How to set cells' background?

Question

How to set the background of several cells within a row (or of a whole row) in OpenXml?

Having read several articles:

1. Coloring cells in excel sheet usi

Answer 1

You have 3 options:

1. Use MS lib ExcelDataReader which requires your server installing Office and usually does not work if your program is running in IIS.

2. Use closed source libs.

3. Use OpenXML.

Try my code using pure OpenXML: https://stackoverflow.com/a/59806422/6782249

Answer 2

In the end I changed my mind to use cell background and used fonts. Thanks to answer by foson in SO Creating Excel document with OpenXml sdk 2.0 I managed to add a new Font and a new CellFormat, having preserved the original cell's formatting (i.e. having changed the font color only):

SpreadsheetDocument doc = SpreadsheetDocument.Open("1.xlsx", true);
Sheet sheet = (Sheet)doc.WorkbookPart.Workbook.Sheets.FirstOrDefault();
WorksheetPart worksheetPart = (WorksheetPart)doc.WorkbookPart
                                                .GetPartById(sheet.Id);
Worksheet worksheet = worksheetPart.Worksheet;

WorkbookStylesPart styles = doc.WorkbookPart.WorkbookStylesPart;
Stylesheet stylesheet = styles.Stylesheet;
CellFormats cellformats = stylesheet.CellFormats;
Fonts fonts = stylesheet.Fonts;

UInt32 fontIndex = fonts.Count;
UInt32 formatIndex = cellformats.Count;

Cell cell = GetCell(worksheet, "A", 19);
cell.CellValue = new CellValue(DateTime.Now.ToLongTimeString());
cell.DataType = new EnumValue<CellValues>(CellValues.String);

CellFormat f = (CellFormat)cellformats.ElementAt((int)cell.StyleIndex.Value);

var font = (Font)fonts.ElementAt((int)f.FontId.Value);
var newfont = (Font)font.Clone();
newfont.Color = new Color() { Rgb = new HexBinaryValue("ff0000") };
fonts.Append(newfont);

CellFormat newformat = (CellFormat)f.Clone();
newformat.FontId = fontIndex;
cellformats.Append(newformat);

stylesheet.Save();

cell.StyleIndex = formatIndex;
doc.Close();