未检测到 MouseListener

Question

我有一个JPanel（网格），嵌套在主JFrame 内。我正在尝试在网格上设置 Mouselistener 并将事件报告给主框架。

App.java （入口点）

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

MainBoard.java （主容器，控制器）

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 （包含我感兴趣的网格的 JPanel）

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（包含 2 个文本行的标题）

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);
}

最终结果：

问题

是根本没有检测到 hover 事件。我尝试直接在BoardPanel 上设置MouseListener，但行为相同。

在这种情况下，如何在鼠标事件上正确设置监听器？

Answer 1

首先，从paintComponent() 中删除addMouseListener()。请注意，paintComponent() 会被重复调用——而且我确定您不打算在每个 repaint() 上继续添加新的鼠标侦听器。

protected void paintComponent(final Graphics g) {
    super.paintComponent(g);
}

在构造函数或某种initGUI() 调用中添加您的监听器：

public BoardPanel() {
    addMouseListener(new BoardMouseListener());
}

在此处添加调试语句。你会看到它确实被调用了。

public void mouseEntered(final MouseEvent e) {
    System.out.println(e);
    if (mHoverListener != null) {
        mHoverListener.onCellHover(e.getX(), e.getY());
    }
}

Answer 2

您检测运动事件的主要问题是您没有分配MouseMotionListener：

例如，为您的面板创建一个构造函数：

public BoardPanel() {

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

或者如果您不想要构造函数，您可以在任何地方设置组件。然后@Override 方法用于您想要检测的任何事件：

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());
    }
}

您的其他问题是：

• 在paintComponent 内调用addMouseListener。每次绘制组件时，您都在创建和注册一个新的侦听器。这很糟糕。
• setVisible 仅应在您完成所有组件的设置后调用。
• 如果您不需要覆盖其所有方法，请使用extends MouseAdapter 而不是implements MouseListener。如果您在移动过程中按下按钮，它将不会被“记录”，因为现在这是一个拖动事件 - 请使用适当的方法。