Not a question - for posterity - JComboBox does not drop in large JDialog

This message was edited 3 times. Last update was at 06/08/2011 11:42:23

I've been going nuts over this for several days. I found the solution without Google's aid (grumble, grumble). Seems to me like it's worthwhile to record this for posterity. And although I haven't posted here many times, I think this is a good site, so I figured maybe I could drive some traffic here if is so happens that someone else has the same problem I did. EDIT I also posted this here -> http://forums.devshed.com/java-help-9/not-a-question-for-posterity-jcombobox-does-not-drop-in-large-jdialog-822739.html

I had the problem where a JComboBox used as a simple drop down (no edit functionality) in a custom dialog would not, um, drop. It started out only manifesting in Windows. Then after a bit of thrashing where I eventually replicated it in Linux, it seemed as if it only happened in certain look and feels. Finally I narrowed it down to the fact that the drop down would only drop if the bottom of drop down would go below the bottom edge of the window. The LNF part was driven by the fact that some LNFs are more compact than others, and so hence sometimes items in the drop down would cause the edge to exceed the window size limit.

Anyway, here's a sample program. This does not work properly. Do not use this!

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

public class DialogTest implements Runnable, ActionListener {
    private JDialog dialog;
    private static final String[] items = {"Item1", "Item2", "Item3", "Item4", "Item5", "Item6", "Item7"};

public DialogTest(String lnf) {
        for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
            if (info.getName().equals(lnf)) {
                try {
                    UIManager.setLookAndFeel(info.getClassName());
                    break;
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
        dialog = new JDialog();
        dialog.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        dialog.setResizable(true);
        JButton ok = new JButton("Ok");
        ok.addActionListener(this);
        JRootPane root = dialog.getRootPane();
        root.setDefaultButton(ok);

root.setLayout(new FlowLayout());
        root.add(new JLabel("Try resizing the dialog to see the problem  "));
        root.add(new JComboBox(items));
        root.add(ok);
        dialog.pack();
    }

public void run() {
        dialog.setVisible(true);
    }

public void actionPerformed(ActionEvent e) {
        System.exit(0);
    }

public static void main(String[] args) {
        Runnable r;
        if(args.length == 0) {
            System.out.println("Try supplying one of these LNFs to see if there's a difference:");
            for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
                System.out.println(info.getName());
            }
            r = new DialogTest(null);
        } else {
            r = new DialogTest(args[0]);
        }
        Thread t = new Thread(r);
        t.start();
    }
}

The problem? I was adding content directly to the root pane. The corrected code which works looks like this:

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

public class DialogTest implements Runnable, ActionListener {
    private JDialog dialog;
    private static final String[] items = {"Item1", "Item2", "Item3", "Item4", "Item5", "Item6", "Item7"};

public DialogTest(String lnf) {
        for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
            if (info.getName().equals(lnf)) {
                try {
                    UIManager.setLookAndFeel(info.getClassName());
                    break;
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        }
        dialog = new JDialog();
        dialog.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        dialog.setResizable(true);
        JButton ok = new JButton("Ok");
        ok.addActionListener(this);
        JRootPane root = dialog.getRootPane();
        root.setDefaultButton(ok);
        
        /** DO NOT DO THIS
        root.setLayout(new FlowLayout());
        root.add(new JLabel("Try resizing the dialog to see the problem  "));
        root.add(new JComboBox(items));
        root.add(ok);
        **/
        //INSTEAD, DO THIS
        Container container = dialog.getContentPane();
        container.setLayout(new FlowLayout());
        container.add(new JLabel("Try resizing the dialog - the problem is gone  "));
        container.add(new JComboBox(items));
        container.add(ok);
        dialog.pack();
    }

public void run() {
        dialog.setVisible(true);
    }

public void actionPerformed(ActionEvent e) {
        System.exit(0);
    }

public static void main(String[] args) {
        Runnable r;
        if(args.length == 0) {
            System.out.println("Try supplying one of these LNFs to see if there's a difference:");
            for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
                System.out.println(info.getName());
            }
            r = new DialogTest(null);
        } else {
            r = new DialogTest(args[0]);
        }
        Thread t = new Thread(r);
        t.start();
    }
}