Unresponsive KeyListener for JFrame

Tomek_29326 0
Viewed 125566

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?

keylistener jframe swing java
12 Answers

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);
bruno_conde_311360

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

Admin1

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.

Tom_Hawtin_-_tackline_47250

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;
}
user_5688350

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);
    }
}
Touko_284820

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.

user_2254660
Related