Unresponsive KeyListener for JFrame

Question

I'm trying to implement a KeyListener for my JFrame. On the constructor, I'm using this code:

System.out.println("test");
addKeyListener(new KeyListener() {
    public void keyPressed(KeyEvent e) { System.out.println( "tester"); }

    public void keyReleased(KeyEvent e) { System.out.println("2test2"); }

    public void keyTyped(KeyEvent e) { System.out.println("3test3"); }
});

When I run it, the test message comes up in my console. However, when I press a key, I don't get any of the other messages, as if the KeyListener was not even there.

I was thinking that it could be because the focus is not on the JFrame
and so they KeyListener doesn't receive any events. But, I'm pretty sure it is.

Is there something that I am missing?

score 135 · Answer 1 · edited Apr 20 '14 at 14:43

If you don't want to register a listener on every component,
you could add your own KeyEventDispatcher to the KeyboardFocusManager:

public class MyFrame extends JFrame {    
    private class MyDispatcher implements KeyEventDispatcher {
        @Override
        public boolean dispatchKeyEvent(KeyEvent e) {
            if (e.getID() == KeyEvent.KEY_PRESSED) {
                System.out.println("tester");
            } else if (e.getID() == KeyEvent.KEY_RELEASED) {
                System.out.println("2test2");
            } else if (e.getID() == KeyEvent.KEY_TYPED) {
                System.out.println("3test3");
            }
            return false;
        }
    }
    public MyFrame() {
        add(new JTextField());
        System.out.println("test");
        KeyboardFocusManager manager = KeyboardFocusManager.getCurrentKeyboardFocusManager();
        manager.addKeyEventDispatcher(new MyDispatcher());
    }

    public static void main(String[] args) {
        MyFrame f = new MyFrame();
        f.pack();
        f.setVisible(true);
    }
}

KeyboardFocusManager is application wide, if you have multi frames, you will get trouble? — neoedmund, Jul 16 '13 at 08:40
So this should work, something like: foreach("focusable components in the frame" as _){ _.addkeylistener(frameKeylistener);} — neoedmund, Jul 16 '13 at 09:55

score 52 · Accepted Answer · answered Nov 13 '08 at 13:01

52

You must add your keyListener to every component that you need. Only the component with the focus will send these events. For instance, if you have only one TextBox in your JFrame, that TextBox has the focus. So you must add a KeyListener to this component as well.

The process is the same:

myComponent.addKeyListener(new KeyListener ...);

Note: Some components aren't focusable like JLabel.

For setting them to focusable you need to:

myComponent.setFocusable(true);

answered Nov 13 '08 at 13:01

bruno conde

47,767
15
98
117

2

yea you were right, when the program starts you can slightly see that the focus is on the button A. adding a keylistener to each button fixed this. thats a little weird, i would think that adding a keylistener to the JFrame would work but i guess not. Thanks! – Tomek Nov 13 '08 at 16:29
i have made a Listener on JFrame which Listens from keyboard. I want to make it work in passive mode, even if the window is not in front (focused). JFrame is not Listening in passive mode. – Usman Sep 16 '15 at 04:57

score 15 · Answer 3 · answered Feb 23 '13 at 00:29

InputMaps and ActionMaps were designed to capture the key events for the component, it and all of its sub-components, or the entire window. This is controlled through the parameter in JComponent.getInputMap(). See How to Use Key Bindings for documentation.

The beauty of this design is that one can pick and choose which key strokes are important to monitor and have different actions fired based on those key strokes.

This code will call dispose() on a JFrame when the escape key is hit anywhere in the window. JFrame doesn't derive from JComponent so you have to use another component in the JFrame to create the key binding. The content pane might be such a component.

InputMap inputMap; 
ActionMap actionMap;
AbstractAction action;
JComponent component;

inputMap  = component.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
actionMap = component.getActionMap();

action    = new AbstractAction()
{
   @Override
   public void actionPerformed(ActionEvent e)
   {
      dispose();
   }
};

inputMap.put(KeyStroke.getKeyStroke(KeyEvent.VK_ESCAPE, 0), "dispose");
actionMap.put("dispose", action);

score 12 · Answer 4 · edited Sep 14 '11 at 08:26

12

I got the same problem until i read that the real problem is about FOCUS the your JFrame has already added Listeners but tour frame is never on Focus because you got a lot of components inside your JFrame that also are focusable so try:

JFrame.setFocusable(true);

Good Luck

edited Sep 14 '11 at 08:26

Jérôme Verstrynge

57,710
92
283
453

answered Apr 27 '09 at 15:30

2

I found that this works only until I use something that is on my JFrame then the KeyListener no longer responds – user3328784 Apr 10 '14 at 20:38

score 10 · Answer 5 · edited May 23 '17 at 12:34

KeyListener is low level and applies only to a single component. Despite attempts to make it more usable JFrame creates a number of component components, the most obvious being the content pane. JComboBox UI is also often implemented in a similar manner.

It's worth noting the mouse events work in a strange way slightly different to key events.

For details on what you should do, see my answer on Application wide keyboard shortcut - Java Swing.

score 9 · Answer 6 · edited Feb 04 '12 at 21:13

Deion (and anyone else asking a similar question), you could use Peter's code above but instead of printing to standard output, you test for the key code PRESSED, RELEASED, or TYPED.

@Override
public boolean dispatchKeyEvent(KeyEvent e) {
    if (e.getID() == KeyEvent.KEY_PRESSED) {
        if (e.getKeyCode() == KeyEvent.VK_F4) {
            dispose();
        }
    } else if (e.getID() == KeyEvent.KEY_RELEASED) {
        if (e.getKeyCode() == KeyEvent.VK_F4) {
            dispose();
        }
    } else if (e.getID() == KeyEvent.KEY_TYPED) {
        if (e.getKeyCode() == KeyEvent.VK_F4) {
            dispose();
        }
    }
    return false;
}

score 4 · Answer 7 · edited Feb 04 '12 at 21:13

in order to capture key events of ALL text fields in a JFrame, one can employ a key event post processor. Here is a working example, after you add the obvious includes.

public class KeyListenerF1Demo extends JFrame implements KeyEventPostProcessor {
    public static final long serialVersionUID = 1L;

    public KeyListenerF1Demo() {
        setTitle(getClass().getName());

        // Define two labels and two text fields all in a row.
        setLayout(new FlowLayout());

        JLabel label1 = new JLabel("Text1");
        label1.setName("Label1");
        add(label1);

        JTextField text1 = new JTextField(10);
        text1.setName("Text1");
        add(text1);

        JLabel label2 = new JLabel("Text2");
        label2.setName("Label2");
        add(label2);

        JTextField text2 = new JTextField(10);
        text2.setName("Text2");
        add(text2);

        // Register a key event post processor.
        KeyboardFocusManager.getCurrentKeyboardFocusManager()
                .addKeyEventPostProcessor(this);
    }

    public static void main(String[] args) {
        JFrame f = new KeyListenerF1Demo();
        f.setName("MyFrame");
        f.pack();
        f.setVisible(true);
    }

    @Override
    public boolean postProcessKeyEvent(KeyEvent ke) {
        // Check for function key F1 pressed.
        if (ke.getID() == KeyEvent.KEY_PRESSED
                && ke.getKeyCode() == KeyEvent.VK_F1) {

            // Get top level ancestor of focused element.
            Component c = ke.getComponent();
            while (null != c.getParent())
                c = c.getParent();

            // Output some help.
            System.out.println("Help for " + c.getName() + "."
                    + ke.getComponent().getName());

            // Tell keyboard focus manager that event has been fully handled.
            return true;
        }

        // Let keyboard focus manager handle the event further.
        return false;
    }
}

For a working example you might consider adding the imports. I usually add 'package imports' to keep them short. Otherwise, +1. Interesting technique. — Andrew Thompson, Jul 16 '11 at 04:36

score 3 · Answer 8 · answered Jun 27 '14 at 15:20

This should help

    yourJFrame.setFocusable(true);
    yourJFrame.addKeyListener(new java.awt.event.KeyAdapter() {


        @Override
        public void keyTyped(KeyEvent e) {
            System.out.println("you typed a key");
        }

        @Override
        public void keyPressed(KeyEvent e) {
            System.out.println("you pressed a key");
        }

        @Override
        public void keyReleased(KeyEvent e) {
            System.out.println("you released a key");
        }
    });

score 2 · Answer 9 · edited Feb 04 '12 at 21:13

Hmm.. what class is your constructor for? Probably some class extending JFrame? The window focus should be at the window, of course but I don't think that's the problem.

I expanded your code, tried to run it and it worked - the key presses resulted as print output. (run with Ubuntu through Eclipse):

public class MyFrame extends JFrame {
    public MyFrame() {
        System.out.println("test");
        addKeyListener(new KeyListener() {
            public void keyPressed(KeyEvent e) {
                System.out.println("tester");
            }

            public void keyReleased(KeyEvent e) {
                System.out.println("2test2");
            }

            public void keyTyped(KeyEvent e) {
                System.out.println("3test3");
            }
        });
    }

    public static void main(String[] args) {
        MyFrame f = new MyFrame();
        f.pack();
        f.setVisible(true);
    }
}

I get all of the messages output also. Run in Windows command line. — Darrel, Nov 13 '08 at 13:13
You get all the messages because in this example the JFrame has the focus. try adding a TextBox component to the JFrame and see what happens. — bruno conde, Nov 13 '08 at 14:22

score 1 · Answer 10 · answered Jan 04 '11 at 02:31

I have been having the same problem. I followed Bruno's advice to you and found that adding a KeyListener just to the "first" button in the JFrame (ie, on the top left) did the trick. But I agree with you it is kind of an unsettling solution. So I fiddled around and discovered a neater way to fix it. Just add the line

myChildOfJFrame.requestFocusInWindow();

to your main method, after you've created your instance of your subclass of JFrame and set it visible.

thanks, had the same problem. oddly the component loses focus even if it's the content pane... — Androbin, Aug 24 '16 at 08:36

score -2 · Answer 11 · answered Jul 10 '12 at 19:24

-2

lol .... all you have to do is make sure that

addKeyListener(this);

is placed correctly in your code.

answered Jul 10 '12 at 19:24

Chris

11

8

You should really explain the "correct place" to make this a helpful answer. – Till Jul 10 '12 at 21:04

score -3 · Answer 12 · answered Nov 09 '12 at 20:22

-3

You could have custom JComponents set their parent JFrame focusable.

Just add a constructor and pass in the JFrame. Then make a call to setFocusable() in paintComponent.

This way the JFrame will always receive KeyEvents regardless of whether other components are pressed.

answered Nov 09 '12 at 20:22

Denizen

335
5
17

4

-1 definitely not - that's complete in more than one respect: a) indecent subclassing b) indecent reference passing c) inappropriate state change while painting d) .. – kleopatra Nov 10 '12 at 10:17

Unresponsive KeyListener for JFrame

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