GridBagLayout - Height of one row causes the width of next row to change

Question

The UI I am working on displays a panel which lets a user select a movie and play. There are controls to play, pause, etc.

The layout seems to look the way I want. The panel uses a GridBagLayout. Row 2 displays a text area for status messages and row 3 displays a panel with buttons and a progress bar.

The problem I am running into is that when I have too many lines of text in the text area, the buttons in row 3 wrap around. This is irrespective of the height of the outer frame.

The height in row 2 is affecting the width in row 3. I don't understand this behavior. I am wondering if someone can tell me what is it that I am doing wrong and how I can fix it? I have attached the code.

On a slightly different topic, if you are looking at the code, can you also suggest a way to leave a margin between the bottom-most component and the outermost panel?

Thank you in advance for your help.

Regards,
Peter

    private static JButton CreateImageButton(String fileName) {
        JButton retVal = new JButton("xxx");
        return retVal;
    }

    public MoviePanel() {
        this.setLayout(new GridBagLayout());
        this.setBackground(Color.WHITE);

        JButton btnRefresh = CreateImageButton("refresh.png");
        GridBagConstraints c = new GridBagConstraints(); 
        c.gridx=0;
        c.gridy=0;
        c.fill = GridBagConstraints.NORTH;
        c.insets.left = 10; c.insets.right = 10; c.insets.top = 10;
        this.add(btnRefresh, c);

        JComboBox cbMovieList = new JComboBox();
        c = new GridBagConstraints();
        c.gridx = 1;
        c.gridy = 0;
        c.fill = GridBagConstraints.HORIZONTAL;
        c.insets.right = 10; c.insets.top = 10;
        c.weightx = 1.0;
        this.add(cbMovieList, c);

        JButton btnAuthorize = new JButton("Get Info");
        c = new GridBagConstraints();
        c.gridx = 1;
        c.gridy = 1;
        c.anchor = GridBagConstraints.WEST;
        c.insets.top = 10;
        this.add(btnAuthorize, c);

        JTextArea txtInfo = new JTextArea();
        txtInfo.setFont( new Font("SansSerif", Font.BOLD, 12));
        txtInfo.setBackground(Color.cyan);
        // txtInfo.setText("abc\ndef");
        txtInfo.setText("abc\ndef\nghi\njkl\nmno\npqr\nstu\nvwx\nyz");
        c = new GridBagConstraints();
        c.gridx = 1;
        c.gridy = 2;
        c.anchor = GridBagConstraints.NORTHWEST;
        c.weighty = 1.0;
        c.insets.top = 10;

        this.add(txtInfo, c);

        JPanel controllerOuter = new JPanel();
        controllerOuter.setLayout(new BoxLayout(controllerOuter, BoxLayout.Y_AXIS));
        controllerOuter.setBorder(BorderFactory.createRaisedBevelBorder());

        FlowLayout controllerLayout = new FlowLayout(FlowLayout.CENTER);
        controllerLayout.setHgap(0);
        JPanel controller = new JPanel(controllerLayout);

        controller.setBorder(new EmptyBorder(10, 10, 10, 10));

        Dimension dim = new Dimension(60, 40);
        JButton btnPlay = CreateImageButton("play.png");
        btnPlay.setPreferredSize(dim);

        controller.add(btnPlay);
        JButton btnPause = CreateImageButton("pause.png");
        btnPause.setPreferredSize(dim);
        controller.add(btnPause);
        JButton btnStop = CreateImageButton("stop.png");
        btnStop.setPreferredSize(dim);
        controller.add(btnStop);
        JButton btnForward = CreateImageButton("forward.png");
        btnForward.setPreferredSize(dim);
        controller.add(btnForward);
        JComboBox cbAspectRatio = new JComboBox();
        cbAspectRatio.setPreferredSize(new Dimension(100, 40));
        cbAspectRatio.setBorder(new EmptyBorder(0, 10, 0, 0));
        controller.add(cbAspectRatio);

        controllerOuter.add(controller);

        JProgressBar pbProgress = new JProgressBar(0, 100);
        pbProgress.setPreferredSize(new Dimension(350, 40));
        pbProgress.setBorder(new EmptyBorder(0, 10, 10, 10));
        pbProgress.setValue(50);
        pbProgress.setString("50/100");
        pbProgress.setStringPainted(true);
        pbProgress.setForeground(Color.BLUE);
        pbProgress.setBorderPainted(true);
        controllerOuter.add(pbProgress);


        c = new GridBagConstraints();
        c.gridx = 0;
        c.gridy = 3;
        c.gridwidth = 2;
        c.weightx = 1.0;
        this.add(controllerOuter, c);
    }

Answer 1

I see several things in your code:

1. You force the preferredSize of the JButton's. If possible, I would remove that because this will often get you more problems than solutions. If you want to force the preferredSize, you should also pay attention to set the minimum and maximum sizes as well, otherwise you get weird behaviour like the one you are observing
2. You use a BoxLayout to display the controls. While this is perfectly acceptable, BoxLayout also relies on min/max size to perform the layout, which you did not set.
3. You use imbricated layouts. This is fine too, but why not use only the GridBagLayout of your MoviePanel?
4. Usually TextAreas are wrapped in JScrollPane, in case the text is too big. You can also setLineWrap(true) on the TextArea, so that it does not go too far on the right. By setting rows/columns on the TextArea, you will define its preferreSize (to prevent it from depending of the text it contains).
5. On your GridBagConstraints, the fill property can only be: NONE, VERTICAL, HORIZONTAL or BOTH (You used VERTICAL for one of them). Also, it is not needed to recreate a new instance, you can reuse the same GridBagConstraint over and over, it is automatically cloned by the LayoutManager when you set the constraint for the component.

Now for the solutions, I found several:

1. When you add the contollerOuter, also specify c.fill = GridBagConstraints.HORIZONTAL; (This is the easiest way to solve your issues)
2. When you set the preferredSize of the JButtons, also force their minimumSize to the same value.
3. Use only the GridBagLayout to layout all components. (This would be my favorite)
4. Replace the FlowLayout by a BoxLayout with a X_AXIS.

Rember that GridBagConstraints properties :

• gridx, gridy: specifies the location
• gridwidth, gridheight: specifies the colspan/rowspan
• weightx, weighty: specifies who gets the extra horizontal/vertical space and in what proportion
• anchor: specifies the alignement of the component withing its "cell", if the "cell" is bigger than the component
• fill: specifies if the component should stretch to the cell width/height

Answer 2

Just adding one JPanel each for Center and Bottom will do the trick for you, so till your JTextArea your GridBagLayout will server the purpose and after that the BorderLayout of the MAIN JPanel will do. Moreover, adding JScrollPane also to the whole thing reduces the effort needed at other areas. Have a look at the code and output :

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

public class JTextPaneExample extends JPanel
{
    private Icon info = UIManager.getIcon("OptionPane.informationIcon");
    private Icon error = UIManager.getIcon("OptionPane.errorIcon");

    private static JButton CreateImageButton(String fileName) {
        JButton retVal = new JButton("xxx");
        return retVal;
    }

    private void createAndDisplayGUI()
    {
        JFrame frame = new JFrame("JTextPane Example");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        this.setLayout(new BorderLayout());
        this.setBackground(Color.WHITE);

        JPanel centerPanel = new JPanel();
        centerPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));
        centerPanel.setLayout(new GridBagLayout());
        centerPanel.setBackground(Color.WHITE);
        JButton btnRefresh = CreateImageButton("refresh.png");
        GridBagConstraints c = new GridBagConstraints(); 
        c.gridx=0;
        c.gridy=0;
        c.fill = GridBagConstraints.NORTH;
        c.insets.left = 10; c.insets.right = 10; c.insets.top = 10;
        centerPanel.add(btnRefresh, c);

        JComboBox cbMovieList = new JComboBox();
        c = new GridBagConstraints();
        c.gridx = 1;
        c.gridy = 0;
        c.fill = GridBagConstraints.HORIZONTAL;
        c.insets.right = 10; c.insets.top = 10;
        c.weightx = 1.0;
        centerPanel.add(cbMovieList, c);

        JButton btnAuthorize = new JButton("Get Info");
        c = new GridBagConstraints();
        c.gridx = 1;
        c.gridy = 1;
        c.anchor = GridBagConstraints.WEST;
        c.insets.top = 10;
        centerPanel.add(btnAuthorize, c);

        JTextArea txtInfo = new JTextArea();
        txtInfo.setFont( new Font("SansSerif", Font.BOLD, 12));
        txtInfo.setBackground(Color.cyan);
        // txtInfo.setText("abc\ndef");
        txtInfo.setText("abc\ndef\nghi\njkl\nmno\npqr\nstu\nvwx\nyz");
        JScrollPane scroller = new JScrollPane();
        scroller.setViewportView(txtInfo);
        c = new GridBagConstraints();
        c.gridx = 1;
        c.gridy = 2;
        c.anchor = GridBagConstraints.NORTHWEST;
        c.fill = GridBagConstraints.HORIZONTAL;
        c.weighty = 1.0;
        c.insets.top = 10;

        centerPanel.add(scroller, c);

        JPanel controllerOuter = new JPanel();
        controllerOuter.setLayout(new BoxLayout(controllerOuter, BoxLayout.Y_AXIS));
        controllerOuter.setBorder(BorderFactory.createRaisedBevelBorder());

        FlowLayout controllerLayout = new FlowLayout(FlowLayout.CENTER);
        controllerLayout.setHgap(0);
        JPanel controller = new JPanel(controllerLayout);

        controller.setBorder(new EmptyBorder(10, 10, 10, 10));

        Dimension dim = new Dimension(60, 40);
        JButton btnPlay = CreateImageButton("play.png");
        btnPlay.setPreferredSize(dim);

        controller.add(btnPlay);
        JButton btnPause = CreateImageButton("pause.png");
        btnPause.setPreferredSize(dim);
        controller.add(btnPause);
        JButton btnStop = CreateImageButton("stop.png");
        btnStop.setPreferredSize(dim);
        controller.add(btnStop);
        JButton btnForward = CreateImageButton("forward.png");
        btnForward.setPreferredSize(dim);
        controller.add(btnForward);
        JComboBox cbAspectRatio = new JComboBox();
        cbAspectRatio.setPreferredSize(new Dimension(100, 40));
        cbAspectRatio.setBorder(new EmptyBorder(0, 10, 0, 0));
        controller.add(cbAspectRatio);

        controllerOuter.add(controller);

        JProgressBar pbProgress = new JProgressBar(0, 100);
        pbProgress.setPreferredSize(new Dimension(350, 40));
        pbProgress.setBorder(new EmptyBorder(0, 10, 10, 10));
        pbProgress.setValue(50);
        pbProgress.setString("50/100");
        pbProgress.setStringPainted(true);
        pbProgress.setForeground(Color.BLUE);
        pbProgress.setBorderPainted(true);
        controllerOuter.add(pbProgress);

        add(centerPanel, BorderLayout.CENTER);
        add(controllerOuter, BorderLayout.PAGE_END);

        frame.getContentPane().add(this);
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String... args)
    {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                new JTextPaneExample().createAndDisplayGUI();
            }           
        });
    }
}

Here is the output as you add more lines :