java - Keylistener not working for JPanel

java – Keylistener not working for JPanel

java – Keylistener not working for JPanel

If you search this problem, youll see that it is asked and has been solved many times.

  • KeyListeners need to be on the focused component to work. One solution is to give your component the focus after first making it focusable.
  • Better by a long shot however is to use Key Bindings. Google the tutorial on this.

Please have a look at my answer to this question for more on this, including many of the gory details.

For reference, Ive create an example using your approach; while it works, it also suggests a focus problem elsewhere in your code. Key Bindings avoid this, as shown here.

Addendum: Heres my working key binding.

private static class TestPanel extends JPanel {

    private static final String LEFT = Left;
    private Action left = new AbstractAction(LEFT) {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println(LEFT);
        }
    };
    private static final String RIGHT = Right;
    private Action right = new AbstractAction(RIGHT) {
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println(RIGHT);
        }
    };

    public TestPanel() {
        this.getInputMap().put(
            KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), LEFT);
        this.getActionMap().put(LEFT, left);
        this.getInputMap().put(
            KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0), RIGHT);
        this.getActionMap().put(RIGHT, right);
    }
}

Original SSCCE:

import java.awt.EventQueue;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import javax.swing.JFrame;
import javax.swing.JPanel;

/**
 * @see https://stackoverflow.com/a/16531380/230513
 */
public class Test {

    private void display() {
        JFrame f = new JFrame(Test);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.add(new TestPanel());
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    private static class TestPanel extends JPanel implements KeyListener {

        public TestPanel() {

            this.addKeyListener(this);
            this.setFocusable(true);
            this.requestFocusInWindow();
        }

        @Override
        public void keyPressed(KeyEvent e) {
            if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
                System.out.println(Right);
            }

            if (e.getKeyCode() == KeyEvent.VK_LEFT) {
                System.out.println(Left);
            }
        }

        @Override
        public void keyTyped(KeyEvent e) {
        }

        @Override
        public void keyReleased(KeyEvent e) {
        }
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Test().display();
            }
        });
    }
}

java – Keylistener not working for JPanel

For receives key events on JPanel you must set focus:

setFocusable(true);
requestFocus(); 

the JPanel now has focus, so it receives key events

Related posts on java  :

Leave a Reply

Your email address will not be published.