Keylistener not working for JPanel
Solution 1
If you search this problem, you'll 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.
Solution 2
For reference, I've 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: Here's 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();
}
});
}
}
Solution 3
For receives key events on JPanel
you must set focus:
setFocusable(true);
requestFocus();
the JPanel
now has focus, so it receives key events
user2373733
Updated on July 13, 2022Comments
-
user2373733 almost 2 years
I am trying to do something when one of the arrow keys are pressed using the KeyListener in my JPanel class. Here is my code:
public class TestPanel extends JPanel implements KeyListener{ public TestPanel(){ this.addKeyListener(this); this.setFocusable(true); this.requestFocusInWindow(); } 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"); } } public void keyTyped(KeyEvent e) {} public void keyReleased(KeyEvent e) {} }
My main method adds a new instance of this panel to a frame and displays it. Do I need to add the keylistener to the JFrame? In my case, this would be difficult and inefficient, so I would like to make it work with this JPanel if possible. Anyone know what I am doing wrong?
EDIT: Key Bindings code that does not work either:
public class GamePanel extends JPanel implements ActionListener{ //Constructor public GamePanel(){ setupKeyBinding(); this.setFocusable(true); this.requestFocusInWindow(); } private void setupKeyBinding() { int condition = JComponent.WHEN_IN_FOCUSED_WINDOW; InputMap inMap = getInputMap(condition); ActionMap actMap = getActionMap(); inMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), "Left"); actMap.put("Left", new leftAction()); } private class leftAction extends AbstractAction { public void actionPerformed(ActionEvent e) { System.out.println("test"); } } public void actionPerformed(ActionEvent e) { //some other game info } }
Can someone tell me why this doesnt work either? (my second action listener is for other stuff needed for my game)