带有用于隐藏JMenu的下拉列表的JMenuBar

Question

想要创建一个JMenuBar。如果window-JFrame.width设置为small以显示JMenuBar的所有JMenu，则JMenuBar中会出现一个Button，并且可以在下拉列表中选择所有隐藏的JMenu。请问我怎么能意识到这一点？

Answer 1

我来看看JToolBar，如图所示。你可以使用任何需要的布局和大多数L&Fs允许栏变成一个浮动窗口。

Answer 2

使用CardLayout可以获得一个面板，该面板包含普通菜单和用按钮实现的菜单。然后向其添加ComponentListener（ComponentAdapter），并在侦听器的componentResized()方法中选择所需的菜单实现。

在代码中，它大致如下：

JMenuBar createCustomMenu() {
    final CardLayout layout = new CardLayout();
    final JMenuBar menu = new JMenuBar();
    menu.setLayout(layout);
    // Here you should create the normal, wide menu
    JComponent normalMenu = createNormalMenu();
    // Here you create the compressed, one button version
    JComponent compressedMenu = createCompressedMenu();
    menu.add(normalMenu, "normal");
    menu.add(compressedMenu, "compressed");
    menu.addComponentListener(new ComponentAdapter() {
        public void componentResized(ComponentEvent e) {
            if (menu.getPreferredSize().getWidth() > menu.getWidth()) {
                layout.show(menu, "compressed");
            } else {
                layout.show(menu, "normal");
            }
        }
    });
    return menu;
}

（编辑：更改为返回JMenuBar，因为它似乎工作得很好）

Answer 3

这是我5年前玩的一些旧代码。时间太长了，我甚至不记得代码的工作效果如何。它是为JToolBar设计的，但它可能会给你一些关于如何使用JMenuBar:的想法

import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
/**
*
* @author subanark
*/
public class PopupMenuLayout implements java.awt.LayoutManager
{
    private JPopupMenu popupMenu = new JPopupMenu();
    private JButton popupButton = new JButton(new PopupAction());
    /** Creates a new instance of PopupMenuLayout */
    public PopupMenuLayout()
    {
    }
    /** If the layout manager uses a per-component string,
    * adds the component <code>comp</code> to the layout,
    * associating it
    * with the string specified by <code>name</code>.
    *
    * @param name the string to be associated with the component
    * @param comp the component to be added
    */
    public void addLayoutComponent(String name, Component comp)
    {
    }
    /**
    * Lays out the specified container.
    * @param parent the container to be laid out
    */
    public void layoutContainer(Container parent)
    {
        //  Position all buttons in the container
        Insets insets = parent.getInsets();
        int x = insets.left;
        int y = insets.top;
        System.out.println("bottom: " + insets.bottom);
        int spaceUsed = insets.right + insets.left;
        for (int i = 0; i < parent.getComponentCount(); i++ )
        {
            Component aComponent = parent.getComponent(i);
            aComponent.setSize(aComponent.getPreferredSize());
            aComponent.setLocation(x,y);
            int componentWidth = aComponent.getPreferredSize().width;
            x += componentWidth;
            spaceUsed += componentWidth;
        }
        //  All the buttons won't fit, add extender button
        //  Note: the size of the extender button changes once it is added
        //  to the container. Add it here so correct width is used.
        int parentWidth = parent.getSize().width;
        if (spaceUsed > parentWidth)
        {
            popupMenu.removeAll();
            parent.add(popupButton);
            popupButton.setSize( popupButton.getPreferredSize() );
            int popupX = parentWidth - insets.right - popupButton.getSize().width;
            popupButton.setLocation(popupX, y );
            spaceUsed += popupButton.getSize().width;
        }
        //  Remove buttons that don't fit and add to the popup menu
//      System.out.println(spaceUsed + " ::: " + parentWidth);
        int lastVisibleButtonIndex = 1;
        while (spaceUsed > parentWidth)
        {
            lastVisibleButtonIndex++;
            int last = parent.getComponentCount() - lastVisibleButtonIndex;
            Component component = parent.getComponent( last );
            component.setVisible( false );
            spaceUsed -= component.getSize().width;
            addComponentToPopup(component);
//          popupButton.setLocation( button.getLocation() );
//          System.out.println(spaceUsed + "  :  " + parentWidth);
        }
    }
    private void addComponentToPopup(Component component)
    {
        System.out.println(component.getClass());
        if (component instanceof JButton)
        {
            JButton button = (JButton)component;
            JMenuItem menuItem = new JMenuItem(button.getText());
            menuItem.setIcon( button.getIcon() );
            ActionListener[] listeners = button.getActionListeners();
            for (int i = 0; i < listeners.length; i++)
                menuItem.addActionListener( listeners[i] );
            popupMenu.insert(menuItem, 0);
        }
        if (component instanceof JToolBar.Separator)
        {
            popupMenu.insert( new JSeparator(), 0);
        }
    }
    /**
    * Calculates the minimum size dimensions for the specified
    * container, given the components it contains.
    * @param parent the component to be laid out
    * @see #preferredLayoutSize
    */
    public Dimension minimumLayoutSize(Container parent)
    {
        return popupButton.getMinimumSize();
    }
    /** Calculates the preferred size dimensions for the specified
    * container, given the components it contains.
    * @param parent the container to be laid out
    *
    * @see #minimumLayoutSize
    */
    public Dimension preferredLayoutSize(Container parent)
    {
        //  Move all components to the container and remove the extender button
        parent.remove(popupButton);
/*
        while ( popupMenu.getComponentCount() > 0 )
        {
            Component aComponent = popupMenu.getComponent(0);
            popupMenu.remove(aComponent);
            parent.add(aComponent);
        }
*/
        //  Calculate the width of all components in the container
        Dimension d = new Dimension();
        d.width += parent.getInsets().right + parent.getInsets().left;
        for (int i = 0; i < parent.getComponents().length; i++)
        {
            Component component = parent.getComponent(i);
            component.setVisible( true );
            d.width += component.getPreferredSize().width;
            d.height = Math.max(d.height, component.getPreferredSize().height);
        }
//      d.height += parent.getInsets().top + parent.getInsets().bottom + 5;
        d.height += parent.getInsets().top + parent.getInsets().bottom;
        return d;
    }
    /** Removes the specified component from the layout.
    * @param comp the component to be removed
    */
    public void removeLayoutComponent(Component comp)
    {
    }
    protected class PopupAction extends AbstractAction
    {
        public PopupAction()
        {
            super(">>");
        }
        public void actionPerformed(ActionEvent e)
        {
            JComponent component = (JComponent)e.getSource();
            popupMenu.show(component,0,component.getHeight());
        }
    }
    public static void main(String[] argv)
    {
        ActionListener simpleAction = new ActionListener()
        {
            public void actionPerformed(ActionEvent e)
            {
                System.out.println(e.getActionCommand());
            }
        };
        JToolBar toolBar = new JToolBar();
        toolBar.setLayout(new PopupMenuLayout());
        toolBar.add( createButton("one", simpleAction) );
        toolBar.add( createButton("two", simpleAction) );
        toolBar.add( createButton("three", simpleAction) );
        toolBar.add( createButton("four", simpleAction) );
        toolBar.add( createButton("five", simpleAction) );
        toolBar.add( createButton("six", simpleAction) );
        toolBar.addSeparator();
        toolBar.add( createButton("seven", simpleAction) );
        toolBar.add( createButton("eight", simpleAction) );
        toolBar.addSeparator();
        toolBar.add( createButton("nine", simpleAction) );
        toolBar.add( createButton("ten", simpleAction) );
        JFrame f = new JFrame();
        f.getContentPane().setLayout(new BorderLayout());
        f.getContentPane().add(toolBar,BorderLayout.NORTH);
        f.setBounds(300,200,400,300);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }
    private static JButton createButton(String text, ActionListener listener)
    {
        JButton button = new JButton(text);
        button.addActionListener( listener );
        return button;
    }
}

在这种情况下，当没有可用空间时，工具栏按钮被转换为JMenu。如果您已经有了JMenu，那么您应该能够将JMenu从JMenuBar移动到弹出菜单。但是，在确定菜单栏的首选大小之前，您需要更改代码以始终将菜单从弹出菜单移回菜单栏。