Is there any way to force GridLayout to leave empty cells?

Question

I have a JTabbedPane with 2 JPanels set to GridLayout(13, 11). The first JPanel has enough of the cells filled out that it leaves the empty cells.

The second JPanel has significantly fewer cells filled and this results in each button getting stretched to fill an entire row.

Is there any way to get GridLayout to honor the empty cells, so the buttons in both JPanels are the same size?

Answer 1

Use nested layouts to get your desired result. Some layouts respect the preferred size of components and some don't. GridLayout is one of the ones that don't. Have a look at this answer to see which one's do and which one's don't.

For example, you could nest the 13 buttons in a GridLayout nested in another JPanel with a FlowLayout

JPanel p1 = new JPanel(new FlowLayout(FlowLayout.LEADING));
JPanel p2 = new JPanel(new GridLayout(13, 1));
for (int i = 0; i < 13; i++) {
    p2.add(new JButton("Button " + i));
}
p1.add(p2);

import java.awt.FlowLayout;
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class Test6 {

    public Test6() {
        JPanel p1 = new JPanel(new FlowLayout(FlowLayout.LEADING));
        JPanel p2 = new JPanel(new GridLayout(13, 1));
        for (int i = 0; i < 13; i++) {
            p2.add(new JButton("Button " + i));
        }
        p1.add(p2);

        JFrame frame = new JFrame("Test Card");
        frame.add(p1);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
        frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                Test6 test = new Test6();
            }
        });
    }
}

Answer 2

Is there any way to get GridLayout to honor the empty cells, so the buttons in both JPanels are the same size?

It is certainly doable with GridLayout, simply 'fill' the blank squares with a JLabel that has no text.

E.G. Here are two grid layouts, both padded to 3 rows.

import java.awt.*;
import java.awt.image.BufferedImage;
import java.util.ArrayList;
import javax.swing.*;
import javax.swing.border.LineBorder;

class FillGridLayout {

    public static final JComponent getPaddedGrid(
            ArrayList<BufferedImage> images, int width, int height) {
        JPanel p = new JPanel(new GridLayout(height, width, 2, 2));
        p.setBorder(new LineBorder(Color.RED));
        int count = 0;
        for (BufferedImage bi : images) {
            p.add(new JButton(new ImageIcon(bi)));
            count++;
        }
        for (int ii=count; ii<width*height; ii++ ) {
            // add invisible component
            p.add(new JLabel());
        }
        return p;
    }

    public static void main(String[] args) {
        final ArrayList<BufferedImage> images = new ArrayList<BufferedImage>();
        int s = 16;
        for (int ii = s/4; ii < s; ii+=s/4) {
            images.add(new BufferedImage(ii, s, BufferedImage.TYPE_INT_RGB));
            images.add(new BufferedImage(s, ii, BufferedImage.TYPE_INT_RGB));
        }
        Runnable r = new Runnable() {
            @Override
            public void run() {
                JPanel gui = new JPanel(new BorderLayout(3,3));
                gui.add(getPaddedGrid(images, 3, 3), BorderLayout.LINE_START);
                gui.add(getPaddedGrid(images, 4, 3), BorderLayout.LINE_END);

                JOptionPane.showMessageDialog(null, gui);
            }
        };
        // Swing GUIs should be created and updated on the EDT
        // http://docs.oracle.com/javase/tutorial/uiswing/concurrency
        SwingUtilities.invokeLater(r);
    }
}