question: @ 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 ) ; }
target:  Override method used to configure the vertical drag. Restrict the motion of the dragged child view along the vertical axis.