JPopupMenu的菜单项没有响应更改...为什么？

Question

我注意到，一旦我的JPopupMenu第一次可见，它的菜单项不反映对它们的下一次可见性所做的更改。下面是代码;

private static void addListener(final JPopupMenu popup, final String someLetter)
{
    popup.addPopupMenuListener(new PopupMenuListener(){            
        @Override
        public void popupMenuWillBecomeVisible(PopupMenuEvent evt)
        {
            JMenuItem menuItem3 = (JMenuItem)popup.getComponent(3); 
            String[] letters = {"A", "B", "C", "D"};
            ArrayList<String> lettersList = new ArrayList<String>();
            lettersList.addAll(Arrays.asList(letters));
            if(lettersList.contains(someLetter)){
                menuItem3.setEnabled(true);
            }
            else{
                menuItem3.setEnabled(false);
            }
        }
    });
}

通常我希望popupMenuWillBecomeVisible下的行总是在popupMenu弹出时执行。但令我惊讶的是，它只适用于第一次，随后不测试指定的条件，以启用或禁用menuItem3。拜托有人帮帮我的兄弟吧!

Answer 1

这对我来说似乎工作得很好。看看下面的例子，它显示了5个菜单项，并在每次执行右键单击时切换它们的"启用":

import java.awt.event.ActionEvent;
import java.util.ArrayList;
import java.util.List;
import javax.swing.AbstractAction;
import javax.swing.JFrame;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JPopupMenu;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.PopupMenuEvent;
import javax.swing.event.PopupMenuListener;
public class TestPopupMenu {
    private void initUI() {
        final JFrame frame = new JFrame(TestPopupMenu.class.getSimpleName());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel();
        final JPopupMenu popup = new JPopupMenu();
        final List<JMenuItem> items = new ArrayList<JMenuItem>();
        for (int i = 0; i < 5; i++) {
            JMenuItem item = new JMenuItem(new AbstractAction("Action " + (i + 1)) {
                @Override
                public void actionPerformed(ActionEvent e) {
                    JOptionPane.showMessageDialog(popup, getValue(NAME) + " has been clicked");
                }
            });
            item.setEnabled(i % 2 == 0);
            items.add(item);
            popup.add(item);
        }
        popup.addPopupMenuListener(new PopupMenuListener() {
            @Override
            public void popupMenuWillBecomeVisible(PopupMenuEvent e) {
                for (JMenuItem item : items) {
                    item.setEnabled(!item.isEnabled());
                }
            }
            @Override
            public void popupMenuWillBecomeInvisible(PopupMenuEvent e) {
            }
            @Override
            public void popupMenuCanceled(PopupMenuEvent e) {
            }
        });
        panel.setComponentPopupMenu(popup);
        frame.add(panel);
        frame.setSize(300, 200);
        frame.setVisible(true);
    }
    public static void main(String[] args) {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InstantiationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (UnsupportedLookAndFeelException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new TestPopupMenu().initUI();
            }
        });
    }
}

Answer 2

感谢@mKorbel推动我尝试在此过程中编写SSCCE cos，我找到了解决方案。这是我的SSCCE，无论如何，它可能只是对别人有用。谁知道呢?只需复制并运行，看看它是如何工作的。

(注意:代码不是很短，因为我打算在这之后提出第二个问题)

import java.awt.Dimension;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JMenuItem;
import javax.swing.JPopupMenu;
import java.util.ArrayList;
import java.util.Arrays;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.PopupMenuEvent;
import javax.swing.event.PopupMenuListener;
public class CustomPopup extends JPopupMenu
{
    private JMenuItem menuItem1 = new JMenuItem("One");
    private JMenuItem menuItem2 = new JMenuItem("Two");
    private JMenuItem menuItem3 = new JMenuItem("Three");
    private JMenuItem menuItem4 = new JMenuItem("Four");
    private JMenuItem menuItem5 = new JMenuItem("Five");
    public CustomPopup()
    {
        this.add(menuItem1);
        this.add(menuItem2);
        this.add(menuItem3);
        this.add(menuItem4);
        this.add(menuItem5);
        addListeners(this);
    }
    private  void addListeners(final JPopupMenu popup /*, final String someLetter*/)
    {
        popup.addPopupMenuListener(new PopupMenuListener(){            
            @Override
            public void popupMenuWillBecomeVisible(PopupMenuEvent evt)
            {
                JMenuItem menuItem = (JMenuItem)popup.getComponent(3); 
                String[] letters = {"A", "B", "C", "D"};
                ArrayList<String> lettersList = new ArrayList<String>();
                lettersList.addAll(Arrays.asList(letters));
                String someLetter = getRandomAlphabet();
                if(lettersList.contains(someLetter)){
                    menuItem.setEnabled(true);
                }
                else{
                    menuItem.setEnabled(false);
                }
            }
            @Override
            public void popupMenuWillBecomeInvisible(PopupMenuEvent evt){
                // No Override
            }
            @Override
            public void popupMenuCanceled(PopupMenuEvent evt){
                // No Override
            }
        });
    }
    private  String getRandomAlphabet()
    {
        String alpha = "";
        String Alphas[] = {"A", "B", "C", "D", "E", "F", "G", "H", "I", "J"};
        double bigNum = Math.random() * 1000000;
        String str = String.valueOf(bigNum);
        int idx = Integer.valueOf(String.valueOf(str.charAt(str.length() - 1)));
        if(idx < 6)
        {
            alpha = Alphas[idx];
        }
        else
        {
            alpha = Alphas[idx - 5];
        }
        return alpha;
    }
    public static void main(String[] args)
    {
        /*try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (InstantiationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (UnsupportedLookAndFeelException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }*/
        JPanel panel = new JPanel();
        JPopupMenu popupMenu = new CustomPopup();
        panel.setComponentPopupMenu(popupMenu);
        panel.setLayout(new GridBagLayout());
        /*JButton button = new JButton("Action");
        button.setSize(new Dimension(60, 20));
        button.addActionListener(new ActionListener(){
            @Override
            public void actionPerformed(ActionEvent e)
            {
                JOptionPane.showMessageDialog(null, "Button was clicked");
            }
        });
        panel.add(button);*/
        JFrame frame = new JFrame("popupTest");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(new Dimension(200, 200));
        frame.add(panel);
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }
}

问题:现在，这做了我想要它做的，(即启用和禁用menuItem4动态基于随机结果从一些指定的计算getRandomAlphabet())，我看了@纪尧姆波莱的可爱的实现和测试它。很好……所以我只是决定添加一个按钮，并测试一个最恼人的问题，我曾经有过使用UIManager，不是原生Java默认弹出窗口时…同样的事情发生了!

我是什么意思?当LnF不是默认的Metal时，在弹出菜单显示后，单击任何其他可操作组件的弹出菜单外，第一次单击不起作用(这只会设置不可见的弹出)。然后你必须再次点击组件(第二次)，才能触发它的Action……很烦人，不是吗?

为了感受这种场景，只需取消上面代码的UIManager部分的注释(我从@Guillaume Polet的漂亮解决方案中获得的)，并取消我添加的Button部分的注释，然后运行程序，看看当您尝试在popupMenu显示后立即单击按钮时会发生什么。有趣的是，这个问题不会发生在使用Java默认的Metal

时。我在Windows 7上使用系统默认的外观和感觉来解决这个问题，但无济于事，所以我决定不要自找麻烦……但老实说，我认为有一个解决办法……我知道肯定有人能破解这玩意……代码块，方向，链接，任何解决这个问题的地方都会让我非常高兴。谢谢善良的人们!