Question

I have a simple JComboBox filter code like this :

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import java.util.List;

import javax.swing.DefaultComboBoxModel;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;

public class FilterComboBox extends JComboBox {
    private List<String> array;

    public FilterComboBox(List<String> array) {
        super(array.toArray());
        this.array = array;
        this.setEditable(true);
        final JTextField textfield = (JTextField) this.getEditor().getEditorComponent();
        textfield.addKeyListener(new KeyAdapter() {
            public void keyReleased(KeyEvent ke) {
                SwingUtilities.invokeLater(new Runnable() {
                    public void run() {
                        comboFilter(textfield.getText());
                    }
                });
            }
        });

    }

    public void comboFilter(String enteredText) {
        List<String> filterArray= new ArrayList<String>();
        for (int i = 0; i < array.size(); i++) {
            if (array.get(i).toLowerCase().contains(enteredText.toLowerCase())) {
                filterArray.add(array.get(i));
            }
        }
        if (filterArray.size() > 0) {
            this.setModel(new DefaultComboBoxModel(filterArray.toArray()));
            this.setSelectedItem(enteredText);
            this.showPopup();
        }
        else {
            this.hidePopup();
        }
    }

    /* Testing Codes */
    public static List<String> populateArray() {
        List<String> test = new ArrayList<String>();
        test.add("");
        test.add("Mountain Flight");
        test.add("Mount Climbing");
        test.add("Trekking");
        test.add("Rafting");
        test.add("Jungle Safari");
        test.add("Bungie Jumping");
        test.add("Para Gliding");
        return test;
    }

    public static void makeUI() {
        JFrame frame = new JFrame("Adventure in Nepal - Combo Filter Test");
        FilterComboBox acb = new FilterComboBox(populateArray());
        frame.getContentPane().add(acb);
        frame.pack();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    public static void main(String[] args) throws Exception {

        //UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel");
        makeUI();
    }
}

The performance of the combo filter is not so good but it is fine for few data set. My problem is – when I remove the comment UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel"); to change look and feel, the filter doesn’t work. In WindowsLookAndFeel, the combo box only takes single character in it by replacing the previously entered character.

Can you please tell me whats going on? Manoj Shrestha’s answer below helps in some way but , can you please provide some other suggestions to achieve combo box filter in Java?

Answer 1

Firstly you are creating new model everytime and then invoking show popup from code which leads to flickering etc. We can modify the model itself. Secondly you set the currently entered text as selected item which seems to have selectAll behavior as noted by others. I have modified the code as follows:

public void comboFilter(String enteredText) {
    if (!this.isPopupVisible()) {
        this.showPopup();
    }

    List<String> filterArray= new ArrayList<String>();
    for (int i = 0; i < array.size(); i++) {
        if (array.get(i).toLowerCase().contains(enteredText.toLowerCase())) {
            filterArray.add(array.get(i));
        }
    }
    if (filterArray.size() > 0) {
        DefaultComboBoxModel model = (DefaultComboBoxModel) this.getModel();
        model.removeAllElements();
        for (String s: filterArray)
            model.addElement(s);

        JTextField textfield = (JTextField) this.getEditor().getEditorComponent();
        textfield.setText(enteredText);
    }
}

Hope it works for you.