MouseListener not getting detected

Question

I have a JPanel (the grid), nested inside the main JFrame. I am trying to set a Mouselistener on the grid & report the event to the main frame.

App.java (Entry point)

public class App {
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new MainBoard("Tic Swing Toe");
            }
        });
    }
}

MainBoard.java (The main container, the controller)

public class MainBoard extends JFrame {

    public static final int WINDOW_MIN_WIDTH = 800;
    public static final int WINDOW_MIN_HEIGHT = 700;

    private HeaderPanel mHeaderPanel; // The header panel
    private BoardPanel mBoardPanel; // The game board panel

    public MainBoard(String windowTitle) {
        // Set window title
        super(windowTitle);

        setMinimumSize(new Dimension(WINDOW_MIN_WIDTH, WINDOW_MIN_HEIGHT));
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setContentPane(new TilePanel());
        setLayout(new BorderLayout());
        pack();
        setVisible(true);

        // Setup components
        initGUI();

        // Setup listeners on child components
        setupChildListeners();
    }

    /**
     * Setup the GUI components
     */
    private void initGUI() {
        mHeaderPanel = new HeaderPanel();
        mBoardPanel = new BoardPanel();

        add(mHeaderPanel, BorderLayout.NORTH);
        add(mBoardPanel, BorderLayout.WEST);
    }

    /**
     * Sets listeners on child components
     */
    private void setupChildListeners() {
        mBoardPanel.setHoverListener((x, y) -> System.out.println(x + " - " + y));
    }

    /**
     * The background of the application
     */
    class TilePanel extends JPanel {

        private BufferedImage mTile;

        public TilePanel() {
            try {
                // Read image from URL, could change it to disk file
                mTile = ImageIO.read(new URL("http://turbo.designwoop.com/uploads/2012/03/01_free_subtle_textures_apple_ios_linen_texture.jpg"));
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            Graphics2D g2d = (Graphics2D) g.create();
            int tileWidth = mTile.getWidth();
            int tileHeight = mTile.getHeight();
            for (int y = 0; y < getHeight(); y += tileHeight) {
                for (int x = 0; x < getWidth(); x += tileWidth) {
                    g2d.drawImage(mTile, x, y, this);
                }
            }
            g2d.dispose();
        }
    }
}

BoardPanel.java (The JPanel containing the grid, which I'm interested in)

public class BoardPanel extends JPanel {

    public static final int BOARD_BORDER_RADIUS = 20;
    public static final int CELL_MARGIN = BOARD_BORDER_RADIUS / 2;
    public static final int CELL_SIZE = 120;
    public static final int BOARD_WIDTH = CELL_SIZE * 3 + CELL_MARGIN * 4;
    public static final int BOARD_HEIGHT = CELL_SIZE * 3 + CELL_MARGIN * 4;

    // The hover listener that shall report to the 
    private CellHoverListener mHoverListener; 

    public void setHoverListener(CellHoverListener listener) {
        mHoverListener = listener;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        addMouseListener(new BoardMouseListener());
    }

    // A custom MouseListener
    class BoardMouseListener implements MouseListener {

        @Override
        public void mouseClicked(MouseEvent e) { }

        @Override
        public void mousePressed(MouseEvent e) { }

        @Override
        public void mouseReleased(MouseEvent e) { }

        @Override
        public void mouseEntered(MouseEvent e) {
            if(mHoverListener != null)
                mHoverListener.onCellHover(e.getX(), e.getY());
        }

        @Override
        public void mouseExited(MouseEvent e) { }
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(BOARD_WIDTH, BOARD_HEIGHT);
    }
}

HeaderPanel.java (The header containing the 2 text lines)

public class HeaderPanel extends JPanel {

    public static final String HEADER_TEXT = "Pure Tic Tac Toe Java - AI";
    public static final String SMALL_HEADER_TEXT =
            "The only game where you are the champion if it's a draw";

    // TODO: figure out a way to fill the whole header dynamically
    public static final int HEADER_WIDTH = 1366; // temporary solution
    public static final int HEADER_HEIGHT = 100;

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        // Draw the dark blue rectangle
        g.drawRect(0, 0, HEADER_WIDTH, HEADER_HEIGHT);
        g.setColor(new Color(33, 33, 33, 240)); // Dark blue
        g.fillRect(0, 0, HEADER_WIDTH, HEADER_HEIGHT);

        // Draw the first line of text
        g.setColor(Color.WHITE);
        FontMetrics fm = g.getFontMetrics();
        Rectangle2D header = fm.getStringBounds(HEADER_TEXT, g);
        int x = (this.getWidth() - (int) header.getWidth()) / 2;
        int y = (this.getHeight() - (int) header.getHeight()) / 4 + fm.getAscent();
        g.drawString(HEADER_TEXT, x, y);

        // Draw the second line of text
        fm = g.getFontMetrics();
        Rectangle2D miniHeader = fm.getStringBounds(SMALL_HEADER_TEXT, g);
        x = (this.getWidth() - (int) miniHeader.getWidth()) / 2;
        y = (this.getHeight() - (int) miniHeader.getHeight()) * 3 / 4 + fm.getAscent();
        g.setColor(new Color(44, 170, 231, 250));
        g.drawString(SMALL_HEADER_TEXT, x, y);
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(HEADER_WIDTH, HEADER_HEIGHT);
    }
}

CellHoverListener.java

public interface CellHoverListener {
    void onCellHover(int x, int y);
}

Final Result:

The problem

is that the hover events are not detected at all. I tried to set a MouseListener directly on the BoardPanel, but same old behavior.

How can I correctly setup a listener on mouse events in this case?

user1803551 · Accepted Answer

Your main problem with detecting movement events is that you are not assigning a MouseMotionListener:

For example, create a constructor for you panel with:

public BoardPanel() {

    BoardMouseListener bml = new BoardMouseListener();
    addMouseListener(bml);
    addMouseMotionListener(bml);
}

or wherever you set up your components if you don't want a constructor. Then @Override methods for whichever events you want to detect:

class BoardMouseListener extends MouseAdapter {

    @Override
    public void mouseEntered(MouseEvent e) {

        System.out.println(e.getX() + " - " + e.getY());
    }

    @Override
    public void mouseMoved(MouseEvent e) {

        System.out.println(e.getX() + " - " + e.getY());
    }
}

Your other problems are:

Calling addMouseListener inside paintComponent. Each time the component is painted you are creating and registering a new listener. This is bad.
setVisible should be called only after you finish setting up all your components.
Use extends MouseAdapterinstead of implements MouseListener if you don't need to override all of its methods. If you press a button during the movement it won't be "recorded" since this is now a dragging event - use the apprropriate method.

MouseListener not getting detected

Final Result:

The problem

Answers (2)

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