java - 在打开时更新 JPopupMenu 菜单项

Question

在我的 UI 中，我有一个 JPopMenu，其值为 ,

例如 A、B、C

场景是，

1. 我打开了 JPopupMenu 并保持打开状态。

2. 在运行计时器的后端，它会定期将内容 B 更新为其他字母表。

   3.我希望 JPopupMenu 在保持打开状态时得到更新。

在当前行为中，如果我关闭并打开 JPopupMenu，则会显示更新的值。

我尝试了repaint()但它没有做任何事情。

最好的方法是什么？我是 Swing 新手，请帮忙。

Answer 1

菜单项可以在运行时更改其内容。如果不查看代码，很难判断您做错了什么，但这是一个有效的示例:

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JMenuItem;
import javax.swing.JPopupMenu;
import javax.swing.SwingUtilities;
import javax.swing.Timer;
import javax.swing.event.PopupMenuEvent;
import javax.swing.event.PopupMenuListener;

public class PopupTest {
    private static final String[] messages = {
        "You are today's 1000th user!",
        "You have won an internet!",
        "Claim your prize!"
    };

    private PopupTest() {
        JFrame frame = new JFrame("You have won");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JLabel lbl = new JLabel("Check your prize!");
        frame.setLocationByPlatform(true);
        frame.add(lbl);
        frame.pack();

        final JPopupMenu menu = new JPopupMenu();
        final JMenuItem item = new JMenuItem(messages[0]);
        menu.add(item);
        menu.add(new JMenuItem("Another item that does not work"));

        final Timer timer = new Timer(1000, new ActionListener() {
            int count;

            @Override
            public void actionPerformed(ActionEvent e) {
                count++;
                count %= messages.length;
                item.setText(messages[count]);
            }
        });

        menu.addPopupMenuListener(new PopupMenuListener() {
            @Override
            public void popupMenuWillBecomeVisible(PopupMenuEvent e) {
            }

            @Override
            public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {
                timer.stop();
            }

            @Override
            public void popupMenuCanceled(PopupMenuEvent e) {
                timer.stop();
            }
        });

        lbl.addMouseListener(new MouseAdapter() {
            @Override
            public void mousePressed(MouseEvent e) {
                maybeShowPopup(e);
            }

            @Override
            public void mouseReleased(MouseEvent e) {
                maybeShowPopup(e);
            }

            private void maybeShowPopup(MouseEvent e) {
                if (e.isPopupTrigger()) {
                    menu.show(e.getComponent(), e.getX(), e.getY());
                    timer.start();
                }
            }
        });

        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new PopupTest();
            }
        });
    }
}