JList custom renderer

Question

Hello everybody.
I have a problem with rendering of JList cells. I have a JList-derived class which sets its own ListCellRenderer. The renderer returns an instance of a JPanel derived class, namely GraphicsPanel, which is responsible for drawing a histogram and a number of other things. In order to accomplish this work, the GraphicsPanel instance contains other JPanel-derived objects, one for each "thing", GridBag-laid out. Now the problem is that the paintComponent method never gets called for those objects, but only for the GraphicsPanel instance. The same is true for the getPreferredSize method and others. I tried to use the same GraphicsPanel class outside the JList and it works perfectly.
Inspecting the swing internal fields during every debug session, it comes out that the child components are not valid and their respective sizes are all 0-0. But the GraphicsPanel preferred size is greater than zero, and, when called from outside the JList, also its children sizes become greater than zero, as expected.
Moreover, calling invalidate(), revalidate(), validate(), repaint() in various places and times does not help, and the problem seems to be independent of the OS, because it is present under both Windows and Linux.
I believe I'm missing something amazingly trivial, but what? Any clues?

Answer 1

This may give you some ideasimport java.awt.*;
import javax.swing.*;
public class Test2 extends JFrame {
  MyObject[] data = {new MyObject("One",1),
                     new MyObject("Two",2),
                     new MyObject("Three",3),
                     new MyObject("Four",4),
                     new MyObject("Five",5),
                     new MyObject("Six",6),
                     new MyObject("Seven",7),
                     new MyObject("Eight",8),
                     new MyObject("Nine",9),
  public Test2() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    Container content = getContentPane();
    JList jl = new JList(data);
    jl.setCellRenderer(new MyRenderer());
    content.add(new JScrollPane(jl), BorderLayout.CENTER);
    setSize(300,300);
  public static void main(String[] args) { new Test2().setVisible(true); }
class MyRenderer extends javax.swing.DefaultListCellRenderer {
  public Component getListCellRendererComponent(JList list, Object value,
                                                int index, boolean selected,
                                                boolean focus) {
    JLabel jl = (JLabel)super.getListCellRendererComponent(list, value,index,
                                                           selected,focus);
    Image i = list.createImage(10,10);
    Graphics g = i.getGraphics();
    g.setColor(Color.red);
    g.fillRect(0,0,10,((MyObject)value).getNum());
    jl.setIcon(new ImageIcon(i));
    return jl;
class MyObject {
  String text; int num;
  public MyObject(String text, int num) { this.text=text; this.num=num; }
  public String toString() { return text; }
  public int getNum() { return num; }
}