java - JList 已更新，但只允许用户选择一次项目

Question

我有一个位于 JScrollPane 中的 JList。该应用程序有一个按钮，供用户浏览文件系统并选择一个类别来显示其文件和文件夹。

第一次用户单击按钮 JList 显示列表并允许用户从列表中进行选择，但如果用户第二次单击浏览按钮，将显示新项目，但他将无法再从列表中选择任何项目。

public class Main {

    private JFrame frame;
    final JFileChooser fc = new JFileChooser();
    private JScrollPane scrollPane;
    File directory;
    JList<File> list;
    private final Action action_1 = new SwingAction_1();
    private final Action action_2 = new SwingAction_2();
    JTextArea message;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    Main window = new Main();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public Main() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.getContentPane().setBackground(Color.WHITE);
        frame.setBounds(100, 100, 800, 600);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        list = new JList<File>();

        JButton btnBut1 = new JButton("Convert1");
        btnBut1.setBounds(401, 6, 114, 29);
        btnBut1.setAction(action_1);

        JButton btnBut2 = new JButton("Convert2");
        btnBut2.setBounds(523, 6, 117, 29);
        btnBut2.setAction(action_2);

        JButton btnChooseDirectory = new JButton("Choose Directory");
        btnChooseDirectory.setBounds(59, 6, 153, 29);
        btnChooseDirectory.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                fc.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
                int returnVal = fc.showOpenDialog(fc);
                if (returnVal == JFileChooser.APPROVE_OPTION) {
                    directory = fc.getSelectedFile();
                    File[] filesInDir = directory.getAbsoluteFile().listFiles();
                    addFilesToList(filesInDir);
                }
            }
        });
        frame.getContentPane().setLayout(null);
        frame.getContentPane().add(btnChooseDirectory);

        JLabel lblFilesMsg = new JLabel("List of files in the directory:");
        lblFilesMsg.setBounds(6, 64, 175, 16);
        frame.getContentPane().add(lblFilesMsg);
        frame.getContentPane().add(btnBut1);
        frame.getContentPane().add(btnBut2);

        message = new JTextArea();
        message.setBounds(6, 426, 788, 146);
        message.setEditable(false);
        message.setLineWrap(true);
        frame.getContentPane().add(message);

        frame.setTitle(APP_NAME);

    }

    private void addFilesToList(File[] filesInDir) {

        list.setListData(filesInDir);

        list.setSelectionMode(ListSelectionModel.MULTIPLE_INTERVAL_SELECTION);
        list.setLayoutOrientation(JList.VERTICAL);

        scrollPane = new JScrollPane(list);

        scrollPane.setBounds(6, 81, 788, 330);
        scrollPane.setBackground(Color.WHITE);
        frame.getContentPane().add(scrollPane);
        scrollPane.revalidate();

    }

    private class SwingAction_1 extends AbstractAction {
        public SwingAction_1() {
            putValue(NAME, "Converter1");
        }

        public void actionPerformed(ActionEvent e) {

            MyAction1 act = new MyAction1();
            act.method1(list.getSelectedValuesList());

        }

    }

    private class SwingAction_2 extends AbstractAction {
        public SwingAction_2() {
            putValue(NAME, "Converter2");
        }

        public void actionPerformed(ActionEvent e) {

             MyAction2 act = new MyAction2();
             act.method2(list.getSelectedValuesList());
        }

    }

}

Answer 1

我建议您的问题从以下开始:

• 在 addFilesToList 方法中创建 JScrollPane:scrollPane = new JScrollPane(list);。创建 JList 和 JScrollPane 一次，无需不断重新创建这些
• 使用null布局。这已经向你建议过很多次了，我都记不清了。说真的，花时间学习布局管理器，它会解决很多小而烦人的问题

问题在这里...

scrollPane.setBounds(6, 81, 788, 330);
scrollPane.setBackground(Color.WHITE);
frame.getContentPane().add(scrollPane);

哪个JScrollPane实际上在屏幕上可见？哪一个实际上包含 JList？您现在拥有多个...

还有另一个简单的、可运行的示例，它有效......

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JFileChooser;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private JFileChooser fc;
        private JList<File> listOfFiles;
        private JLabel selectedFile;

        public TestPane() {
            setLayout(new BorderLayout());
            JButton browse = new JButton("Browse");
            browse.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    if (fc == null) {
                        fc = new JFileChooser();
                        fc.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
                    }
                    int returnVal = fc.showOpenDialog(fc);
                    if (returnVal == JFileChooser.APPROVE_OPTION) {
                        File directory = fc.getSelectedFile();
                        File[] filesInDir = directory.getAbsoluteFile().listFiles();
                        addFilesToList(filesInDir);
                    }
                }

                protected void addFilesToList(File[] filesInDir) {
                    DefaultListModel<File> model = (DefaultListModel<File>) listOfFiles.getModel();
                    model.removeAllElements();
                    for (File file : filesInDir) {
                        model.addElement(file);
                    }
                }
            });
            add(browse, BorderLayout.NORTH);

            listOfFiles = new JList<>(new DefaultListModel<File>());
            listOfFiles.addListSelectionListener(new ListSelectionListener() {
                @Override
                public void valueChanged(ListSelectionEvent e) {
                    if (!e.getValueIsAdjusting()) {
                        File file = listOfFiles.getSelectedValue();
                        selectedFile.setText("You selected: " + (file == null ? "Nothing" : file.getPath()));
                    }
                }
            });
            add(new JScrollPane(listOfFiles));

            selectedFile = new JLabel("You selected: Nothing");
            add(selectedFile, BorderLayout.SOUTH);

        }

    }

}