Alter JComboBox popup size without disturbing Look and Feel?

Question

I\'m looking for a way to alter the width of a JComboBox\'s popup. Basically, the popup should be as wide as the widest combobox entry requires, not as wide as the combobox curr

Answer 1

This hack seems to work with Java6/7. It basically overrides getSize() to detect if the method is called from within the popup UI. If it detects it is, it lies about the combobox's current size. The popup then determines its size according to faked size value.

The detection code is brutal (it looks at the call stack) and built around the assumption that the calling class' name contains ComboPopup. It may fail to detect the condition on some UI implementations, in that case it will simply retain the default behavior.

public class PopupHackComboBox extends JComboBox {

    // --------------------------------------------------------------
    // ---
    // --- Hack to get control of combobox popup size
    // ---
    // --------------------------------------------------------------
    /**
     * Gets the width the combo's popup should use.
     * 
     * Can be overwritten to return any width desired.
     */
    public int getPopupWidth() {
        final Dimension preferred = getPreferredSize();
        return Math.max(getWidth(), preferred.width);
    }

    @SuppressWarnings("deprecation")
    @Override
    public Dimension size() {
        return getSize((Dimension) null);
    }

    @Override
    public Dimension getSize() {
        return getSize((Dimension) null);
    }

    @Override
    public Dimension getSize(final Dimension dimension) {
        // If the method was called from the ComboPopup,
        // simply lie about the current size of the combo box.
        final int width = isCalledFromComboPopup() ? getPopupWidth() : getWidth();
        if (dimension == null) {
            return new Dimension(width, getHeight());
        }
        dimension.width = width;
        dimension.height = getHeight();
        return dimension;
    }

    /**
     * Hack method to determine if called from within the combo popup UI.
     */
    public boolean isCalledFromComboPopup() {
        try {
            final Throwable t = new Throwable();
            t.fillInStackTrace();
            StackTraceElement[] st = t.getStackTrace();
            // look only at top 5 elements of call stack
            int max = Math.min(st.length, 5);
            for (int i=0; i<max; ++i) {
                final String name = st[i].getClassName();
                if (name != null && name.contains("ComboPopup")) {
                    return true;
                }
            }
        } catch (final Exception e) {
            // if there was a problem, assume not called from combo popup
        }
        return false;
    }

}

Answer 2

1. by using GBC you are be able to set proper height and weight in the container

2. as @trashgod mentioned next way is to set for PreferredSize by using JComboBox.setPrototypeDisplayValue()

3. use Combo Box Popup by @camickr

4. for derived JPopup must be used pack() otherwise too hard to change its Dimension easilly

.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.plaf.basic.*;

public class ComboBoxExample extends JPanel implements ActionListener {
//http://stackoverflow.com/a/5058210/714968

    private static final long serialVersionUID = 1L;
    private JComboBox comboBox;

    public ComboBoxExample() {
        String[] petStrings = {"Select Pet", "Bird", "Cat", "Dog", "Rabbit", "Pig", "Other"};
        comboBox = new JComboBox(petStrings);
        comboBox.setPrototypeDisplayValue("XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX");
        add(comboBox, BorderLayout.PAGE_START);
        JFrame frame = new JFrame("ComboBoxExample");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(comboBox);
        frame.setName("ComboBoxExample");
        frame.setLocation(150, 150);
        frame.pack();
        frame.setVisible(true);
        Timer timer = new javax.swing.Timer(2000, this);
        timer.start();
    }

    public void actionPerformed(ActionEvent e) {
        comboBox.showPopup();
        Object child = comboBox.getAccessibleContext().getAccessibleChild(0);
        BasicComboPopup popup = (BasicComboPopup) child;
        popup.setName("BasicComboPopup");
        JList list = popup.getList();
        Container c = SwingUtilities.getAncestorOfClass(JScrollPane.class, list);
        JScrollPane scrollPane = (JScrollPane) c;
        Dimension size = scrollPane.getSize();
        if (size.width > 30) {
            size.width -= 5;
        }
        scrollPane.setPreferredSize(size);
        scrollPane.setMaximumSize(size);
        Dimension popupSize = popup.getSize();
        popupSize.width = size.width;
        Component parent = popup.getParent();
        parent.setSize(popupSize);
        parent.validate();
        parent.repaint();
        Window mainFrame = SwingUtilities.windowForComponent(comboBox);
        //Returns the first Window ancestor of c, or null if c is not contained inside a Window.
        System.out.println(mainFrame.getName());
        Window popupWindow = SwingUtilities.windowForComponent(popup);
        System.out.println(popupWindow.getName());
        Window popupWindowa = SwingUtilities.windowForComponent(c);
        System.out.println(popupWindowa.getName());

        Window mainFrame1 = SwingUtilities.getWindowAncestor(comboBox);
        //Returns the first Window ancestor of c, or null if c is not contained inside a Window.
        System.out.println(mainFrame1.getName());
        Window popupWindow1 = SwingUtilities.getWindowAncestor(popup);
        System.out.println(popupWindow1.getName());

        Component mainFrame2 = SwingUtilities.getRoot(comboBox);
        //Returns the root component for the current component tree.
        System.out.println(mainFrame2.getName());
        Component popupWindow2 = SwingUtilities.getRoot(popup);
        System.out.println(popupWindow2.getName());
        //  For heavy weight popups you need always to pack() for the window
        if (popupWindow != mainFrame) {
            popupWindow.pack();
        }
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {

            public void run() {
                ComboBoxExample comboBoxExample = new ComboBoxExample();
            }
        });
    }
}