动态将JLabel添加到JPanel

Question

I know there are many topics on this subject, but I didn't find my answer.

I'm using NetBeans, so I created all my static components using the Designer. But, at some point, I need to create dynamically JLabels.

I have one JFrame which contains 2 JPanels
First one HeaderPanel, we don't care
Second one BodyPanel, has a CardLayout that allows me to navigate between my different screens (which are JPanels). The screen i'm struggling with is MappingPanel

        try {
        stmt = conn.createStatement();
        String sql;
        sql = "**working select query**";
        System.out.println(sql);
        ResultSet rs = stmt.executeQuery(sql);

        while(rs.next()){
            System.out.println(rs.getString("Field1")); //Display the right text in console
            JLabel a = new JLabel(rs.getString("Field1"));
            a.setVisible(true);
            MappingPanel.add(a); 
        }
    } catch (SQLException ex) {
        Logger.getLogger(MyFrame.class.getName()).log(Level.SEVERE, null, ex);
    }
    MappingPanel.revalidate();
    MappingPanel.repaint();
    BodyPanel.revalidate();
    BodyPanel.repaint();
    this.pack();
}         

I can't get text to be displayed.

Thanks a lot for any help

Answer 1

If you are displaying a single column of data from your ResultSet, then easiest would be to use a JList. You'd create a JList with a DefaultListModel<String> , and then in your while loop above, populate the JList with data by calling .addElement(element) on the model.

Something like:

Declared in class:

private DefaultListModel<String> listModel = new DefaultListModel<>();
private JList<String> myList = new JList<>();

... and in some event code:

     try {
        stmt = conn.createStatement();
        String sql;
        sql = "**working select query**";
        System.out.println(sql);
        ResultSet rs = stmt.executeQuery(sql);

        while (rs.next()) {
           listModel.addElement(rs.getString("Field1"));
        }
     } catch (SQLException ex) {
        Logger.getLogger(ListFun.class.getName()).log(Level.SEVERE, null, ex);
     }

Note that for safest Swing threading, the above code should be done in a background thread such as a SwingWorker, the field1 String should be exposed to the GUI on the Swing event thread such as through a SwingWorker's publish/process method pair. You'd also want to use a prepared statement to query the database with.

The JList of course would be held by one of the JPanels of your GUI.

Note that if you need to display multicolumn data, then I recommend use of a JTable. If you absolutely must add JLabels, then a key here is the layout manager of the container JPanel that holds the JLabels (as I'm sure that your search results have already told you). You'd probably want it to be GridLayout(0, 1) or something similar -- which means a GridLayout with one column and a variable number of rows. The container JPanel should be held in a JScrollPane.