How to get a GridBagLayout to arrange column widths?

Question

Here is a pretty simple layout (code included) where non-uniform column sizes could improve packing.

Is there a way, using a single GridBagLayout, to get the components to fit together nicely?

I thought that using a width of 3 for the top two components, then a width of 5 & 1 for the next two rows would influence the alignment, but I cannot get it to stay flush. My current solution (not included) is to create a sub panel with the red and green panels.

import javax.swing.*;
import java.awt.*;

public class GridBagWrong{
    public static void main(String[] args){
        JPanel content = new JPanel(new GridBagLayout());
        GridBagConstraints gbc = new GridBagConstraints();
        //create five panels to layout.
        JPanel a = new JPanel();
        a.setPreferredSize( new Dimension(300, 30) );
        a.setBorder( BorderFactory.createLineBorder(Color.BLUE) );
        JPanel b = new JPanel();
        b.setPreferredSize( new Dimension(300, 30) );
        b.setBorder( BorderFactory.createLineBorder(Color.BLUE) );
        JPanel c = new JPanel();
        c.setPreferredSize( new Dimension(500, 30) );
        c.setBorder( BorderFactory.createLineBorder(Color.GREEN) );
        JPanel d = new JPanel();
        d.setPreferredSize( new Dimension(500, 30) );
        d.setBorder( BorderFactory.createLineBorder(Color.GREEN) );
        JPanel e = new JPanel();
        e.setPreferredSize( new Dimension(100, 60) );
        e.setBorder( BorderFactory.createLineBorder(Color.RED) );
        //place them in a gridbaglayout.
        gbc.gridwidth = 3;
        content.add(a, gbc);
        gbc.gridx = 3;
        content.add(b, gbc);
        gbc.gridx = 0;
        gbc.gridy = 1;
        gbc.gridwidth = 5;
        content.add(c, gbc);
        gbc.gridy = 2;
        content.add(d, gbc);
        
        gbc.gridy = 1;
        gbc.gridx = 5;
        gbc.gridheight = 2;
        gbc.gridwidth = 1;
        content.add(e, gbc);
        
        JFrame frame = new JFrame("test");        
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.setContentPane( content );
        frame.pack();
        frame.setVisible(true);
    }

}

In theory, yes, based on your example code, for some reason, when ever I add `c` (testing it one panel at a time), it adds "more" space to the container, which throws out the sizing on the right hand side ... and I don't know why — MadProgrammer, Nov 10 '21 at 20:46
1) How should extra width and height be assigned to the various panel containers? 2) Are you set on using a `GridBagLayout`? I started turning the constraints of panel placement over in my head and realised a combination of other layouts *might* (see (1)) be easier. — Andrew Thompson, Nov 10 '21 at 20:46
You can't just randomly using a gridwidth of 3 and 5. That only works if you actually have 6 components in one of the rows. Then using a gridwidth of 3 or 5 makes sense. However you can configure a minimum width for each column. Then it would make sense to specify the gridwidth. See: https://stackoverflow.com/questions/59009741/creating-a-board-game-layout-using-jlayeredpane/59022153#59022153 for an example of this approach. — camickr, Nov 10 '21 at 20:47
@camickr I thought, incorrectly, that using more grid elements would let me cut up the layout better. Consider just having 1 panel on the top row added gridwidth 2, and 2 panels on the bottom row gridwith 1 each. Then the layout gets packed ok, even if the second row has different sized panels. — matt, Nov 11 '21 at 09:50
The "gridwidth" constraint basically says "ignore the preferred width of the component and base the width on components found in other rows". The width of a column is based on the width of the largest component added in that column with `gridwidth = 1`. The second row has two components so the preferred width of each column can be calculated. Then the width of the component in the first row can be calculated. Adding more components with `gridwidth = 1` will help. That is effectively what my answer does. It creates more columns without using actual components. — camickr, Nov 11 '21 at 15:08
Check out: https://stackoverflow.com/a/57463596/131872 for another example of this approach. As you noted, nesting panels with different layout managers can often simplify the layout. Without a concrete example of what you are trying to achieve I can't give a specific solution, only explain (my understanding of) what is happening. — camickr, Nov 11 '21 at 15:24

camickr · Accepted Answer · 2021-11-10T21:47:59.917

Following up on my comment from above you can use:

//JPanel content = new JPanel(new GridBagLayout());
GridBagLayout gbl = new GridBagLayout();
int[] columns = new int[6];
Arrays.fill(columns, 100);
gbl.columnWidths = columns;
JPanel content = new JPanel(gbl);

The above code states each of the 6 columns will have a minimum width of 100.

If a component is added to a column with gridwidth = 1, then the preferred size of that component will be used as the width of the column.

So now when you specify gridwidth = 3 it has a meaning because the layout can use either the width of a component added to the columnn or the minimum width to determine the actual size of the component.

This answers the question, but it would be nice to not have to set the width manually. In this trivial example it works well. In my use case, using a sub-layout is a bit more practical. — matt, Nov 10 '21 at 22:20

score 1 · Answer 2 · answered Nov 10 '21 at 21:21

For some reason GridBagLayout is adding addition space to it's calculations, but I'm not sure why. At first I thought it was the LineBorder, but when I modified your code to remove the border, it still didn't work...

I don't know where the extra spacing on the right is coming from (it's probably really obvious, but I can't see it)

Sooo, this is one of those moments where I "flip the table" and "rage quite" and instead, "hack it"

Since there seems to be a disconnect between the first and second row, for some reason, I combined the two panels from the first row into a single panel and got rid of all the gridwidths (more or less)

import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import javax.swing.JFrame;
import javax.swing.JPanel;

public class Test {

    public static void main(String[] args) {
        new Test();
    }

    public Test() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            //create five panels to layout.
            JPanel a = new LayoutPane();
            a.setForeground(Color.BLUE);
            a.setPreferredSize(new Dimension(300, 30));

            JPanel b = new LayoutPane();
            b.setPreferredSize(new Dimension(300, 30));
            b.setForeground(Color.BLUE);

            JPanel c = new LayoutPane();
            c.setPreferredSize(new Dimension(500, 30));
            c.setForeground(Color.GREEN);

            JPanel d = new LayoutPane();
            d.setPreferredSize(new Dimension(500, 30));
            d.setForeground(Color.GREEN);

            JPanel e = new LayoutPane();
            e.setPreferredSize(new Dimension(100, 60));
            e.setForeground(Color.RED);

            JPanel topPane = new JPanel(new GridBagLayout());

            //place them in a gridbaglayout.
            gbc.gridx = 0;
            gbc.gridy = 0;
            gbc.fill = GridBagConstraints.HORIZONTAL;            
            topPane.add(a, gbc);
            gbc.gridx++;
            topPane.add(b, gbc);

            gbc = new GridBagConstraints();
            gbc.gridwidth = GridBagConstraints.REMAINDER;
            gbc.gridx = 0;
            gbc.gridy = 0;
            gbc.fill = GridBagConstraints.HORIZONTAL;            
            add(topPane, gbc);


            gbc = new GridBagConstraints();
            gbc.gridx = 0;
            gbc.gridy = 1;
            gbc.anchor = GridBagConstraints.WEST;
            add(c, gbc);

            gbc.gridy = 2;
            add(d, gbc);

            gbc = new GridBagConstraints();
            gbc.gridy = 1;
            gbc.gridx++;
            gbc.gridheight = 2;
            gbc.anchor = GridBagConstraints.EAST;
            add(e, gbc);
        }

    }

    public class LayoutPane extends JPanel {

        public LayoutPane() {
            setOpaque(false);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setColor(getForeground());
            g2d.drawRect(0, 0, getWidth() - 1, getHeight() - 1);
            String text = getWidth() + "x" + getHeight();
            FontMetrics fm = g2d.getFontMetrics();
            int x = (getWidth() - fm.stringWidth(text)) / 2;
            int y = ((getHeight() - fm.getHeight()) / 2) + fm.getAscent();
            g2d.drawString(text, x, y);
            g2d.dispose();
        }

    }
}

It's weird, if I use two rows. Top row 1 panel gridwidth of 2 and bottom row 2 panels gridwidth of 1 but different sizes, it gets distributed correctly. The problem seems to happen when the none of the columns line up. We could draw column sizes that would correctly pack the elements, but the default algorithm wouldn't manage that. — matt, Nov 11 '21 at 09:47
@matt Its been a while since I took a deep dive into `GridBagLayout`, but it could be that spanning columns is adding the remaining width of the component + max width of all the other components within that column or something like that and it's adding "extra" space which isn't required - but I'm just guessing — MadProgrammer, Nov 11 '21 at 20:40

How to get a GridBagLayout to arrange column widths?

2 Answers2