In C# can't introduce a formula in Excel

// Using EPPlus  

 

public void UpdateExcelUsingEPPlus(string fileName)  
{  
    FileInfo fileInfo = new FileInfo(fileName);  
    ExcelPackage p = new ExcelPackage(fileInfo);  
    ExcelWorksheet myWorksheet = p.Workbook.Worksheets["Sheet1"];  
    myWorksheet.Cells["B15"].Formula = "SUM(B2:B7)";  
    p.Save();  
}  
 

// Using Open XML SDK  

 

public static void UpdateExcelUsingOpenXMLSDK(string fileName)  
{  
// Open the document for editing.  
    using (SpreadsheetDocument spreadSheet = SpreadsheetDocument.Open(fileName, true))  
    {  
        // Access the main Workbook part, which contains all references.  
        WorkbookPart workbookPart = spreadSheet.WorkbookPart;  
        // get sheet by name  
        Sheet sheet = workbookPart.Workbook.Descendants().Where(s => s.Name == "Sheet1").FirstOrDefault();  
        // get worksheetpart by sheet id  
        WorksheetPart worksheetPart = workbookPart.GetPartById(sheet.Id.Value) as WorksheetPart;  
        // The SheetData object will contain all the data.  
        SheetData sheetData = worksheetPart.Worksheet.GetFirstChild();  
        Cell formulaCell = InsertCellInWorksheet("B", 10, worksheetPart);  
        formulaCell.DataType = new EnumValue(CellValues.Number);  
        formulaCell.CellFormula = new CellFormula("SUM(B2:B7)");  
        // Save the worksheet.  
        worksheetPart.Worksheet.Save();  
        // for recacluation of formula  
        spreadSheet.WorkbookPart.Workbook.CalculationProperties.ForceFullCalculation = true;  
        spreadSheet.WorkbookPart.Workbook.CalculationProperties.FullCalculationOnLoad = true;  
    }  
}  
  
private static Cell InsertCellInWorksheet(string columnName, uint rowIndex, WorksheetPart worksheetPart)  
{  
    Worksheet worksheet = worksheetPart.Worksheet;  
    SheetData sheetData = worksheet.GetFirstChild();  
    string cellReference = columnName + rowIndex;  
    // If the worksheet does not contain a row with the specified row index, insert one.  
    Row row;  
    if (sheetData.Elements().Where(r => r.RowIndex == rowIndex).Count() != 0)  
    {  
        row = sheetData.Elements().Where(r => r.RowIndex == rowIndex).First();  
    }  
    else  
    {  
        row = new Row() { RowIndex = rowIndex };  
        sheetData.Append(row);  
    }  
    // If there is not a cell with the specified column name, insert one.  
    if (row.Elements().Where(c => c.CellReference.Value == columnName + rowIndex).Count() > 0)  
    {  
        return row.Elements().Where(c => c.CellReference.Value == cellReference).First();  
    }  
    else  
    {  
        // Cells must be in sequential order according to CellReference. Determine where to insert the new cell.  
        Cell refCell = null;  
        foreach (Cell cell in row.Elements())  
        {  
            if (cell.CellReference.Value.Length == cellReference.Length)  
            {  
                if (string.Compare(cell.CellReference.Value, cellReference, true) > 0)  
                {  
                    refCell = cell;  
                    break;  
                }  
            }  
        }  
    Cell newCell = new Cell() { CellReference = cellReference };  
    row.InsertBefore(newCell, refCell);  
    worksheet.Save();  
    return newCell;  
    }  
}