使用NPOI快速导出多sheet Excel表格

用的时候直接复制这些代码，然后再导出按钮的click事件里边调用就行了，另外还需要添加一个dll文件 


/// <summary> 
        /// 由DataSet导出Excel 
        /// </summary> 
        /// <param name="sourceTable">要导出数据的DataTable</param> 
        /// <param name="sheetName">工作表名称</param> 
        /// <returns>Excel工作表</returns> 
        private static Stream ExportDataSetToExcel(DataSet sourceDs, string sheetName)
        {
            HSSFWorkbook workbook = new HSSFWorkbook();
            MemoryStream ms = new MemoryStream();
            string[] sheetNames = sheetName.Split(',');
            for (int i = 0; i < sheetNames.Length; i++)
            {
                HSSFSheet sheet = (NPOI.HSSF.UserModel.HSSFSheet)workbook.CreateSheet(sheetNames[i]);
                HSSFRow headerRow = (NPOI.HSSF.UserModel.HSSFRow)sheet.CreateRow(0);
                // handling header. 
                foreach (DataColumn column in sourceDs.Tables[i].Columns)
                    headerRow.CreateCell(column.Ordinal).SetCellValue(column.ColumnName);
                // handling value. 
                int rowIndex = 1;
                foreach (DataRow row in sourceDs.Tables[i].Rows)
                {
                    HSSFRow dataRow = (NPOI.HSSF.UserModel.HSSFRow)sheet.CreateRow(rowIndex);

                    foreach (DataColumn column in sourceDs.Tables[i].Columns)
                    {
                        dataRow.CreateCell(column.Ordinal).SetCellValue(row[column].ToString());