Resizing by blocks

Question

Hello,
I'm creating a custom JComponent that has lots of lines, like a JList, but they are all part of the same component. I want to make it resizable, but in a way that it only grows or shrinks if there's space for each line to change its size, because the lines need to be all the same size. For example: if there are 10 lines, then resizing its container by up to 9 pixels wouldn't change anything.
I've considered using a ComponentListener to watch when the JPanel (where this component is in) is resized, but the API says that's not a good idea.
The problem is finding the way to make the getPreferredSize() and getMinimumSize() work, or finding an alternative solution. I'm using a GridBagLayout.

Answer 1

I hope I understood what you were asking for. Weirdly enough, reading the source code of FlowLayout really helped me. Using a GridBagLayout is another option but I don't like them too much.import javax.swing.*;
import java.awt.*;
* User: weebib
* Date: 15 janv. 2005
* Time: 17:39:25
public class MultiLine {
     private static class ListLayout implements LayoutManager {
          public void removeLayoutComponent(Component comp) {}
          public void addLayoutComponent(String name, Component comp) {}
          public void layoutContainer(Container target) {
               synchronized (target.getTreeLock()) {
                    Insets insets = target.getInsets();
                    int nmembers = target.getComponentCount();
                    int x = insets.left;
                    int y = insets.top;
                    int height = target.getHeight() / nmembers;
                    for (int i = 0; i < nmembers; i++) {
                         Component m = target.getComponent(i);
                         if (m.isVisible()) {
                              Dimension d = m.getPreferredSize();
                              m.setBounds(x, y, target.getWidth(), height);
                              y += height;
          public Dimension preferredLayoutSize(Container target) {
               synchronized (target.getTreeLock()) {
                    Dimension dim = new Dimension(0, 0);
                    int nmembers = target.getComponentCount();
                    for (int i = 0; i < nmembers; i++) {
                         Component m = target.getComponent(i);
                         if (m.isVisible()) {
                              Dimension d = m.getPreferredSize();
                              dim.height += d.height;
                              dim.width = Math.max(dim.width, d.width);
                    Insets insets = target.getInsets();
                    dim.width += insets.left + insets.right;
                    dim.height += insets.top + insets.bottom;
                    return dim;
          public Dimension minimumLayoutSize(Container target) {
               synchronized (target.getTreeLock()) {
                    Dimension dim = new Dimension(0, 0);
                    int nmembers = target.getComponentCount();
                    for (int i = 0; i < nmembers; i++) {
                         Component m = target.getComponent(i);
                         if (m.isVisible()) {
                              Dimension d = m.getMinimumSize();
                              dim.height += d.height;
                              dim.width = Math.max(dim.width, d.width);
                    Insets insets = target.getInsets();
                    dim.width += insets.left + insets.right;
                    dim.height += insets.top + insets.bottom;
                    return dim;
     public static void main(String[] args) {
          try {
               UIManager.setLookAndFeel(UIManager.getCrossPlatformLookAndFeelClassName());
          } catch (Exception e) {
               e.printStackTrace();
          final JFrame frame = new JFrame(MultiLine.class.getName());
          frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
          JPanel panel = new JPanel(new ListLayout());
          for (int i = 0; i < 3; i++) {
               panel.add(new JLabel("label"));
               panel.add(new JTextField(20));
               JPanel subPanel = new JPanel();
               subPanel.setOpaque(true);
               subPanel.setBackground(Color.RED);
               panel.add(subPanel);
               panel.add(new JTextArea());
          frame.setContentPane(new JScrollPane(panel));
          SwingUtilities.invokeLater(new Runnable() {
               public void run() {
                    frame.setSize(400, 300);
                    frame.show();
}