有人可以告诉我为什么键绑定不起作用吗？

Question

ok so I'm new to java and I'm trying to learning making 2d games but I have done all the things the tutorial guy has done and the keybinds apparently work for him and not mine
these are the files

main

import javax.swing.JFrame;

public class main {
    public static void main(String[] args) {
        JFrame window = new JFrame();
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setResizable(false);
        window.setVisible(true);
        
        MyPanel panel = new MyPanel();
        window.add(panel);
        window.pack();
        
        window.setLocationRelativeTo(null);
        window.setTitle("2D Adventure");
        
        panel.startGameThread();
}
}

the game panel

import java.awt.Color;


import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JPanel;

@SuppressWarnings("serial")

public class MyPanel extends JPanel implements Runnable {
    final int originalTileSize = 16;
    final int scale = 3;

final int tileSize = originalTileSize * scale;
final int maxScreenCol = 16;
final int maxScreenRow = 12;
final int screenwidth = tileSize * maxScreenCol;
final int screenHeight = tileSize * maxScreenRow;
int FPS = 60;

keyHandler keyh = new keyHandler();
Thread gameThread;


int playerX = 100;
int playerY = 100;
int playerSpeed = 4;




public MyPanel() {
    this.setPreferredSize(new Dimension(screenwidth, screenHeight));
    this.setBackground(Color.black);
    this.setDoubleBuffered(true);
    this.addKeyListener(new keyHandler());
    this.setFocusable(true);}

public void startGameThread() {
    gameThread = new Thread(this);
    gameThread.start();
}

@Override
public void run() {
    //nanoseconds into fps
    double drawInterval = 1000000000/FPS;
    double nextDrawTime = System.nanoTime() + drawInterval;
    
    
    while (gameThread != null) {
        

        
        update();
        
        repaint();
        

        try {
            double remainingTime = nextDrawTime - drawInterval;
            remainingTime /= 1000000;
            Thread.sleep((long) remainingTime);
            
            if (remainingTime < 0) {
                remainingTime = 0;
            }
            
            nextDrawTime += drawInterval;
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }
}

public void update() {
    if (keyh.uPressed == true) {
        playerY -= playerSpeed;
        //added this print command to see if the keyHandlers work but apparently they don't
        System.out.println("" + true);
    }
    else if (keyh.lPressed == true) {
        playerX -= playerSpeed;
    }
    else if (keyh.dPressed == true) {
        playerY += playerSpeed;
    }
    else if (keyh.rPressed == true) {
        playerX += playerSpeed;
    }
}

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    
    Graphics2D g2 = (Graphics2D)g;
    
    g2.setColor(Color.WHITE);
    g2.fillRect(playerX, playerY, tileSize, tileSize);
    
    //and here the player x and y are not changing
    System.out.println("" + playerX + playerY);
    g2.dispose();
}

}

and the keyHandler

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

public class keyHandler implements KeyListener {
    public boolean rPressed = false;
    public boolean dPressed = false;
    public boolean lPressed = false;
    public boolean uPressed = false;
    
    @Override
    public void keyTyped(KeyEvent e) {
        // TODO Auto-generated method stub
        
    }

    @SuppressWarnings("static-access")
    @Override
    public void keyPressed(KeyEvent e) {
        int code = e.getKeyCode();
        String key = e.getKeyText(code);
        switch (key) {
        case "W":
            uPressed = true;
        case "S":
            dPressed = true;
        case "A":
            lPressed = true;
        case "D":
            rPressed = true;
        }
        
    }

    @SuppressWarnings("static-access")
    @Override
    public void keyReleased(KeyEvent e) {
        int code = e.getKeyCode();
        String key = e.getKeyText(code);
        switch (key) {
        case "W":
            uPressed = false;
        case "S":
            dPressed = false;
        case "A":
            lPressed = false;
        case "D":
            rPressed = false;
        }
    }

}

sorry, it will be hard for you to figure out what all this code is but please respond soon. thanks

Answer 1

In MyPanel you are adding a new instance of the keyHandler (ie, this.addKeyListener(new keyHandler()); ) to your panel, instead of passing the one you instantiated out of the contructor. So, you should have:

this.addKeyListener(keyh);