Export Data from Dataset to Excell in c# :

   private void btnprint_Click(object sender, EventArgs e)
        {
            try
            {
                if (dataGridView1.Rows.Count <= 0)
                {
                    return;
                }

                DataTable dt2 = new DataTable();
                dt2 = (DataTable)dataGridView1.DataSource;
                DataSet ds1 = new DataSet();
                ds1.Tables.Add(dt2.Copy());

                string filename = "";
                SaveFileDialog saveFileDialog1 = new SaveFileDialog();
                saveFileDialog1.DefaultExt = "txt";
                saveFileDialog1.Filter = "Text files (*.xls)|*.xls|All files (*.*)|*.*";
                if (saveFileDialog1.ShowDialog() == DialogResult.OK)
                {
                    filename = saveFileDialog1.FileName;
                }

                using (var workbook = SpreadsheetDocument.Create(filename, DocumentFormat.OpenXml.SpreadsheetDocumentType.Workbook))
                {
                    var workbookPart = workbook.AddWorkbookPart();
                    workbook.WorkbookPart.Workbook = new DocumentFormat.OpenXml.Spreadsheet.Workbook();
                    workbook.WorkbookPart.Workbook.Sheets = new DocumentFormat.OpenXml.Spreadsheet.Sheets();

                    uint sheetId = 1;

                    foreach (System.Data.DataTable table in ds1.Tables)
                    {
                        var sheetPart = workbook.WorkbookPart.AddNewPart<WorksheetPart>();
                        var sheetData = new DocumentFormat.OpenXml.Spreadsheet.SheetData();
                        sheetPart.Worksheet = new DocumentFormat.OpenXml.Spreadsheet.Worksheet(sheetData);

                        DocumentFormat.OpenXml.Spreadsheet.Sheets sheets = workbook.WorkbookPart.Workbook.GetFirstChild<DocumentFormat.OpenXml.Spreadsheet.Sheets>();
                        string relationshipId = workbook.WorkbookPart.GetIdOfPart(sheetPart);

                        if (sheets.Elements<DocumentFormat.OpenXml.Spreadsheet.Sheet>().Count() > 0)
                        {
                            sheetId =
                                sheets.Elements<DocumentFormat.OpenXml.Spreadsheet.Sheet>().Select(s => s.SheetId.Value).Max() + 1;
                        }

                        DocumentFormat.OpenXml.Spreadsheet.Sheet sheet = new DocumentFormat.OpenXml.Spreadsheet.Sheet() { Id = relationshipId, SheetId = sheetId, Name = table.TableName };
                        sheets.Append(sheet);

                        DocumentFormat.OpenXml.Spreadsheet.Row headerRow = new DocumentFormat.OpenXml.Spreadsheet.Row();

                        List<String> columns = new List<string>();
                        foreach (DataColumn column in table.Columns)
                        {
                            columns.Add(column.ColumnName);

                            DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
                            cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
                            cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue(column.ColumnName);
                            headerRow.AppendChild(cell);
                        }

                        sheetData.AppendChild(headerRow);

                        foreach (DataRow dsrow in table.Rows)
                        {
                            DocumentFormat.OpenXml.Spreadsheet.Row newRow = new DocumentFormat.OpenXml.Spreadsheet.Row();
                            foreach (String col in columns)
                            {
                                DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
                                cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
                                cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue(dsrow[col].ToString()); //
                                newRow.AppendChild(cell);
                            }

                            sheetData.AppendChild(newRow);
                        }
                    }
                }

                System.Diagnostics.Process.Start(filename);
                ds1.Clear();
            }
            catch
            {
            }
        }