After submitting my implementation of a searchable JComboBox, I discovered that what the reporter actually wanted was quite different. They want the combo box field to stay non-editable but also to see typed symbols. The only way to achieve it is to introduce a separate text field in the dropdown menu (it’s how I see it, anyways)

I did it, but it doesn’t work. Specifically, the text field, while technically editable (as confirmed through the debugger), does not allow any characters. I don’t even see a caret

package di;

import org.apache.commons.lang3.StringUtils;

import javax.swing.*;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.plaf.ComboBoxUI;
import javax.swing.plaf.basic.BasicComboBoxUI;
import javax.swing.plaf.basic.BasicComboPopup;
import javax.swing.plaf.basic.ComboPopup;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Vector;

public class ComboBoxes {
    private ComboBoxes() {
    }

    public static <T> JComboBox<T> searchableComboBox() {
        return searchableComboBox(new ArrayList<>());
    }

    public static <T> JComboBox<T> searchableComboBox(Collection<T> items) {
        ComboBoxModel<T> model = new DefaultComboBoxModel<>(new Vector<>(items));
        JComboBox<T> comboBox = new JComboBox<>(model);
        JTextField searchTextField = new JTextField();
        comboBox.setUI(searchableComboBoxUi(searchTextField));
        searchTextField.getDocument().addDocumentListener(searchableComboBoxDocumentListener(searchTextField, comboBox, model));
        return comboBox;
    }

    private static <T> DocumentListener searchableComboBoxDocumentListener(JTextField searchTextField, JComboBox<T> comboBox, ComboBoxModel<T> model) {
        return new DocumentListener() {
            @Override
            public void insertUpdate(DocumentEvent e) {
                updateComboBoxModel();
            }

            @Override
            public void removeUpdate(DocumentEvent e) {
                updateComboBoxModel();
            }

            private void updateComboBoxModel() {
                String enteredText = searchTextField.getText();
                ArrayList<T> matchingElements = findMatchingElements(enteredText);
                DefaultComboBoxModel<T> modelWithOnlyMatchingElements = new DefaultComboBoxModel<>(new Vector<>(matchingElements));
                comboBox.setModel(modelWithOnlyMatchingElements);
                comboBox.showPopup();
            }

            private ArrayList<T> findMatchingElements(String enteredText) {
                ArrayList<T> matchingElements = new ArrayList<>();
                for (int i = 0; i < model.getSize(); i++) {
                    T modelElement = model.getElementAt(i);
                    if (StringUtils.containsIgnoreCase(modelElement.toString(), enteredText))
                        matchingElements.add(modelElement);
                }
                return matchingElements;
            }

            @Override
            public void changedUpdate(DocumentEvent e) {
            }
        };
    }

    private static ComboBoxUI searchableComboBoxUi(JTextField searchTextField) {
        return new BasicComboBoxUI() {
            @Override
            protected ComboPopup createPopup() {
                return new BasicComboPopup(comboBox) {
                    @Override
                    protected void configurePopup() {
                        super.configurePopup();
                        add(searchTextField, 0);
                    }

                    @Override
                    public void show() {
                        super.show();
                        searchTextField.requestFocus();
                    }
                };
            }
        };
    }
}

package demos.combo;

import di.ComboBoxes;

import javax.swing.*;
import java.awt.event.ItemEvent;
import java.util.ArrayList;

public class SearchableComboBoxDemo {
    public static void main(String[] args) {
        JFrame frame = new JFrame("Searchable Combo Box Demo");
        JPanel mainPanel = new JPanel();
        JComboBox<Plant> searchableCombo = ComboBoxes.searchableComboBox();
        searchableCombo.addItemListener(SearchableComboBoxDemo::onItemSelection);
        comboBoxItems().forEach(searchableCombo::addItem);
        mainPanel.add(searchableCombo);
        frame.setContentPane(mainPanel);
        frame.pack();
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    private static void onItemSelection(ItemEvent event) {
        if (event.getStateChange() != ItemEvent.SELECTED) return;
        Plant selectedItem = (Plant) event.getItem();
        System.out.printf("Selected item: " + selectedItem + "n");
    }

    private static ArrayList<Plant> comboBoxItems() {
        ArrayList<Plant> items = new ArrayList<>();
        items.add(new Plant("Potato"));
        items.add(new Plant("Peach"));
        items.add(new Plant("Banana"));
        items.add(new Plant("Orange"));
        items.add(new Plant("Carrot"));
        items.add(new Plant("Cabbage"));
        return items;
    }
}

package demos.combo;

public class Plant {
    private final String name;

    public Plant(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return name;
    }
}

searchable jcombobox

It doesn’t have to do with the `setFocusable(false)` call in the configurePopup() super implementation as calling setFocusable(true) in the override doesn’t fix the problem

                    @Override
                    protected void configurePopup() {
                        super.configurePopup();
                        setFocusable(true);
                        add(searchTextField, 0);
                    }

How do I resolve this issue and make the popup’s search field really editable?