Android SurfaceView使用详解（很好的实战例子）

1. SurfaceView的定义
前面已经介绍过View了，下面来简单介绍一下SurfaceView，参考SDK文档和网络资料：SurfaceView是View的子类，它内嵌了一个专门用于绘制的Surface，你可以控制这个Surface的格式和尺寸，Surfaceview控制这个Surface的绘制位置。surface是纵深排序(Z-ordered)的，说明它总在自己所在窗口的后面。SurfaceView提供了一个可见区域，只有在这个可见区域内的surface内容才可见。surface的排版显示受到视图层级关系的影响，它的兄弟视图结点会在顶端显示。这意味者 surface的内容会被它的兄弟视图遮挡，这一特性可以用来放置遮盖物(overlays)(例如，文本和按钮等控件)。注意，如果surface上面有透明控件，那么每次surface变化都会引起框架重新计算它和顶层控件的透明效果，这会影响性能。
SurfaceView默认使用双缓冲技术的，它支持在子线程中绘制图像，这样就不会阻塞主线程了，所以它更适合于游戏的开发。

2. SurfaceView的使用
首先继承SurfaceView，并实现SurfaceHolder.Callback接口，实现它的三个方法：surfaceCreated，surfaceChanged，surfaceDestroyed。
surfaceCreated(SurfaceHolder holder)：surface创建的时候调用，一般在该方法中启动绘图的线程。
surfaceChanged(SurfaceHolder holder, int format, int width,int height)：surface尺寸发生改变的时候调用，如横竖屏切换。
surfaceDestroyed(SurfaceHolder holder) ：surface被销毁的时候调用，如退出游戏画面，一般在该方法中停止绘图线程。
还需要获得SurfaceHolder，并添加回调函数，这样这三个方法才会执行。

3. SurfaceView实战
下面通过一个小demo来学习SurfaceView在实际项目中的使用，绘制一个精灵，该精灵有四个方向的行走动画，让精灵沿着屏幕四周不停的行走。游戏中精灵素材和最终实现的效果图:

首先创建核心类GameView.java，源码如下：

public class GameView extends SurfaceView implements
        SurfaceHolder.Callback {
    //屏幕宽高
    public static int SCREEN_WIDTH;
    public static int SCREEN_HEIGHT;
    private Context mContext;
    private SurfaceHolder mHolder;
    //最大帧数 (1000 / 30)
    private static final int DRAW_INTERVAL = 30;
    private DrawThread mDrawThread;
    private FrameAnimation []spriteAnimations;
    private Sprite mSprite;
    private int spriteWidth = 0;
    private int spriteHeight = 0;
    private float spriteSpeed = (float)((500  * SCREEN_WIDTH / 480) * 0.001);
    private int row = 4;
    private int col = 4;
    public GameSurfaceView(Context context) {
        super(context);
        this.mContext = context;
        mHolder = this.getHolder();
        mHolder.addCallback(this);
        initResources();
        mSprite = new Sprite(spriteAnimations,0,0,spriteWidth,spriteHeight,spriteSpeed);
    }
    private void initResources() {
        Bitmap[][] spriteImgs = generateBitmapArray(mContext, R.drawable.sprite, row, col);
        spriteAnimations = new FrameAnimation[row];
        for(int i = 0; i < row; i ++) {
            Bitmap []spriteImg = spriteImgs[i];
            FrameAnimation spriteAnimation = new FrameAnimation(spriteImg,new int[]{150,150,150,150},true);
            spriteAnimations[i] = spriteAnimation;
        }
    }
    public Bitmap decodeBitmapFromRes(Context context, int resourseId) {
        BitmapFactory.Options opt = new BitmapFactory.Options();
        opt.inPreferredConfig = Bitmap.Config.RGB_565;
        opt.inPurgeable = true;
        opt.inInputShareable = true;
        InputStream is = context.getResources().openRawResource(resourseId);
        return BitmapFactory.decodeStream(is, null, opt);
    }
    public Bitmap createBitmap(Context context, Bitmap source, int row,
            int col, int rowTotal, int colTotal) {
        Bitmap bitmap = Bitmap.createBitmap(source,
                (col - 1) * source.getWidth() / colTotal,
                (row - 1) * source.getHeight() / rowTotal, source.getWidth()
                        / colTotal, source.getHeight() / rowTotal);
        return bitmap;
    }
    public Bitmap[][] generateBitmapArray(Context context, int resourseId,
            int row, int col) {
        Bitmap bitmaps[][] = new Bitmap[row][col];
        Bitmap source = decodeBitmapFromRes(context, resourseId);
        this.spriteWidth = source.getWidth() / col;
        this.spriteHeight = source.getHeight() / row;
        for (int i = 1; i <= row; i++) {
            for (int j = 1; j <= col; j++) {
                bitmaps[i - 1][j - 1] = createBitmap(context, source, i, j,
                        row, col);
            }
        }
        if (source != null && !source.isRecycled()) {
            source.recycle();
            source = null;
        }
        return bitmaps;
    }
    public void surfaceChanged(SurfaceHolder holder, int format, int width,
            int height) {
    }
    public void surfaceCreated(SurfaceHolder holder) {
        if(null == mDrawThread) {
            mDrawThread = new DrawThread();
            mDrawThread.start();
        }
    }
    public void surfaceDestroyed(SurfaceHolder holder) {
        if(null != mDrawThread) {
            mDrawThread.stopThread();
        }
    }
    private class DrawThread extends Thread {
        public boolean isRunning = false;
        public DrawThread() {
            isRunning = true;
        }
        public void stopThread() {
            isRunning = false;
            boolean workIsNotFinish = true;
            while (workIsNotFinish) {
                try {
                    this.join();// 保证run方法执行完毕
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
                workIsNotFinish = false;
            }
        }
        public void run() {
            long deltaTime = 0;
            long tickTime = 0;
            tickTime = System.currentTimeMillis();
            while (isRunning) {
                Canvas canvas = null;
                try {
                    synchronized (mHolder) {
                        canvas = mHolder.lockCanvas();
                        //设置方向
                        mSprite.setDirection();
                        //更新精灵位置
                        mSprite.updatePosition(deltaTime);
                        drawSprite(canvas);
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                    if (null != mHolder) {
                        mHolder.unlockCanvasAndPost(canvas);
                    }
                }
                deltaTime = System.currentTimeMillis() - tickTime;
                if(deltaTime < DRAW_INTERVAL) {
                    try {
                        Thread.sleep(DRAW_INTERVAL - deltaTime);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                tickTime = System.currentTimeMillis();
            }
        }
    }
    private void drawSprite(Canvas canvas) {
        //清屏操作
        canvas.drawColor(Color.BLACK);
        mSprite.draw(canvas);
    }
}

GameView.java中包含了一个绘图线程DrawThread，在线程的run方法中锁定Canvas、绘制精灵、更新精灵位置、释放Canvas等操作。因为精灵素材是一张大图，所以这里进行了裁剪生成一个二维数组。使用这个二维数组初始化了精灵四个方向的动画，下面看Sprite.java的源码。

public class Sprite {
    public static final int DOWN = 0;
    public static final int LEFT = 1;
    public static final int RIGHT = 2;
    public static final int UP = 3;
    public float x;
    public float y;
    public int width;
    public int height;
    //精灵行走速度
    public double speed;
    //精灵当前行走方向
    public int direction;
    //精灵四个方向的动画
    public FrameAnimation[] frameAnimations;
    public Sprite(FrameAnimation[] frameAnimations, int positionX,
            int positionY, int width, int height, float speed) {
        this.frameAnimations = frameAnimations;
        this.x = positionX;
        this.y = positionY;
        this.width = width;
        this.height = height;
        this.speed = speed;
    }
    public void updatePosition(long deltaTime) {
        switch (direction) {
        case LEFT:
            //让物体的移动速度不受机器性能的影响,每帧精灵需要移动的距离为：移动速度*时间间隔
            this.x = this.x - (float) (this.speed * deltaTime);
            break;
        case DOWN:
            this.y = this.y + (float) (this.speed * deltaTime);
            break;
        case RIGHT:
            this.x = this.x + (float) (this.speed * deltaTime);
            break;
        case UP:
            this.y = this.y - (float) (this.speed * deltaTime);
            break;
        }
    }
    /**
     * 根据精灵的当前位置判断是否改变行走方向
     */
    public void setDirection() {
        if (this.x <= 0
                && (this.y + this.height) < GameSurfaceView.SCREEN_HEIGHT) {
            if (this.x < 0)
                this.x = 0;
            this.direction = Sprite.DOWN;
        } else if ((this.y + this.height) >= GameSurfaceView.SCREEN_HEIGHT
                && (this.x + this.width) < GameSurfaceView.SCREEN_WIDTH) {
            if ((this.y + this.height) > GameSurfaceView.SCREEN_HEIGHT)
                this.y = GameSurfaceView.SCREEN_HEIGHT - this.height;
            this.direction = Sprite.RIGHT;
        } else if ((this.x + this.width) >= GameSurfaceView.SCREEN_WIDTH
                && this.y > 0) {
            if ((this.x + this.width) > GameSurfaceView.SCREEN_WIDTH)
                this.x = GameSurfaceView.SCREEN_WIDTH - this.width;
            this.direction = Sprite.UP;
        } else {
            if (this.y < 0)
                this.y = 0;
            this.direction = Sprite.LEFT;
        }
    }
    public void draw(Canvas canvas) {
        FrameAnimation frameAnimation = frameAnimations[this.direction];
        Bitmap bitmap = frameAnimation.nextFrame();
        if (null != bitmap) {
            canvas.drawBitmap(bitmap, x, y, null);
        }
    }
}

精灵类主要是根据当前位置判断行走的方向，然后根据行走的方向更新精灵的位置，再绘制自身的动画。由于精灵的动画是一帧一帧的播放图片，所以这里封装了FrameAnimation.java，源码如下：

public class FrameAnimation{
    /**动画显示的需要的资源 */
    private Bitmap[] bitmaps;
    /**动画每帧显示的时间 */
    private int[] duration;
    /**动画上一帧显示的时间 */
    protected Long lastBitmapTime;
    /**动画显示的索引值，防止数组越界 */
    protected int step;
    /**动画是否重复播放 */
    protected boolean repeat;
    /**动画重复播放的次数*/
    protected int repeatCount;
    /**
     * @param bitmap:显示的图片<br/>
     * @param duration:图片显示的时间<br/>
     * @param repeat:是否重复动画过程<br/>
     */
    public FrameAnimation(Bitmap[] bitmaps, int duration[], boolean repeat) {
        this.bitmaps = bitmaps;
        this.duration = duration;
        this.repeat = repeat;
        lastBitmapTime = null;
        step = 0;
    }
    public Bitmap nextFrame() {
        // 判断step是否越界
        if (step >= bitmaps.length) {
            //如果不无限循环
            if( !repeat ) {
                return null;
            } else {
                lastBitmapTime = null;
            }
        }
        if (null == lastBitmapTime) {
            // 第一次执行
            lastBitmapTime = System.currentTimeMillis();
            return bitmaps[step = 0];
        }
        // 第X次执行
        long nowTime = System.currentTimeMillis();
        if (nowTime - lastBitmapTime <= duration[step]) {
            // 如果还在duration的时间段内,则继续返回当前Bitmap
            // 如果duration的值小于0,则表明永远不失效,一般用于背景
            return bitmaps[step];
        }
        lastBitmapTime = nowTime;
        return bitmaps[step++];// 返回下一Bitmap
    }
}

FrameAnimation根据每一帧的显示时间返回当前的图片帧，若没有超过指定的时间则继续返回当前帧，否则返回下一帧。
接下来需要做的是让Activty显示的View为我们之前创建的GameView，然后设置全屏显示。

public void onCreate(Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
             WindowManager.LayoutParams.FLAG_FULLSCREEN);
     requestWindowFeature(Window.FEATURE_NO_TITLE);
     getWindow().setFlags(WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON,
             WindowManager.LayoutParams.FLAG_KEEP_SCREEN_ON);
     DisplayMetrics outMetrics = new DisplayMetrics();
     this.getWindowManager().getDefaultDisplay().getMetrics(outMetrics);
     GameSurfaceView.SCREEN_WIDTH = outMetrics.widthPixels;
     GameSurfaceView.SCREEN_HEIGHT = outMetrics.heightPixels;
     GameSurfaceView gameView = new GameSurfaceView(this);
     setContentView(gameView);
 }

现在运行Android工程，应该就可以看到一个手持宝剑的武士在沿着屏幕不停的走了。