Question

import javax.swing.*;
import javax.swing.event.MenuEvent;
import javax.swing.event.MenuListener;
import java.awt.*;

class displaymsg extends JFrame {
    public static void main(String args []){
        JFrame f = new JFrame();
        JMenuBar mb = new JMenuBar();
        JMenu supply = new JMenu("supply");
        JMenuItem addnew = new JMenuItem("add");

        addnew.addMenuListener(new MenuListener(){
            @Override
            public void menuSelected(MenuEvent me){
                JOptionPane.showMessageDialog(f,"under construction");
            }
        });
        f.add(mb); mb.add(supply);
        supply.add("New Product");
        f.setSize(400, 400);
        f.setJMenuBar(mb);
        f.setLayout(null);
        f.setLocationRelativeTo(null);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }
}

这是我的menuListener代码，但我还没有得到如何做到这一点如果有人对我可能做错了什么有任何想法，请指出

Answer 1

请参阅以下mcve中的评论：

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener; 
import javax.swing.JFrame;
import javax.swing.JMenu;
import javax.swing.JMenuBar;
import javax.swing.JMenuItem;
import javax.swing.JOptionPane;

//see https://www.javatpoint.com/java-naming-conventions
//the class does not need to extend JFrame if not used as JFrame
public class DisplayMsg{

    public static void main(String args []){
        JFrame f = new JFrame();

        JMenu supply = new JMenu("Supply");
        supply.add("New Product");
        JMenuItem addNew = new JMenuItem("Add"); //naming conventions

        addNew.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                JOptionPane.showMessageDialog(f,"under construction");
            }
        });

        JMenuBar mb = new JMenuBar();
        mb.add(supply);
        mb.add(addNew); //missing in your code
        //f.add(mb); this would add the menu to the content pane 
        f.setJMenuBar(mb); 

        f.setSize(400, 400);
        //f.setLayout(null);  // do not use null layout
                              //see https://docs.oracle.com/javase/tutorial/uiswing/layout/visual.html
        f.setLocationRelativeTo(null);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }
}

可以将MenuListener添加到JSenu，而不是添加到JMenuItem。如果你想使用它将addNew更改为JMenu：

    JMenu addNew = new JMenu("Add"); 
    addNew.addMenuListener(new MenuListener(){
        @Override
        public void menuSelected(MenuEvent me){
            JOptionPane.showMessageDialog(f,"under construction");
        }

        @Override
        public void menuCanceled(MenuEvent e) {}

        @Override
        public void menuDeselected(MenuEvent e) {}
    });

Answer 2

试一试。这就是重点。菜单是一种组织事物的方式。您有一个JMenuBar，其中包含一组Menu个。每个菜单都有一组MenuItems。您只需向ActionListener添加MenuItem即可处理事件。

public class DisplayMsg {

    public static void main(String[] args) {
        JFrame f = new JFrame();
        JMenuBar mb = new JMenuBar();
        JMenu supply;
        JMenuItem addnew;
        supply = new JMenu("supply");
        addnew = new JMenuItem("add");
        // JButton b = new JButton("click me");
        // b.setBounds(100,120,100,40);
        addnew.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                JOptionPane.showMessageDialog(f, "under construction");

            }
        });
        // f.add(b);
        f.add(mb);
        mb.add(supply);
        supply.add(addnew);
        supply.add("New Product");
        f.setSize(400, 400);
        f.setJMenuBar(mb);
        f.setLayout(null);
        f.setLocationRelativeTo(null);
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }

}

菜单监听器操作已执行

2 个答案: