如何从另一个JLIst动态更新JList？

Question

I have two Jlist(blockList and layerList) and I am trying to update the values of the blockList when I click on a different item from the layerList. For some reason it is not working. Here is my code:

  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);

}

When I choose the file the selected index of layersList is 0 which means that the selected item is "Layer 1" and the blockList is showing the correct array. But when I press item "Layer 2" it is not updating.

Any ideas why ? Thank you in advance!

Answer 1

The problem is that you're creating a new JList , and setting the data of that:

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

The new list has not been added to the container, so it won't be visible anywhere. You should simply change the data of the already existing JList instead.

Answer 2

@chikito1990: Reason is you are instantiating blockList in valueChanged() that is why every time it is re instantiating while you should have one instantiate and for that you should instantiate blockList in the constructor.

public MainPage() {
...

blockList = new JList();

...

}

try this, it will work.