VelocityTracker使用

public class VelocityTrackerAct extends Activity {
    private VelocityTracker velocityTracker;
    private TextView tv;
    private float downX,downY;
    private ViewConfiguration viewConfiguration;
    private int slop;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        tv = new TextView(this);
        tv.setTextSize(30);
        setContentView(tv);

        viewConfiguration = ViewConfiguration.get(this);
        slop = viewConfiguration.getScaledTouchSlop();
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        int action = event.getAction();
        switch (action){
            case MotionEvent.ACTION_DOWN:
                 downX = event.getX();
                 downY = event.getY();
                break;
            case MotionEvent.ACTION_MOVE:
                recoInfo(event);
                break;
            case MotionEvent.ACTION_UP:
                release();
                break;
            case MotionEvent.ACTION_CANCEL:
                release();
                break;
        }
        return super.onTouchEvent(event);
    }

    private void release() {
        if(velocityTracker != null){
            velocityTracker.clear();
            velocityTracker.recycle();
            velocityTracker = null;
        }
    }

    private void recoInfo(MotionEvent event) {
        float deltaX = event.getX() - downX;

        velocityTracker = VelocityTracker.obtain();
        velocityTracker.addMovement(event);
        velocityTracker.computeCurrentVelocity(1000);
        if(Math.abs(deltaX) > slop){
            tv.setText("velocity X:"+velocityTracker.getXVelocity());
        }else{
            tv.setText("velocity Y:"+velocityTracker.getYVelocity());
        }

    }

}