How to Dynamically Size a JDialog with a Maximum Limit?

Setting a Maximum Size for a JDialog

In a quest to limit the dimensions of a JDialog, you may encounter unexpected behavior even after utilizing the setMaximumSize() method. This article aims to clarify this issue and provide a solution.

The Issue: Unsuccessful Maximum Size Limit

When working with a JDialog containing a scroll pane and a fixed-size panel, the goal is to let the dialog expand dynamically based on the size of the embedded panel. However, attempts to set a maximum size using setMaximumSize() have no apparent effect.

The Explanation: Default Maximum Size

The default maximum size of a component is often set to the size of the monitor. This is because the maximum size is inherited from the parent component, which may have set the maximum size to a large value.

Solution: Setting Preferred Size for the Scroll Pane

To achieve the desired dynamic sizing within a specific limit, consider setting the preferred size for the scroll pane. When the scroll pane's preferred size is set, the JDialog will expand accordingly until the threshold is reached. At that point, scrollbars will appear.

Example: Dynamically Sized Dialog

The following Java code snippet demonstrates how to implement this solution using a JList:

<code class="java">import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;

public class ListDialog {

    private static final int N = 12;
    private JDialog dlg = new JDialog();
    private DefaultListModel model = new DefaultListModel();
    private JList list = new JList(model);
    private JScrollPane sp = new JScrollPane(list);
    private int count;

    public ListDialog() {
        JPanel panel = new JPanel();
        panel.add(new JButton(new AbstractAction("Add") {

            @Override
            public void actionPerformed(ActionEvent e) {
                append();
                if (count <= N) {
                    list.setVisibleRowCount(count);
                    dlg.pack();
                }
            }
        }));
        for (int i = 0; i < N - 2; i++) {
            this.append();
        }
        list.setVisibleRowCount(N - 2);
        dlg.add(sp, BorderLayout.CENTER);
        dlg.add(panel, BorderLayout.SOUTH);
        dlg.pack();
        dlg.setLocationRelativeTo(null);
        dlg.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
        dlg.setVisible(true);
    }

    private void append() {
        model.addElement("String " + count++);
        list.ensureIndexIsVisible(count - 1);
    }

    public static void main(String[] a_args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                ListDialog pd = new ListDialog();
            }
        });
    }
}</code>

This code dynamically adjusts the size of the JDialog based on the number of items in the JList. Once the maximum size (in this case, 12 rows) is reached, the scrollbars will appear.

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