如何在 Java 中创建带有子菜单的弹出菜单

Question

我想为我的程序添加右键菜单。我使用以下代码添加了基本菜单：

            Pmenu = new JPopupMenu("Menu");
            menuItem = new JMenuItem("Sections");
            Pmenu.add(menuItem);
            menuItem = new JMenuItem("Numbers");
            Pmenu.add(menuItem);

但是我想向这些菜单添加子菜单，例如用户将鼠标悬停在“部分”菜单中，子菜单将打开并显示部分。

Answer 1

首先，对象名称通常以小写字母开头，大写字母通常用于类/接口名称。

对于您的问题，这里是子菜单的代码

//parent menu
JPopupMenu pmenu = new JPopupMenu("Menu");

//sub menu
JMenu sectionsMenu = new JMenu("Sections");
JMenuItem menuItem1 = new JMenuItem("Item1");
sectionsMenu .add(menuItem1 );
JMenuItem menuItem2 = new JMenuItem("Item2");
sectionsMenu .add(menuItem2 );

pmenu.add(sectionsMenu);

//regular menu item
menuItem = new JMenuItem("Numbers");
pmenu.add(menuItem);

JMenu tutorial 或 submenu examble

Answer 2

将JMenu 实例添加到您的JPopupMenu。 JMenu 当然应该包含 JMenuItem 实例。

请参阅http://download.oracle.com/javase/tutorial/uiswing/components/menu.html，了解有关 Swing 菜单的教程。

Answer 3

public JMenuBar createMenuBar() {
    JMenuBar menuBar;
    JMenu menu, submenu;
    JMenuItem menuItem;
    JRadioButtonMenuItem rbMenuItem;
    JCheckBoxMenuItem cbMenuItem;

    //Create the menu bar.
    menuBar = new JMenuBar();

    //Build the first menu.
    menu = new JMenu("A Menu");
    menu.setMnemonic(KeyEvent.VK_A);
    menu.getAccessibleContext().setAccessibleDescription(
            "The only menu in this program that has menu items");
    menuBar.add(menu);

    //a group of JMenuItems
    menuItem = new JMenuItem("A text-only menu item",
                             KeyEvent.VK_T);
    //menuItem.setMnemonic(KeyEvent.VK_T); //used constructor instead
    menuItem.setAccelerator(KeyStroke.getKeyStroke(
            KeyEvent.VK_1, ActionEvent.ALT_MASK));
    menuItem.getAccessibleContext().setAccessibleDescription(
            "This doesn't really do anything");
    menuItem.addActionListener(this);
    menu.add(menuItem);

    ImageIcon icon = createImageIcon("images/middle.gif");
    menuItem = new JMenuItem("Both text and icon", icon);
    menuItem.setMnemonic(KeyEvent.VK_B);
    menuItem.addActionListener(this);
    menu.add(menuItem);

    menuItem = new JMenuItem(icon);
    menuItem.setMnemonic(KeyEvent.VK_D);
    menuItem.addActionListener(this);
    menu.add(menuItem);

    //a group of radio button menu items
    menu.addSeparator();
    ButtonGroup group = new ButtonGroup();

    rbMenuItem = new JRadioButtonMenuItem("A radio button menu item");
    rbMenuItem.setSelected(true);
    rbMenuItem.setMnemonic(KeyEvent.VK_R);
    group.add(rbMenuItem);
    rbMenuItem.addActionListener(this);
    menu.add(rbMenuItem);

    rbMenuItem = new JRadioButtonMenuItem("Another one");
    rbMenuItem.setMnemonic(KeyEvent.VK_O);
    group.add(rbMenuItem);
    rbMenuItem.addActionListener(this);
    menu.add(rbMenuItem);

    //a group of check box menu items
    menu.addSeparator();
    cbMenuItem = new JCheckBoxMenuItem("A check box menu item");
    cbMenuItem.setMnemonic(KeyEvent.VK_C);
    cbMenuItem.addItemListener(this);
    menu.add(cbMenuItem);

    cbMenuItem = new JCheckBoxMenuItem("Another one");
    cbMenuItem.setMnemonic(KeyEvent.VK_H);
    cbMenuItem.addItemListener(this);
    menu.add(cbMenuItem);

    //a submenu
    menu.addSeparator();
    submenu = new JMenu("A submenu");
    submenu.setMnemonic(KeyEvent.VK_S);

    menuItem = new JMenuItem("An item in the submenu");
    menuItem.setAccelerator(KeyStroke.getKeyStroke(
            KeyEvent.VK_2, ActionEvent.ALT_MASK));
    menuItem.addActionListener(this);
    submenu.add(menuItem);

    menuItem = new JMenuItem("Another item");
    menuItem.addActionListener(this);
    submenu.add(menuItem);
    menu.add(submenu);

    //Build second menu in the menu bar.
    menu = new JMenu("Another Menu");
    menu.setMnemonic(KeyEvent.VK_N);
    menu.getAccessibleContext().setAccessibleDescription(
            "This menu does nothing");
    menuBar.add(menu);

    return menuBar;
}

public Container createContentPane() {
    //Create the content-pane-to-be.
    JPanel contentPane = new JPanel(new BorderLayout());
    contentPane.setOpaque(true);

    //Create a scrolled text area.
    output = new JTextArea(5, 30);
    output.setEditable(false);
    scrollPane = new JScrollPane(output);

    //Add the text area to the content pane.
    contentPane.add(scrollPane, BorderLayout.CENTER);

    return contentPane;
}

public void createPopupMenu() {
    JMenuItem menuItem;

    //Create the popup menu.
    JPopupMenu popup = new JPopupMenu();
    menuItem = new JMenuItem("A popup menu item");
    menuItem.addActionListener(this);
    popup.add(menuItem);
    menuItem = new JMenuItem("Another popup menu item");
    menuItem.addActionListener(this);
    popup.add(menuItem);

    //Add listener to the text area so the popup menu can come up.
    MouseListener popupListener = new PopupListener(popup);
    output.addMouseListener(popupListener);
}

public void actionPerformed(ActionEvent e) {
    JMenuItem source = (JMenuItem)(e.getSource());
    String s = "Action event detected."
               + newline
               + "    Event source: " + source.getText()
               + " (an instance of " + getClassName(source) + ")";
    output.append(s + newline);
    output.setCaretPosition(output.getDocument().getLength());
}

public void itemStateChanged(ItemEvent e) {
    JMenuItem source = (JMenuItem)(e.getSource());
    String s = "Item event detected."
               + newline
               + "    Event source: " + source.getText()
               + " (an instance of " + getClassName(source) + ")"
               + newline
               + "    New state: "
               + ((e.getStateChange() == ItemEvent.SELECTED) ?
                 "selected":"unselected");
    output.append(s + newline);
    output.setCaretPosition(output.getDocument().getLength());
}

// Returns just the class name -- no package info.
protected String getClassName(Object o) {
    String classString = o.getClass().getName();
    int dotIndex = classString.lastIndexOf(".");
    return classString.substring(dotIndex+1);
}

/** Returns an ImageIcon, or null if the path was invalid. */
protected static ImageIcon createImageIcon(String path) {
    java.net.URL imgURL = PopupMenuDemo.class.getResource(path);
    if (imgURL != null) {
        return new ImageIcon(imgURL);
    } else {
        System.err.println("Couldn't find file: " + path);
        return null;
    }
}

/**
 * Create the GUI and show it.  For thread safety,
 * this method should be invoked from the
 * event-dispatching thread.
 */




private static void createAndShowGUI() {
    //Create and set up the window.
    JFrame frame = new JFrame("PopupMenuDemo");
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create/set menu bar and content pane.
    PopupMenuDemo demo = new PopupMenuDemo();
    frame.setJMenuBar(demo.createMenuBar());
    frame.setContentPane(demo.createContentPane());

    //Create and set up the popup menu.
    demo.createPopupMenu();

    //Display the window.
    frame.setSize(450, 260);
    frame.setVisible(true);
}

public static void main(String[] args) {
    //Schedule a job for the event-dispatching thread:
    //creating and showing this application's GUI.
    javax.swing.SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            createAndShowGUI();
        }
    });
}

class PopupListener extends MouseAdapter {
    JPopupMenu popup;

    PopupListener(JPopupMenu popupMenu) {
        popup = popupMenu;
    }

    public void mousePressed(MouseEvent e) {
        maybeShowPopup(e);
    }

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

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

}