如何从另一个JLIst动态更新JList？

Question

我有两个Jlist（blockList和layerList），当我单击来自layerList的另一个项目时，我试图更新blockList的值。 由于某种原因，它不起作用。 这是我的代码：

  JButton openButton, saveButton;
  JTextArea log;
  JFileChooser fc;
  JList layerList;
  JList blockList;
  DefaultListModel model;
  String[] layers = {"Layer 1", "Layer 2", "Layer 3", "Layer 4", "Layer 5"};
  String[] blocksListMenu1 = {"Block 1", "Block 2", "Block 3", "Block 4", "Block 5"};
  String[] blocksListMenu2 = {"Block 6", "Block 7", "Block 8", "Block 9", "Block 10"};
  String[] blocksListMenu3 = {"Block 11", "Block 12", "Block 13", "Block 14", "Block 15"};
  String[] blocksListMenu4 = {"Block 16", "Block 17", "Block 18", "Block 19", "Block 20"};
  String[] blocksListMenu5 = {"Block 21", "Block 22", "Block 23", "Block 24", "Block 25"};

public MainPage() {
super(new BorderLayout());  

JPanel content = new JPanel(new BorderLayout());

final JPanel layerPanel = new JPanel(new BorderLayout());
layerPanel.setBackground(Color.WHITE);
layerPanel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));

JLabel layerLabel = new JLabel("Layers:");
layerList = new JList(layers);
layerList.setSelectedIndex(0);
layerList.addListSelectionListener(new ListSelectionListener() {
     @Override
     public void valueChanged(ListSelectionEvent e) {
        blockList = new JList();
        String selectedLayer = layers[layerList.getSelectedIndex()];
        if(selectedLayer.equals("Layer 1"))
             blockList.setListData(blocksListMenu1);
        else if(selectedLayer.equals("Layer 2"))
             blockList.setListData(blocksListMenu2);
        else if(selectedLayer.equals("Layer 3"))
             blockList.setListData(blocksListMenu3);
        else if(selectedLayer.equals("Layer 4"))
             blockList.setListData(blocksListMenu4);
        else if(selectedLayer.equals("Layer 5"))
             blockList.setListData(blocksListMenu5);;
    }
});

layerPanel.add(layerLabel, BorderLayout.PAGE_START);
layerPanel.add(layerList, BorderLayout.CENTER);
layerPanel.setVisible(false);

//--------------------------------------------------------------------------

final JPanel blockPanel = new JPanel(new BorderLayout());
blockPanel.setBackground(Color.WHITE);
blockPanel.setBorder(BorderFactory.createEmptyBorder(5, 5, 5, 5));

JLabel blockLabel = new JLabel("Blcoks:");
blockList = new JList(blocksListMenu1);
blockPanel.add(blockLabel, BorderLayout.PAGE_START);
blockPanel.add(blockList, BorderLayout.CENTER);
blockPanel.setVisible(false);

final JTextField path = new JTextField();
JButton button = new JButton("Select File");
button.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent ae) {
      JFileChooser fileChooser = new JFileChooser();
      FileNameExtensionFilter filter = new FileNameExtensionFilter("DXF Files", "dxf");
      fileChooser.setFileFilter(filter);
      int returnValue = fileChooser.showOpenDialog(null);
      if (returnValue == JFileChooser.APPROVE_OPTION) {
        File selectedFile = fileChooser.getSelectedFile();
        System.out.println(selectedFile.getName());
        path.setText(selectedFile.getPath());
        layerPanel.setVisible(true);
        blockPanel.setVisible(true);
      }
    }
});    

content.add(path, BorderLayout.CENTER);
content.add(button, BorderLayout.LINE_END);
content.setBorder(BorderFactory.createEmptyBorder(7, 7, 7, 7));
add(content, BorderLayout.PAGE_START);
add(layerPanel, BorderLayout.LINE_START);
add(blockPanel, BorderLayout.LINE_END);

}

当我选择文件时，所选的layersList索引为0，这意味着所选项目为“第1层”，并且blockList显示正确的数组。 但是当我按项目“第2层”时，它没有更新。

有什么想法吗？ 先感谢您！

Answer 1

问题是您要创建一个新的JList并设置其数据：

public void valueChanged(ListSelectionEvent e) {
    blockList = new JList();
    ...

新列表尚未添加到容器中，因此在任何地方都不可见。 您应该简单地更改现有JList的数据。

Answer 2

@ chikito1990：原因是您要在valueChanged()中实例化blockList ，这就是为什么每次重新实例化时都应该有一个实例化，因此您应该在构造函数中实例化blockList 。

public MainPage() {
...

blockList = new JList();

...

}

试试这个，它将起作用。