GUI编程

04 贪吃蛇小游戏

4.3 第三步：让小蛇动起来(键盘控制)

首先，在构造器中要获取焦点事件、键盘监听事件并加入定时器(定时器定义需要实现ActionListener接口并重写actionPerformed方法)：

//构造器public GamePanel() {init();this.setFocusable(true);  //获取焦点事件this.addKeyListener(this);  //获取键盘监听事件timer.start();  //游戏一开始，定时器就启动}

然后，在键盘监听事件中，通过定时器来实现监听(即通过固定的时间进行刷新)，并加入对上下左右按键的判断，以实现改变小蛇身体的对应走向：

//键盘监听事件@Overridepublic void keyPressed(KeyEvent e) {int keyCode = e.getKeyCode();  //获取键盘按键if (keyCode == KeyEvent.VK_SPACE) {isStart = !isStart;repaint();}//键盘监听到按键后画上对应方向的蛇头if (keyCode == KeyEvent.VK_UP) {direction = "U";} else if (keyCode == KeyEvent.VK_DOWN) {direction = "D";} else if (keyCode == KeyEvent.VK_LEFT) {direction = "L";} else if (keyCode == KeyEvent.VK_RIGHT) {direction = "R";}}

下面对实现ActionListener接口的actionPerformed方法进行重写：

//事件监听需要定时器来实现，即通过固定的时间进行刷新(例如1s=10次)@Overridepublic void actionPerformed(ActionEvent e) {if (isStart) {//小蛇身体右移for (int i = length - 1; i > 0; i--) {  //后一节身体移动至前一节 snakeX[1] = snakeX[0]snakeX[i] = snakeX[i - 1];snakeY[i] = snakeY[i - 1];}//判断蛇头走向switch (direction) {case "R":snakeX[0] += 25;//边界判断if (snakeX[0] > 850) {snakeX[0] = 25;}break;case "L":snakeX[0] -= 25;//边界判断if (snakeX[0] < 25) {snakeX[0] = 850;}break;case "U":snakeY[0] -= 25;//边界判断if (snakeY[0] < 75) {snakeY[0] = 650;}break;case "D":snakeY[0] += 25;//边界判断if (snakeY[0] > 650) {snakeY[0] = 75;}break;}repaint();}timer.start();}

综上，GamePanel类中代码如下：

package com.duo.snake;import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.Objects;//游戏的面板
public class GamePanel extends JPanel implements KeyListener, ActionListener {//定义蛇的数据结构int length;  //小蛇总长int[] snakeX = new int[600];  //蛇的X坐标 25*25int[] snakeY = new int[500];  //蛇的Y坐标 25*25String direction;  //蛇头方向boolean isStart = false;  //默认未开始游戏//定时器Timer timer = new Timer(250, this);  //100ms执行一次//构造器public GamePanel() {init();this.setFocusable(true);  //获取焦点事件this.addKeyListener(this);  //获取键盘监听事件timer.start();  //游戏一开始，定时器就启动}//初始化方法public void init() {length = 3;snakeX[0] = 100; snakeY[0] = 100;  //脑袋的坐标snakeX[1] = 75; snakeY[1] = 100;  //第一节身体的坐标snakeX[2] = 50; snakeY[2] = 100;  //第二节身体的坐标direction = "R";  //蛇头初始向右}//绘制静态面板@Overrideprotected void paintComponent(Graphics g) {super.paintComponent(g);  //起到清屏的作用Data.header.paintIcon(this, g, 25, 11);  //将广告栏画入面板g.fillRect(25, 75, 850, 600);  //默认的游戏界面(黑色区域)this.setBackground(Color.white);//将小蛇画入面板中的游戏区域，且蛇头部分需要判断方向switch (direction) {case "R":Data.right.paintIcon(this, g, snakeX[0], snakeY[0]);break;case "L":Data.left.paintIcon(this, g, snakeX[0], snakeY[0]);break;case "U":Data.up.paintIcon(this, g, snakeX[0], snakeY[0]);break;case "D":Data.down.paintIcon(this, g, snakeX[0], snakeY[0]);break;}//画小蛇的身体部分for (int i = 1; i < length; i++) {Data.body.paintIcon(this, g, snakeX[i], snakeY[i]);}//绘制当前游戏状态if (!isStart) {g.setColor(Color.white);g.setFont(new Font("宋体", Font.BOLD, 40));g.drawString("按下空格开始游戏", 300, 300);}}//键盘监听事件@Overridepublic void keyPressed(KeyEvent e) {int keyCode = e.getKeyCode();  //获取键盘按键if (keyCode == KeyEvent.VK_SPACE) {isStart = !isStart;repaint();}//键盘监听到按键后画上对应方向的蛇头if (keyCode == KeyEvent.VK_UP) {direction = "U";} else if (keyCode == KeyEvent.VK_DOWN) {direction = "D";} else if (keyCode == KeyEvent.VK_LEFT) {direction = "L";} else if (keyCode == KeyEvent.VK_RIGHT) {direction = "R";}}//事件监听需要定时器来实现，即通过固定的时间进行刷新(例如1s=10次)@Overridepublic void actionPerformed(ActionEvent e) {if (isStart) {//小蛇身体右移for (int i = length - 1; i > 0; i--) {  //后一节身体移动至前一节 snakeX[1] = snakeX[0]snakeX[i] = snakeX[i - 1];snakeY[i] = snakeY[i - 1];}//判断蛇头走向switch (direction) {case "R":snakeX[0] += 25;//边界判断if (snakeX[0] > 850) {snakeX[0] = 25;}break;case "L":snakeX[0] -= 25;//边界判断if (snakeX[0] < 25) {snakeX[0] = 850;}break;case "U":snakeY[0] -= 25;//边界判断if (snakeY[0] < 75) {snakeY[0] = 650;}break;case "D":snakeY[0] += 25;//边界判断if (snakeY[0] > 650) {snakeY[0] = 75;}break;}repaint();}timer.start();}@Overridepublic void keyReleased(KeyEvent e) {}@Overridepublic void keyTyped(KeyEvent e) {}
}

运行结果如下：

游戏未开始时：

未按方向键，小蛇默认一直向右移动直到边界，满足边界判断条件并重新回到界面左端：

按下下键，小蛇向下移动：

至此，小蛇可根据键盘按键进行对应方向的移动。此时还未加入食物，且当蛇头触碰蛇身时并不会触发游戏失败，这将在下一篇内容中给出。