我正在尝试编写贪吃蛇游戏，但 KeyListener 不起作用

Question

我曾尝试将侦听器添加到我创建的 Snake class 的对象、Window class 的对象和 JFrame class 的对象在 Snake class 的构造函数中，但它仍然不起作用。如果我按任意键，必须写入的字符和蛇必须转动，但它不会发生。难道是因为 snakeThread？

public class Main {

    public static void main(String[] args) {
        Window window = new Window();
        System.out.print("k");
    }
}

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

public class Window  extends JPanel {
    private Snake snake; 


    public Window() {
        super(true);
        snake = Snake.getSnake(50, 50);
        Thread snakeThread = new Thread(snake);
        snakeThread.start();
     

    }

    @Override
    public void paint(Graphics g) {
        super.paint(g);
        snake.paint(g);
    }
}

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


public class Snake extends JPanel implements Runnable {

    public static int length;
    public static ArrayList<Point> parts;
    public static Field field;
    public static Food food;
    public static int speedX=0;
    public static int speedY=1;

private static Snake snake = null;

    public static final int TIME_DELTA = 1000;
public static  Snake getSnake(int w, int h)
{
    if(snake == null) {
        snake = new Snake(w, h);
        snake.addKeyListener(new Turn(snake));
    }
    return snake;
}

    private Snake(int Width, int Heigth) {

        JFrame jf = new JFrame();
        jf.setSize(500,500);
        jf.add(this); //this - это Jpanel которым расширяется Snake
        jf.setVisible(true);


        food = new Food();field = Field.getField();
        Point start = new Point((int)Width/2, (int)Heigth/2); //размеры поля, а не окна
        parts = new ArrayList<>();parts.add(start);
        Point p1 = new Point((int)start.getX(), ((int)start.getY())-1);parts.add(p1);
        Point p2 = new Point((int)start.getX(), ((int)p1.getY())-1);
        parts.add(p2);length = 3;
    }
  

    private boolean checkHead()
    {
        for (int i=1; i<parts.size(); ++i)
        {
            if(parts.get(parts.size()-1).getLocation() == parts.get(i).getLocation())
                return false;
        }

        if(parts.get(parts.size()-1).getX() <=0 || parts.get(parts.size()-1).getX() >= field.sizeX ||
                parts.get(parts.size()-1).getY() <=0 || parts.get(parts.size()-1).getY() >= field.sizeY )
            return false;

        return true;
    }

    public static void move()
    {
        for (Point i: parts)
        {
            i.y=i.y-1*speedY;
            i.x-=1*speedX;
        }
    }
    public static void eat()
    {
        Point np = new Point ((int)parts.get(length).getX(),(int)parts.get(length).getY()-1 );
        parts.add(np);
        ++length;
        food.respawn();
    }

    public static boolean checkFood()
    {
        if(parts.get(parts.size()-1).getX() == food.x &&  parts.get(parts.size()-1).getY()==food.y)
            return true;
        else
            return false;
    }

  
    @Override
    public void paint(Graphics g) {
        super.paint(g);
        for (Point i: parts) 
            g.fillRect((int) i.getX() * 10, (int) i.getY() * 10, 8, 8);

       g.setColor(Color.RED);
       g.fillRect(food.x * 10, food.y * 10, 8, 8);
       g.setColor(Color.BLACK);
    }

    @Override

            public void run() {
        while (checkHead()) {
            move();
            repaint();
            if(checkFood())
                eat();
            try {
                Thread.sleep(TIME_DELTA);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
            }

            public  void turn(char Key)
            {
                int delta = 0;
                for(Point i: parts)
                {
                    switch (Key) {
                        case 'a':
                            i.y=parts.get(parts.size()-1).y;
                            i.x=parts.get(parts.size()-1).x+delta;
                            break;
                        case'd':
                            i.y=parts.get(parts.size()-1).y;
                            i.x=parts.get(parts.size()-1).x-delta;
                            break;

                        case 'w':
                            i.x=parts.get(parts.size()-1).x;
                            i.y=parts.get(parts.size()-1).y-delta;
                            break;
                        case's':
                            i.x=parts.get(parts.size()-1).x;
                            i.y=parts.get(parts.size()-1).y+delta;
                            break;
                    }
                    ++delta;
                }
                repaint();
            }


}

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

public class Food extends JPanel {
    public static  int x;
    public static int y;
    private static Random random;

    public Food()
    {
        super(true);
        random = new Random();
        
       x =  random.nextInt(50);
       y = random.nextInt(50);
    }

    @Override
   public void paint(Graphics g) {
        super.paint(g);
        g.setColor(Color.RED);
        g.fillRect(x * 10, y * 10, 8, 8);
        g.setColor(Color.BLACK);
    }

    public  void respawn()
    {
        x = random.nextInt(40);
        y = random.nextInt(40);
        repaint();
    }
}

听众在此：

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


public class Turn implements KeyListener {
   private char key = 'O';
   private Snake snake;

   public Turn(Snake s)
   {
       this.snake = s;
   }


    @Override
    public void keyTyped(KeyEvent e) {
        System.out.println("0");//when I press a button, "0" must be written, but it doesn't
        if(e.getKeyChar() == 'A')
        {
            System.out.println("a");//this character too
            if(snake.speedX==0)
            {
                snake.speedX=-1;//speedX was not changed
                snake.speedY=0;
                key='a';
            }
        }
        else if (e.getKeyChar() == 'W')
        {
            System.out.println("w");
            if(snake.speedY==0)
            {
                snake.speedY=-1;
                snake.speedX=0;
                key='w';
            }

        }
        else if (e.getKeyChar() == 'S')
        {
            System.out.println("s");
            if(snake.speedY==0)
            {
                snake.speedY=1;
                snake.speedX=0;
                key='s';
            }

        }
        else if (e.getKeyChar() == 'D')
        {
            System.out.println("d");
            if(snake.speedX==0)
            {
                snake.speedX=1;
                snake.speedY=0;
                key='d';
            }
        }
        if(key!='O')
snake.turn(key);
    }

    @Override
    public void keyPressed(KeyEvent e) {

    }

    @Override
    public void keyReleased(KeyEvent e) {

    }
}

Answer 1

切勿直接在组件上调用 paint(...)。如果你需要绘制一个组件，你可以在该组件上调用 repaint() 。然后 Swing 将 paint(...) 该组件并在添加到面板的所有子组件上调用 paint(...)。
所以这意味着您需要将 Snake 组件添加到父游戏面板。这也意味着没有理由覆盖 Window 面板的 paint() 方法。
不要使用静态变量和方法。这表明设计不当。从变量和方法中删除 static 关键字。
对于动画，您应该使用 Swing Timer，而不是线程。对 Swing 组件的更新应该在事件调度线程 (EDT) 上完成。定时器将在 EDT 上执行代码。
不要使用 KeyListener。 Swing 旨在与键绑定一起使用。请参阅：Motion Using the Keyboard 了解更多信息和示例。
自定义绘画是通过覆盖 paintComponent(...) 而不是 paint(...) 完成的。
main() 方法的要点是创建框架并将游戏面板添加到框架中。游戏面板不应创建框架。

Answer 2

我同意 camickr 回答中的所有内容。您的代码中有很多错误，从头开始记住这些错误将有助于避免您面临的许多问题。

但是，您的实际问题是这一行 private static Snake snake = null; 和这种方法：

public static  Snake getSnake(int w, int h)
{
    if(snake == null) {
        snake = new Snake(w, h);
        snake.addKeyListener(new Turn(snake));
    }
    return snake;
}

您永远不需要像那样在 class 中创建自引用。 Snake class 已经是一个 Snake 对象，所以在 class 中使用 private static Snake snake = null; 只是创建一个新的引用到一个全新的和不同的 Snake 在你的 Snake 内。相反，您需要使用 this 关键字来引用 Snake 对象，例如 this.addKeyListener(new Turn(this)); 而不是 snake.addKeyListener(new Turn(snake));

Delete/remove getSnake 方法，你试图混合静态和非静态对象，但不需要，我们可以将方法的 keylistener 部分移到我们的构造函数中（见下文） .请注意，如果您想更新蛇的宽度和高度，那么您应该使用不同的方法分别更新 parts 和 p1 以及 p2。

修复蛇class:

固定的 Snake class 可能看起来像这样：

public class Snake extends JPanel implements Runnable {

    //None of the variables or methods should be static
    //remove the static keyword from everywhere in the Snake class
    public int length;
    public ArrayList<Point> parts;
    public Field field;
    public Food food;
    public int speedX=0;
    public int speedY=1;

    public final int TIME_DELTA = 1000;

    //The constructor needs to be a public method (Not private)
    public Snake(int Width, int Heigth) {
        //Delete all the JFrame code,
        //it should be done in the main method

        //Add the key ilstener here (moved from the getSnake method)
        this.addKeyListener(new Turn(this));
        
        //Create the snake
        food = new Food();
        field = Field.getField();
        Point start = new Point((int)Width/2, (int)Heigth/2); //размеры поля, а не окна
        parts = new ArrayList<>();
        parts.add(start);
        Point p1 = new Point((int)start.getX(), ((int)start.getY())-1);parts.add(p1);
        Point p2 = new Point((int)start.getX(), ((int)p1.getY())-1);
        parts.add(p2);
        length = 3;
    }

    //Rest of the code removed for clarity
    ...
}

修复主要方法并删除 Window class:

要使用此更新的 Snake class，您可以完全删除 Window class 并在主 class:

中使用类似的内容

public class Main {

    public static void main(String[] args) {
        //Create JFrame
        JFrame jf = new JFrame();
        jf.setSize(500,500);

        //Create Snake
        Snake snake = new Snake(50, 50);

        //Add Snake to JFrame and set the frame visible
        jf.add(snake);
        jf.setVisible(true);
        
        //Finally start the Snake thread
        Thread snakeThread = new Thread(snake);
        snakeThread.start();
    }
}

还有很多问题需要修复，但这应该可以解决您的关键侦听器无法正常工作的问题。

其他修复：

更好的解决方案是使用键绑定，而不是键监听器。我们可以在您的主方法中创建这样的键绑定：

//Key binding to trigger when KeyEvent.VK_W ('w') is pressed
snake.getInputMap().put(KeyStroke.getKeyStroke(KeyEvent.VK_W, 0), "NORTH");
snake.getActionMap().put("NORTH", new AbstractAction()
     {
     @Override
     public void actionPerformed(ActionEvent e)
     {
         //Your code here to change the snake direction
         //we can call the turn method from inside this snake object/class
         snake.turn('w');
     }
     });

你应该在你的 Snake class 中覆盖 protected void paintComponent(Graphics g) 而不是 public void paint(Graphics g)，像这样：

@Override
protected void paintComponent(Graphics g){
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D) g;
    for (Point i: parts) 
        g2d.fillRect((int) i.getX() * 10, (int) i.getY() * 10, 8, 8);

   g2d.setColor(Color.RED);
   g2d.fillRect(food.x * 10, food.y * 10, 8, 8);
   g2d.setColor(Color.BLACK);
}

最后，与其让你的 Snake class 实现 Runniable，不如在你的 Snake class 中创建一个简单的独立摆动计时器，如下所示：

void startTimer(){
    //Start timer to update snake location every 100ms
    Timer timer = new Timer(100, new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent ae){
            //Your code here to update and repaint the snake location
            snake.updateLocation();
        }
    });
    timer.start();
}

并且在您的主要方法中，您可以简单地使用 snake.startTimer(); 而不是 Thread snakeThread = new Thread(snake); 和 snakeThread.start();

我正在尝试编写贪吃蛇游戏，但 KeyListener 不起作用

I'm trying to write a snake game, but the KeyListener does not work

java

multithreading

listener

keylistener

game-development

修复蛇class:

修复主要方法并删除 Window class:

其他修复：