How to Dynamically Adjust the Size of a JDialog with a Maximum Height Limit?

How Set the Maximum Size of a JDialog

Problem:

In a JDialog with a BorderLayout containing a scroll pane and control buttons below it, the required behavior is for the dialog to dynamically adjust its size to accommodate the content of the scroll pane until a specified maximum size is reached. However, setting the maximum size using setMaximumSize() seems to have no effect.

Answer:

While the setMaximumSize() method should indeed limit the maximum size of the dialog, it might not be working as expected due to the interaction between the BorderLayout, scroll pane, and preferred size settings.

To address this, consider using the following approach:

1. Provide Useful Information: Determine if any of the components in the scroll pane can provide information for setting the preferred size of the viewport.
   For instance, JList has a convenient setVisibleRowCount() method that can help define the preferred size of the viewport.
2. Dynamically Adjust Viewport Size: Set the preferred size of the viewport based on the information obtained from the component in Step 1. For JList, list.setVisibleRowCount(count) can be used to adjust the height of the viewport as items are added.
3. Revalidate and Repack the Dialog: After modifying the viewport size, revalidate and repack the dialog to apply the changes. dlg.revalidate(); dlg.pack(); will ensure that the dialog adapts to the new preferred size.

Example:

To demonstrate this approach, consider the following JDialog with a JList that dynamically adds items. The dialog expands until it reaches a maximum height, after which scrollbars appear.

<code class="java">import java.awt.BorderLayout;
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 {

    // Initial number of items and maximum height
    private static final int INITIAL_COUNT = 5;
    private static final int MAX_HEIGHT = 200;

    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 = INITIAL_COUNT;

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

            @Override
            public void actionPerformed(ActionEvent e) {
                append();
                sp.revalidate();
                dlg.pack();

                // Check if maximum height exceeded
                if (dlg.getHeight() &gt; MAX_HEIGHT) {
                    list.setVisibleRowCount(count);
                }
            }
        }));

        // Create initial items
        for (int i = 0; i &lt; INITIAL_COUNT; i++) {
            this.append();
        }

        list.setVisibleRowCount(INITIAL_COUNT);
        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) {
        new ListDialog();
    }
}</code>

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