npoi

 DataSet ds = new DataSet();
            DataTable dt = null;

            OpenFileDialog sflg = new OpenFileDialog();
            sflg.Filter = "Excel(*.xls)|*.xls|Excel(*.xlsx)|*.xlsx";
            if (sflg.ShowDialog() == System.Windows.Forms.DialogResult.Cancel)
            {
                return;
            }
            FileStream fs = new FileStream(sflg.FileName, FileMode.Open, FileAccess.Read);
            NPOI.HSSF.UserModel.HSSFWorkbook book = new NPOI.HSSF.UserModel.HSSFWorkbook(fs);
            int sheetCount = book.NumberOfSheets;
            for (int sheetIndex = 0; sheetIndex < sheetCount; sheetIndex++)
            {
                NPOI.SS.UserModel.ISheet sheet = book.GetSheetAt(sheetIndex);
                if (sheet == null) continue;
                
                NPOI.SS.UserModel.IRow row = sheet.GetRow(0);
                if (row == null) continue;

                int firstCellNum = row.FirstCellNum;
                int lastCellNum = row.LastCellNum;
                if (firstCellNum == lastCellNum) continue;

                dt = new DataTable(sheet.SheetName);
                for (int i = firstCellNum; i < lastCellNum; i++)
                {
                    dt.Columns.Add(row.GetCell(i).StringCellValue, typeof(string));
                }

                for (int i = 1; i <= sheet.LastRowNum; i++)
                {
                    DataRow newRow = dt.Rows.Add();
                    for (int j = firstCellNum; j < lastCellNum; j++)
                    {
                        newRow[j] = sheet.GetRow(i).GetCell(j).StringCellValue;
                    }
                }

                ds.Tables.Add(dt);
            }           
        }

        private void btnExport_Click(object sender, EventArgs e)
        {
            SaveFileDialog sflg = new SaveFileDialog();
            sflg.Filter = "Excel(*.xls)|*.xls|Excel(*.xlsx)|*.xlsx";
            if (sflg.ShowDialog() == System.Windows.Forms.DialogResult.Cancel)
            {
                return;
            }
            //this.gridView1.ExportToXls(sflg.FileName);
            //NPOI.xs book = new NPOI.HSSF.UserModel.HSSFWorkbook();
            NPOI.SS.UserModel.IWorkbook book = null;
            if (sflg.FilterIndex == 1)
            {
                book = new NPOI.HSSF.UserModel.HSSFWorkbook();
            }
            else
            {
                book = new NPOI.XSSF.UserModel.XSSFWorkbook();
            }

            NPOI.SS.UserModel.ISheet sheet = book.CreateSheet("test_001");

            // 添加表头
            NPOI.SS.UserModel.IRow row = sheet.CreateRow(0);
            int index = 0;
            foreach (GridColumn item in this.gridView1.Columns)
            {
                if (item.Visible)
                {
                    NPOI.SS.UserModel.ICell cell = row.CreateCell(index);
                    cell.SetCellType(NPOI.SS.UserModel.CellType.String);                    
                    cell.SetCellValue(item.Caption);
                    index++;
                }
            }

            // 添加数据
           
            for (int i = 0; i < this.gridView1.DataRowCount; i++)
            {
                index = 0;
                row = sheet.CreateRow(i + 1);
                foreach (GridColumn item in this.gridView1.Columns)
                {
                    if (item.Visible)
                    {
                        NPOI.SS.UserModel.ICell cell = row.CreateCell(index);
                        cell.SetCellType(NPOI.SS.UserModel.CellType.String);
                        cell.SetCellValue(this.gridView1.GetRowCellValue(i, item).ToString());
                        index++;
                    }
                }
            }
            // 写入 
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            book.Write(ms);
            book = null;

            using (FileStream fs = new FileStream(sflg.FileName, FileMode.Create, FileAccess.Write))
            {
                byte[] data = ms.ToArray();
                fs.Write(data, 0, data.Length);
                fs.Flush();
            }

            ms.Close();
            ms.Dispose();