java - Java 中的定时器和按键事件

Question

我在创建一个正方形的动画时遇到问题，当按下其中一个箭头键时，该动画将以一定的速度移动。我已经实现了 keyPressed 和 actionPerformed 方法，并且还在构造函数末尾启动了计时器的滴答声。但是方 block 仍然不会移动。我做错了什么？

下面是 JPanel。

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

public class A3JPanel extends JPanel implements KeyListener, ActionListener{
public static final int JFRAME_AREA_WIDTH = A3Constants.JFRAME_AREA_WIDTH;
public static final int JFRAME_AREA_HEIGHT = A3Constants.JFRAME_AREA_HEIGHT;;

public static final Rectangle HOME_AREA = A3Constants.HOME_AREA;
public static final Rectangle LEO_LEFT_AREA = A3Constants.LEO_LEFT_AREA;
public static final Rectangle ALL_WALLS_AREA = A3Constants.ALL_WALLS_AREA;
public static final Rectangle EXITING_SLIDES_AREA = A3Constants.EXITING_SLIDES_AREA;

public static final Color NICE_GRAY_COLOUR = A3Constants.NICE_GRAY_COLOUR;
public static final Color GAME_SCREEN_COLOUR = A3Constants.GAME_SCREEN_COLOUR;
public static final Color SLIDES_AREA_COLOUR = A3Constants.SLIDES_AREA_COLOUR;
public static final Color LEO_AREA_COLOUR = A3Constants.LEO_AREA_COLOUR; 
public static final Color HOME_AREA_COLOUR = A3Constants.HOME_AREA_COLOUR;
public static final Color WALL_COLOUR = A3Constants.WALL_COLOUR;

public static final int MAX_WALLS = A3Constants.MAX_WALLS;

public static final Font TINY_FONT = A3Constants.TINY_FONT;
public static final Font LARGE_FONT = A3Constants.LARGE_FONT;
public static final Font HUGE_FONT = A3Constants.HUGE_FONT;

public static final int LARGE_FONT_SIZE = A3Constants.LARGE_FONT_SIZE;
public static final int HUGE_FONT_SIZE = A3Constants.HUGE_FONT_SIZE;

public static final Point TICKS_POSITION = A3Constants.TICKS_POSITION;
public static final Point WINNER_LOSER_INFO_POSITION = A3Constants.WINNER_LOSER_INFO_POSITION;  
public static final Point INFORMATION_POSITION1 = A3Constants.INFORMATION_POSITION1;
public static final Point INFORMATION_POSITION2 = A3Constants.INFORMATION_POSITION2;
public static final Point INFORMATION_POSITION3 = A3Constants.INFORMATION_POSITION3;

public static final int TICKS_ALLOWED = A3Constants.TICKS_ALLOWED; 
public static final int UP = A3Constants.UP;
public static final int DOWN = A3Constants.DOWN;
public static final int LEFT = A3Constants.LEFT;
public static final int RIGHT = A3Constants.RIGHT;

private CoolCat coolCat;
private Timer t;

public A3JPanel() {
    setBackground(Color.GREEN);
    coolCat = new CoolCat(A3Constants.LEO_START_AREA.x, A3Constants.LEO_START_AREA.y);
    addKeyListener(this);
    t = new Timer(30,this);
    t.start();
    //t.addActionListener(this);

}

public void paintComponent(Graphics g){
    super.paintComponent(g);
    drawGameArea(g);
    coolCat.draw(g);
}

private void drawGameArea(Graphics g){
    g.setColor(A3Constants.LEO_AREA_COLOUR);
    g.fillRect(A3Constants.LEO_LEFT_AREA.x, A3Constants.LEO_LEFT_AREA.y, A3Constants.LEO_LEFT_AREA.width, A3Constants.LEO_LEFT_AREA.height);
    g.setColor(A3Constants.WALL_COLOUR);
    g.fillRect(A3Constants.ALL_WALLS_AREA.x, A3Constants.ALL_WALLS_AREA.y, A3Constants.ALL_WALLS_AREA.width, A3Constants.ALL_WALLS_AREA.height);
    g.setColor(A3Constants.HOME_AREA_COLOUR);
    g.fillRect(A3Constants.HOME_AREA.x, A3Constants.HOME_AREA.y, A3Constants.HOME_AREA.width, A3Constants.HOME_AREA.height);

}

public void keyPressed(KeyEvent e){
    if(e.getKeyCode() == KeyEvent.VK_UP){
        coolCat.setDirection(A3Constants.UP);
    }
    if(e.getKeyCode() == KeyEvent.VK_DOWN){
        coolCat.setDirection(A3Constants.DOWN);
    }
    if(e.getKeyCode() == KeyEvent.VK_LEFT){
        coolCat.setDirection(A3Constants.LEFT);
    }
    if(e.getKeyCode() == KeyEvent.VK_RIGHT){
        coolCat.setDirection(A3Constants.RIGHT);
    }
}

public void keyReleased(KeyEvent e){}
public void keyTyped(KeyEvent e){}


public void actionPerformed(ActionEvent e){
    coolCat.move();
    repaint();
}

}

下面是另一个类。

import java.awt.*;

public class CoolCat {
public static final Rectangle LEO_START_AREA = A3Constants.LEO_START_AREA;

public static final int GAME_SCREEN_AREA_TOP = A3Constants.GAME_SCREEN_AREA_TOP;
public static final int GAME_SCREEN_AREA_BOTTOM = A3Constants.GAME_SCREEN_AREA_BOTTOM;
public static final int GAME_SCREEN_AREA_LEFT = A3Constants.GAME_SCREEN_AREA_LEFT;
public static final int GAME_SCREEN_AREA_RIGHT = A3Constants.GAME_SCREEN_AREA_RIGHT;

public static final int UP = A3Constants.UP;
public static final int DOWN = A3Constants.DOWN;
public static final int LEFT = A3Constants.LEFT;
public static final int RIGHT = A3Constants.RIGHT;

private Rectangle area;
private int speed;
private int direction;

public CoolCat(int x, int y){

    this.speed = speed;
    speed = (int)(Math.random() * (8 - 4 + 1)) + 4;
    area = new Rectangle(A3Constants.LEO_START_AREA.x, A3Constants.LEO_START_AREA.y);
    direction = RIGHT;

}

public Rectangle getArea(){
    area = new Rectangle(LEO_START_AREA.x, LEO_START_AREA.y, LEO_START_AREA.width, LEO_START_AREA.height);
    return area;

}

public void setDirection(int direction){
    this.direction = direction;
}

//public boolean hasReachedHome(Rectangle zhomeArea){}

public void move(){
    if(direction == A3Constants.UP){
        area.y -= speed;
    } else if(direction == A3Constants.DOWN){
        area.y += speed;
    } else if(direction == A3Constants.LEFT){
        area.x -= speed;
    } else if(direction == A3Constants.RIGHT){
        area.x += speed;
    }
}

public void draw(Graphics g){
    g.setColor(Color.RED);
    g.fillOval(A3Constants.LEO_START_AREA.x, A3Constants.LEO_START_AREA.y, A3Constants.LEO_START_AREA.width, A3Constants.LEO_START_AREA.height);
}

}

Answer 1

您正在向 JPanel 添加 KeyListener，该组件默认情况下无法接受焦点，而关键监听器需要焦点才能工作。

一个简单的解决方案是允许您的 JPanel 接受焦点，然后请求将焦点授予它。

更好的解决方案是避免在 Swing 应用程序中使用 KeyListener，而是使用键绑定(bind)(正如之前在类似问题中多次讨论的那样)。例如，请查看:How to make an image move while listening to a keypress in Java.