How to Dynamically Resize a JDialog to Accommodate Content with Maximum Size Constraints?

How to Set the Maximum Size of a JDialog

In Swing, a JDialog is a pop-up window that can be used to display information or gather user input. By default, the maximum size of a JDialog is the size of the user's monitor. However, it is possible to set a custom maximum size using the setMaximumSize() method.

Problem Statement

When attempting to use the setMaximumSize() method to limit the size of a JDialog that contains a scroll pane and a panel with commit buttons, the method appears to have no effect. The preferred size method, on the other hand, sets the dialog to a fixed size regardless of its contents.

Solution

To dynamically resize a JDialog around its content up to a specified maximum size, it is important to consider the following:

1. Use the setVisibleRowCount() method of components like JList to provide useful information for setting the viewport's preferred size.
2. The maximum size setting interacts with the BorderLayout used in the JDialog. The example below demonstrates how to set the preferred size of a JList dynamically and adjust the JDialog's size accordingly.

Example

The following code creates a JDialog with a JList that dynamically grows as items are added. When the number of items reaches N, scrollbars begin to appear:

<code class="java">import javax.swing.*;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;

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();
                }
            }
        }));
        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 " + String.valueOf(++count));
        list.ensureIndexIsVisible(count - 1);
    }

    public static void main(String[] a_args) {
        ListDialog pd = new ListDialog();
    }
}</code>

In summary, setting the preferred size using the setVisibleRowCount() method can help achieve the desired dynamic resizing behavior while also respecting the user's choice of maximum size through the setMaximumSize() method.

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