【贪吃蛇—Java程序员写Android游戏】系列 1.Android SDK Sample-Snake详解

Snake也是一个经典游戏了，Nokia蓝屏机的王牌游戏之一。AndroidSDK 1.5就有了它的身影。我们这里就来详细解析一下Android SDKSample中的Snake工程。本工程基于SDK 2.3.3版本中的工程，路径为：%Android_SDK_HOME%/samples/android-10/Snake

一、Eclipse工程

通过File-New Project-Android-Android Project，选择“Create project fromexisting sample”创建自己的应用SnakeAndroid，如下图：

运行效果如下图：

二、工程结构和类图

其实Snake的工程蛮简单的，源文件就三个：Snake.javaSnakeView.java TileView.java。Snake类是这个游戏的入口点，TitleView类进行游戏的绘画，SnakeView类则是对游戏控制操作的处理。Coordinate，RefreshHandler是2个辅助类，也是SnakeView类中的内部类。其中，Coordinate是一个点的坐标（x，y），RefreshHandler将RefreshHandler对象绑定某个线程并给它发送消息。如下图：

任何游戏都需要有个引擎来推动游戏的运行，最简化的游戏引擎就是：在一个线程中While循环，检测用户操作，对用户的操作作出反应，更新游戏的界面，直到用户退出游戏。

在Snake这个游戏中，辅助类RefreshHandler继承自Handler，用来把RefreshHandler与当前线程进行绑定，从而可以直接给线程发送消息并处理消息。注意一点：Handle对消息的处理都是异步。RefreshHandler在Handler的基础上增加sleep()接口，用来每隔一个时间段后给当前线程发送一个消息。handleMessage()方法在接受消息后，根据当前的游戏状态重绘界面，运行机制如下：

这比较类似定时器的概念，在特定的时刻发送消息，根据消息处理相应的事件。update()与sleep()间接的相互调用就构成了一个循环。这里要注意：mRedrawHandle绑定的是Avtivity所在的线程，也就是程序的主线程；另外由于sleep()是个异步函数，所以update()与sleep()之间的相互调用才没有构成死循环。

最后分析下游戏数据的保存机制，如下：

这里考虑了Activity的生命周期：如果用户在游戏期间离开游戏界面，游戏暂停；或者由于内存比较紧张，Android关闭游戏释放内存，那么当用户返回游戏界面的时候恢复到上次离开时的界面。

三、源码解析

详细解析下源代码，由于代码量不大，以注释的方式列出如下：

1、Snake.java

/** * <p>Title: Snake</p> * <p>Copyright: (C) 2007 The Android Open Source Project. Licensed under the Apache License, Version 2.0 (the "License")</p> * @author Gavin 标注 */package com.deaboway.snake;import android.app.Activity;import android.os.Bundle;import android.widget.TextView;/** * Snake: a simple game that everyone can enjoy. * * This is an implementation of the classic Game "Snake", in which you control a * serpent roaming around the garden looking for apples. Be careful, though, * because when you catch one, not only will you become longer, but you'll move * faster. Running into yourself or the walls will end the game. * */// 贪吃蛇： 经典游戏，在一个花园中找苹果吃，吃了苹果会变长，速度变快。碰到自己和墙就挂掉。public class Snake extends Activity {private SnakeView mSnakeView;private static String ICICLE_KEY = "snake-view";/** * Called when Activity is first created. Turns off the title bar, sets up * the content views, and fires up the SnakeView. * */// 在 activity 第一次创建时被调用@Overridepublic void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.snake_layout);mSnakeView = (SnakeView) findViewById(R.id.snake);mSnakeView.setTextView((TextView) findViewById(R.id.text));// 检查存贮状态以确定是重新开始还是恢复状态if (savedInstanceState == null) {// 存储状态为空，说明刚启动可以切换到准备状态mSnakeView.setMode(SnakeView.READY);} else {// 已经保存过，那么就去恢复原有状态Bundle map = savedInstanceState.getBundle(ICICLE_KEY);if (map != null) {// 恢复状态mSnakeView.restoreState(map);} else {// 设置状态为暂停mSnakeView.setMode(SnakeView.PAUSE);}}}// 暂停事件被触发时@Overrideprotected void onPause() {super.onPause();// Pause the game along with the activitymSnakeView.setMode(SnakeView.PAUSE);}// 状态保存@Overridepublic void onSaveInstanceState(Bundle outState) {// 存储游戏状态到View里outState.putBundle(ICICLE_KEY, mSnakeView.saveState());}}

 

2、SnakeView.java

/** * <p>Title: Snake</p> * <p>Copyright: (C) 2007 The Android Open Source Project. Licensed under the Apache License, Version 2.0 (the "License")</p> * @author Gavin 标注 */package com.deaboway.snake;import java.util.ArrayList;import java.util.Random;import android.content.Context;import android.content.res.Resources;import android.os.Handler;import android.os.Message;import android.util.AttributeSet;import android.os.Bundle;import android.util.Log;import android.view.KeyEvent;import android.view.View;import android.widget.TextView;/** * SnakeView: implementation of a simple game of Snake * * */public class SnakeView extends TileView {private static final String TAG = "Deaboway";/** * Current mode of application: READY to run, RUNNING, or you have already * lost. static final ints are used instead of an enum for performance * reasons. */// 游戏状态，默认值是准备状态private int mMode = READY;// 游戏的四个状态 暂停 准备 运行 和 失败public static final int PAUSE = 0;public static final int READY = 1;public static final int RUNNING = 2;public static final int LOSE = 3;// 游戏中蛇的前进方向，默认值北方private int mDirection = NORTH;// 下一步的移动方向，默认值北方private int mNextDirection = NORTH;// 游戏方向设定 北 南 东 西private static final int NORTH = 1;private static final int SOUTH = 2;private static final int EAST = 3;private static final int WEST = 4;/** * Labels for the drawables that will be loaded into the TileView class */// 三种游戏元private static final int RED_STAR = 1;private static final int YELLOW_STAR = 2;private static final int GREEN_STAR = 3;/** * mScore: used to track the number of apples captured mMoveDelay: number of * milliseconds between snake movements. This will decrease as apples are * captured. */// 游戏得分private long mScore = 0;// 移动延迟private long mMoveDelay = 600;/** * mLastMove: tracks the absolute time when the snake last moved, and is * used to determine if a move should be made based on mMoveDelay. */// 最后一次移动时的毫秒时刻private long mLastMove;/** * mStatusText: text shows to the user in some run states */// 显示游戏状态的文本组件private TextView mStatusText;/** * mSnakeTrail: a list of Coordinates that make up the snake's body * mAppleList: the secret location of the juicy apples the snake craves. */// 蛇身数组(数组以坐标对象为元素)private ArrayList<Coordinate> mSnakeTrail = new ArrayList<Coordinate>();// 苹果数组(数组以坐标对象为元素)private ArrayList<Coordinate> mAppleList = new ArrayList<Coordinate>();/** * Everyone needs a little randomness in their life */// 随机数private static final Random RNG = new Random();/** * Create a simple handler that we can use to cause animation to happen. We * set ourselves as a target and we can use the sleep() function to cause an * update/invalidate to occur at a later date. */// 创建一个Refresh Handler来产生动画： 通过sleep()来实现private RefreshHandler mRedrawHandler = new RefreshHandler();// 一个Handlerclass RefreshHandler extends Handler {// 处理消息队列@Overridepublic void handleMessage(Message msg) {// 更新View对象SnakeView.this.update();// 强制重绘SnakeView.this.invalidate();}// 延迟发送消息public void sleep(long delayMillis) {this.removeMessages(0);sendMessageDelayed(obtainMessage(0), delayMillis);}};/** * Constructs a SnakeView based on inflation from XML * * @param context * @param attrs */// 构造函数public SnakeView(Context context, AttributeSet attrs) {super(context, attrs);// 构造时初始化initSnakeView();}public SnakeView(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);initSnakeView();}// 初始化private void initSnakeView() {// 可选焦点setFocusable(true);Resources r = this.getContext().getResources();// 设置贴片图片数组resetTiles(4);// 把三种图片存到Bitmap对象数组loadTile(RED_STAR, r.getDrawable(R.drawable.redstar));loadTile(YELLOW_STAR, r.getDrawable(R.drawable.yellowstar));loadTile(GREEN_STAR, r.getDrawable(R.drawable.greenstar));}// 开始新的游戏——初始化private void initNewGame() {// 清空ArrayList列表mSnakeTrail.clear();mAppleList.clear();// For now we're just going to load up a short default eastbound snake// that's just turned north// 创建蛇身mSnakeTrail.add(new Coordinate(7, 7));mSnakeTrail.add(new Coordinate(6, 7));mSnakeTrail.add(new Coordinate(5, 7));mSnakeTrail.add(new Coordinate(4, 7));mSnakeTrail.add(new Coordinate(3, 7));mSnakeTrail.add(new Coordinate(2, 7));// 新的方向 ：北方mNextDirection = NORTH;// 2个随机位置的苹果addRandomApple();addRandomApple();// 移动延迟mMoveDelay = 600;// 初始得分0mScore = 0;}

 

3、TileView.java

/** * <p>Title: Snake</p> * <p>Copyright: (C) 2007 The Android Open Source Project. Licensed under the Apache License, Version 2.0 (the "License")</p> * @author Gavin 标注 */package com.deaboway.snake;import android.content.Context;import android.content.res.TypedArray;import android.graphics.Bitmap;import android.graphics.Canvas;import android.graphics.Paint;import android.graphics.drawable.Drawable;import android.util.AttributeSet;import android.view.View;/** * TileView: a View-variant designed for handling arrays of "icons" or other * drawables. * */// View 变种，用来处理 一组 贴片—— “icons”或其它可绘制的对象public class TileView extends View {/** * Parameters controlling the size of the tiles and their range within view. * Width/Height are in pixels, and Drawables will be scaled to fit to these * dimensions. X/Y Tile Counts are the number of tiles that will be drawn. */protected static int mTileSize;// X轴的贴片数量protected static int mXTileCount;// Y轴的贴片数量protected static int mYTileCount;// X偏移量private static int mXOffset;// Y偏移量private static int mYOffset;/** * A hash that maps integer handles specified by the subclasser to the * drawable that will be used for that reference */// 贴片图像的图像数组private Bitmap[] mTileArray;/** * A two-dimensional array of integers in which the number represents the * index of the tile that should be drawn at that locations */// 保存每个贴片的索引——二维数组private int[][] mTileGrid;// Paint对象（画笔、颜料）private final Paint mPaint = new Paint();// 构造函数public TileView(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);TypedArray a = context.obtainStyledAttributes(attrs,R.styleable.TileView);mTileSize = a.getInt(R.styleable.TileView_tileSize, 12);a.recycle();}public TileView(Context context, AttributeSet attrs) {super(context, attrs);TypedArray a = context.obtainStyledAttributes(attrs,R.styleable.TileView);mTileSize = a.getInt(R.styleable.TileView_tileSize, 12);a.recycle();}/** * Rests the internal array of Bitmaps used for drawing tiles, and sets the * maximum index of tiles to be inserted * * @param tilecount */// 设置贴片图片数组public void resetTiles(int tilecount) {mTileArray = new Bitmap[tilecount];}// 回调：当该View的尺寸改变时调用，在onDraw()方法调用之前就会被调用，所以用来设置一些变量的初始值// 在视图大小改变的时候调用，比如说手机由垂直旋转为水平@Overrideprotected void onSizeChanged(int w, int h, int oldw, int oldh) {// 定义X轴贴片数量mXTileCount = (int) Math.floor(w / mTileSize);mYTileCount = (int) Math.floor(h / mTileSize);// X轴偏移量mXOffset = ((w - (mTileSize * mXTileCount)) / 2);// Y轴偏移量mYOffset = ((h - (mTileSize * mYTileCount)) / 2);// 定义贴片的二维数组mTileGrid = new int[mXTileCount][mYTileCount];// 清空所有贴片clearTiles();}/** * Function to set the specified Drawable as the tile for a particular * integer key. * * @param key * @param tile */// 给mTileArray这个Bitmap图片数组设置值public void loadTile(int key, Drawable tile) {Bitmap bitmap = Bitmap.createBitmap(mTileSize, mTileSize,Bitmap.Config.ARGB_8888);Canvas canvas = new Canvas(bitmap);tile.setBounds(0, 0, mTileSize, mTileSize);// 把一个drawable转成一个Bitmaptile.draw(canvas);// 在数组里存入该BitmapmTileArray[key] = bitmap;}/** * Resets all tiles to 0 (empty) * */// 清空所有贴片public void clearTiles() {for (int x = 0; x < mXTileCount; x++) {for (int y = 0; y < mYTileCount; y++) {// 全部设置为0setTile(0, x, y);}}}/** * Used to indicate that a particular tile (set with loadTile and referenced * by an integer) should be drawn at the given x/y coordinates during the * next invalidate/draw cycle. * * @param tileindex * @param x * @param y */// 给某个贴片位置设置一个状态索引public void setTile(int tileindex, int x, int y) {mTileGrid[x][y] = tileindex;}// onDraw 在视图需要重画的时候调用，比如说使用invalidate刷新界面上的某个矩形区域@Overridepublic void onDraw(Canvas canvas) {super.onDraw(canvas);for (int x = 0; x < mXTileCount; x += 1) {for (int y = 0; y < mYTileCount; y += 1) {// 当索引大于零，也就是不空时if (mTileGrid[x][y] > 0) {// mTileGrid中不为零时画此贴片canvas.drawBitmap(mTileArray[mTileGrid[x][y]], mXOffset + x* mTileSize, mYOffset + y * mTileSize, mPaint);}}}}}

 

四、工程文件下载

为了方便大家阅读，可以到如下地址下载工程源代码：

http://download.csdn.net/source/3145349

五、小结及下期预告：

本次详细解析了Android SDK 自带Sample——Snake的结构和功能。下次将会把这个游戏移植到J2ME平台上，并且比较Android和J2ME的区别和相通之处，让从事过J2ME开发的朋友对Android开发有个更加直观的认识。