JavaFX RandomNameChooser 项目 - NullPointerException 错误(可能是一个简单的修复，但我仍然很困惑)

Question

我正在制作一个程序，它获取文本输入并选择随机行。

但是，我的代码有问题。当通过与其关联的 GUI 按钮调用方法“randomizeButton”时，我的 ArrayList 出现 NullPointerException。

代码:

RandomNameChooser.java

package randomnamechooser;

import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;

/**
 *
 * @author Mally
 */
public class RandomNameChooser extends Application {

    @Override
    public void start(Stage stage) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("FXMLDocument.fxml"));

        Scene scene = new Scene(root);
        stage.setTitle("Random Name Chooser");
        stage.setScene(scene);
        stage.show();
    }

    /**
     * The main() method is ignored in correctly deployed JavaFX application.
     * main() serves only as fallback in case the application can not be
     * launched through deployment artifacts, e.g., in IDEs with limited FX
     * support. NetBeans ignores main().
     *
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        launch(args);
    }

}

FXMLDocument.fxml

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

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

<AnchorPane prefHeight="200.0" prefWidth="200.0" xmlns:fx="http://javafx.com/fxml/1" xmlns="http://javafx.com/javafx/2.2" fx:controller="randomnamechooser.FXMLDocumentController">
  <children>
    <Button layoutX="31.0" layoutY="46.0" mnemonicParsing="false" onAction="#loadButton" text="Load" />
    <Button layoutX="98.0" layoutY="46.0" mnemonicParsing="false" onAction="#randomizeButton" text="Randomize" textAlignment="JUSTIFY" />
    <Label layoutX="74.0" layoutY="92.0" text="Winner is:" />
    <Label id="label" layoutX="84.0" layoutY="117.0" text="" />
  </children>
</AnchorPane>

FXMLDocumentController.java

package randomnamechooser;

import java.awt.Label;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.ResourceBundle;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.stage.FileChooser;

/**
 *
 * @author Mally
 */
public class FXMLDocumentController implements Initializable {

    List<String> list = new ArrayList<String>();

    @FXML
    private Label label;

    @FXML
    private void loadButton() {
        FileChooser fileChooser = new FileChooser();
        fileChooser.setTitle("Select File");
        //Set extention filter
        fileChooser.getExtensionFilters().addAll(
                new FileChooser.ExtensionFilter("Text Files", "*.txt"));
        //Show open file dialog for one file
        File file = fileChooser.showOpenDialog(null);

        try {
            //Read the file input
            BufferedReader input = new BufferedReader(new FileReader(file.getPath()));
            try {
                String line = null;
                //Using the readLine command and updating the variable each line
                while ((line = input.readLine()) != null) {
                    list.add(line);
                }
            } finally {
                input.close();
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        }

        //For loop that prints out each element of the List
        for (String i : list) {
            System.out.println(i);
        }
    }

    @FXML
    private void randomizeButton() {
        Random rand = new Random();

        int random = rand.nextInt(list.size() - 1);

        label.setText(list.get(random));
    }

    @Override
    public void initialize(URL url, ResourceBundle rb) {
        // TODO
    }

}

Answer 1

您的标签未初始化。您在 FXML 中使用了 id="label" 而不是 fx:id="label"。