JComboBox: adding automatic completion-Maximum Match
//Code from: http://www.orbital-computer.de/JComboBox/
/*
Inside JComboBox: adding automatic completion
Author: Thomas Bierhance
thomas@orbital-computer.de
*/
/*
Maximum Match
This feature is about reducing the amount of key strokes a user has to do to select an item.
In our five name example it is obvious that when the user types 'J' he either means "Jordi",
"Jordina" or "Jorge". All three of them start with "Jor". This can be taken into account when
making the selection of the completed text. A picture makes it clear how this mechanism is
supposed to work...
The user needs only two keystrokes instead of four to select "Jorge". This feature is not a
really big advantage in the five name case from this article, but imagine a combo box with a
list of chemical substances to choose from - like...
* ...
* 2-Chloro-2-methylbutane
* 2-Chloro-2-methylpropane, Reagent
* 2-Chloro-3-pyridinol
* 2-Chloro-5-nitrobenzaldehyde
* 2-Chloro-5-nitropyridine
* 2-Chloro-5-methylphenol
* 2-Chloromethylquinoline Hydrochloride
* 2-Chlorophenylhydrazine Hydrochloride
* 2-Chloropropane
* ...
In cases like this one you might consider the maximum match feature (e.g. it takes 4
keystrokes instead of 18 to select the second entry).
However, take care in other circumstances: users don't like things happening out of their
control. This feature can produce more confusion than clarity.
Enough warnings - how is it implemented?
As before, an item has been looked up in regard to the user's input. Now an iteration is done
over all items again and other items that would have matched the user's input are collected.
All these candidates are compared to find out if they have a common starting text. The common
starting text won't be highlighted after the completion as if it was entered by the user. The
main method to consider does the comparison...
// calculates how many characters are predetermined by the given pattern.
private int getMaximumMatchingOffset(String pattern, Object selectedItem) {
String selectedAsString=selectedItem.toString();
int match=selectedAsString.length();
// look for items that match the given pattern
for (int i=0, n=model.getSize(); i < n; i++) {
String itemAsString = model.getElementAt(i).toString();
if (startsWithIgnoreCase(itemAsString, pattern)) {
// current item matches the pattern
// how many leading characters have the selected and the current item in common?
int tmpMatch=equalStartLength(itemAsString, selectedAsString);
if (tmpMatch < match) match=tmpMatch;
}
}
return match;
}
Other modifications have been made to the insert method.
*/
import javax.swing.*;
import javax.swing.text.*;
import java.awt.event.*;
public class S16MaximumMatch extends PlainDocument {
JComboBox comboBox;
ComboBoxModel model;
JTextComponent editor;
// flag to indicate if setSelectedItem has been called
// subsequent calls to remove/insertString should be ignored
boolean selecting=false;
boolean hidePopupOnFocusLoss;
boolean hitBackspace=false;
boolean hitBackspaceOnSelection;
public S16MaximumMatch(final JComboBox comboBox) {
this.comboBox = comboBox;
model = comboBox.getModel();
editor = (JTextComponent) comboBox.getEditor().getEditorComponent();
editor.setDocument(this);
comboBox.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
if (!selecting) highlightCompletedText(0);
}
});
editor.addKeyListener(new KeyAdapter() {
public void keyPressed(KeyEvent e) {
if (comboBox.isDisplayable()) comboBox.setPopupVisible(true);
hitBackspace=false;
switch (e.getKeyCode()) {
// determine if the pressed key is backspace (needed by the remove method)
case KeyEvent.VK_BACK_SPACE : hitBackspace=true;
hitBackspaceOnSelection=editor.getSelectionStart()!=editor.getSelectionEnd();
break;
// ignore delete key
case KeyEvent.VK_DELETE : e.consume();
comboBox.getToolkit().beep();
break;
}
}
});
// Bug 5100422 on Java 1.5: Editable JComboBox won't hide popup when tabbing out
hidePopupOnFocusLoss=System.getProperty("java.version").startsWith("1.5");
// Highlight whole text when gaining focus
editor.addFocusListener(new FocusAdapter() {
public void focusGained(FocusEvent e) {
highlightCompletedText(0);
}
public void focusLost(FocusEvent e) {
// Workaround for Bug 5100422 - Hide Popup on focus loss
if (hidePopupOnFocusLoss) comboBox.setPopupVisible(false);
}
});
// Handle initially selected object
Object selected = comboBox.getSelectedItem();
if (selected!=null) setText(selected.toString());
highlightCompletedText(0);
}
public void remove(int offs, int len) throws BadLocationException {
// return immediately when selecting an item
if (selecting) return;
if (hitBackspace) {
// user hit backspace => move the selection backwards
// old item keeps being selected
if (offs>0) {
if (hitBackspaceOnSelection) offs--;
} else {
// User hit backspace with the cursor positioned on the start => beep
comboBox.getToolkit().beep(); // when available use: UIManager.getLookAndFeel().provideErrorFeedback(comboBox);
}
highlightCompletedText(offs);
} else {
super.remove(offs, len);
}
}
public void insertString(int offs, String str, AttributeSet a) throws BadLocationException {
// return immediately when selecting an item
if (selecting) return;
// insert the string into the document
super.insertString(offs, str, a);
// lookup and select a matching item
boolean match=false;
Object item = lookupItem(getText(0, getLength()));
if (item != null) {
match=true;
setSelectedItem(item);
} else {
// keep old item selected if there is no match
item = comboBox.getSelectedItem();
// imitate no insert (later on offs will be incremented by str.length(): selection won't move forward)
offs = offs-str.length();
// provide feedback to the user that his input has been received but can not be accepted
comboBox.getToolkit().beep(); // when available use: UIManager.getLookAndFeel().provideErrorFeedback(comboBox);
}
if (match) offs = getMaximumMatchingOffset(getText(0, getLength()), item);
else offs+=str.length();
setText(item.toString());
// select the completed part
highlightCompletedText(offs);
}
private void setText(String text) {
try {
// remove all text and insert the completed string
super.remove(0, getLength());
super.insertString(0, text, null);
} catch (BadLocationException e) {
throw new RuntimeException(e.toString());
}
}
private void highlightCompletedText(int start) {
editor.setCaretPosition(getLength());
editor.moveCaretPosition(start);
}
private void setSelectedItem(Object item) {
selecting = true;
model.setSelectedItem(item);
selecting = false;
}
private Object lookupItem(String pattern) {
Object selectedItem = model.getSelectedItem();
// only search for a different item if the currently selected does not match
if (selectedItem != null && startsWithIgnoreCase(selectedItem.toString(), pattern)) {
return selectedItem;
} else {
// iterate over all items
for (int i=0, n=model.getSize(); i < n; i++) {
Object currentItem = model.getElementAt(i);
// current item starts with the pattern?
if (startsWithIgnoreCase(currentItem.toString(), pattern)) {
return currentItem;
}
}
}
// no item starts with the pattern => return null
return null;
}
// checks if str1 starts with str2 - ignores case
private boolean startsWithIgnoreCase(String str1, String str2) {
return str1.toUpperCase().startsWith(str2.toUpperCase());
}
// calculates how many characters are predetermined by the given pattern.
private int getMaximumMatchingOffset(String pattern, Object selectedItem) {
String selectedAsString=selectedItem.toString();
int match=selectedAsString.length();
// look for items that match the given pattern
for (int i=0, n=model.getSize(); i < n; i++) {
String itemAsString = model.getElementAt(i).toString();
if (startsWithIgnoreCase(itemAsString, pattern)) {
// current item matches the pattern
// how many leading characters have the selected and the current item in common?
int tmpMatch=equalStartLength(itemAsString, selectedAsString);
if (tmpMatch < match) match=tmpMatch;
}
}
return match;
}
// returns how many leading characters two strings have in common?
private static int equalStartLength(String str1, String str2) {
char[] ch1 = str1.toUpperCase().toCharArray();
char[] ch2 = str2.toUpperCase().toCharArray();
int n = ch1.length>ch2.length?ch2.length:ch1.length;
for (int i=0; i<n; i++) {
if (ch1[i]!=ch2[i]) return i;
}
return n;
}
private static void createAndShowGUI() {
// the combo box (add/modify items if you like to)
JComboBox comboBox = new JComboBox(new Object[] {"Ester", "Jordi", "Jordina", "Jorge", "Sergi"});
// has to be editable
comboBox.setEditable(true);
// change the editor's document
new S16MaximumMatch(comboBox);
// create and show a window containing the combo box
JFrame frame = new JFrame();
frame.setDefaultCloseOperation(3);
frame.getContentPane().add(comboBox);
frame.pack(); frame.setVisible(true);
}
public static void main(String[] args) {
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}
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