Disable items in JList

Question

I'm using a JList as part of a wizard to display all the steps to be performed (it also allows clicking on a step to go to it). Some steps will not always be needed, based on what's done in previous steps. It's these inapplicable steps I'd like to disable in the list.

How can I go about disabling (preventing the selection of) certain items in the list? Is there a better way than subclassing JList and overriding every selection-related method?

Thielen

Answer 1

you have to implements DefaultListSelectionModel, then you can set the Flag if isEnabled or not

simple example

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;

public class JListDisabledItemDemo implements ItemListener, Runnable {

    private JFrame f = new JFrame("Colors");
    private static final String ITEMS[] = {" black ", " blue ", " green ",
        " orange ", " purple ", " red ", " white ", " yellow "};
    private JList jList;
    private JCheckBox[] checkBoxes;
    private boolean[] enabledFlags;

    @Override
    public void run() {
        JPanel pnlEnablers = new JPanel(new GridLayout(0, 1));
        pnlEnablers.setBorder(BorderFactory.createTitledBorder("Enabled Items"));
        checkBoxes = new JCheckBox[ITEMS.length];
        enabledFlags = new boolean[ITEMS.length];
        for (int i = 0; i < ITEMS.length; i++) {
            checkBoxes[i] = new JCheckBox(ITEMS[i]);
            checkBoxes[i].setSelected(true);
            checkBoxes[i].addItemListener(this);
            enabledFlags[i] = true;
            pnlEnablers.add(checkBoxes[i]);
        }
        jList = new JList(ITEMS);
        jList.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        jList.setSelectionModel(new DisabledItemSelectionModel());
        jList.setCellRenderer(new DisabledItemListCellRenderer());
        jList.addListSelectionListener(new ListSelectionListener() {

            @Override
            public void valueChanged(ListSelectionEvent e) {
                if (!e.getValueIsAdjusting()) {
                    System.out.println("selection");
                }
            }
        });
        JScrollPane scroll = new JScrollPane(jList);
        scroll.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
        scroll.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

        Container contentPane = f.getContentPane();
        contentPane.setLayout(new GridLayout(1, 2));
        contentPane.add(pnlEnablers);
        contentPane.add(scroll);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setLocation(240, 280);
        UIManager.put("List.background", Color.lightGray);
        UIManager.put("List.selectionBackground", Color.orange);
        UIManager.put("List.selectionForeground", Color.blue);
        UIManager.put("Label.disabledForeground", Color.magenta);
        SwingUtilities.updateComponentTreeUI(f);
        f.pack();
        javax.swing.SwingUtilities.invokeLater(new Runnable() {

            @Override
            public void run() {
                f.setVisible(true);
            }
        });
    }

    @Override
    public void itemStateChanged(ItemEvent event) {
        JCheckBox checkBox = (JCheckBox) event.getSource();
        int index = -1;
        for (int i = 0; i < ITEMS.length; i++) {
            if (ITEMS[i].equals(checkBox.getText())) {
                index = i;
                break;
            }
        }
        if (index != -1) {
            enabledFlags[index] = checkBox.isSelected();
            jList.repaint();
        }
    }

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

    private class DisabledItemListCellRenderer extends DefaultListCellRenderer {

        private static final long serialVersionUID = 1L;

        @Override
        public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
            Component comp = super.getListCellRendererComponent(list, value, index, false, false);
            JComponent jc = (JComponent) comp;
            if (enabledFlags[index]) {
                if (isSelected & cellHasFocus) {
                    comp.setForeground(Color.black);
                    comp.setBackground(Color.red);
                } else {
                    comp.setForeground(Color.blue);
                }
                if (!isSelected) {
                    if ((value.toString()).trim().equals("yellow")) {
                        comp.setForeground(Color.orange);
                        comp.setBackground(Color.magenta);
                    }
                }
                return comp;
            }
            comp.setEnabled(false);
            return comp;
        }
    }

    private class DisabledItemSelectionModel extends DefaultListSelectionModel {

        private static final long serialVersionUID = 1L;

        @Override
        public void setSelectionInterval(int index0, int index1) {
            if (enabledFlags[index0]) {
                super.setSelectionInterval(index0, index0);
            } else {
                /*
                 * The previously selected index is before this one,
                 * so walk forward to find the next selectable item.
                 */
                if (getAnchorSelectionIndex() < index0) {
                    for (int i = index0; i < enabledFlags.length; i++) {
                        if (enabledFlags[i]) {
                            super.setSelectionInterval(i, i);
                            return;
                        }
                    }
                } /*
                 * Otherwise, walk backward to find the next selectable item.
                 */ else {
                    for (int i = index0; i >= 0; i--) {
                        if (enabledFlags[i]) {
                            super.setSelectionInterval(i, i);
                            return;
                        }
                    }
                }
            }
        }
    }
}

Hobbs

This is a good answer when you want to show the disabled items. There are some use cases where it is in fact better to do so. I have such a use case and this worked like a charm. – Steinbach

Answer 2

It would be easier if you removed the inapplicable items from the list model, instead of disabling them. Would users really want to see disabled items? I don't believe it adds any value, but instead adds visual clutter.

Mantooth

This is a good point. After some thought I decided to gray them out but allow them to be selected. They're skipped when using next/previous, but if they go to a grayed-out step deliberately there will be a message explaining what actions are necessary to "enable" the step – Thielen

Answer 3

I wanted a JList with cells that couldn't be select AND were transparent. So here's what I did:

class DisabledItemListCellRenderer extends JLabel implements ListCellRenderer<Object> {

    private static final long serialVersionUID = 1L;

    public DisabledItemListCellRenderer() {
        setOpaque(false);
    }

    @Override
    public Component getListCellRendererComponent(JList<?> list, Object value,
            int index, boolean isSelected, boolean cellHasFocus) {
        String txt = (String) value;
        setText(txt);

        return this;
    }       
}

Talithatalk

Answer 4

One solution: You might want to look up AbstractAction in the Java API. Then, implement the COMMAND pattern.

The idea is to give methods states by making them into classes (which implement AbstractAction). Then, they can disable each other.

http://en.wikipedia.org/wiki/Command_pattern

http://docs.oracle.com/javase/6/docs/api/

Shanahan