JList得到更新，但只允许用户选择一次项目 [英] JList gets updated but just allow users to select items once

问题描述

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fileSystem并选择一个类别来显示其文件和文件夹。

I have a JList that is located in a JScrollPane. The application has a button for users to browse fileSystem and select a category to show its files and folders.

首次用户点击按钮JList显示列表并启用用户要从列表中进行选择，但如果用户第二次点击浏览按钮，则会显示新项目但是
他将无法再从列表中选择任何项目。

First time user clicks on the button JList shows the list and enables user to select from the list but if user clicks on the browse button for the second time new items will be shown but he wont be able to select any item from the list anymore.

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());
        }

    }

}

推荐答案

我建议您的问题始于：

• 创建 JSCrollPane 在 addFilesToList 方法中： scrollPane = new JScrollPane（list）; 。创建 JList AND JScrollPane ONCE，不需要不断重新创建这些


• 使用 null 布局。这已被建议给你多次，我记得。说真的，花时间学习布局管理器，它会解决这么多小烦恼的问题

• Creating a JScrollPane within the addFilesToList method: scrollPane = new JScrollPane(list);. Create the JList AND JScrollPane ONCE, there should be no need to continuously recreate these
• Use of null layouts. This has been suggested to you more times then I care to remember. Seriously, make the time to learn the layout managers, it will solve so many small and annoying problems

这里的问题......

The problem here...

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

是，哪个 JScrollPane 实际上是可见的屏幕？哪一个实际包含 JList ？你现在有不止一个......

Is, which JScrollPane is actually visible on the screen? Which one actually contains the JList? You have more than one now...

然而，另一个简单的，可运行的例子，它有效......

And yet, another, simple, runnable example, which works...

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);

        }

    }

}

这篇关于JList得到更新，但只允许用户选择一次项目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IT屋！