Stepped ComboBox refresh

Question

A Stepped ComboBox is very useful to make the drop-down pop-up wider than the text field. However when new content is added to the list, the pop-up gets its initial width back.

By default

After refresh (new element)

SSCCE

import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Vector;

import javax.swing.ComboBoxModel;
import javax.swing.DefaultComboBoxModel;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.plaf.basic.BasicComboPopup;
import javax.swing.plaf.basic.ComboPopup;
import javax.swing.plaf.metal.MetalComboBoxUI;

public class SteppedComboBoxRefresh extends JFrame {
    private List<String> list;
    private final SteppedComboBox combo;

    public SteppedComboBoxRefresh() {
        super("SteppedComboBox Refresh");

        this.list = new ArrayList<String>(Arrays.asList(new String[]{
                "AAA", "AAAAAA"
        }));

        this.combo = new SteppedComboBox(this.list.toArray());
        this.combo.setDimensions(50);

        JButton addButton = new JButton("Add longer string");
        addButton.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                list.add(list.get(list.size()-1) + "AAA");
                combo.setModel(new DefaultComboBoxModel(list.toArray()));
                combo.setDimensions(50);
            }
        });

        getContentPane().setLayout(new FlowLayout());
        getContentPane().add(this.combo);
        getContentPane().add(addButton);
    }

    public static void main (String args[]) {
        SteppedComboBoxRefresh f = new SteppedComboBoxRefresh();
        f.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        f.setSize (300, 100);
        f.setVisible(true);
    }
}

class SteppedComboBoxUI extends MetalComboBoxUI {
    @Override
    protected ComboPopup createPopup() {
        BasicComboPopup popup = new BasicComboPopup( this.comboBox ) {

            @Override
            public void show() {
                Dimension popupSize = ((SteppedComboBox)this.comboBox).getPopupSize();
                popupSize.setSize( popupSize.width,
                        getPopupHeightForRowCount( this.comboBox.getMaximumRowCount() ) );
                Rectangle popupBounds = computePopupBounds( 0,
                        this.comboBox.getBounds().height, popupSize.width, popupSize.height);
                this.scroller.setMaximumSize( popupBounds.getSize() );
                this.scroller.setPreferredSize( popupBounds.getSize() );
                this.scroller.setMinimumSize( popupBounds.getSize() );
                this.list.invalidate();
                int selectedIndex = this.comboBox.getSelectedIndex();
                if ( selectedIndex == -1 ) {
                    this.list.clearSelection();
                } else {
                    this.list.setSelectedIndex( selectedIndex );
                }
                this.list.ensureIndexIsVisible( this.list.getSelectedIndex() );
                setLightWeightPopupEnabled( this.comboBox.isLightWeightPopupEnabled() );

                show( this.comboBox, popupBounds.x, popupBounds.y );
            }
        };
        popup.getAccessibleContext().setAccessibleParent(this.comboBox);
        return popup;
    }
}

class SteppedComboBox extends JComboBox {
    protected int popupWidth;

    public SteppedComboBox(ComboBoxModel aModel) {
        super(aModel);
        setUI(new SteppedComboBoxUI());
        this.popupWidth = 0;
    }

    public SteppedComboBox(final Object[] items) {
        super(items);
        setUI(new SteppedComboBoxUI());
        this.popupWidth = 0;
    }

    public SteppedComboBox(Vector items) {
        super(items);
        setUI(new SteppedComboBoxUI());
        this.popupWidth = 0;
    }

    public void setPopupWidth(int width) {
        this.popupWidth = width;
    }

    public Dimension getPopupSize() {
        Dimension size = getSize();
        if (this.popupWidth < 1) {
            this.popupWidth = size.width;
        }
        return new Dimension(this.popupWidth, size.height);
    }

    public void setDimensions(int width) {
        Dimension d = getPreferredSize();
        setPreferredSize(new Dimension(width, d.height));
        setPopupWidth(d.width);
    }
}

Answer 1

You could use the Combo Box Popup.

It is a more flexible version of the Stepped Combo Box. Best of all it can be used on any combo box since the logic is implemented in a `PopupMenuListener'.

You can control the maximum width of the popup. You can even have the popup display above the combo box instead of below.

Answer 2

The ComboBox still uses its previous PreferredSize. It's needed to set the preferred size back to null, so that we get the size which is preferred by the new content in the list.

void javax.swing.JComponent.setPreferredSize(Dimension preferredSize)

Sets the preferred size of this component. If preferredSize is null, the UI will be asked for the preferred size.

public void setDimensions(int width) {
    setPreferredSize(null);
    Dimension d = getPreferredSize();
    setPreferredSize(new Dimension(width, d.height));
    setPopupWidth(d.width);
}

Result