正确加载并注释了所有内容后，setText()上出现NullPointer异常

问题描述

我收到以下异常，试图从start()方法在带注释的标签上调用setText().我已经看到了类似的问题，但是它对那个人不起作用的原因是因为他的标签没有注释，而我的标签没有注释.

I'm receiving the following exception trying to call setText() on my annotated label, from the start() method. I've seen a similar question, but the reason why it didn't work for that person is because his label isn't annotated, while mine is.

java.lang.NullPointerException
at io.github.blubdalegend.openbravery.OpenBravery.applyBuild(OpenBravery.java:67)
at io.github.blubdalegend.openbravery.OpenBravery.start(OpenBravery.java:58)
at com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$162(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$runAndWait$175(Unknown Source)
at com.sun.javafx.application.PlatformImpl.lambda$null$173(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at com.sun.javafx.application.PlatformImpl.lambda$runLater$174(Unknown Source)
at com.sun.glass.ui.InvokeLaterDispatcher$Future.run(Unknown Source)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.lambda$null$148(Unknown Source)
at java.lang.Thread.run(Unknown Source)

这是我的主要课程:

public class OpenBravery extends Application implements Initializable {

    @FXML
    private Button rerollButton;

    @FXML
    private Label champL;

    public static void main(String[] args) {
        System.out.println("Downloading files from Dropbox...");
        updateFiles();
        System.out.println("Download complete!");
        Application.launch(OpenBravery.class, (java.lang.String[]) null);

    }

    @Override
    public void initialize(URL location, ResourceBundle resources) {
        rerollButton.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent event) {

            }
        });
    }

    private static void updateFiles() {
        FileManager fm = new FileManager();
        fm.downloadChamps();
        fm.downloadItems();
    }

    @Override
    public void start(Stage stage) {
        try {
            Pane pane = (Pane) FXMLLoader.load(OpenBravery.class.getResource("build.fxml"));
            Scene scene = new Scene(pane);
            stage.setScene(scene);
            stage.setTitle("OpenBravery");
            stage.setResizable(false);
            applyBuild();
            stage.show();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void applyBuild() {
        Build build = new Build();
        champL.setText(build.getChamp());
    }

}

我的 build.fxml 开始是这样的:

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

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


<Pane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity"
    minWidth="-Infinity" prefHeight="297.0" prefWidth="362.0"
    xmlns="http://javafx.com/javafx/8" xmlns:fx="http://javafx.com/fxml/1"
    fx:controller="io.github.blubdalegend.openbravery.OpenBravery">
    <children>
        <Label layoutX="14.0" layoutY="14.0" text="Your build:">
            <font>
                <Font size="32.0" />
            </font>
        </Label>
        <Label fx:id="champL" layoutX="14.0" layoutY="61.0" prefHeight="32.0"
            prefWidth="288.0" text="Label">
            <font>
                <Font size="17.0" />
            </font>
        </Label>

那我在这里想念什么?

推荐答案

您不是在控制器上调用applyBuild()，而是在应用程序实例上调用它. @FXML注释的字段仅在控制器中初始化.最好使控制器和应用程序分开的类，以避免这种混淆.创建Application类的两个实例也是不好的做法.

You're not calling applyBuild() on the controller, you're calling it on the application instance. The @FXML-annotated fields are only initialized in the controller. It's much better to make the controller and the application separate classes, to avoid this kind of confusion. It is also bad practice to create two instances of the Application class.

写一个单独的类作为控制器:不要使用Application子类作为控制器类.

Write a separate class as the controller: do not use the Application subclass as the controller class.

这篇关于正确加载并注释了所有内容后，setText()上出现NullPointer异常的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！