Android -- VelocityTracker

//获取一个VelocityTracker对象, 用完后记得回收 //回收后代表你不需要使用了，系统将此对象在此分配到其他请求者  static public VelocityTracker obtain(); public void recycle(); //计算当前速度, 其中units是单位表示， 1代表px/毫秒, 1000代表px/秒, .. //maxVelocity此次计算速度你想要的最大值  public void computeCurrentVelocity(int units, float maxVelocity); //经过一次computeCurrentVelocity后你就可以用一下几个方法获取此次计算的值 //id是touch event触摸点的ID, 来为多点触控标识，有这个标识在计算时可以忽略 //其他触点干扰，当然干扰肯定是有的  public float getXVelocity(); public float getYVelocity(); public float getXVelocity(int id); public float getYVelocity(int id);

public class VelocityTrackerTest extends Activity { private TextView mInfo; private VelocityTracker mVelocityTracker; private int mMaxVelocity; private int mPointerId; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mInfo = new TextView(this); mInfo.setLines(4); mInfo.setLayoutParams(new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT)); mInfo.setTextColor(Color.WHITE); setContentView(mInfo); mMaxVelocity = ViewConfiguration.get(this).getMaximumFlingVelocity(); } @Override public boolean onTouchEvent(MotionEvent event) { if(null == mVelocityTracker) { mVelocityTracker = VelocityTracker.obtain(); } mVelocityTracker.addMovement(event); final VelocityTracker verTracker = mVelocityTracker; switch (event.getAction()) { case MotionEvent.ACTION_DOWN: //求第一个触点的id， 此时可能有多个触点，但至少一个  mPointerId = event.getPointerId(0); break; case MotionEvent.ACTION_MOVE: //求伪瞬时速度  verTracker.computeCurrentVelocity(1000, mMaxVelocity); float velocityX = verTracker.getXVelocity(mPointerId); float velocityY = verTracker.getYVelocity(mPointerId); recodeInfo(velocityX, velocityY); break; case MotionEvent.ACTION_UP: case MotionEvent.ACTION_CANCEL: if(null != mVelocityTracker) { mVelocityTracker.clear(); mVelocityTracker.recycle(); mVelocityTracker = null; } break; default: break; } return super.onTouchEvent(event); } private static final String sFormatStr = "velocityX=%f\nvelocityY=%f"; /** * 记录当前速度 * * @param velocityX x轴速度 * @param velocityY y轴速度 */ private void recodeInfo(final float velocityX, final float velocityY) { final String info = String.format(sFormatStr, velocityX, velocityY); mInfo.setText(info); } }