How to disable certain items in a JComboBox

Question

I have a ComboBox in which I have 8 Items out of which I want to display all but on a certain condition, the user should only be able to select the first two of the

Answer 1

First of all...

This is going to require some hand coding. The GUI Builder is not going to help you out here.

As for the rendering...

You can implement your own BasicComboBoxRenderer, where you pass to it a ListSelectionModel. Based on the model you pass to it, only the selected interval will get rendered with the standard renderer. The remaining indices will get rendered in a disable fashion, by change the foreground color and it's selection background.

^{Note: this is only going to affect the rendering of the items, not the actual selection events}

import java.awt.Color;
import java.awt.Component;
import javax.swing.JList;
import javax.swing.ListSelectionModel;
import javax.swing.UIManager;
import javax.swing.plaf.basic.BasicComboBoxRenderer;

public class EnabledComboBoxRenderer extends BasicComboBoxRenderer {

    private ListSelectionModel enabledItems;

    private Color disabledColor = Color.lightGray;

    public EnabledComboBoxRenderer() {}

    public EnabledComboBoxRenderer(ListSelectionModel enabled) {
        super();
        this.enabledItems = enabled;
    }

    public void setEnabledItems(ListSelectionModel enabled) {
        this.enabledItems = enabled;
    }

    public void setDisabledColor(Color disabledColor) {
        this.disabledColor = disabledColor;
    }

    @Override
    public Component getListCellRendererComponent(JList list, Object value,
            int index, boolean isSelected, boolean cellHasFocus) {

        Component c = super.getListCellRendererComponent(list, value, index,
                isSelected, cellHasFocus);

        if (!enabledItems.isSelectedIndex(index)) {// not enabled
            if (isSelected) {
                c.setBackground(UIManager.getColor("ComboBox.background"));
            } else {
                c.setBackground(super.getBackground());
            }

            c.setForeground(disabledColor);

        } else {
            c.setBackground(super.getBackground());
            c.setForeground(super.getForeground());
        }
        return c;
    }
}

As for selecting items...

You can use two separate listeners. One for when the items are enabled and one for when the items are disabled. When the items are enabled, you can 1. Change the selection model 2. Add the enabled listener 3. Remove the disabled listener

private class EnabledListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        System.out.println(((JComboBox) e.getSource()).getSelectedItem());
    }
}

private class DisabledListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        if (((JComboBox) e.getSource()).getSelectedIndex() != SELECTION_INTERVAL[0]
                && ((JComboBox) e.getSource()).getSelectedIndex() != SELECTION_INTERVAL[1]) {
            JOptionPane.showMessageDialog(null,
                    "You can't Select that Item", "ERROR",
                    JOptionPane.ERROR_MESSAGE);
        } else {
            System.out.println(((JComboBox) e.getSource())
                    .getSelectedItem());
        }
    }
}

protected void enableItemsInComboBox() {
    comboBox.removeActionListener(disabledListener);
    comboBox.addActionListener(enabledListener);
    model.setSelectionInterval(SELECTION_INTERVAL[0], comboBox.getModel()
        .getSize() - 1);
}

And vice versa

protected void disableItemsInComboBox() {
    comboBox.removeActionListener(enabledListener);
    comboBox.addActionListener(disabledListener);
    model.setSelectionInterval(SELECTION_INTERVAL[0], SELECTION_INTERVAL[1]);
}

Here's a complete running example, using EnabledComboBoxRenderer from above

import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;

import javax.swing.DefaultListSelectionModel;
import javax.swing.JCheckBox;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.SwingUtilities;

public class ComboBoxDisabledItemsDemo {
    private static final int[] SELECTION_INTERVAL = { 0, 1 };

    private JComboBox comboBox;
    private JCheckBox disableCheckBox;
    private DefaultListSelectionModel model = new DefaultListSelectionModel();
    private EnabledComboBoxRenderer enableRenderer = new EnabledComboBoxRenderer();

    private EnabledListener enabledListener = new EnabledListener();
    private DisabledListener disabledListener = new DisabledListener();

    public ComboBoxDisabledItemsDemo() {
        comboBox = createComboBox();

        disableCheckBox = createCheckBox();
        disableCheckBox.setSelected(true); // this adds the action listener to
                                            // the
                                            // to the combo box

        JFrame frame = new JFrame("Disabled Combo Box Items");
        frame.setLayout(new GridBagLayout());
        frame.add(comboBox);
        frame.add(disableCheckBox);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(300, 300);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private JComboBox createComboBox() {
        String[] list = { "Item 1", "Item 2", "Item 3", "Item 4", "Item 5",
                "Item 6", "Item 7" };
        JComboBox cbox = new JComboBox(list);
        model.addSelectionInterval(SELECTION_INTERVAL[0], SELECTION_INTERVAL[1]);
        enableRenderer.setEnabledItems(model);
        cbox.setRenderer(enableRenderer);
        return cbox;
    }

    private class EnabledListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println(((JComboBox) e.getSource()).getSelectedItem());
        }
    }

    private class DisabledListener implements ActionListener {
        @Override
        public void actionPerformed(ActionEvent e) {
            if (((JComboBox) e.getSource()).getSelectedIndex() != SELECTION_INTERVAL[0]
                    && ((JComboBox) e.getSource()).getSelectedIndex() != SELECTION_INTERVAL[1]) {
                JOptionPane.showMessageDialog(null,
                        "You can't Select that Item", "ERROR",
                        JOptionPane.ERROR_MESSAGE);
            } else {
                System.out.println(((JComboBox) e.getSource())
                        .getSelectedItem());
            }
        }
    }

    protected void disableItemsInComboBox() {
        comboBox.removeActionListener(enabledListener);
        comboBox.addActionListener(disabledListener);
        model.setSelectionInterval(SELECTION_INTERVAL[0], SELECTION_INTERVAL[1]);
    }

    protected void enableItemsInComboBox() {
        comboBox.removeActionListener(disabledListener);
        comboBox.addActionListener(enabledListener);
        model.setSelectionInterval(SELECTION_INTERVAL[0], comboBox.getModel()
                .getSize() - 1);
    }

    private JCheckBox createCheckBox() {
        JCheckBox checkBox = new JCheckBox("diabled");
        checkBox.addItemListener(new ItemListener() {
            public void itemStateChanged(ItemEvent e) {
                if (e.getStateChange() == ItemEvent.SELECTED) {
                    disableItemsInComboBox();
                } else if (e.getStateChange() == ItemEvent.DESELECTED) {
                    enableItemsInComboBox();
                }
            }
        });
        return checkBox;
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new ComboBoxDisabledItemsDemo();
            }
        });
    }
}