Question

所以，我在下面有一个构造函数，我是Java的新手，所以它可能比它应该更长，但它基本上做的是创建一个具有Jlist，播放按钮和暂停按钮的窗口。在Jlist中将是音乐文件的名称。首次启动时，程序应该希望询问存储音乐的目录。

我的问题是我想给用户选择，选择一个新目录，但我不知道如何更新Jpanel上的Jlist，因为所有这些都是在构造函数中确定的。我唯一的想法是重绘整个Jframe，面板和组件，但这似乎是一个坏主意。在我的构造函数下面，我发布了我试图做的但是没有用。

Player(){
        preferences = Preferences.userRoot().node(this.getClass().getName());
        ID = "Preferred Directory";
        preferences.get(ID,"");
        features = new PlayerFeatures();
        Ispaused = false;
        DataLine.Info dataInfo = new DataLine.Info(Clip.class,null);
        fileExplorer = new JFileChooser();
        fileExplorer.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
        if(preferences.get(ID,"").equals("")){
            int returnVal = fileExplorer.showOpenDialog(chooseDirectory);
            if(returnVal == JFileChooser.APPROVE_OPTION){
                directory = fileExplorer.getCurrentDirectory();
                preferences.put(ID,directory.toString());
            }

        }

        directory = new File(preferences.get(ID,""));
        //get resource grabs things, with get resource we can grab things that are sitting in side the class folder.
        //directory = new File("C:\\Users\\Jude\\Documents\\musicalChairs\\src");

        List<String> list = makePlayList(directory);
        System.out.println(list);
        songs = new String[list.size()];
        songs = list.toArray(songs);
        playList = new JList(songs);
        playList.addMouseListener(new listMouseListener());
        playList.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
        playList.setLayoutOrientation(JList.HORIZONTAL_WRAP);
        playList.setVisibleRowCount(-1);
        frame = new JFrame();
        panelTop = new JPanel();
        panelBottom = new JPanel();
        panelBottom.setLayout(new BoxLayout(panelBottom,BoxLayout.X_AXIS));
        play = new JButton();
        play.addActionListener(new playListener());
        pause = new JButton();
        pause.addActionListener(new pauseListener());
        scrollPane = new JScrollPane(playList);
        scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
        scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        panelTop.add(scrollPane);
        menuBar = new JMenuBar();
        menu = new JMenu("File");
        menu.setMnemonic(KeyEvent.VK_F);
        chooseDirectory = new JMenuItem("Select Music Folder",KeyEvent.VK_S);
        chooseDirectory.setAccelerator(KeyStroke.getKeyStroke(KeyEvent.VK_1,ActionEvent.ALT_MASK));
        chooseDirectory.addActionListener(new chooseDirectoryListener());
        menu.add(chooseDirectory);
        menuBar.add(menu);
        frame.setJMenuBar(menuBar);
        try{
            Image img = ImageIO.read(getClass().getResource("Play24.gif"));
            Image pauseImg = ImageIO.read(getClass().getResource("Pause16.gif"));
            play.setIcon(new ImageIcon(img));
            pause.setIcon(new ImageIcon(pauseImg));
            Dimension buttonDimensions = new Dimension(25,26);
            play.setPreferredSize(buttonDimensions);
            pause.setPreferredSize(buttonDimensions);


        }catch(IllegalArgumentException ex){
            System.out.println("No input exist");
            ex.printStackTrace();
        }catch(IOException ioe){
            System.out.println("Error while reading");
            ioe.printStackTrace();
        }


        features.songURL = Player.class.getResource(songs[0]);
        panelBottom.add(play);
        panelBottom.add(pause);
        frame.getContentPane().add(BorderLayout.WEST,panelTop);
        frame.getContentPane().add(BorderLayout.SOUTH,panelBottom);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300,250);
        frame.setVisible(true);
    }
class chooseDirectoryListener implements ActionListener{
        @Override
        public void actionPerformed(ActionEvent e) {
            int returnVal = fileExplorer.showOpenDialog(chooseDirectory);
            if(returnVal == JFileChooser.APPROVE_OPTION){
                directory = fileExplorer.getCurrentDirectory();
                preferences.put(ID,directory.toString());
                List<String> list = makePlayList(directory);
                songs = new String[list.size()];
                songs = list.toArray(songs);
                playList = new JList(songs);
                playList.addMouseListener(new listMouseListener());
                playList.setSelectionMode(ListSelectionModel.SINGLE_INTERVAL_SELECTION);
                playList.setLayoutOrientation(JList.HORIZONTAL_WRAP);
                playList.setVisibleRowCount(-1);
                scrollPane = new JScrollPane(playList);
                scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
                scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
                panelTop.add(scrollPane);
                System.out.println("why");
                panelTop.revalidate();
                panelTop.repaint();

            }

        }
    }

Answer 1

您实现了您想要做的事情，使用DefaultListModel。像这样的东西应该工作，虽然没有经过测试。

private DefaultListModel model = new DefaultListModel;

public Constructor () {
    JList playlist = new JList(model);
    panelTop.add(playlist);
    ...
}

public void addItem (String item) {
    model.add(0, item);
}

public void removeItem (String item) {
    model.remove(model.indexOf(item));
}

public void clearItems () {
    model.clear();
}

下面是一个相对仓促的尝试，以测试在删除和添加项目后列表是否会更新。它已按预期执行测试。

JFrame frame = new JFrame();
JPanel panel = new 

DefaultListModel model = new DefaultListModel();
model.add(0, "Item 0");
model.add(1, "Item 1");

JList list = new JList(model);

frame.add(panel);
panel.add(list);

frame.setVisible(true);

model.remove(0);
model.add(1, "Item 234");

如何在构造函数中创建JComponent时更新它？

1 个答案: