java - 添加 JMenuItems 的有效方法

Question

好吧，在我的 INV 程序是删除菜单项之前，但后来我就想……这太多了。那么，如果我为特定的右键单击项目添加菜单项而不是每次都删除呢？

因此，如果您右键单击第 1 项，则会将“使用”和“放置”添加到菜单中。然后，一旦您选择了选项，JMenu 就会删除所有内容，因此它就在我们开始的地方。然后，如果您右键单击 ITem 2，它会添加“使用”和“取消”。看到我要去哪里了吗？

我尝试自己做，但我就是不知道该怎么做——例如，要添加一个新的 JMenuItem，您需要这样做:

popup.add(item = new JMenuItem("Cancel"));
item.addActionListener(menuListener);

并且，如您所见，添加一个 Action 监听器。我无法在 if (actItemx == "Item 1") { 下执行此操作，所以...我该怎么办？

无论如何，这是我到目前为止所拥有的:

import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseAdapter;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;
import javax.swing.border.*;
import javax.swing.event.*;

public class inv extends JApplet implements MouseListener
{
    public JList listbox;
    public JPopupMenu popup;
    public JMenuItem item;

    public void init()
    {
        ActionListener menuListener = new ActionListener()
        {
            public void actionPerformed(ActionEvent event)
            {
                String invAction = event.getActionCommand();


                int itemSelect = listbox.getSelectedIndex();
                Object actItem = listbox.getModel().getElementAt(itemSelect);

                System.out.println("Popup menu item [" + invAction + "] [ " + actItem + " ] was pressed.");
            }
        };

        popup = new JPopupMenu();

        popup.add(item = new JMenuItem("Use"));
        item.addActionListener(menuListener);

        popup.add(item = new JMenuItem("Drop"));
        item.addActionListener(menuListener);

        popup.add(item = new JMenuItem("Cancel"));
        item.addActionListener(menuListener);



        String listData[] =
        {
            "Item 1","Item 2","Item 3","Item 4"
        };

        listbox = new JList( listData );
        listbox.addMouseListener( new MouseAdapter()
        {
            public void mousePressed(MouseEvent e)
            {
                if ( SwingUtilities.isRightMouseButton(e) )
                {
                    System.out.println("Row: " + getRow(e.getPoint()));
                    listbox.setSelectedIndex(getRow(e.getPoint()));
                }
            }
        }
        );

        listbox.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
        add(listbox);
        listbox.setVisible(true);
        listbox.setFocusable(false);


        listbox.addMouseListener(new MousePopupListener());
    }

    class MousePopupListener extends MouseAdapter
    {
        public void mousePressed(MouseEvent e)
        {
            checkPopup(e);
        }

        public void mouseClicked(MouseEvent e)
        {
            checkPopup(e);
        }

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

        private void checkPopup(MouseEvent e)
        {
            if (e.isPopupTrigger())
            {

                int itemSelectx = listbox.getSelectedIndex();
                Object actItemx = listbox.getModel().getElementAt(itemSelectx);
                System.out.println("You pressed on " + actItemx);

            if (actItemx == "Item 1") {
                System.out.println("Removed cancel for " + actItemx);
                popup.remove(itemSelectx); // So upon right-click on Item 1, you won't see "Cancel" menu.
            }

                popup.show(inv.this, e.getX(), e.getY());
                popup.revalidate();
            }
        }
    }

    private int getRow(Point point)
    {
        return listbox.locationToIndex(point);
    }

    public void mouseEntered(MouseEvent e)
    {
    }

    public void mouseReleased(MouseEvent e)
    {
    }

    public void mousePressed(MouseEvent e)
    {
    }

    public void mouseClicked(MouseEvent e)
    {
    }

    public void mouseExited(MouseEvent e)
    {
    }
}

Answer 1

为每种类型的项目设置不同的 JPopup 菜单怎么样？我的意思是你有看起来像这样的东西:

public JPopupMenu useDropPopup;
public JPopupMenu useCancelPopup;

public void init() {
   ActionListener menuListener = new ActionListener()
        {
            public void actionPerformed(ActionEvent event)
            {
                String invAction = event.getActionCommand();


                int itemSelect = listbox.getSelectedIndex();
                Object actItem = listbox.getModel().getElementAt(itemSelect);

                System.out.println("Popup menu item [" + invAction + "] [ " + actItem + " ] was pressed.");
            }
        };

   useDropPopup = new JPopupMenu();
   useCancelPopup = new JPopupMenu();

   JMenuItem useMenuItem = new JMenuItem("Use");
   useMenuItem.addActionListener(menuListener);
   JMenuItem dropMenuItem = new JMenuItem("Drop");
   dropMenuItem.addActionListener(menuListener);
   JMenuItem cancelMenuItem = new JMenuItem("Cancel");
   cancelMenuItem.addActionListener(menuListener);

   useDropPopup.add(useMenuItem);
   useDropPopup.add(dropMenuItem);

   useCancelPopup.add(useMenuItem);
   useCancelPopup.add(cancelMenuItem);

   // ... etc bring up the appropriate popup depending on the item.
}

此外，您不应将 JMenuItem 分配给方法调用内部的项目。这是不好的做法。还可以考虑为每个菜单项使用不同的 Action 监听器，以便您可以分离每个菜单项的功能代码，例如:

useMenuItem.addActionListener(new ActionListener() {
   public void actionPerformed(ActionEvent event) {
      useMenuAction(event);
   }
};

// ... after the init method

public void useMenuAction(ActionEvent evt) {
   // Add specific use menu code here.
}