Question

  private boolean checkTouchSlop(View child, float dx, float dy) {
    if (child == null) {
      return false;
    }
    final boolean checkHorizontal = mCallback.getViewHorizontalDragRange(child) > 0;
    final boolean checkVertical = mCallback.getViewVerticalDragRange(child) > 0;

    if (checkHorizontal && checkVertical) {
      return dx * dx + dy * dy > mTouchSlop * mTouchSlop;
    } else if (checkHorizontal) {
      return Math.abs(dx) > mTouchSlop;
    } else if (checkVertical) {
      return Math.abs(dy) > mTouchSlop;
    }
    return false;
  }

用来根据 mTouchSlop 最小拖动的距离来判断是否属于拖动, mTouchSlop 根据我们设定的灵敏度决定。