java - JPopupMenu 在鼠标输入时消失

Question

我有下一个结构:JPopupMenu包含JPanel，其中包含JMenuItems。问题是，我无法使用它，因为当鼠标进入任何菜单项时，JPopupMenu就会消失。

SSCCE:

public class PopupTest {
    public static void main(String[] a) {
        final JFrame frame = new JFrame();
        frame.setSize(500, 500);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        final JPanel panel = new JPanel(new BorderLayout());
        panel.setBorder(BorderFactory.createLineBorder(Color.RED));

        panel.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                if (e.getButton() == MouseEvent.BUTTON3) {
                    final JPopupMenu menu = new JPopupMenu();
                    JPanel menuPanel = new JPanel();
                    menuPanel.setBorder(BorderFactory.createLineBorder(Color.GREEN));
                    menuPanel.setLayout(new BoxLayout(menuPanel, BoxLayout.Y_AXIS));

                    for (int i = 0; i < 10; i++) {
                        JMenuItem item = new JMenuItem(String.valueOf(i));
                        menuPanel.add(item);
                    }

                    menu.add(menuPanel);
                    menu.show(panel, e.getX(), e.getY());
                }
            }
        });
        frame.setContentPane(panel);
        frame.setUndecorated(true);
        frame.setBackground(new Color(50, 50, 50, 200));

        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                frame.setVisible(true);
            }
        });
    }
}

顺便说一句，当 JPopupMenu 及其项目之间没有 JPanel 时，问题不会重复。

有谁知道如何防止这种情况吗？

Answer 1

没有直接回答您的问题，但我认为，当它支持直接添加 JMenuitem 时，您没有必要向 JPopupMenu 添加带有框布局的 panel到它。检查以下代码片段:

                 final JPopupMenu menu = new JPopupMenu();
                   JPanel menuPanel = new JPanel();
                    menuPanel.setBorder(BorderFactory.createLineBorder(Color.GREEN));
                  //  menuPanel.setLayout(new BoxLayout(menuPanel, BoxLayout.Y_AXIS));

                    for (int i = 0; i < 10; i++) {
                             JLabel item = new JLabel(i+"");
                             menuPanel.add(item);
                            }

                    menu.add(menuPanel);

                    menu.show(panel, e.getX(), e.getY());