Android重力传感器实现滚动的弹球

public class MySurfaceView extends SurfaceView implements Callback, Runnable {
 private SurfaceHolder sfh;
 private Paint paint;
 private Thread th;
 private boolean flag;
 private Canvas canvas;
 private int screenW, screenH;
 //声明一个传感器管理器
 private SensorManager sm;
 //声明一个传感器
 private Sensor sensor;
 //声明一个传感器监听器
 private SensorEventListener mySensorListener;
 //圆形的X,Y坐标
 private int arc_x, arc_y;
 //传感器的xyz值
 private float x = 0, y = 0, z = 0;
 /**
 * SurfaceView初始化函数
 */
 public MySurfaceView(Context context) {
 super(context);
 sfh = this.getHolder();
 sfh.addCallback(this);
 paint = new Paint();
 paint.setColor(Color.WHITE);
 paint.setAntiAlias(true);
 setFocusable(true);
 //获取传感器管理类实例
 sm = (SensorManager) MainActivity.instance.getSystemService(Service.SENSOR_SERVICE);
 //实例一个重力传感器实例 
 sensor = sm.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
 //实例传感器监听器
 mySensorListener = new SensorEventListener() {
  @Override
  //传感器获取值发生改变时在响应此函数 
  public void onSensorChanged(SensorEvent event) {
  x = event.values[0]; 
  //x>0 说明当前手机左翻 x<0右翻 
  y = event.values[1];
  //y>0 说明当前手机下翻 y<0上翻 
  z = event.values[2]; 
  //z>0 手机屏幕朝上 z<0 手机屏幕朝下 
  arc_x -= x;
  arc_y += y;
  }
  @Override
  //传感器的精度发生改变时响应此函数 
  public void onAccuracyChanged(Sensor sensor, int accuracy) {
  }
 };
 //为传感器注册监听器
 sm.registerListener(mySensorListener, sensor, SensorManager.SENSOR_DELAY_GAME);
 }
 /**
 * SurfaceView视图创建，响应此函数
 */
 @Override
 public void surfaceCreated(SurfaceHolder holder) {
 screenW = this.getWidth();
 screenH = this.getHeight();
 flag = true;
 //实例线程
 th = new Thread(this);
 //启动线程
 th.start();
 }
 /**
 * 游戏绘图
 */
 public void myDraw() {
 try {
  canvas = sfh.lockCanvas();
  if (canvas != null) {
  canvas.drawColor(Color.BLACK);
  paint.setColor(Color.RED);
  canvas.drawArc(new RectF(arc_x, arc_y, arc_x + 50, arc_y + 50), 0, 360, true, paint);
  paint.setColor(Color.YELLOW);
  canvas.drawText("当前重力传感器的值:", arc_x - 50, arc_y - 30, paint);
  canvas.drawText("x=" + x + ",y=" + y + ",z=" + z, arc_x - 50, arc_y, paint);
  String temp_str = "tony提示： ";
  String temp_str2 = "";
  String temp_str3 = "";
  if (x <1 && x > -1 && y <1 && y > -1) {
   temp_str += "当前手机处于水平放置的状态";
   if (z > 0) {
   temp_str2 += "并且屏幕朝上";
   } else {
   temp_str2 += "并且屏幕朝下,提示别躺着玩手机，对眼睛不好哟~";
   }
  } else {
   if (x > 1) {
   temp_str2 += "当前手机处于向左翻的状态";
   } else if (x <-1) {
   temp_str2 += "当前手机处于向右翻的状态";
   }
   if (y > 1) {
   temp_str2 += "当前手机处于向下翻的状态";
   } else if (y <-1) {
   temp_str2 += "当前手机处于向上翻的状态";
   }
   if (z > 0) {
   temp_str3 += "并且屏幕朝上";
   } else {
   temp_str3 += "并且屏幕朝下,提示别躺着玩手机，对眼睛不好哟~";
   }
  }
  paint.setTextSize(10);
  canvas.drawText(temp_str, 0, 50, paint);
  canvas.drawText(temp_str2, 0, 80, paint);
  canvas.drawText(temp_str3, 0, 110, paint);
  }
 } catch (Exception e) {
  // TODO: handle exception
 } finally {
  if (canvas != null)
  sfh.unlockCanvasAndPost(canvas);
 }
 }
 /**
 * 触屏事件监听
 */
 @Override
 public boolean onTouchEvent(MotionEvent event) {
 return true;
 }
 /**
 * 按键事件监听
 */
 @Override
 public boolean onKeyDown(int keyCode, KeyEvent event) {
 return super.onKeyDown(keyCode, event);
 }
 /**
 * 游戏逻辑
 */
 private void logic() {
 }
 @Override
 public void run() {
 while (flag) {
  long start = System.currentTimeMillis();
  myDraw();
  logic();
  long end = System.currentTimeMillis();
  try {
  if (end - start <50) {
   Thread.sleep(50 - (end - start));
  }
  } catch (InterruptedException e) {
  e.printStackTrace();
  }
 }
 }
 /**
 * SurfaceView视图状态发生改变，响应此函数
 */
 @Override
 public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) {
 }
 /**
 * SurfaceView视图消亡时，响应此函数
 */
 @Override
 public void surfaceDestroyed(SurfaceHolder holder) {
 flag = false;
 }
} 

public class MainActivity extends Activity {
 public static MainActivity instance;
 @Override
 public void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 instance = this;
 //设置全屏
 this.getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
 requestWindowFeature(Window.FEATURE_NO_TITLE);
 //显示自定义的SurfaceView视图
 setContentView(new MySurfaceView(this));
 }
}