android游戏开发入门： 贪吃蛇 源代码分析

贪吃蛇是一款足够经典的游戏。它的经典，在于用户操作的简单，在于技术实现的简介，在于他的经久不衰。

这里的贪吃蛇的android实现，是SDK Samples中的开源例程。可能各位都有看过~界面如下图啦~



作为一个刚入门或者还没入门的新手，着实花了我一些力气来理解这段代码。

对于各种不懂的地方，慢慢查询资料，对于新的方法，通过修改代码尝试效果。到现在终于能算个一知半解。

在代码中，对于自己有所收获的地方，我都做了相应的注释。

回过头来，觉得从这段代码中，能学到不少东西~~

包括android应用的基本架构，他的面向对象的思想，以及代码的简洁明了。

于是，我想到，何不将这些东西分享出来，如果碰巧对感兴趣的朋友们有搜帮助，那就更好了~

好了，闲话不说~代码和注释如下（处于对源码的敬意，原本的英文注释部分都没有删去~大家可以配合理解）：

PS：最近我正在写自己的“贪吃蛇”，说事贪吃蛇，其实完全颠覆了这个经典版本的设计理念和操作方式。具体细节先卖一个关子，作品准备参加这次第二届大学生android应用开发大赛。

应该一个月内能完成，到时候也会开源出代码来~欢迎大家讨论指正·~

************************************************************************************************************************************

Snake工程中，总共有三个文件： *TileView是基于Android的View类实现的方块图类，用来支撑上层类的调用，绘制方块图的显示界面。通过这些代码，能打之了解如何 扩展View，实现特色的界面效果。 *SnakeView调用了TileView，实现了游戏逻辑 和 具体的显示。 *Snake为主Activity类。

建议大家按照上面的顺序看三个文件，可能逻辑上更舒服一点～～

下面贴上代码和注释。

PS: 调试版本为android2.2。 其他版本应该也没问题吧，不过得用虚拟机。因为它是上下左右按键操作，现在大多数android机是没有方向键的吧。

TileView.java

package com.example.android.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.
 * 
 */

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; //每个tile的边长的像素数量

    protected static int mXTileCount; //屏幕内能容纳的 X方向上方块的总数量
    protected static int mYTileCount;//屏幕内能容纳的 Y方向上方块的总数量

    private static int mXOffset; //原点坐标，按pixel计。
    private static int mYOffset;

    /**
     * A hash that maps integer handles specified by the subclasser to the
     * drawable that will be used for that reference
     * 存储着不同种类的bitmap图。通过resetTiles，loadTile，将游戏中的方块加载到这个数组。
     * 可以理解为 砖块字典
     */
    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
     * 存储整个界面内每个tile位置应该绘制的tile。
     * 可看作是我们直接操作的画布。
     * 通过setTile、clearTile 进行图形显示的修改操作。 
     * 
     */
    private int[][] mTileGrid; 

    //画笔，canvas的图形绘制，需要画笔Paint实现。
    private final Paint mPaint = new Paint();

    
    public TileView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        //使用TypedArray，获取在attrs.xml中为TileView定义的新属性tileSize 。参考： http://weizhulin.blog.51cto.com/1556324/311453         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
     * 重置清零mTileArray，在游戏初始的时候使用。
     * 即清空砖块字典
     * @param tilecount
     */
    public void resetTiles(int tilecount) {
    	mTileArray = new Bitmap[tilecount];
    }

    
    /*
     * 当改变屏幕大小尺寸时，同时修改tile的相关计数指标。
     */
    
    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        mXTileCount = (int) Math.floor(w / mTileSize);
        mYTileCount = (int) Math.floor(h / mTileSize);

        //mXOffset mYOffset是绘图的起点坐标。
        mXOffset = ((w - (mTileSize * mXTileCount)) / 2);
        mYOffset = ((h - (mTileSize * mYTileCount)) / 2);

        mTileGrid = new int[mXTileCount][mYTileCount];
        clearTiles();
    }

    
    /**
     * Function to set the specified Drawable as the tile for a particular
     * integer key.
     * 加载具体的砖块图片 到 砖块字典。
     * 即将对应的砖块的图片 对应的加载到 mTileArray数组中
     * @param key
     * @param tile
     */
    public void loadTile(int key, Drawable tile) {
        //这里做了一个 Drawable 到 bitmap 的转换。由于外部程序使用的时候是直接读取资源文件中的图片，
    	//是drawable格式，而我们的数组是bitmap格式，方便最终的绘制。所以，需要进行一次到 bitmap的转换。
    	Bitmap bitmap = Bitmap.createBitmap(mTileSize, mTileSize, Bitmap.Config.ARGB_8888);
        Canvas canvas = new Canvas(bitmap);
        tile.setBounds(0, 0, mTileSize, mTileSize);
        tile.draw(canvas);
        
        mTileArray[key] = bitmap;
    }

    /**
     * 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.
     * 在相应的坐标位置绘制相应的砖块
     * 记得哦，mTileGrid其实就是我们直接操作的画布。
     * @param tileindex
     * @param x
     * @param y
     */
    public void setTile(int tileindex, int x, int y) {
        mTileGrid[x][y] = tileindex;
    }

    /**
     * Resets all tiles to 0 (empty)
     * 清空图形显示。
     * 用以更新画面。
     * 调用了绘图的setTile()。
     */
    public void clearTiles() {
        for (int x = 0; x < mXTileCount; x++) {
            for (int y = 0; y < mYTileCount; y++) {
                setTile(0, x, y);
            }
        }
    }

/*
 * 将我们直接操作的画布绘制到手机界面上！
 * @see android.view.View#onDraw(android.graphics.Canvas)
 */
    @Override
    public void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        for (int x = 0; x < mXTileCount; x += 1) {
            for (int y = 0; y < mYTileCount; y += 1) {
                if (mTileGrid[x][y] > 0) {
                    canvas.drawBitmap(mTileArray[mTileGrid[x][y]], 
                    		mXOffset + x * mTileSize,
                    		mYOffset + y * mTileSize,
                    		mPaint);
                }
            }
        }
    }

}

SnakeView.java

package com.example.android.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 = "SnakeView";

    /**
     * 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.
     * 游戏的四种状态。初始时为 预备开始的状态。
     */
    private int mMode = READY;    
    public static final int PAUSE = 0;	//暂停
    public static final int READY = 1;	//准备好了，预备开始
    public static final int RUNNING = 2;//正在运行
    public static final int LOSE = 3;	//结束,输了游戏

    /**
     * Current direction the snake is headed.
     * 蛇体运动的方向标识。
     */
    private int mDirection = NORTH;
    private int mNextDirection = NORTH;
    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
     * 游戏中仅有的三种砖块对应的数值。
     */	
    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.
     */
    private long mScore = 0;   //记录获得的分数。
    private long mMoveDelay = 600;  //每移动一步的延时。初始时设置为600ms，以后每吃一个果子，打个9折
               					//造成的结果是速度越来越快。
    
    /**
     * mLastMove: tracks the absolute time when the snake last moved, and is used
     * to determine if a move should be made based on mMoveDelay.
     * 记录上次移动的确切时间。
     * 同mMoveDelay一起处理与用户的异步操作的协同问题。
     */
    private long mLastMove;
    
    
    /**
     * mStatusText: text shows to the user in some run states
     * 用来显示游戏状态的TextView
     */
    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.
     * 两个链表，分别用来存储 蛇体 和 果子的坐标。
     * 每次蛇体的运动，蛇体的增长，产生新的苹果，被吃掉苹果，都会在这里记录。
     */
    private ArrayList<Coordinate> mSnakeTrail = new ArrayList<Coordinate>();
    private ArrayList<Coordinate> mAppleList = new ArrayList<Coordinate>();

    /**
     * Everyone needs a little randomness in their life
     * 随机数生成器。用来产生随机的苹果。在addRandomApple()中使用。
     */
    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.
     * 用Handler机制实现定时刷新。
     * 为什么使用Handler呢？大家可以参考 android 的线程模型（注意UI线程不是线程安全的～）
     * 具体使用方法网上的资源很多，在此不赘述～
     */
    private RefreshHandler mRedrawHandler = new RefreshHandler();

    class RefreshHandler extends Handler {

    	//获取消息并处理
        @Override
        public void handleMessage(Message msg) {
            SnakeView.this.update();
            SnakeView.this.invalidate(); //刷新view为基类的界面
        }

        //定时发送消息给UI线程，以此达到更新的效果。
        public void sleep(long delayMillis) {
        	this.removeMessages(0); //清空消息队列，Handler进入对新消息的等待
            sendMessageDelayed(obtainMessage(0), delayMillis); //定时发送新消息,激活handler
        }
    };

    
    public SnakeView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initSnakeView();  //构造函数中，别忘了，初始化游戏～
   }

    public SnakeView(Context context, AttributeSet attrs, int defStyle) {
    	super(context, attrs, defStyle);
    	initSnakeView();
    }

    //初始化SnakeView类，注意，这根初始化游戏是不一样的。
    private void initSnakeView() {
        setFocusable(true); //设置焦点，由于存在 文字界面 和 游戏界面的跳转。这个focus是不可或缺的。

        //取得资源中的图片，加载到 砖块字典 中。
        Resources r = this.getContext().getResources();
        resetTiles(4);
        loadTile(RED_STAR, r.getDrawable(R.drawable.redstar));
        loadTile(YELLOW_STAR, r.getDrawable(R.drawable.yellowstar));
        loadTile(GREEN_STAR, r.getDrawable(R.drawable.greenstar));
    	
    }
    
    //如果不是从暂停中回复，就绪要 初始化游戏了。
    private void initNewGame() {
        //清空保存蛇体和果子的数据结构。
    	mSnakeTrail.clear();
        mAppleList.clear();

        // For now we're just going to load up a short default eastbound snake
        // that's just turned north
        // 设定初始状态的蛇体的位置。 
        
        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));
        mNextDirection = NORTH;

        // Two apples to start with
        addRandomApple();
        addRandomApple();

        mMoveDelay = 600;
        mScore = 0;
    }

    /**
     * Given a ArrayList of coordinates, we need to flatten them into an array of
     * ints before we can stuff them into a map for flattening and storage.
     * 
     * @param cvec : a ArrayList of Coordinate objects
     * @return : a simple array containing the x/y values of the coordinates
     * as [x1,y1,x2,y2,x3,y3...】
     * 在游戏暂停时，需要通过Bundle方式保存数据。见saveState()。
     * Bundle支持简单的数组。
     * 所以需要将我们的部分数据结构，如蛇体和苹果位置的数组，转换成简单的序列化的int数组。
     */
    private int[] coordArrayListToArray(ArrayList<Coordinate> cvec) {
        int count = cvec.size();
        int[] rawArray = new int[count * 2];
        for (int index = 0; index < count; index++) {
            Coordinate c = cvec.get(index);
            rawArray[2 * index] = c.x;
            rawArray[2 * index + 1] = c.y;
        }
        return rawArray;
    }

    /**
     * Save game state so that the user does not lose anything
     * if the game process is killed while we are in the 
     * background.
     * 在意外情况下，暂时性保存游戏数据，在下次打开游戏时，可以继续游戏。如来电话了。
     * @return a Bundle with this view's state
     */
    public Bundle saveState() {
        Bundle map = new Bundle();

        map.putIntArray("mAppleList", coordArrayListToArray(mAppleList));
        map.putInt("mDirection", Integer.valueOf(mDirection));
        map.putInt("mNextDirection", Integer.valueOf(mNextDirection));
        map.putLong("mMoveDelay", Long.valueOf(mMoveDelay));
        map.putLong("mScore", Long.valueOf(mScore));
        map.putIntArray("mSnakeTrail", coordArrayListToArray(mSnakeTrail));

        return map;
    }

    /**
     * Given a flattened array of ordinate pairs, we reconstitute them into a
     * ArrayList of Coordinate objects
     * 是coordArrayListToArray（）的逆过程，用来读取保存在Bundle中的数据。
     * @param rawArray : [x1,y1,x2,y2,...]
     * @return a ArrayList of Coordinates
     */
    private ArrayList<Coordinate> coordArrayToArrayList(int[] rawArray) {
        ArrayList<Coordinate> coordArrayList = new ArrayList<Coordinate>();

        int coordCount = rawArray.length;
        for (int index = 0; index < coordCount; index += 2) {
            Coordinate c = new Coordinate(rawArray[index], rawArray[index + 1]);
            coordArrayList.add(c);
        }
        return coordArrayList;
    }

    /**
     * Restore game state if our process is being relaunched
     * 回复游戏数据。是saveState()的逆过程
     * @param icicle a Bundle containing the game state
     */
    public void restoreState(Bundle icicle) {
        setMode(PAUSE);

        mAppleList = coordArrayToArrayList(icicle.getIntArray("mAppleList"));
        mDirection = icicle.getInt("mDirection");
        mNextDirection = icicle.getInt("mNextDirection");
        mMoveDelay = icicle.getLong("mMoveDelay");
        mScore = icicle.getLong("mScore");
        mSnakeTrail = coordArrayToArrayList(icicle.getIntArray("mSnakeTrail"));
    }

    /*
     * handles key events in the game. Update the direction our snake is traveling
     * based on the DPAD. Ignore events that would cause the snake to immediately
     * turn back on itself.
     * 按键的监听。
     * 现在大多数的android手机都没有按键了。
     * 笔者就是在自己的模拟机上才能正常的使用这款小游戏的 - -#
     * @see android.view.View#onKeyDown(int, android.os.KeyEvent)
     */
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent msg) {
    	//这里是游戏的基本逻辑。如果你还没尝试一下它，先玩玩再说吧。那有助于你对代码的理解～
        if (keyCode == KeyEvent.KEYCODE_DPAD_UP) {
            if (mMode == READY | mMode == LOSE) {
                /*
                 * At the beginning of the game, or the end of a previous one,
                 * we should start a new game.
                 */
                initNewGame();
                setMode(RUNNING);
                update(); //update()实现了对游戏数据的更新，是整个游戏的推动力。
                return (true);
            }

            if (mMode == PAUSE) {
                /*
                 * If the game is merely paused, we should just continue where
                 * we left off.
                 */
                setMode(RUNNING);
                update();
                return (true);
            }

            if (mDirection != SOUTH) {  //如果按键的方向 跟蛇本身的运动方向完全相反，则无法执行
                mNextDirection = NORTH;  
            }
            return (true);
        }

        if (keyCode == KeyEvent.KEYCODE_DPAD_DOWN) {
            if (mDirection != NORTH) {
                mNextDirection = SOUTH;
            }
            return (true);
        }

        if (keyCode == KeyEvent.KEYCODE_DPAD_LEFT) {
            if (mDirection != EAST) {
                mNextDirection = WEST;
            }
            return (true);
        }

        if (keyCode == KeyEvent.KEYCODE_DPAD_RIGHT) {
            if (mDirection != WEST) {
                mNextDirection = EAST;
            }
            return (true);
        }

        return super.onKeyDown(keyCode, msg);
    }

    /**
     * Sets the TextView that will be used to give information (such as "Game
     * Over" to the user.
     * 起初不明白这个方法有什么作用。删除了以后才发现错误。Snake类会调用到它，来绑定到相应的textview.
     */
    public void setTextView(TextView newView) {  
        mStatusText = newView;
    }

    /**
     * Updates the current mode of the application (RUNNING or PAUSED or the like)
     * as well as sets the visibility of textview for notification
     * 
     * @param newMode
     */
    public void setMode(int newMode) {
        int oldMode = mMode;
        mMode = newMode;

        if (newMode == RUNNING & oldMode != RUNNING) {
            mStatusText.setVisibility(View.INVISIBLE); //游戏开始后，将TextView的文字显示设置为不可见。
            update(); //注意到，在initGame中也有update(),不过放心～ 多次重复 update不会影响效果的，
             			//蛇的移动有mLastMove 和 mMoveDelay 来校验。这会在Update()中体现。
            			//当然，经过实验，注释掉这个update()似乎不会影响结果噢。
            return;
        }

        Resources res = getContext().getResources();
        CharSequence str = "";
        if (newMode == PAUSE) {
            str = res.getText(R.string.mode_pause);
        }
        if (newMode == READY) {
            str = res.getText(R.string.mode_ready);
        }
        if (newMode == LOSE) {
            str = res.getString(R.string.mode_lose_prefix) + mScore
                  + res.getString(R.string.mode_lose_suffix);
        }

        mStatusText.setText(str);
        mStatusText.setVisibility(View.VISIBLE);
    }

    /**
     * Selects a random location within the garden that is not currently covered
     * by the snake. Currently _could_ go into an infinite loop if the snake
     * currently fills the garden, but we'll leave discovery of this prize to a
     * truly excellent snake-player.
     * 在地图上随机的增加果子。注意苹果的位置不可以是蛇体所在噢～这里有个小bug，没有检测
     * 产生的果子位置 可能与 另一个果子位置重合。
     * 新产生的果子的坐标会增加到mApplist的数组上。
     */
    private void addRandomApple() {
        Coordinate newCoord = null;
        boolean found = false;
        while (!found) {
            // Choose a new location for our apple
        	//注意别产生在边框上的果子
            int newX = 1 + RNG.nextInt(mXTileCount - 2);
            int newY = 1 + RNG.nextInt(mYTileCount - 2);
            newCoord = new Coordinate(newX, newY);

            // Make sure it's not already under the snake
            boolean collision = false;
            int snakelength = mSnakeTrail.size();
            for (int index = 0; index < snakelength; index++) {
                if (mSnakeTrail.get(index).equals(newCoord)) {
                    collision = true;
                }
            }
            // if we're here and there's been no collision, then we have
            // a good location for an apple. Otherwise, we'll circle back
            // and try again
            found = !collision;
        }
        if (newCoord == null) {
            Log.e(TAG, "Somehow ended up with a null newCoord!");
        }
        mAppleList.add(newCoord);
    }

    /**
     * Handles the basic update loop, checking to see if we are in the running
     * state, determining if a move should be made, updating the snake's location.
     * 刷新游戏状态。每次游戏画面的更新、游戏数据的更新，都是依靠这个update()来完成的。
     */
    public void update() {
        if (mMode == RUNNING) {
            long now = System.currentTimeMillis();

            if (now - mLastMove > mMoveDelay) {  //这里是对蛇体游戏刚开始时连续的两个移动速率的控制
            						//主要作用应该是mMode变化时，对update()正确效果的保障。
                clearTiles(); 		//清空 界面画布。		
                updateWalls();      //重新绘制墙壁
                updateSnake(); 	   //对蛇的 游戏逻辑 的处理 以及绘制
                updateApples();   //对果子的 游戏逻辑 的处理 以及绘制
                mLastMove = now;
            }
            mRedrawHandler.sleep(mMoveDelay);   //利用Handler进行 定时刷新的控制
        }

    }

    /**
     * Draws some walls.
     * 用setTile绘制墙壁
     */
    private void updateWalls() {
        for (int x = 0; x < mXTileCount; x++) {
            setTile(GREEN_STAR, x, 0);
            setTile(GREEN_STAR, x, mYTileCount - 1);
        }
        for (int y = 1; y < mYTileCount - 1; y++) {
            setTile(GREEN_STAR, 0, y);
            setTile(GREEN_STAR, mXTileCount - 1, y);
        }
    }

    /**
     * Draws some apples.
     * 绘制果子
     */
    private void updateApples() {
        for (Coordinate c : mAppleList) {
            setTile(YELLOW_STAR, c.x, c.y);
        }
    }

    /**
     * Figure out which way the snake is going, see if he's run into anything (the
     * walls, himself, or an apple). If he's not going to die, we then add to the
     * front and subtract from the rear in order to simulate motion. If we want to
     * grow him, we don't subtract from the rear.
     * 
     */
    private void updateSnake() {
        boolean growSnake = false;  //吃过果子的蛇会长长。这个变量即为它的标记。

        // grab the snake by the head
        Coordinate head = mSnakeTrail.get(0);  //头部很重要，只有头部可能碰到果子。
        Coordinate newHead = new Coordinate(1, 1); //蛇下一步一定会前移，也就试newHead。长长只会从尾部增加。
        				//那么为啥不用Coordinate newHead 呢？反正肯定会给他赋值的。
        				//注意到之后咱们的程序是在switch语句中给newHead赋值的，这个是编译无法通过的～
        mDirection = mNextDirection;

        switch (mDirection) {
        case EAST: {
            newHead = new Coordinate(head.x + 1, head.y);
            break;
        }
        case WEST: {
            newHead = new Coordinate(head.x - 1, head.y);
            break;
        }
        case NORTH: {
            newHead = new Coordinate(head.x, head.y - 1);
            break;
        }
        case SOUTH: {
            newHead = new Coordinate(head.x, head.y + 1);
            break;
        }
        }

        // Collision detection
        // For now we have a 1-square wall around the entire arena
        //撞墙检测
        if ((newHead.x < 1) || (newHead.y < 1) || (newHead.x > mXTileCount - 2)
                || (newHead.y > mYTileCount - 2)) {
            setMode(LOSE);
            return;

        }

        // Look for collisions with itself
        //撞自己检测
        int snakelength = mSnakeTrail.size();
        for (int snakeindex = 0; snakeindex < snakelength; snakeindex++) {
            Coordinate c = mSnakeTrail.get(snakeindex);
            if (c.equals(newHead)) {
                setMode(LOSE);
                return;
            }
        }

        // Look for apples
        //吃果子检测
        int applecount = mAppleList.size();
        for (int appleindex = 0; appleindex < applecount; appleindex++) {
            Coordinate c = mAppleList.get(appleindex);
            if (c.equals(newHead)) {
                mAppleList.remove(c);
                addRandomApple();
                
                mScore++;
                mMoveDelay *= 0.9;

                growSnake = true;
            }
        }

        // push a new head onto the ArrayList and pull off the tail
        //前进
        mSnakeTrail.add(0, newHead);
        // except if we want the snake to grow
        if (!growSnake) {
            mSnakeTrail.remove(mSnakeTrail.size() - 1);
        }

        //绘制新的蛇体
        int index = 0;
        for (Coordinate c : mSnakeTrail) {
            if (index == 0) {
                setTile(YELLOW_STAR, c.x, c.y);
            } else {
                setTile(RED_STAR, c.x, c.y);
            }
            index++;
        }

    }

    /**
     * Simple class containing two integer values and a comparison function.
     * There's probably something I should use instead, but this was quick and
     * easy to build.
     * 这是坐标点的类。很简单的存储XY坐标。
     */
    private class Coordinate {
        public int x;
        public int y;

        public Coordinate(int newX, int newY) {
            x = newX;
            y = newY;
        }

        public boolean equals(Coordinate other) {
            if (x == other.x && y == other.y) {
                return true;
            }
            return false;
        }

        @Override
        public String toString() {
            return "Coordinate: [" + x + "," + y + "]";
        }
    }
    
}

Snake.java

package com.example.android.snake;

import android.app.Activity;
import android.os.Bundle;
import android.view.Window;
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.
 */

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.
     * 
     */
    @Override
    public 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));

        if (savedInstanceState == null) {
            // We were just launched -- set up a new game
            mSnakeView.setMode(SnakeView.READY);
        } else {
            // We are being restored
            Bundle map = savedInstanceState.getBundle(ICICLE_KEY);
            if (map != null) {
                mSnakeView.restoreState(map);
            } else {
                mSnakeView.setMode(SnakeView.PAUSE);
            }
        }
    }

    @Override
    protected void onPause() {
        super.onPause();
        // Pause the game along with the activity
        mSnakeView.setMode(SnakeView.PAUSE);
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        //Store the game state
        outState.putBundle(ICICLE_KEY, mSnakeView.saveState());
    }

}