Thread: Problem with Key listener to JComboBox

Hi,
I am trying to add a key Listener to a JComboBox so that when you hit the delete key, it deletes the item selected from the Combo box. Here is the code that registers the listener to the combo box.

jcboCountries.addKeyListener(new KeyAdapter() {
	  public void keyPressed(KeyEvent e) {
	    System.out.println("In key pressed");
	    if (e.getKeyCode() == KeyEvent.VK_DELETE){
		  System.out.println("Delete key hit");
		  Object item = model.getSelectedItem();
		  jcboCountries.removeItem(item); 
		}
	  }
	});

I also added this line to set the combo box focus.

jcboCountries.setFocusable(true);

But when I hit the delete button nothing happens. The println lines don't print. Nothing.

Any help is appreciated.

Does the JComboBox have the focus? That determines what component gets key events.

Originally Posted by Norm

Does the JComboBox have the focus? That determines what component gets key events.

I thought so. I thought jcboCountries.setFocusable(true) was supposed to do that. Am I using the wrong method?

Originally Posted by Norm

Add a focus listener to it and see if it gets the focus.

Also when using Adapters, be sure to use the @Override notation. The compiler is happy to let you add any methods you want. You want to be sure you are overriding one of the Adapter's methods and not adding a new one.

I added the focus listener but nothing happened so it is not getting focus. Here is my entire code.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class Exercise35_13 extends JApplet {
  private final static int NUMBER_OF_NATIONS = 7;
  private String[] nations = new String[] {"Denmark",
    "Germany", "China", "India", "Norway", "UK", "US"};
  private ImageIcon[] icons = new ImageIcon[NUMBER_OF_NATIONS];
  private ImageIcon[] bigIcons = new ImageIcon[NUMBER_OF_NATIONS];
 
  // Create a combo box model
  private DefaultComboBoxModel model = new DefaultComboBoxModel();
 
  // Create a combo box with the specified model
  private JComboBox jcboCountries = new JComboBox(model);
 
  // Create a list cell renderer
  private MyListCellRenderer renderer = new MyListCellRenderer();
 
  // Create a label for displaying iamge
  private JLabel jlblImage = new JLabel("", JLabel.CENTER);
 
  /** Construct the applet */
  public Exercise35_13() {
    // Load small and large image icons
    for (int i = 0; i < NUMBER_OF_NATIONS; i++) {
      icons[i] = new ImageIcon(getClass().getResource(
        "/image/flagIcon" + i + ".gif"));
      model.addElement(new Object[]{icons[i], nations[i]});
 
      bigIcons[i] = new ImageIcon(getClass().getResource(
        "/image/flag" + i + ".gif"));
    }
 
    // Set list cell renderer for the combo box
	jcboCountries.setFocusable(true);
    jcboCountries.setRenderer(renderer);
    jlblImage.setIcon(bigIcons[0]);
    add(jcboCountries, java.awt.BorderLayout.NORTH);
    add(jlblImage, java.awt.BorderLayout.CENTER);
 
    // Register listener
    jcboCountries.addActionListener(new ActionListener() {
      public void actionPerformed(java.awt.event.ActionEvent e) {
        jlblImage.setIcon(bigIcons[jcboCountries.getSelectedIndex()]);
      }
    });
	// Register listener
	jcboCountries.addKeyListener(new KeyAdapter() {
	  @Override
	  public void keyPressed(KeyEvent e) {
	    System.out.println("In key pressed");
	    if (e.getKeyCode() == KeyEvent.VK_DELETE){
		  System.out.println("Delete key hit");
		  Object item = model.getSelectedItem();
		  jcboCountries.removeItem(item); 
		}
	  }
	});
	// Register listener
	jcboCountries.addFocusListener(new FocusAdapter() {
	  public void focusGained(FocusEvent e) {
	    System.out.println("Focus Gained");
 
	  }
	});
  }
 
  /** Main method */
  public static void main(String[] args) {
    ComboBoxCellRendererDemo applet = new ComboBoxCellRendererDemo();
    JFrame frame = new JFrame();
    //EXIT_ON_CLOSE == 3
    frame.setDefaultCloseOperation(3);
    frame.setTitle("ComboBoxCellRendererDemo");
    frame.getContentPane().add(applet, BorderLayout.CENTER);
    applet.init();
    applet.start();
    frame.setSize(400,320);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }
}

the posted code does not compile without changes.

Using the code as an applet, it works for me. Running it in AppletViewer:

Focus Gained
key pressed e=java.awt.event.KeyEvent[KEY_PRESSED,keyCode=127,keyText=Delete,keyChar=Del ete,keyLocation=KEY_LOCATION_STANDARD] on javax.swing.JComboBox[,0,0,500x25,layout=javax.swing.plaf.metal.MetalCom boBoxUI$MetalComboBoxLayoutManager,alignmentX=0.0, alignmentY=0.0,border=,flags=16777544,maximumSize= ,minimumSize=,preferredSize=,isEditable=false,ligh tWeightPopupEnabled=true,maximumRowCount=8,selecte dItemReminder=[Ljava.lang.Object;@b6548]
Delete key hit
key pressed e=java.awt.event.KeyEvent[KEY_PRESSED,keyCode=10,keyText=Enter,keyChar=Enter ,keyLocation=KEY_LOCATION_STANDARD] on javax.swing.JComboBox[,0,0,500x25,layout=javax.swing.plaf.metal.MetalCom boBoxUI$MetalComboBoxLayoutManager,alignmentX=0.0, alignmentY=0.0,border=,flags=16777544,maximumSize= ,minimumSize=,preferredSize=,isEditable=false,ligh tWeightPopupEnabled=true,maximumRowCount=8,selecte dItemReminder=[Ljava.lang.Object;@1358f03]

Wow, you are right. I put the class file in an html page and it worked fine as an applet. But it does not run as a standalone application.
Thanks