通过revalidate（）和repaint（）更新Swing中的JMenu不起作用

Question

In the process of logging in, if the administrator is being logged in I want to enable JMenuItem called Admin . When program starts, its visibility is set to false. So when a user clicks Log In I run JMenu again and trying to recreate it just with Admin now set on true. Here's the code of my initialize method that's being run if it detects the user is an admin. The method is inside the JMenuBar class that the application uses.

public void initialize() {

    file = new JMenu("File");
    file.setName("File Menu");
    file.addMouseListener(this);

    help = new JMenu("Help");
    help.setName("Help Menu");
    help.addMouseListener(this);

    login = new JMenu("Login");
    login.setName("Login Menu");
    login.addMouseListener(this);

    language = new JMenu("Language");
    language.setName("Language Menu");
    language.addMouseListener(this);

    admin = new JMenu("Admin");
    admin.setName("Admin Menu");
    if(LoginDialog.AdminLoggedIn) {
        admin.setEnabled(true);
    } else
        admin.setEnabled(false);
    admin.addMouseListener(this);   

    add(file);
    add(login);
    add(help);
    add(language);
    add(admin);

    this.revalidate();
    this.repaint();

}

Thanks.

Answer 1

I would suggest not re-creating your JMenu but rather modifying it, depending on the Administrator state of your program. You could give the program a Privileges enum, one with REGULAR and ADMINISTRATOR (and possibly other) fields, something like:

public enum Privileges {
    REGULAR("Regular"), ADMINISTRATOR("Administrator");
    private String text;
    private Privileges(String text) {
        this.text = text;
    }

    @Override
    public String toString() {
        return text;
    }
}

And then change the state of your JMenu depending on the program's Privileges state. Also side note: don't use a MouseListener on your menus since these do not respect the enabled/disabled state of your menus / menuitems / buttons. For example, here is my small MVCE example, one that uses a Model-View-Controller structure (of sorts):

import java.awt.Dimension;
import java.awt.GridLayout;
import java.awt.event.KeyEvent;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;

import javax.swing.*;
import javax.swing.event.SwingPropertyChangeSupport;

@SuppressWarnings("serial")
public class MenuChanger extends JPanel {
    private CreateMenu createMenu = new CreateMenu();
    private MenuChngModel model = new MenuChngModel();
    private ButtonGroup buttonGroup = new ButtonGroup();

    public MenuChanger() {
        setPreferredSize(new Dimension(400, 300));
        model.addPropertyChangeListener(MenuChngModel.PRIVILEGES, new ModelListener());

        JPanel privilegesPanel = new JPanel();
        privilegesPanel.setLayout(new GridLayout(0, 1, 5, 5));
        privilegesPanel.setBorder(BorderFactory.createTitledBorder("Privileges"));

        for (final Privileges privileges : Privileges.values()) {
            JRadioButton rBtn = new JRadioButton(privileges.toString());
            if (privileges == Privileges.REGULAR) {
                rBtn.setSelected(true);
            }
            rBtn.addActionListener(e -> {
                createMenu.setPrivileges(privileges);
            });
            buttonGroup.add(rBtn);
            privilegesPanel.add(rBtn);
        }

        add(privilegesPanel);

    }

    public CreateMenu getCreateMenu() {
        return createMenu;
    }

    private class ModelListener implements PropertyChangeListener {
        @Override
        public void propertyChange(PropertyChangeEvent evt) {
            Privileges privileges = (Privileges) evt.getNewValue();
            createMenu.setPrivileges(privileges);
        }
    }

    private static void createAndShowGui() {
        MenuChanger mainPanel = new MenuChanger();

        JFrame frame = new JFrame("MenuChanger");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.setJMenuBar(mainPanel.getCreateMenu().getMenubar());
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

class MenuChngModel {
    public static final String PRIVILEGES = "privileges";
    private SwingPropertyChangeSupport pcSupport = new SwingPropertyChangeSupport(this);
    private Privileges privileges = Privileges.REGULAR;

    public Privileges getPrivileges() {
        return privileges;
    }

    public void setPrivileges(Privileges privileges) {
        Privileges oldValue = this.privileges;
        Privileges newValue = privileges;
        this.privileges = privileges;
        pcSupport.firePropertyChange(PRIVILEGES, oldValue, newValue);
    }

    public void addPropertyChangeListener(PropertyChangeListener listener) {
        pcSupport.addPropertyChangeListener(listener);
    }

    public void removePropertyChangeListener(PropertyChangeListener listener) {
        pcSupport.removePropertyChangeListener(listener);
    }

    public void addPropertyChangeListener(String name, PropertyChangeListener listener) {
        pcSupport.addPropertyChangeListener(name, listener);
    }

    public void removePropertyChangeListener(String name, PropertyChangeListener listener) {
        pcSupport.removePropertyChangeListener(name, listener);
    }

}

enum Privileges {
    REGULAR("Regular"), ADMINISTRATOR("Administrator");
    private String text;
    private Privileges(String text) {
        this.text = text;
    }

    @Override
    public String toString() {
        return text;
    }
}

class CreateMenu {
    private JMenuBar menubar = new JMenuBar();
    private JMenu fileMenu = new JMenu("File");
    private JMenu adminMenu = new JMenu("Administrator");
    private JMenuItem fileMenuItem = new JMenuItem("File Menu Item");
    private JMenuItem adminFileMenuItem = new JMenuItem("Admin File Menu Item");


    public CreateMenu() {
        fileMenu.setMnemonic(KeyEvent.VK_F);
        adminMenu.setMnemonic(KeyEvent.VK_A);

        fileMenu.add(fileMenuItem);
        fileMenu.add(adminFileMenuItem);       
        adminMenu.add(new JMenuItem("Foo 1"));
        adminMenu.add(new JMenuItem("Foo 2"));
        adminFileMenuItem.setEnabled(false);
        adminMenu.setEnabled(false);
        menubar.add(fileMenu);
        menubar.add(adminMenu);
    }

    public void setPrivileges(Privileges privileges) {
        switch (privileges) {
        case REGULAR:
            adminMenu.setEnabled(false);
            adminFileMenuItem.setEnabled(false);
            break;
        case ADMINISTRATOR:
            adminMenu.setEnabled(true);
            adminFileMenuItem.setEnabled(true);
            break;

        default:
            break;
        }
    }

    public JMenuBar getMenubar() {
        return menubar;
    }

}