GridbagLayout - how to get the size of a gridbag cell?

Question

Hi,
i'd like to create a swing widget that automatically rescales the labels inside according to its cell size.
Therefore i had the idea to get the cell size and set the font size according to this size ( subtracting some inset )
finally it should look like that:
|     title text    |
|   val1  |  val2   |
|   val3  |  val4   |
-----------------------the title needs to span 2 cells horizontal,
the values (valx) span 1 cell
by resizing the mainPanel, the labels should also resize according to their available space.
i use this code by now for setting up the widget.
// title label
GridBagConstraints gBC_title = new GridBagConstraints();
jl_title.setFont(titleFont);
gBC_title.gridx = 0;
gBC_title.gridy = 0;
gBC_title.gridwidth = 2; // grid spanning
gBC_title.weightx = 1;
gBC_title.weighty = 0.2;
gBC_title.anchor = GridBagConstraints.CENTER;
gBC_title.fill = GridBagConstraints.BOTH;              
mainPanel.add(jl_title, gBC_title); 
//one of the value labels
GridBagConstraints gBC_v1 = new GridBagConstraints();
jl_val1.setFont(valueFont);
gBC_v1.weightx = 0.5;
gBC_v1.weighty = 0.4;
gBC_v1.gridx = 0;
gBC_v1.gridy = 1;
gBC_v1.anchor = GridBagConstraints.LINE_END;
gBC_v1.fill = GridBagConstraints.BOTH;     
mainPanel.add(jl_val1, gBC_v1);
(...) The mainPanel is the panel with the Gridbaglayout.
by resizing the widget i call this method:
public void adjustFontSize(JLabel label){
                int adjustedFontSize;
     int inset = 2; // space surrounding the label
     int parentHeight = label.getHeight();     
     int parentWidth = label.getWidth();
//     System.out.println("available space for  "+label.getText()+": "+ parentWidth +"*"+ parentHeight);     
     if (parentHeight <= parentWidth){
          adjustedFontSize = parentHeight - inset;
     } else {
          adjustedFontSize = parentWidth - inset;
     label.setFont(new Font(null, Font.BOLD, adjustedFontSize));
     System.out.println("adjusting font size for "+label.getText()+": "+adjustedFontSize);
}//end adjustFontSizethe problem is, that the resizing doesn't really work.
any ideas?
the best thing would be to get the parent cell size of the label to resize, and set the font size to allmost this value
, but i am not able to get the cell size to adjust the label or font size:
thanks for your help
Edited by: Sniezn on Mar 12, 2010 1:05 AM

Answer 1

To make this function properly, you may need to create your own layout manager or do something even more hackish.Here's something more hackish. But first, setting GBC anchor with fill=BOTH doesn't have any effect as the component is resized to fill its cell, so might as well be anchored at all the four corners. Also, there's no need to create a new GBC instance for adding each component.
Is this the layout you were looking for?import java.awt.*;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.font.FontRenderContext;
import java.awt.geom.Rectangle2D;
import javax.swing.*;
public class ZoomLabelTest {
  public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
      @Override
      public void run() {
        new ZoomLabelTest().makeUI();
  public void makeUI() {
    JLabel labelTitle = new ZoomLabel("title text");
    labelTitle.setHorizontalAlignment(JLabel.CENTER);
    JLabel labelVal1 = new ZoomLabel("val1");
    labelVal1.setHorizontalAlignment(JLabel.RIGHT);
    JLabel labelVal2 = new ZoomLabel("val2");
    JLabel labelVal3 = new ZoomLabel("val3");
    labelVal3.setHorizontalAlignment(JLabel.RIGHT);
    JLabel labelVal4 = new ZoomLabel("val4");
    JPanel panel = new JPanel(new GridBagLayout());
    GridBagConstraints gbc = new GridBagConstraints();
    gbc.fill = GridBagConstraints.BOTH;
    gbc.gridwidth = 2;
    gbc.gridx = 0;
    gbc.gridy = 0;
    gbc.weightx = 1;
    gbc.weighty = 0.2;
    panel.add(labelTitle, gbc);
    gbc.gridwidth = 1;
    gbc.weightx = 0.5;
    gbc.weighty = 0.4;
    gbc.gridy = 1;
    panel.add(labelVal1, gbc);
    gbc.gridx = 1;
    panel.add(labelVal2, gbc);
    gbc.gridx = 0;
    gbc.gridy = 2;
    panel.add(labelVal3, gbc);
    gbc.gridx = 1;
    panel.add(labelVal4, gbc);
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 400);
    frame.setLocationRelativeTo(null);
    frame.setContentPane(panel);
    frame.setVisible(true);
class ZoomLabel extends JLabel {
  ComponentListener listener = new ZoomListener();
  public ZoomLabel(String text) {
    super(text);
    addComponentListener(listener);
  private class ZoomListener extends ComponentAdapter {
    @Override
    public void componentResized(ComponentEvent e) {
      // doesn't make a difference for GBL but does for some
      // other layouts, notably BorderLayout
      setPreferredSize(getSize());
      Insets insets = getInsets();
      Font font = getFont();
      int width = getWidth() - insets.left - insets.right;
      int height = getHeight() - insets.top - insets.bottom;
      boolean increased = false;
      boolean decreased = false;
      do {
        Rectangle2D textRect = font.getStringBounds(getText(),
                new FontRenderContext(null, true, false));
        int textWidth = (int) textRect.getWidth();
        int textHeight = (int) textRect.getHeight();
        if (textWidth > width || textHeight > height) {
          font = font.deriveFont((float) font.getSize() - 1);
          if (increased) {
            break;
          decreased = true;
        } else {
          if (decreased) {
            break;
          font = font.deriveFont((float) font.getSize() + 1);
          increased = true;
      } while (true);
      setFont(font);
}db
PS Now somebody tell me that it's not a good idea to setPreferredSize in componentResized ... along with an alternative that's clean(er) ;-)
edit No, that needs a lot more work to be stable with GBL (or maybe it never will be). It appears to be stable only with the same weightx / weighty for all columns/rows.
Edited by: DarrylBurke