Using open XML, how do I format header column bold in excel sheet?

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C#4.0

OpenXML

With help of lot of reference in internet i am able to create an method that export data set to excel file, creating multiple tab for each table in Dataset.

this is my code:

public static void ExportDataSet(DataSet dataset, string excelFilePath)
{
try
{
using(var workbook = SpreadsheetDocument.Create(excelFilePath, 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();

foreach(System.Data.DataTable table in dataset.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);

uint sheetId = 1;
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>();


if(table.Rows.Count == 0)
{
DocumentFormat.OpenXml.Spreadsheet.Cell cell = new DocumentFormat.OpenXml.Spreadsheet.Cell();
cell.DataType = DocumentFormat.OpenXml.Spreadsheet.CellValues.String;
cell.CellValue = new DocumentFormat.OpenXml.Spreadsheet.CellValue("** Nothing for today **");
headerRow.AppendChild(cell);
sheetData.AppendChild(headerRow);
}

else
{
foreach(System.Data.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(System.Data.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);
}
}
}
}

}

catch(Exception)
{

throw;
}
}
Now i need to set header to bold. How do i do it?

What I have tried:

I found out this method, which throws null reference exception. What do i need to make change in this method looking at my above code. I would be grateful if anyone could help me out.

public static void SetSpreadsheetHeaderBold(string excelFilePath)
       {

           using(SpreadsheetDocument spreadsheetDocument = SpreadsheetDocument.Open(excelFilePath, true))
           {

               WorkbookPart workbookPart = spreadsheetDocument.WorkbookPart;

               WorksheetPart worksheetPart = workbookPart.WorksheetParts.First();
               SheetData sheetData = worksheetPart.Worksheet.Elements<SheetData>().First();


               WorkbookStylesPart stylesPart = spreadsheetDocument.WorkbookPart.WorkbookStylesPart;

               DocumentFormat.OpenXml.Spreadsheet.Font font1 = new DocumentFormat.OpenXml.Spreadsheet.Font(
                       new Bold(),
                       new FontSize() { Val = 11 },
                       new Color() { Rgb = new HexBinaryValue() { Value = "000000" } },
                       new FontName() { Val = "Calibri" });
               stylesPart.Stylesheet.Fonts.Append(font1);
               stylesPart.Stylesheet.Save();

               UInt32Value fontId = Convert.ToUInt32(stylesPart.Stylesheet.Fonts.ChildElements.Count - 1);
               CellFormat cf = new CellFormat() { FontId = fontId, FillId = 0, BorderId = 0, ApplyFont = true };

               stylesPart.Stylesheet.CellFormats.Append(cf);

               Row r = sheetData.Elements<Row>().First<Row>();

               int index1 = stylesPart.Stylesheet.CellFormats.ChildElements.Count - 1;
               foreach(Cell c in r.Elements<Cell>())
               {
                   c.StyleIndex = Convert.ToUInt32(index1);
                   worksheetPart.Worksheet.Save();
               }
               spreadsheetDocument.Close();

           }
       }