Android中贪吃蛇游戏的学习（三）

视图VIew的类的Snake的，主要关注的学习的类。

package com.easyway.dev.android.snake;

import java.util.ArrayList;
import java.util.Random;

import android.content.Context;
import android.content.res.Resources;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.util.AttributeSet;
import android.util.Log;
import android.view.KeyEvent;
import android.view.View;
import android.widget.TextView;

/**
 * View类是Android的一个超类，这个类几乎包含了所有的屏幕类型。但它们之间有一些不同。每一个view
 * 都有一个用于绘画的画布。这个画布可以用来进行任意扩展。
 * 
 * 一个项目的R.java文件是一个定义所有资源的索引文件。 使用这个类就像使用一种速记方式来引用你项
 * 目中包含的资源。这个有点特别的强大像对于Eclipse这类IDE的代码编译特性，因为它使你快速的，互动
 * 式的定位你正在寻找的特定引用。
 * 
 * 到目前需要注意的重要事情是叫做”layout”的内部类和他的成员变量”main”, 插件会通知你添加一个新
 * 的XML布局文件，然后从新产生这个R.java文件，比如你添加了新的资源到你的项目，你将会看到R.java
 * 也相应的改变了。放在你的项目目录的res/ 文件夹下。 “res”是”resources”的缩写，它是存放所有非
 * 代码资源的文件夹，包含象图片，本地化字符串和XML布局文件。
 * 
 * 
 * SnakeView: implementation of a simple game of Snake
 * 创建的view中一般要传入一个Context的实例，Context 可以控制系统的调用，它提供了诸如资源解析
 * ，访问数据库等。Activty类继承自Context类。 
 * 
 * 视图也可以被嵌套，但和J2ME不同，我们可以将定制的视图和Android团队发布的Widgets一起使用。
 * 在J2ME中，开发人员被迫选择GameCanvas和J2ME应用程序画布。这就意味着如果我们想要一个定制
 * 的效果，就必须在GameCanvas上重新设计我们所有的widget。Android还不仅仅是这些，视图类型
 * 也可以混合使用。Android还带了一个widget库，这个类库包括了滚动条，文本实体，进度条以及其
 * 他很多控件。这些标准的widget可以被重载或被按着我们的习惯定制。
 * 
 */
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.
     */
    private int mMode = READY;
    public static final int PAUSE = 0;
    public static final int READY = 1;
    public static final int RUNNING = 2;
    public static final int LOSE = 3;

    /**
     * 设置方向
     * Current direction the snake is headed.
     */
    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
     */
    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;
    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.
     */
    private long mLastMove;
    
    /**
     * mStatusText: text shows to the user in some run states
     */
    private TextView mStatusText;

    /**
     * 用于存储贪吃蛇中，苹果和蛇的点阵的坐标的信息的集合
     * mSnakeTrail: a list of Coordinates that make up the snake's body
     * mAppleList: the secret location of the juicy apples the snake craves.
     */
    private ArrayList<Coordinate> mSnakeTrail = new ArrayList<Coordinate>();
    private ArrayList<Coordinate> mAppleList = new ArrayList<Coordinate>();

    /**
     * 为创建苹果坐标使用随机对象
     * Everyone needs a little randomness in their life
     */
    private static final Random RNG = new Random();

    /**
     * 刷新界面处理器
     * 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.
     */
    private RefreshHandler mRedrawHandler = new RefreshHandler();
    /**
     * 实现刷新的功能：
     *在J2ME中，刷新都是在canvas中通过调用线程结合repaint()来刷新， 他们使线程不断去循环，
     *去调用canvas, 笔者在android 入门时也曾经想用J2ME的模式用在android 中，结果报异常了， 
     *为什么呢？ 很多人认为Dalvik虚拟机是一个Java虚拟机，因为Android的编程语言恰恰就是Java语言。
     *但是这种说法并不准确，因为Dalvik虚拟机并不是按照Java虚拟机的规范来实现的，两者并不兼容；
     *同时还要两个明显的不同： Java虚拟机运行的是Java字节码，而Dalvik虚拟机运行的则是其专有的
     *文件格式DEX（Dalvik Executable）。所以在以前JAVA 里面能使用的模式， 可能在android 
     *里面用不起来 。在自带的例子里面他是通过消息的机制来刷新的。而在android的消定义比较广泛，
     * 比如，手机的暂停， 启动， 来电话、短信，键盘按下，弹起都是一个消息。总的来说， 事件就是消息；
     * 只要继承Handler类就可以对消息进行控制，或者处理， 根据具体情况进行具体处理： 
     * 
     * @author Administrator
     * @date 2010-5-24
     * @version 1.0
     * @since JDK6.0
     */
    class RefreshHandler extends Handler {

    	/**
    	 * 响应消息
    	 */
        @Override
        public void handleMessage(Message msg) {
            SnakeView.this.update();
            SnakeView.this.invalidate();
        }
        /**
         * 向外提供人工的调用消息的接口
         * @param delayMillis
         */
        public void sleep(long delayMillis) {
        	//注销消息
        	this.removeMessages(0);
            //添加消息
        	sendMessageDelayed(obtainMessage(0), delayMillis);
        }
    };


    /**
     * Constructs a SnakeView based on inflation from XML
     * 
     * @param context
     * @param attrs
     */
    public SnakeView(Context context, AttributeSet attrs) {
        super(context, attrs);
        initSnakeView();
   }

    public SnakeView(Context context, AttributeSet attrs, int defStyle) {
    	super(context, attrs, defStyle);
    	initSnakeView();
    }
    /**
     * 初始化界面的
     */
    private void initSnakeView() {
        setFocusable(true);

        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));
    	
    }
    
    /**
     * 初始化新的游戏
     */
    private void initNewGame() {
        mSnakeTrail.clear();
        mAppleList.clear();

        // For now we're just going to load up a short default eastbound snake
        // that's just turned north
        //设置初始化蛇的位置 
        
        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
        //设置苹果的位置
        addRandomApple();
        addRandomApple();
        //
        mMoveDelay = 600;
        //设置积分的
        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...]
     */
    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.
     * 
     * @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
     * 
     * @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
     * 
     * @param icicle a Bundle containing the game state
     */
    public void restoreState(Bundle icicle) {
        setMode(PAUSE);
        //从资源中获取ArrayList
        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"));
    }

    /** 
     * 重点的控制代码 
     * 
     * 实现键盘事件： 键盘主要起操作作用， 在任何的手机游戏中键盘都是起重要的用，要本游戏中，
     *  他就是起控制蛇的行走方向： 现在我们分析他的代码： 
     *   就是通过判断那个键按下， 然后再给要走的方向（mDirection）赋值。 
     *   
     * 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.
     * 
     * (non-Javadoc)
     * 
     * @see android.view.View#onKeyDown(int, android.os.KeyEvent)
     */
    @Override
    public boolean onKeyDown(int keyCode, KeyEvent msg) {

        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();
                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) {
                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.
     * 
     * @param newView
     */
    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);
            update();
            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);
    }

    /**
     * 
     * 生成苹果位置的代码：
     * 苹果的位置就是更简单了，他是随机生成的， 而且必须在现在蛇的位置相对远距离。
     * 
     * 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.
     * 
     */
    private void addRandomApple() {
        Coordinate newCoord = null;
        boolean found = false;
        while (!found) {
        	//随机生成新的X，Y位置
            // Choose a new location for our apple
            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++) {
            	//检查一下存放的位置是否合理
                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!");
        }
        //添加苹果的列表中的
        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.
     */
    public void update() {
        if (mMode == RUNNING) {
            long now = System.currentTimeMillis();

            if (now - mLastMove > mMoveDelay) {
                clearTiles();
                updateWalls();
                updateSnake();
                updateApples();
                mLastMove = now;
            }
            mRedrawHandler.sleep(mMoveDelay);
        }

    }

    /**
     * 调用以上的方法以循环的方式位置数组赋值以及图片的索引。
     * 
     * Draws some walls.
     * 
     */
    private void updateWalls() {
        for (int x = 0; x < mXTileCount; x++) {
            setTile(GREEN_STAR, x, 0);  //设置顶部的界限的位置 
            setTile(GREEN_STAR, x, mYTileCount - 1);   //设置底部界限的位置 
        }
        for (int y = 1; y < mYTileCount - 1; y++) {
            setTile(GREEN_STAR, 0, y);			//设置顶部的界限的位置 
            setTile(GREEN_STAR, mXTileCount - 1, y);   //设置底部界限的位置 
        }
    }

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

    /**
     * 设置当前蛇的方向位置：
     * 从以上的键盘代码我们可以看得出，程序中是通过触发来改变坐标（+1，-1）的方式来改蛇头的方向，
     *  可见坐标在游戏编程中的作用， 这个也是根据手机的屏幕是点阵的方式来显示， 所以坐标就是一个
     *  定位器。 在这里大家可能还有一个疑问。 就是就这个蛇什么能够以“7”字形来移动行走， 其实我们
     *  稍微仔细观察一下就知道了，在这里面， 他们也是通过坐标的传递来实现的， 只要把头部的坐标点
     *  依次赋给下一个点， 后面的每一个点都走过了头部所走过的点，而蛇的头部就是负责去获取坐标，整
     *  个蛇的行走起来就很自然和连贯。  坐标的方向变换又是通过判断那个方向按键的按下来改变的， 这
     *  样一来， 键盘的作用就发挥出来了。蛇吃苹果又是怎样去实现？上面我所说到的坐标就起了作用。在蛇
     *  所经过的每一个坐标， 他们都要在苹果所在的（ArrayList<Coordinate> mAppleList = new
     *   ArrayList<Coordinate>()）坐标集里面集依次判断，若是坐标相同，那个这个苹果就被蛇吃了 。 
     *   
     * 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;

        // grab the snake by the head
        //获取蛇的头部
        Coordinate head = mSnakeTrail.get(0);
        //创建一个新的蛇的头部应该的位置 
        Coordinate newHead = new Coordinate(1, 1);
        //根据当前的为方向设置坐标的信息
        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
        if ((newHead.x < 1) || (newHead.y < 1) || (newHead.x > mXTileCount - 2)
                || (newHead.y > mYTileCount - 2)) {
            setMode(LOSE);
            return;

        }

        // Look for collisions with itself
        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
        //查找苹果设置苹果新的位置的信息
        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++;
                //设置的移动的速度
                mMoveDelay *= 0.9;

                growSnake = true;
            }
        }
        //将蛇头的位置信息放在第一个的对象中方取值
        // push a new head onto the ArrayList and pull off the tail
        mSnakeTrail.add(0, newHead);
        // except if we want the snake to grow
        if (!growSnake) {
            mSnakeTrail.remove(mSnakeTrail.size() - 1);
        }

        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++;
        }

    }

    /**
     * 用于存储每一个位点的x，y坐标信息
     * 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.
     * 
     */
    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 + "]";
        }
    }
    
}