@Override public int clampViewPositionVertical(View child,int top,int dy){
  if (mDraggedView == null) {
    return 0;
  }
  final int viewMargin=mDraggedView.getTopBottomMargin();
  final int topBound=getPaddingTop() - viewMargin;
  final int bottomBound=getHeight() - mDraggedView.getHeight() + viewMargin;
  return Math.min(Math.max(top,topBound),bottomBound);
}

@ Override public int clampViewPositionVertical ( View child , int top , int dy ) { if ( mDraggedView == null ) { return 0 ; } final int viewMargin = mDraggedView . getTopBottomMargin ( ) ; final int topBound = getPaddingTop ( ) - viewMargin ; final int bottomBound = getHeight ( ) - mDraggedView . getHeight ( ) + viewMargin ; return Math . min ( Math . max ( top , topBound ) , bottomBound ) ; }
override method used to configure the vertical drag . restrict the motion of the dragged child view along the vertical axis .
