java - JPopupMenu 不起作用

Question

我编写了一个简单的程序来了解 JPopupMenu 的工作原理。但我的代码有问题，它没有正确显示弹出菜单。请问谁能告诉我原因吗？

public class PopUpMenu extends JFrame implements ActionListener {

JPanel panel;
JPopupMenu popMenu;
JMenuItem cut;
JMenuItem copy;

public PopUpMenu() {

    setVisible(true);
    setSize(300, 300);
    setDefaultCloseOperation(EXIT_ON_CLOSE);

    panel = new JPanel();
    popMenu = new JPopupMenu();
    cut = new JMenuItem();
    popMenu.add(cut);
    copy = new JMenuItem();
    popMenu.add(copy);

    add(panel);
    panel.setComponentPopupMenu(popMenu);

    addMouseListener(new MouseAdapter() {
        public void mouseReleased(MouseEvent Me) {
            if (Me.isPopupTrigger()) {
                popMenu.show(Me.getComponent(), Me.getX(), Me.getY());
            }
        }
    });

}

public void actionPerformed(ActionEvent arg0) {

}

public static void main(String[] args) {

    Runnable r = new Runnable() {
        public void run() {
            PopUpMenu pop = new PopUpMenu();
        }
    };
    SwingUtilities.invokeLater(r);

}

}

Answer 1

您的代码是完美的(不需要鼠标监听器，并且应该将面板添加到 JFrame 的内容 Pane 中)，但它可以工作。如果您为菜单项提供一些文本，也许效果会更好:

cut = new JMenuItem("Cut");