Question

我正在研究一个项目（是的，这是为了学校，不，我不想让任何人为我写。我有太多的自豪感！）使用java的一些GUI组件。它仍处于相当粗糙的阶段，只有一件事让我无法完成这项工作。我试着不去寻求帮助，除非我真的需要它，因为通常当我确实认为这是一个简单的错误，所以如果是这样的情况，请放轻松我。无论如何，等等代码。这是一个小组项目，所以我的一些评论是给我的合作伙伴的。我会问他们，但现在是凌晨4点......无论如何，这里是。不知道为什么它在所有这些单独的盒子里。我正在搞砸的听众是ActionPerformed，靠近底部。我提前慷慨地感谢你的帮助。

import javax.swing.*;
import javax.swing.event.ListSelectionEvent;
import javax.swing.event.ListSelectionListener;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;


public class GUI extends JFrame
{
  private JPanel panel;
  private JFrame frame;
  private JTextArea text;
  private MP3List list = new MP3List();
  private JList songList;
  private JScrollPane scrollList;
  private JMenuBar menuBar;
  private JMenu menu;
  private JMenuItem menuAdd;
  private String[] songs;
  private static String mp3msg = "Project 2: MP3 Tracker"; // Header for JOptionPane


  public GUI()
  {
    super("mp3");
    panel = new JPanel();
    createGUI();
    add(panel);
  }


  public void createGUI()
  {


//This creates the frame(createGUI)
    frame = new JFrame();

//Here, I made an array of the song titles and gave them to a JList
//for display. Do you think we should sort the songs?
    songs = new String[list.getSize()];
    for (int i = 0; i < list.getSize(); i++)
    {
      songs[i] = list.get(i).getSongTitle();
    }
    songList = new JList(songs);

//Set the selection mode to single as I want to fill in fields with info on a clicked song. More on
//that to come.
    songList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
//Made a scroll bar(vertical and horizontal just in case)
    scrollList = new JScrollPane(songList, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
        JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);


    text = new JTextArea(30, 30);
    text.setText("This section will hold information about songs and somesuch.");


    menuBar = new JMenuBar();
    menu = new JMenu("File");
    menuAdd = new JMenuItem("Add Song");
    menuAdd.addActionListener(new menuListener());
    menu.add(menuAdd);
    menuBar.add(menu);


    frame.setLayout(new Border());

    songList.addListSelectionListener(new ListSelectionListener()
    {
      public void valueChanged(ListSelectionEvent e)
      {

        int selectedVar;
        selectedVar = songList.getSelectedIndex();
        text.setText(("Song Title: " + list.get(selectedVar).getSongTitle())
            + ("\nArtist: " + list.get(selectedVar).getArtistName())
            + ("\nPlayback Time: " + list.get(selectedVar).getPlayBackTime())
            + ("  ||  Cost: " + list.get(selectedVar).getDownloadCost())
            + ("  ||  Size: " + list.get(selectedVar).getFileSize()));
      }
    });

  }


  public class Border extends JFrame implements LayoutManager
  {
    private static final long serialVersionUID = 1L;
    private final int WINDOW_WIDTH = 400;
    private final int WINDOW_HEIGHT = 300;

    public Border()
    {
      super("MP3 Editor");
      setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
      setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      add(scrollList, BorderLayout.CENTER);
      add(text, BorderLayout.SOUTH);
      setJMenuBar(menuBar);
      setVisible(true);
    }


    @Override
    public void addLayoutComponent(String name, Component comp)
    {
      // TODO Auto-generated method stub


    }

    @Override
    public void layoutContainer(Container parent)
    {
      // TODO Auto-generated method stub

    }

    @Override
    public Dimension minimumLayoutSize(Container parent)
    {
      // TODO Auto-generated method stub
      return null;
    }

    @Override
    public Dimension preferredLayoutSize(Container parent)
    {
      // TODO Auto-generated method stub
      return null;
    }

    @Override
    public void removeLayoutComponent(Component comp)
    {
      // TODO Auto-generated method stub

    }
  }

  public class menuListener extends JMenuItem implements ActionListener
  {

    /**
     *
     */
    private static final long serialVersionUID = 1L;

/*public menuListener()
{
  menuItem.addActionListener(this);
}*/

    public void actionPerformed(ActionEvent e)
    {
      MP3 aSong = getInfo();
      list.add(aSong);
      songs = new String[list.getSize()];
      for (int i = 0; i < list.getSize(); i++)
      {
        songs[i] = list.get(i).getSongTitle();
      }
      songList = new JList(songs);
      scrollList = new JScrollPane(songList, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
          JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);
      int index = 0;
      songList.setSelectedIndex(index);
      songList.ensureIndexIsVisible(index);
    }

  }

  /**
   * Input one set of MP3 file information and produce a report <br>
   * <p/>
   * <hr>
   * Date created: Sep 22, 2010 <br>
   * Date last modified: Sep 22, 2010 <br>
   * <p/>
   * <hr>
   */

  public static MP3 getInfo()
  {

    // Gather all information using JOptionPane
    String title = JOptionPane.showInputDialog(null,
        "Enter Title: ",
        mp3msg,
        JOptionPane.QUESTION_MESSAGE);
    String artist = JOptionPane.showInputDialog(null,
        "Enter Artist: ",
        mp3msg,
        JOptionPane.QUESTION_MESSAGE);
    int seconds = Integer.parseInt(JOptionPane.showInputDialog(null,
        "Enter playback time in seconds: ",
        mp3msg,
        JOptionPane.QUESTION_MESSAGE));
    double cost = Double.parseDouble(JOptionPane.showInputDialog(null,
        "Enter download cost: ",
        mp3msg,
        JOptionPane.QUESTION_MESSAGE));
    double size = Double.parseDouble(JOptionPane.showInputDialog(null,
        "Enter file size in megabytes (MB): ",
        mp3msg,
        JOptionPane.QUESTION_MESSAGE));
    MP3 asong = new MP3(title, artist, seconds, cost, size);
    return asong;
  }


}

Answer 1

您的代码存在许多小问题，但我认为最重要的一个问题是您在动作监听器中添加新MP3的部分（您说要帮助的部分）。在这里，您创建了一个全新的JList并覆盖了之前的JList，并为其创建了一个新的滚动窗格，但是不将新的JList添加到你的GUI所以旧的遗留下来（所以你永远不会看到任何变化）。

理想情况下，您应始终保持相同的列表，并只更新内容。有几种方法可以做到这一点，但最简单的方法之一就是简单地调用songList.setListData(songs)。或者，不是创建字符串数组，而是创建Vector，因为JLists也可以使用向量。

您可能想要了解的其他问题：

private JFrame frame;从未使用过。
您的班级Border是JFrame，但也被用作LayoutManager，这非常令人困惑和错误。你应该摆脱它。

就个人而言，我建议你从头开始重写GUI。这是一个简单的例子，有一个工作的JList供你检查：

package examples;

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.util.Vector;

import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JList;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;

public class GUI extends JFrame {

    private final Vector<String> myVector = new Vector<String>();
    private final JList myList = new JList();

    public static void main(String... args) {
        new GUI().setVisible(true);
    }

    public GUI() {
        super("List");
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new BorderLayout());
        add(new JButton(new AddItemAction()), BorderLayout.NORTH);
        add(new JScrollPane(myList), BorderLayout.CENTER);
        pack();
    }

    private class AddItemAction extends AbstractAction {
        public AddItemAction() {
            super("Add Item");
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            String newItem = JOptionPane.showInputDialog("Add a new item:");

            if (newItem != null) {
                myVector.add(newItem);
                myList.setListData(myVector);
            }
        }
    }

}

Answer 2

阅读JList API并按照Swing教程中关于“如何使用列表”的secton的链接，该链接提供了在单击按钮时向JList添加值的工作示例。将您的代码与工作代码进行比较，看看有什么区别。

使用ActionListener添加到JList并在添加后重新设置GUI框架

2 个答案: