private IList <WinInterface> GetListOfItf(WinInterface itf) { if (ListNotAssing.Contains(itf)) { return(ListNotAssing); } if (ListBackground.Contains(itf)) { return(ListBackground); } if (ListBottom.Contains(itf)) { return(ListBottom); } if (ListForeground.Contains(itf)) { return(ListForeground); } return(null); //todo: trow error }