在 Java GUI 中更改卡时 KeyListener 不起作用

Question

以下是我的代码的简化版本。菜单面板只有一个开始按钮，而游戏面板只是一个黑屏，带有一个正方形，当按下箭头键时它应该会移动。因此，当我单击菜单面板中的按钮开始游戏时，图形加载正常，但按键监听器根本不起作用。这似乎只有在涉及多个面板或在它们之间切换时才会出现问题。我是一个完整的初学者，所以任何建议都会非常有帮助。

主类

import javax.swing.JFrame;

public class Main {
    public static void main(String[] args) {
        MyFrame frame= new MyFrame();  
        frame.setSize(1000,1000);  
        frame.setVisible(true);  
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
    }

MyFrame 类

import java.awt.*;  
import java.awt.event.*;  
  
import javax.swing.*;  
  
public class MyFrame extends JFrame implements ActionListener{  
CardLayout card;  
JButton b1;
Container c; 
MyPanel game;
JPanel menu;
   public MyFrame(){  
          
        c=getContentPane();  
        card=new CardLayout();  
        c.setLayout(card);  
        
        game = new MyPanel();
        menu = new JPanel();
          
        b1=new JButton("Start");  
        b1.addActionListener(this);  
     
    
        c.add("p", menu);    
        menu.add("a",b1); 
        c.add("d", game);
        
        
                          
    }  
    public void actionPerformed(ActionEvent e) {  
        card.show(c, "d");  
        
    
    }  
   
}

MyPanel 类

import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.*;
import javax.swing.JPanel;
import javax.swing.*;


public class MyPanel extends JPanel implements ActionListener, MouseListener, MouseMotionListener, KeyListener{
    
    
    Timer myTimer;
    int x = 0;
    int y = 0;
    int xVel, yVel;


    public MyPanel() {
        myTimer = new Timer(50, this); 
        myTimer.start();
        
        
        this.addKeyListener(this);
        this.setFocusable(true);
        this.requestFocusInWindow();
        this.addMouseListener(this);
        this.addMouseMotionListener(this);
    
    
    }
    
    public void startTimer() {
        myTimer.start();
    }
    
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        this.setBackground(Color.BLACK);
        g.setColor(Color.CYAN);
        g.drawRect(x, y, 100, 100);

        
        
    }
    
    public void actionPerformed(ActionEvent e) {
        if(e.getSource()==myTimer) {
            repaint();
        
            x += xVel;
            y += yVel;
    
                    
                
        }
        
                
    }


    public void mouseDragged(MouseEvent e) {}
    public void mouseMoved(MouseEvent e) {}
    public void mouseClicked(MouseEvent e) {
    }
    public void mousePressed(MouseEvent e) {}
    public void mouseReleased(MouseEvent e) {}
    public void mouseEntered(MouseEvent e) {}
    public void mouseExited(MouseEvent e) {}
    public void keyTyped(KeyEvent e) {
    }


    public void keyPressed(KeyEvent e) {
        
        int key = e.getKeyCode();
        
        if(key== KeyEvent.VK_UP) {
            up();
        }
        
        if(key== KeyEvent.VK_DOWN) {
            
            down();
            
        }
        
        if(key== KeyEvent.VK_RIGHT) {
        
            right();
            
        }
        
        if(key== KeyEvent.VK_LEFT) {
    
            left();
            
        }
        
        
        
        
    }

    public void keyReleased(KeyEvent e) {
        xVel = 0;
        yVel = 0;
        
        
    }
    
    public void up() {
        xVel = 0;
        yVel = -5;
        
        
    }
    
    public void down() {
        xVel = 0;
        yVel = 5;
    }
    
    public void right() {
        xVel = 5;
        yVel = 0;
    }
    
    public void left() {
        xVel = -5;
        yVel = 0;
        
    }

}

Answer 1

一个简单的解决方法是在MyFrame 类的actionPerformed 方法中添加game.requestFocusInWindow();。