java – 在显示之前获取JPopupMenu大小

我点击鼠标右键显示JPopupMenu.我希望JPopupMenu的右上角位于点击位置(默认情况下不是左上角).要执行此操作,我需要将X坐标设置为mouseEvent.getX() – popupMenu.getWidth().问题是,在第一次显示弹出窗口之前,其宽度等于0.

SSCCE：

public class PopupTest2 {
    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));

        final JPopupMenu menu = new JPopupMenu();

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

        panel.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                if (e.getButton() == MouseEvent.BUTTON3) {
                    // first time works wrong
                    menu.show(panel, e.getX() - menu.getWidth(), 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);
            }
        });
    }
}

解决方法:

在显示之前,JPopupMenu的首选大小是多少？

标签：java,swing,preferredsize,jpopupmenu,sizing
来源： https://codeday.me/bug/20190728/1565207.html