Java 我的键盘监听器不工作

请帮帮我，伙计们。我就是不能运行KeyListener。但是我已经添加了你所需要的一切（我想）。我真的不知道这个代码出了什么问题。我添加了一个键侦听器，实现了一个键侦听器并包含了所有类，那么我忘记了什么/

import java.awt.Button;
import java.awt.CardLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.Rectangle;

/******Key classes are included*********/
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.io.IOException;

import javax.swing.JButton;
import javax.swing.JPanel;
import javax.swing.Timer;

/********Key listener is Implemented********/
public class Game extends JPanel implements KeyListener,Runnable
{

    JPanel m_mainPanel;
    Thread moveBall = new Thread();
    Timer t = new Timer(5, this);

    int radius = 50;

    int posx = 400;
    int posy = 400;

    int RectPosX = 10;
    int RectPosY = 400;

    int velocityX = 0;
    int velocityY = 0;

    //Konstruktor
    public Game(JPanel mainPanel) {
        m_mainPanel = mainPanel;
        setLayout(new GridLayout(3, 1));

        JPanel north_panel = new JPanel();
        north_panel.setLayout(new FlowLayout(FlowLayout.LEFT));

        /**********I didn't forget this********/
        this.addKeyListener(this);


        /*******Focus is set**********/
        setFocusable(true);
        setFocusTraversalKeysEnabled(false);

        add(north_panel);

    }

    //Painting rectangle
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        g.setColor(Color.BLACK);
        g.fillRect(RectPosX, RectPosY, radius, radius);
    }



    //the key event wich isn't called
    @Override
    public void keyPressed(KeyEvent e) 
    {
        System.out.println("Key pressed");

        if(e.getKeyCode() == KeyEvent.VK_UP)
        {
            velocityY = 10;
        }

        if(e.getKeyCode() == KeyEvent.VK_DOWN)
        {
            velocityY = -10;
        }
    }

    @Override
    public void keyTyped(KeyEvent e) {

    }

    @Override
    public void keyReleased(KeyEvent e) {

    }

    @Override
    public void run() 
    {
        while(true)
        {
            repaint();
        }
    }
}

---

以下是MCVE的一个小示例：

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

import javax.swing.JFrame;
import javax.swing.JPanel;



public class Main extends JPanel{


    public Main(){
        addKeyListener(new KeyListener(){

            @Override
            public void keyTyped(KeyEvent e) {
                System.out.println("Typed: " + e.getKeyChar());
            }

            @Override
            public void keyPressed(KeyEvent e) {
                System.out.println("Pressed: " + e.getKeyChar());
            }

            @Override
            public void keyReleased(KeyEvent e) {
                System.out.println("Released: " + e.getKeyChar());
            }

        });
    }

    public static void main(String[] args){
        JFrame frame = new JFrame("test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new Main());
        frame.setSize(300, 300);
        frame.setVisible(true);
    }
}

此程序显示出与您相同的问题：从未调用密钥侦听器！这是因为焦点在JFrame上，而不是JPanel上

要改变这一点，您必须使JPanel可聚焦。只需调用setFocusable（）方法即可实现这一点。现在，您的JPanel将重点关注：

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

import javax.swing.JFrame;
import javax.swing.JPanel;



public class Main extends JPanel{


    public Main(){
        addKeyListener(new KeyListener(){

            @Override
            public void keyTyped(KeyEvent e) {
                System.out.println("Typed: " + e.getKeyChar());
            }

            @Override
            public void keyPressed(KeyEvent e) {
                System.out.println("Pressed: " + e.getKeyChar());
            }

            @Override
            public void keyReleased(KeyEvent e) {
                System.out.println("Released: " + e.getKeyChar());
            }

        });

        setFocusable(true);
    }

    public static void main(String[] args){
        JFrame frame = new JFrame("test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(new Main());
        frame.setSize(300, 300);
        frame.setVisible(true);
    }
}

---

更复杂的程序可能需要requestFocusInWindow（）函数。或者您可能希望研究使用键绑定。但是你的主要问题是由焦点问题引起的。

焦点是什么？我跟你赌5美元，这是JFrame而不是JPanel。要么将KeyListener添加到JFrame，要么将焦点赋予JPanel。如何更改焦点？编辑：JFrame没有实现KeyListener Google是您的朋友，但是requestFocusInWindow（）是一个很好的开始。我拒绝了焦点请求：/I我准备在构造函数中实现设置的焦点：有MCVE:Game类：Menu类；菜单项类：菜单按钮类：