KeyListener 在 JFrame 中没有响应

Question

我为非常简单的 pong 编写了这段代码，一切正常，只是我不知道如何使 KeyListener 工作。我不知道在哪里放置 Listener 或如何使用它。欢迎任何其他提示，我是菜鸟，所以请解释到那个级别。

package pong;

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;

public class Pong extends JPanel implements KeyListener
{   
    int border = 15;

    int enemyScore = 0;
    int playerScore = 0;

    int ballx = 248;
    int bally = 170;

    int playerx = 482;
    double playery = 162;
    int playeryy = 162;

    int enemyx = 0;
    double enemyy = 162;
    int enemyyy = 162;

    boolean gameReset = true;

    boolean down;
    boolean right;

    //ball movement
    private void moveBall()
    {
        Random rand = new Random();

        while (gameReset == true)
        {
            ballx = 240;
            bally = 170;
            down = rand.nextBoolean();
            right = rand.nextBoolean();
            gameReset = false;
        }

        if (right == true)
        {
            ballx++;
        }
        else
        {
            ballx--;
        }

        if (down == true)
        {
            bally++;
        }
        else
        {
            bally--;
        }

        if(bally == getHeight()-border)
        {
            down = false;
        }
        else if (bally == 0)
        {
            down = true;
        }

        if (playeryy < bally+14 && playeryy+59 > bally && ballx == 468)
        {
            right = false;
        } 
        else if (ballx == getWidth()-border)
        {
            gameReset = true;
            enemyScore ++;
        }
        else if (enemyyy < bally+14 && enemyyy+59 > bally && ballx == 13)
        {
            right = true;
        } 
        else if (ballx == 0)
        {
            gameReset = true;
            playerScore ++;
        }
    }


    //enemy movement
    private void moveEnemy()
    {
        if (right == false && bally > enemyy+8 && enemyy < 294)
        {
            enemyy += 0.8;
            enemyyy = (int) enemyy;
        }
        else if (right == false && bally < enemyy+8 && enemyy > 0)
        {
            enemyy -= 0.8;
            enemyyy = (int) enemyy;
        }
    }

    //Drawing
    @Override                               
    public void paint(Graphics g)
    {
        super.paint(g);
        g.fillRect(enemyx, enemyyy, 15, 60);
        g.fillRect(playerx, playeryy, 15, 60);
        g.fill3DRect(ballx, bally, 15, 15, true);
        System.out.println("Enemy Score: " + enemyScore + " Player Score: "+ playerScore);
    }

    public static void main(String[] args) throws InterruptedException
    {

        JFrame frame = new JFrame("p0ng");                      //makes new frame
        frame.setSize(512,384);                                 //sets the size
        frame.setVisible(true);                                 //makes it visble
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);   //allows it to sleep
        Pong game = new Pong();
        frame.add(game);

        while(true)
        {
            game.moveBall();
            game.moveEnemy();
            game.repaint();

            Thread.sleep(10);
        }     
    }  

    @Override
    public void keyTyped(KeyEvent ke) {
        //not being used
    }

    //Player movement
     @Override
    public void keyPressed(KeyEvent e) 
    {  
        if (e.getKeyCode() == KeyEvent.VK_UP && playery < 294)
        {
            playery += .8;
            playeryy = (int) playery;
        }
            else if (e.getKeyCode() == KeyEvent.VK_DOWN && playery > 0)
        {
            playery -= .8;
            playeryy = (int) playery;
        }
        repaint();
    }

    @Override
    public void keyReleased(KeyEvent ke) {
        //not being used
    }
}

Answer 1

欢迎任何其他提示

• 不要使用KeyListener，它太不可靠了，尤其是当有更好的选择时。首先看看How to Use Key Bindings
• 一般来说，您应该覆盖paintComponent 而不是paint。看看Performing Custom Painting 和Painting in AWT and Swing
• 您违反了 Swing 的单线程规则，并冒着核心逻辑和 UI 之间竞争条件的风险。查看Concurrency in Swing 了解更多详情，查看How to use Swing Timers 了解简单解决方案
• 您的“主”循环设置错误。循环的每次迭代都应该更新需要绘制的当前状态。您不应该使用“保持”循环来“暂停”状态，而应使用 if 语句根据当前状态阻止您需要/不需要执行的部分

Answer 2

public Pong(){
addKeyListner(this);
}

您需要将您的panel 注册到keyListner。 您可以使用 addKeyListner 方法来执行此操作，因为您已将 Keylistner 实现为相同的 class 。您可以使用this 关键字。您可以在constructor 中执行此操作。