过去，当一个 JPopupMenu 可见时，它的第一项将默认被选中:http://weblogs.java.net/blog/alexfromsun/archive/2008/02/jtrayicon_updat.html

如今，默认行为是在未选择任何项目的情况下弹出菜单。我想创建一个 JPopupMenu，其中包含一个项目，该项目将被选中并在鼠标指针下方居中。我已经设法让该项目在鼠标下方居中弹出，但我 JMenuItem 拒绝呈现，就好像它被选中一样。如果我将鼠标移出该项目并返回，则会正确选择。

有什么想法吗？

这是我的测试用例:

import java.awt.Component;
import java.awt.Point;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JMenuItem;
import javax.swing.JPopupMenu;

public class Test extends JFrame
{
    public static void main(String[] args)
    {
        JFrame frame = new JFrame();
        frame.setSize(800, 600);
        frame.getContentPane().addMouseListener(new MouseAdapter()
        {
            @Override
            public void mousePressed(MouseEvent e)
            {
                if (e.isPopupTrigger())
                    popupTriggered(e);
            }

            @Override
            public void mouseReleased(MouseEvent e)
            {
                if (e.isPopupTrigger())
                    popupTriggered(e);
            }

            private void popupTriggered(MouseEvent e)
            {
                JPopupMenu menu = new JPopupMenu();
                final JMenuItem item = new JMenuItem("This is a JMenuItem");
                menu.add(item);
                Point point = e.getPoint();
                int x = point.x - (item.getPreferredSize().width / 2);
                int y = point.y - (item.getPreferredSize().height / 2);
                menu.show((Component) e.getSource(), x, y);
            }
        });
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.setVisible(true);
    }
}

最佳答案

secret 原来是MenuSelectionManager.defaultManager().setSelectedPath(new MenuElement[]{menu, ...});

import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JMenuItem;
import javax.swing.JPopupMenu;
import javax.swing.MenuElement;
import javax.swing.MenuSelectionManager;
import javax.swing.SwingUtilities;

/**
 * Demonstrates programmatic {@link JMenuItem} selection;
 * specifically how to make the first item selected by default
 */
public class TestPopup extends JFrame {
  public static void main(String[] args) {
    final JFrame frame = new JFrame("TestPopup");
    frame.setSize(640, 480);
    frame.getContentPane().addMouseListener(new MouseAdapter() {
      @Override
      public void mousePressed(MouseEvent e) {
        if (e.isPopupTrigger()) {
          popupTriggered(e);
        }
      }
      private void popupTriggered(MouseEvent e) {
        final JPopupMenu menu = new JPopupMenu();
        final JMenuItem item0 = new JMenuItem("JMenuItem 0");
        final JMenuItem item1 = new JMenuItem("JMenuItem 1");
        menu.add(item0);
        menu.add(item1);
        menu.pack();
        // use invokeLater or just do this after the menu has been shown
        SwingUtilities.invokeLater(new Runnable() {
          public void run() {
            MenuSelectionManager.defaultManager().setSelectedPath(new MenuElement[]{menu, item0});
          }
        });
        int x = (int) ((int) (frame.getSize().width - (menu.getPreferredSize().width / 2.)) / 2.);
        int y = (int) ((int) (frame.getSize().height - (menu.getPreferredSize().height / 2.)) / 2.);
        menu.show(frame, x, y);
        // doesn't work:
        //item0.setSelected(true);
        // doesn't work:
        //menu.getSelectionModel().setSelectedIndex(0);
        // bingo; see also MenuKeyListener / MenuKeyEvent
//        MenuSelectionManager.defaultManager().setSelectedPath(new MenuElement[]{menu, item0});
      }
    });
    frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }
}

关于java - 如何在 JPopupMenu 中选择第一项？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/482041/