Question

I’m using GroupLayout to manage components in some dynamically generated data input forms. The layout is more or less like so:

*-----------------------------------------------*
| label A     |   field A                       | 
| label B     |   field B                       |
| label C     |   field C                       |
*-----------------------------------------------*

I’m using 2 parallel groups for the horizontal layout, and a single sequential group for the vertical layout. For the most part, everything is working just fine.

I want to limit the maximum width of the labels (which are just instances of JLabel) to 1/3 of the width of the parent JFrame. If the JFrame was a fixed size this would be trivial, but I have to deal with it being resized.

I’m picking up ComponentListener.componentResized() events from the JFrame but I’m a bit stuck on what to do once I receive such an event.

I’ve tried this approach without any luck:

public void componentResized(ComponentEvent e) {
    int maxW = parentFrame.getWidth() / 3;
    for (JLabel l : labels) {
        l.setMaximumSize( // have also tried setSize() and setPreferredSize()
            new Dimension(
                Math.min(l.getSize().width, maxW),
                l.getMaximumSize().height));
    }
    groupLayout.invalidateLayout(getContentSpace());
}

Can anyone suggest a way to limit the width of the labels which will work?

I could probably rebuild the layout from scratch every time, but I feel like there ought to be a simpler way.

Answer 1

In this example, GroupLayout can simply rely on the preferred size of the label, without having to resort to any setXXXSize() method. In this approach,

• The space for the labels always accommodates the largest label.
• The text fields are resizable in a useful way.
• The result is correct across platforms and fonts.
• “You do not need to specify anything for most of the components…because the components themselves have the desired resizing behavior as default.”—How to Use GroupLayout: Component Size and Resizability

The use of GroupLayout.Alignment.TRAILING to right justify the labels is a personal preference, and I’ve added a second panel to show how it works nested in another layout.

import java.awt.EventQueue;
import javax.swing.BorderFactory;
import javax.swing.Box;
import javax.swing.BoxLayout;
import javax.swing.GroupLayout;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

/** @see http://stackoverflow.com/questions/8492065 */
public class GroupPanel extends JPanel {

    private JLabel label1 = new JLabel("Primary:");
    private JTextField field1 = new JTextField(16);
    private JLabel label2 = new JLabel("Secondary:");
    private JTextField field2 = new JTextField(16);
    private JLabel label3 = new JLabel("Tertiary:");
    private JTextField field3 = new JTextField(16);

    public GroupPanel(int n) {
        this.setBorder(BorderFactory.createTitledBorder("Panel " + n));
        GroupLayout layout = new GroupLayout(this);          
        this.setLayout(layout);
        layout.setAutoCreateGaps(true);
        layout.setAutoCreateContainerGaps(true);
        layout.setHorizontalGroup(layout.createSequentialGroup()
            .addGroup(layout.createParallelGroup(GroupLayout.Alignment.TRAILING)
                .addComponent(label1)
                .addComponent(label2)
                .addComponent(label3))
            .addGroup(layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                .addComponent(field1)
                .addComponent(field2)
                .addComponent(field3))
        );
        layout.setVerticalGroup(layout.createSequentialGroup()
            .addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                .addComponent(label1)
                .addComponent(field1))
            .addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                .addComponent(label2)
                .addComponent(field2))
            .addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE)
                .addComponent(label3)
                .addComponent(field3))
        );
    }

    private static void display() {
        JFrame f = new JFrame("GroupPanel");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setLayout(new BoxLayout(f.getContentPane(), BoxLayout.Y_AXIS));
        f.add(new GroupPanel(1));
        f.add(new GroupPanel(2));
        f.add(Box.createVerticalGlue());
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                display();
            }
        });
    }
}