLock(QuantumToolkit.java:389)
    at javafx.graphics/com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:433)
    at javafx.graphics/com.sun.glass.ui.View.handleMouseEvent(View.java:556)
    at javafx.graphics/com.sun.glass.ui.View.notifyMouse(View.java:942)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:175)
    at java.base/java.lang.Thread.run(Thread.java:844)

现在，当我想将TextFields和TextAreas的文本（tfTitle，tfAuthor，taChapters）设置为指定的值时，它在Controller的第37行上给出了一个“java.lang.NullPointerException”，这就是这个：

tfTitle.setText(book1.getTitle());

并且有关您的信息：“Book”是章节的存储类。

因为它被要求，我的另一个.fxml：

<GridPane xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/2.2"
          fx:controller="zli.BooksFX.Controller">
<ListView fx:id="listView" prefWidth="400" />
</GridPane>

Answer 1

可能你没有初始化你的Texfield。在tfTitle声明

上使用@FXML注释

@FXML
public TextField tfTitle;

其他领域也是如此。

Answer 2

您使用类Controller作为两个不同fxml文件的控制器。

第一个只声明listView但不声明tfTitle，tfAuthor和taChapters因此您在tfTitle.setText(book1.getTitle());

处获得了NullPointerException

在OpenNewWindow中加载第二个fxml文件时，您还会创建一个新的Controller对象。

现在您可以重复使用fxmlLoader.setController(this);的第一个控制器并从fx:controller="zli.BooksFX.Controller"删除NewWindow.fxml（不要这样做，因为您会遇到类似的问题< /强>）。

或者为每个fxml文件创建两个独立的控制器，并在控制器之间传递书籍。

对于第二个控制器，您需要以下内容：

public void setBook(Book book) { tfTitle.setText(book.getTitle()); tfAuthor.setText(book.getAuthor()); taChapters.setText(book.toStringChapters()); }

在((BookDetailController)fxmlLoader.getController()).setBook(book1);
之后使用fxmlLoader.load()传递该书

在fxml中使用Textfield的NullPointerException

2 个答案: