Swing GroupLayout: Resizing and limiting component sizes

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.

Ahearn

don't setXXSize ever: #7229726 – Wrinkly

Is there any reason for a label to grow larger than the preferred size of the largest label? – Bartels

@Bartels No there isn't. I'm wanting to set an upper bound on the width of the labels, not a minimum bound. Have edited the question to make that clearer. – Ahearn

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();
            }
        });
    }
}

Bartels

That's a very clear example, so thank you for that. The code you've provided is almost identical to that which I have already implemented myself, but the key bit was the "You do not need to specify anything for most of the components…because the components themselves have the desired resizing behavior as default.". I figure my labels need to be custom implementations which override getPreferredSize(). – Ahearn

Excellent; see also this (less flexible) example. – Bartels

See also this (more flexible) example. – Bartels

I went five years between uses of GroupLayout, so I had to refer again to the above example by @trashgod. It was an excellent way to refresh my memory on how to use that layout. Bravo! – Weeper