What mistake am I making in adding my key listener?

Question

My launcher object (represented by a bald eagle picture) for a game I'm making doesn't respond to key events. I know it's an issue with how I'm declaring the listener, but I'm not sure what I'm doing wrong.

Here's my code:

public class Main {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) throws IOException {
    GameTest t = new GameTest();
}

public static class GameTest extends JFrame {

    private static final int WINDOW_WIDTH = 800;
    private static final int WINDOW_HEIGHT = 500;
    private GamePanel gamePanel;
    private GameTest gameTest;

    public GameTest() throws IOException {
        super("Deep Fried Freedom");
        setResizable(false);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setSize(WINDOW_WIDTH, WINDOW_HEIGHT);
        setLayout(new BorderLayout());
        gamePanel = new GamePanel();
        add(gamePanel);
        center(this);
        setVisible(true);
        this.addKeyListener(new aKeyListener());
        this.setFocusable(true);
    }

    public void center(JFrame frame) {
        GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();
        Point center = ge.getCenterPoint();

        int w = frame.getWidth();
        int h = frame.getHeight();

        int x = center.x - w / 2, y = center.y - h / 2;
        frame.setBounds(x, y, w, h);
        frame.validate();
    }//end of center method  

    public class aKeyListener implements KeyListener {

        @Override
        public void keyTyped(KeyEvent e) {
        }//end empty keyTyped method

        @Override
        public void keyPressed(KeyEvent e) {
            Launcher.lRun -= 5;
            gamePanel.move();
        }//end keyPressed method

        @Override
        public void keyReleased(KeyEvent e) {
        }//end empty keyReleased method

    }//end aKeyListener class

}//end GameTest class
}// end main class


public class GamePanel extends JPanel {
Launcher launcher1;
Background bground1;

public GamePanel() throws IOException {
    super();
    launcher1 = new Launcher();
    bground1 = new Background();
}//end constructor

@Override
protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    g.drawImage(bground1.background, 0, 0, getWidth(), getHeight(), null);
    g.drawImage(launcher1.baldEagleImage, 350, 415, null);//paint the launcher
}//end paintComponent method

public void move() {
    launcher1.moveX();
    repaint();
}//end move method
}//end GamePanel class



public class Launcher {

public static int lxCoord;        //the launcher's x coordinate
public static final int lyCoord = 415;
public static int lRun = 0;           //the launcher's x change
public static BufferedImage baldEagleImage;

//Constructor
public Launcher() throws IOException {
    lxCoord = 350;
    baldEagleImage = ImageIO.read(new File("baldeagleimage.jpg"));
}

/**
 * The movement of the launcher in the x direction
 */
public void moveX() {
    lxCoord += lRun;
}//end moveX method


}//end Launcher class


public class Background extends JPanel {

BufferedImage background; 

public Background() throws IOException {
    background = ImageIO.read(new File("flagbackground.jpg"));
}//end constructor
}//end Background class

I did a quick skim - but it doesn't look like you're using `setKeyListener()` or whatever the requisite function is. — sdasdadas, Apr 22 '14 at 20:48
The **real** solution is [not to use `KeyListener` at all - use key binding instead](http://stackoverflow.com/questions/22741215/how-to-use-key-bindings-instead-of-key-listeners). — user1803551, Apr 22 '14 at 20:55

score 1 · Answer 1 · answered Apr 22 '14 at 20:51

1

You created a KeyListener but never added it to anything. Also, your KeyListener probably doesn't need to be a JFrame and you may have focus issues so I would recommend switching over to key bindings for a game.

answered Apr 22 '14 at 20:51

NESPowerGlove

5,496
17
28

Mumfi · Answer 2 · 2014-04-22T20:58:43.960

1

addKeyListener( new aKeyListener() );

in the JFrame constructor should do it. You should not extend your aKeyListener with JFrame.

Also, consider using an inner class for your KeyListener, as it will probably not be needed for other classes.

edited Apr 22 '14 at 20:58

answered Apr 22 '14 at 20:53

Mumfi

405
4
15

I appreciate the response. I'm still not getting any response, so I guess I messed up implementing your suggestions. I updated my code, is there any chance you could look back over it and guide me to where I'm going wrong? I don't want the solution, just a helping hand. I'm new to OOP, and programming in general. – Ben Apr 22 '14 at 21:38
@Ben - I tested your code, and your implementation of the KeyListener is fine (although I recommend to extend `KeyAdapter` instead of implementing `KeyListener` to your inner class to get rid of unused methods, such as keyReleased). Try to put a `System.out.print("something");` in your keyPressed and you'll notice that it will type that out whenever your press a button. The problem lies elsewhere. – Mumfi Apr 22 '14 at 22:07
Thanks, I realized that my paintComponent method was just repainting the launcher in its initial position every time I called repaint(). I fixed that and now it moves when I hit the "a" button. I appreciate the help! – Ben Apr 22 '14 at 22:29

What mistake am I making in adding my key listener?

2 Answers2