FileHelpers.ExcelNPOIStorage.ExcelNPOIStorage.CreateWorkbook C# (CSharp) Method

        private void CreateWorkbook(string filename)
        {
            var extension = Path.GetExtension(filename);

            if (extension.ToLowerInvariant() == ".xlsx")
                mWorkbook = new XSSFWorkbook();
            else if (extension.ToLowerInvariant() == ".xls")
                mWorkbook = new HSSFWorkbook();
            mSheet =  mSheet = String.IsNullOrEmpty(SheetName) ? mWorkbook.CreateSheet() : mWorkbook.CreateSheet(SheetName);
            mWorkbook.SetActiveSheet(0);
        }