Prevent JComboBox's Text Field to be Override

Question

I realize, if I didn't not include line

jComboBox1.addItem("Cause Text Field To Override");

When I type in "A" in JComboBox's text field, "A" will shown in JComboBox's text field.

However, If I include the addItem code, JComboBox's text field will be override. (The lower boundary line also dissapear, not sure why)

I wish to able to addItem, and showPopup without override the content in JCombBoBox's text field. May I know how I can do so?

package javaapplication5;

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

/**
 *
 * @author yccheok
 */
public class NewJDialog extends javax.swing.JDialog {

    /** Creates new form NewJDialog */
    public NewJDialog(java.awt.Frame parent, boolean modal) {
        super(parent, modal);
        initComponents();

        jComboBox1.getEditor().getEditorComponent().addKeyListener(new KeyAdapter() {
            @Override
            public void keyReleased(KeyEvent e) {
                jComboBox1.addItem("Cause Text Field To Override");
                jComboBox1.showPopup();
            }
        });
    }

    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {

        jComboBox1 = new javax.swing.JComboBox();

        setDefaultCloseOperation(javax.swing.WindowConstants.DISPOSE_ON_CLOSE);

        jComboBox1.setEditable(true);
        jComboBox1.setModel(new javax.swing.DefaultComboBoxModel(new String[] { "Hello", "World", "Bye" }));

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(124, 124, 124)
                .addComponent(jComboBox1, javax.swing.GroupLayout.PREFERRED_SIZE, 184, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(92, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addGap(76, 76, 76)
                .addComponent(jComboBox1, javax.swing.GroupLayout.PREFERRED_SIZE, javax.swing.GroupLayout.DEFAULT_SIZE, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(204, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>

    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                NewJDialog dialog = new NewJDialog(new javax.swing.JFrame(), true);
                dialog.addWindowListener(new java.awt.event.WindowAdapter() {
                    public void windowClosing(java.awt.event.WindowEvent e) {
                        System.exit(0);
                    }
                });
                dialog.setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify
    private javax.swing.JComboBox jComboBox1;
    // End of variables declaration

}

Answer 1

It's been a long time since I've done Swing, but I suspect that when you do your AddItem is causing a contentsChanged callback as the combo box is ListDataListener, and that based on that the combo-box is re-setting the selected item to the first item in its model.

I'd suggest you look at what JComboBox does in its implementation of ListDataListener and debug a bit.

However it looks like what you're trying to do goes against the natural swing of swing a bit - i.e. typing a key changes what is in the model by adding to the model.

Rather than using keyEvents on the combo-box, you would be better off adding listeners to the model that then manipulate results in the way you need.