NPOI导出自动换行效果

string filename = "test.xls";
            Response.ContentType = "application/vnd.ms-excel";
            Response.AddHeader("Content-Disposition", string.Format("attachment;filename={0}", filename));
            Response.Clear();
            string reuslt = "0.8锌铁板制做烤漆字、食人鱼防水LED模组(三颗灯)、4mm厚黑白板(特殊材料,白天黑色,打灯后发白光) ";
            int splitnum = 25;
            int num = reuslt.Length;
            int rownum = num / splitnum + ((num % splitnum) > 0 ? 1 : 0);
            HSSFWorkbook workbook = new HSSFWorkbook();
            HSSFSheet sheet = (HSSFSheet)workbook.CreateSheet();
            int rowIndex = 0;
            int cellIndex = 0;
            HSSFRow row = (HSSFRow)sheet.CreateRow(rowIndex);
            row.HeightInPoints = rownum * 17;
            HSSFCell cell = (HSSFCell)row.CreateCell(cellIndex);
            HSSFCellStyle style = (HSSFCellStyle)workbook.CreateCellStyle();
            style.WrapText = true;
            string modify = "";
            for (int i = 0; i < rownum; i++)
            {
                int start = splitnum * i;
                int leave = num%(num - start);
                modify+=(reuslt.Substring(start, leave == 0 ? splitnum : leave + 1) + "\n");
            }
            cell.CellStyle = style;
            cell.SetCellValue(modify.TrimEnd('\n'));
            MemoryStream file = new MemoryStream();
            workbook.Write(file);
            file.WriteTo(Response.OutputStream);
            Response.End();