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How to add colour to particular excel columns based on conditions using openxml?

I'm generating an excel sheet and I want to color the excel columns based on conditions. Now my all excel columns get red colors. I want to color only particular column names.
I'm using open XML for generating excel, is there any way to find the cells to apply color
using (SpreadsheetDocument document = SpreadsheetDocument.Create(path, SpreadsheetDocumentType.Workbook))
{
WorkbookPart workbookPart = document.AddWorkbookPart();
workbookPart.Workbook = new Workbook();
WorksheetPart worksheetPart = workbookPart.AddNewPart<WorksheetPart>();
worksheetPart.Worksheet = new Worksheet();
Sheets sheets = workbookPart.Workbook.AppendChild(new Sheets());
Sheet sheet = new Sheet() { Id = workbookPart.GetIdOfPart(worksheetPart), SheetId = 1, Name = "Template" };
sheets.Append(sheet);
var stylesheet = new Stylesheet() { MCAttributes = new MarkupCompatibilityAttributes() { Ignorable = "x14ac" } };
stylesheet.AddNamespaceDeclaration("mc", "http: //schemas.openxmlformats.org/markup-compatibility/2006");
stylesheet.AddNamespaceDeclaration("x14ac", "http: //schemas.microsoft.com/office/spreadsheetml/2009/9/ac");
var fills = new Fills() { Count = 5U };
var fonts = new Fonts() { Count = 1U, KnownFonts = true };
// var cellFormats = new CellFormats();
Font font = new Font();
font.Append(new Color() { Rgb = "ff0000" });
fonts.Append(font);
// cellFormats.AppendChild(new CellFormat() { FontId = 0U });
stylesheet.Append(fonts);
stylesheet.Append(fills);
//stylesheet.Append(cellFormats);
//stylesheet.Append(fill);
var stylePart = workbookPart.AddNewPart<WorkbookStylesPart>();
stylePart.Stylesheet = stylesheet;
stylePart.Stylesheet.Save();
workbookPart.Workbook.Save();
SheetData sheetData = worksheetPart.Worksheet.AppendChild(new SheetData());
// Constructing header
Row row = new Row();
foreach (DataExchangeDefinition a in importColList)
{
defnExist = true;
if (a.MustFieldYN == true)
{
row.Append(
ConstructCell(a.FieldCaption, CellValues.String));
}
else
{
row.Append(
ConstructCell(a.FieldCaption, CellValues.String));
}
}
if (defnExist == false)
{
row.Append(
ConstructCell("Excel Template Definition Missing", CellValues.String));
}
// Insert the header row to the Sheet Data
sheetData.AppendChild(row);
// Inserting each employee
worksheetPart.Worksheet.Save();
}
Here is construct cell method
private Cell ConstructCell(string value, CellValues dataType)
{
Cell c = new Cell()
{
CellValue = new CellValue(value),
DataType = new EnumValue<CellValues>(dataType)
//StyleIndex=0U
};
return c;
}
Is there any way to solve this?

1) Add style sheet to your WorkBookPart
WorkbookPart workbookPart = document.AddWorkbookPart();
workbookPart.Workbook = new Workbook();
WorkbookStylesPart stylePart = workbookPart.AddNewPart<WorkbookStylesPart>();
stylePart.Stylesheet = GenerateStylesheet();
stylePart.Stylesheet.Save();
Note: Add above WorkbookStylesPart code just below the WorkbookPart otherwise you can't get it to work.
2) Add below function that return stylesheet,
private Stylesheet GenerateStylesheet()
{
Stylesheet styleSheet = null;
Fonts fonts = new Fonts(
new Font( // Index 0 - default
new FontSize() { Val = 10 }
),
new Font( // Index 1 - header
new FontSize() { Val = 10 },
new Bold(),
new Color() { Rgb = "FFFFFF" }
));
Fills fills = new Fills(
new Fill(new PatternFill() { PatternType = PatternValues.None }), // Index 0 - default
new Fill(new PatternFill() { PatternType = PatternValues.Gray125 }), // Index 1 - default
new Fill(new PatternFill(new ForegroundColor { Rgb = new HexBinaryValue() { Value = "66666666" } })
{ PatternType = PatternValues.Solid }) // Index 2 - header
);
Borders borders = new Borders(
new Border(), // index 0 default
new Border( // index 1 black border
new LeftBorder(new Color() { Auto = true }) { Style = BorderStyleValues.Thin },
new RightBorder(new Color() { Auto = true }) { Style = BorderStyleValues.Thin },
new TopBorder(new Color() { Auto = true }) { Style = BorderStyleValues.Thin },
new BottomBorder(new Color() { Auto = true }) { Style = BorderStyleValues.Thin },
new DiagonalBorder())
);
CellFormats cellFormats = new CellFormats(
new CellFormat(), // default
new CellFormat { FontId = 0, FillId = 0, BorderId = 1, ApplyBorder = true }, // body
new CellFormat { FontId = 1, FillId = 2, BorderId = 1, ApplyFill = true } // header
);
styleSheet = new Stylesheet(fonts, fills, borders, cellFormats);
return styleSheet;
}
3) And your ConstructCell method,
private Cell ConstructCell(string value, CellValues dataType, uint styleIndex = 0)
{
return new Cell()
{
CellValue = new CellValue(value),
DataType = new EnumValue<CellValues>(dataType),
StyleIndex = styleIndex
};
}
4) And call your above method like
If you dont want to apply style then use below
ConstructCell(a.FieldCaption, CellValues.String));
And if you want to apply style on body cell then use below
ConstructCell(a.FieldCaption, CellValues.String, 1);
And if you want to apply style on header cell then use below
ConstructCell(a.FieldCaption, CellValues.String, 2);

'The file is corrupt and cannot be opened' OpenXML

I got that code from OpenXML sdk and instead of SpreadsheetDocument.Create, I used SpreadsheetDocument.Open
This code is working and add an image in .xlsx, after image added to the file. I open the file which shows ->
The file is corrupt and cannot be opened
If you want more details Please! let me know.
Reference URL -> https://code.msdn.microsoft.com/office/How-to-insert-image-into-93964561
Thanks for the help!
/// <summary>
/// add sheet in xlsx then add image into it.
/// </summary>
/// <param name="sFile"></param>
/// <param name="imageFileName"></param>
public void InsertimginExcel(string sFile, string imageFileName)
{
try
{
// Create a spreadsheet document by supplying the filepath.
using (SpreadsheetDocument spreadsheetDocument = SpreadsheetDocument.
Open(sFile, true))
{
// Add a WorkbookPart to the document.
//WorkbookPart workbookpart = spreadsheetDocument.AddWorkbookPart();
//workbookpart.Workbook = new Workbook();
// Add a WorksheetPart to the WorkbookPart.
WorksheetPart worksheetPart = spreadsheetDocument.WorkbookPart.AddNewPart<WorksheetPart>();
worksheetPart.Worksheet = new Worksheet(new SheetData());
// Add Sheets to the Workbook.
Sheets sheets = spreadsheetDocument.WorkbookPart.Workbook.
AppendChild<Sheets>(new Sheets());
// Append a new worksheet and associate it with the workbook.
Sheet sheet = new Sheet()
{
Id = spreadsheetDocument.WorkbookPart.GetIdOfPart(worksheetPart),
SheetId = 1,
Name = "mySheet"
};
sheets.Append(sheet);
var drawingsPart = worksheetPart.AddNewPart<DrawingsPart>();
if (!worksheetPart.Worksheet.ChildElements.OfType<DocumentFormat.OpenXml.Spreadsheet.Drawing>().Any())
{
worksheetPart.Worksheet.Append(new DocumentFormat.OpenXml.Spreadsheet.Drawing { Id = worksheetPart.GetIdOfPart(drawingsPart) });
}
if (drawingsPart.WorksheetDrawing == null)
{
drawingsPart.WorksheetDrawing = new WorksheetDrawing();
}
var worksheetDrawing = drawingsPart.WorksheetDrawing;
var imagePart = drawingsPart.AddImagePart(ImagePartType.Jpeg);
using (var stream = new FileStream(imageFileName, FileMode.Open))
{
imagePart.FeedData(stream);
}
Bitmap bm = new Bitmap(imageFileName);
DocumentFormat.OpenXml.Drawing.Extents extents = new DocumentFormat.OpenXml.Drawing.Extents();
var extentsCx = (long)bm.Width * (long)((float)914400 / bm.HorizontalResolution);
var extentsCy = (long)bm.Height * (long)((float)914400 / bm.VerticalResolution);
bm.Dispose();
var colOffset = 0;
var rowOffset = 0;
int colNumber = 5;
int rowNumber = 10;
var nvps = worksheetDrawing.Descendants<Xdr.NonVisualDrawingProperties>();
var nvpId = nvps.Count() > 0 ?
(UInt32Value)worksheetDrawing.Descendants<Xdr.NonVisualDrawingProperties>().Max(p => p.Id.Value) + 1 :
1U;
var oneCellAnchor = new Xdr.OneCellAnchor(
new Xdr.FromMarker
{
ColumnId = new Xdr.ColumnId((colNumber - 1).ToString()),
RowId = new Xdr.RowId((rowNumber - 1).ToString()),
ColumnOffset = new Xdr.ColumnOffset(colOffset.ToString()),
RowOffset = new Xdr.RowOffset(rowOffset.ToString())
},
new Xdr.Extent { Cx = extentsCx, Cy = extentsCy },
new Xdr.Picture(
new Xdr.NonVisualPictureProperties(
new Xdr.NonVisualDrawingProperties { Id = nvpId, Name = "Picture " + nvpId, Description = imageFileName },
new Xdr.NonVisualPictureDrawingProperties(new A.PictureLocks { NoChangeAspect = true })
),
new Xdr.BlipFill(
new A.Blip { Embed = drawingsPart.GetIdOfPart(imagePart), CompressionState = A.BlipCompressionValues.Print },
new A.Stretch(new A.FillRectangle())
),
new Xdr.ShapeProperties(
new A.Transform2D(
new A.Offset { X = 0, Y = 0 },
new A.Extents { Cx = extentsCx, Cy = extentsCy }
),
new A.PresetGeometry { Preset = A.ShapeTypeValues.Rectangle }
)
),
new Xdr.ClientData()
);
worksheetDrawing.Append(oneCellAnchor);
//workbookpart.Workbook.Save();
// Close the document.
spreadsheetDocument.Close();
}
}
catch (Exception ex)
{
Console.WriteLine(ex.Message);
//log.Error("error occur while creating sheet and adding image --> " + ex.Message.ToString());
}
}

Not sure how many workbookparts and worksheetparts a xlsx file can handle and if the SheetId must be document unique for all Sheets. Try changing the Id to e.g. 5 if that does not help: do not create a new workbookpart for the sheet, use existig one, if possible.

The file is corrupt and cannot be opened
Uncheck all the options under Protected View and confirm by pressing OK.
Restart Excel and try to open the broken Excel documents.
Ref: https://answers.microsoft.com/en-us/office/forum/office_2010-excel/the-file-is-corrupt-and-cannot-be-opened-error-on/93af59c1-946c-4f5f-83c1-bd6f58dbd94f
If that doesn't work, typically when you create XSLX files and there is an error, you see this:
Can you check your Temporary Internet Files for the log. The log file should have info on what is malformed. Please update your question with any additional info.

How to make excel work sheet header row bold using OpenXML

I am using openXML, Asp.net and c# to create an Excel workbook, I have a requirement that to make Header row of all sheets should be bold.
WorkbookStylesPart stylesPart = workbookpart.AddNewPart<WorkbookStylesPart>();
stylesPart.Stylesheet = CreateStylesheet();
stylesPart.Stylesheet.Save();
}
private static Stylesheet CreateStylesheet()
{
Stylesheet ss = new Stylesheet();
Fonts fts = new Fonts();
DocumentFormat.OpenXml.Spreadsheet.Font ft = new DocumentFormat.OpenXml.Spreadsheet.Font();
Bold fbld = new Bold();
FontName ftn = new FontName();
ftn.Val = "Calibri";
DocumentFormat.OpenXml.Spreadsheet.FontSize ftsz = new DocumentFormat.OpenXml.Spreadsheet.FontSize();
ftsz.Val = 11;
ft.FontName = ftn;
ft.FontSize = ftsz;
ft.Bold = fbld;
fts.Append(ft);
fts.Count = (uint)fts.ChildElements.Count;
ss.Append(fts);
return ss;
}
It is making all the cells bold, I am missing the code that apply this to a particular row/cells
Thanks in Advance,
AR

I got the Answer from another post.
Create Excel file with style tag using OpenXmlWriter SAX
private static Stylesheet CreateStylesheet()
{
Stylesheet ss = new Stylesheet();
Font font0 = new Font(); // Default font
Font font1 = new Font(); // Bold font
Bold bold = new Bold();
font1.Append(bold);
Fonts fonts = new Fonts(); // <APENDING Fonts>
fonts.Append(font0);
fonts.Append(font1);
// <Fills>
Fill fill0 = new Fill(); // Default fill
Fills fills = new Fills(); // <APENDING Fills>
fills.Append(fill0);
// <Borders>
Border border0 = new Border(); // Defualt border
Borders borders = new Borders(); // <APENDING Borders>
borders.Append(border0);
CellFormat cellformat0 = new CellFormat() { FontId = 0, FillId = 0, BorderId = 0 }; // Default style : Mandatory | Style ID =0
CellFormat cellformat1 = new CellFormat(){FontId = 1};
CellFormats cellformats = new CellFormats();
cellformats.Append(cellformat0);
cellformats.Append(cellformat1);
ss.Append(fonts);
ss.Append(fills);
ss.Append(borders);
ss.Append(cellformats);
return ss;
}

Create Excel file with style tag using OpenXmlWriter SAX

I am trying to write an Excel Xlsx spreadsheet with styling using OpenXmlWriter (SAX).
I am able to create the file with rows and columns (populate them as strings).
I am looking for a simple code on how to make the first row (header) with bold font.
I do not have a template file to start with as the file will be dynamic.
I found a few articles on how to add WorkbookStylesPart, but they are all using the DOM. As i need to write large number of rows, the DOM will not work for me.
Could anyone point me at the right direction?
Simple code to add a header row as bold when using WriteStartElement and OpenXmlAttribute.
Thanks, odansky

Adding StyleSheet is one time work. After that you just need to simply refer the defined style ID when creating new cells.
Hot to add a stylesheet to spreadsheet [With Bold text style]
private WorkbookStylesPart AddStyleSheet(SpreadsheetDocument spreadsheet)
{
WorkbookStylesPart stylesheet = spreadsheet.WorkbookPart.AddNewPart<WorkbookStylesPart>();
Stylesheet workbookstylesheet = new Stylesheet();
Font font0 = new Font(); // Default font
Font font1 = new Font(); // Bold font
Bold bold = new Bold();
font1.Append(bold);
Fonts fonts = new Fonts(); // <APENDING Fonts>
fonts.Append(font0);
fonts.Append(font1);
// <Fills>
Fill fill0 = new Fill(); // Default fill
Fills fills = new Fills(); // <APENDING Fills>
fills.Append(fill0);
// <Borders>
Border border0 = new Border(); // Defualt border
Borders borders = new Borders(); // <APENDING Borders>
borders.Append(border0);
// <CellFormats>
CellFormat cellformat0 = new CellFormat() { FontId = 0, FillId = 0, BorderId = 0 }; // Default style : Mandatory | Style ID =0
CellFormat cellformat1 = new CellFormat() { FontId = 1 }; // Style with Bold text ; Style ID = 1
// <APENDING CellFormats>
CellFormats cellformats = new CellFormats();
cellformats.Append(cellformat0);
cellformats.Append(cellformat1);
// Append FONTS, FILLS , BORDERS & CellFormats to stylesheet <Preserve the ORDER>
workbookstylesheet.Append(fonts);
workbookstylesheet.Append(fills);
workbookstylesheet.Append(borders);
workbookstylesheet.Append(cellformats);
// Finalize
stylesheet.Stylesheet = workbookstylesheet;
stylesheet.Stylesheet.Save();
return stylesheet;
}
Now when you create a cell do following to refer to the Bold text
Cell c1 = new Cell(){StyleIndex = Convert.ToUInt32(1)}; // Assign our defined style with Bold text ; Style ID 1
Additional Note : You need to add stylesheet after adding workbookpart of the spreadsheet.
More regarding SAX approach : You can define styles when you first create the template file which you gonna open to insert data cells. And when adding data cells refer to the defined styles using ID.
A simple working spreadsheet with style (MSDN)
public static void CreateSpreadsheetWorkbook(string filepath)
{
// Create a spreadsheet document by supplying the filepath.
// By default, AutoSave = true, Editable = true, and Type = xlsx.
SpreadsheetDocument spreadsheetDocument = SpreadsheetDocument.Create(filepath, SpreadsheetDocumentType.Workbook);
// Add a WorkbookPart to the document.
WorkbookPart workbookpart = spreadsheetDocument.AddWorkbookPart();
workbookpart.Workbook = new Workbook();
AddStyleSheet(spreadsheetDocument) // <== Adding stylesheet using above function
// Add a WorksheetPart to the WorkbookPart.
WorksheetPart worksheetPart = workbookpart.AddNewPart<WorksheetPart>();
worksheetPart.Worksheet = new Worksheet(new SheetData());
// Add Sheets to the Workbook.
Sheets sheets = spreadsheetDocument.WorkbookPart.Workbook.AppendChild<Sheets>(new Sheets());
// Append a new worksheet and associate it with the workbook.
Sheet sheet = new Sheet() { Id = spreadsheetDocument.WorkbookPart.GetIdOfPart(worksheetPart), SheetId = 1, Name = "mySheet" };
sheets.Append(sheet);
workbookpart.Workbook.Save();
// Close the document.
spreadsheetDocument.Close();
}

You set the style index the same way you set the datatype for the cell:
oxa.Add(new OpenXmlAttribute("s", null, "1"));

How to insert a date to an Open XML worksheet?

I'm using Microsoft Open XML SDK 2 and I'm having a really hard time inserting a date into a cell. I can insert numbers without a problem by setting Cell.DataType = CellValues.Number, but when I do the same with a date (Cell.DataType = CellValues.Date) Excel 2010 crashes (2007 too).
I tried setting the Cell.Text value to many date formats as well as Excel's date/numeric format to no avail. I also tried to use styles, removing the type attribute, plus many other pizzas I threw at the wall…
Can anyone point me to an example inserting a date to a worksheet?

I used the code provided by Andrew J, but the DataType CellValues.Date produced a corrupted xlsx-file for me.
The DataType CellValues.Number worked fine for me (Don't forget to set NumberFormatId):
cell.DataType = new EnumValue<CellValues>(CellValues.Number);
My whole code:
DateTime valueDate = DateTime.Now;
string valueString = valueDate.ToOADate().ToString();
CellValue cellValue = new CellValue(valueString);
Cell cell = new Cell();
cell.DataType = new EnumValue<CellValues>(CellValues.Number);
cell.StyleIndex = yourStyle; //StyleIndex of CellFormat cfBaseDate -> See below
cell.Append(cellValue);
My CellFormat for this cell in the Stylesheet looks like:
CellFormat cfBaseDate = new CellFormat() {
ApplyNumberFormat = true,
NumberFormatId = 14, //14 is a localized short Date (d/m/yyyy) -> See list below
//Some further styling parameters
};
If you'd like to format your date another way, here is a list of all default Excel NumberFormatId's
ID FORMAT CODE
0 General
1 0
2 0.00
3 #,##0
4 #,##0.00
9 0%
10 0.00%
11 0.00E+00
12 # ?/?
13 # ??/??
14 d/m/yyyy
15 d-mmm-yy
16 d-mmm
17 mmm-yy
18 h:mm tt
19 h:mm:ss tt
20 H:mm
21 H:mm:ss
22 m/d/yyyy H:mm
37 #,##0 ;(#,##0)
38 #,##0 ;[Red](#,##0)
39 #,##0.00;(#,##0.00)
40 #,##0.00;[Red](#,##0.00)
45 mm:ss
46 [h]:mm:ss
47 mmss.0
48 ##0.0E+0
49 #
Source of list: https://github.com/ClosedXML/ClosedXML/wiki/NumberFormatId-Lookup-Table
I know this list is from ClosedXML, but it's the same in OpenXML.

When creating new SpreadsheetDocument from scratch, for Date formatting to work, minimal Stylesheet has to be created.
Critical are those few lines:
new CellFormat
{
NumberFormatId = 14,
ApplyNumberFormat = true
})
Full Stylesheet class:
using (var spreadSheet = SpreadsheetDocument.Create(ms, SpreadsheetDocumentType.Workbook))
{
// Workbook
var workbookPart = spreadSheet.AddWorkbookPart();
workbookPart.Workbook =
new Workbook(new Sheets(new Sheet { Name = "Sheet1", SheetId = (UInt32Value) 1U, Id = "rId1" }));
// Add minimal Stylesheet
var stylesPart = spreadSheet.WorkbookPart.AddNewPart<WorkbookStylesPart>();
stylesPart.Stylesheet = new Stylesheet
{
Fonts = new Fonts(new Font()),
Fills = new Fills(new Fill()),
Borders = new Borders(new Border()),
CellStyleFormats = new CellStyleFormats(new CellFormat()),
CellFormats =
new CellFormats(
new CellFormat(),
new CellFormat
{
NumberFormatId = 14,
ApplyNumberFormat = true
})
};
// Continue creating `WorksheetPart`...
After Stylesheet is added, DateTime can be formatted:
if (valueType == typeof(DateTime))
{
DateTime date = (DateTime)value;
cell.CellValue = new CellValue(date.ToOADate().ToString(CultureInfo.InvariantCulture));
// "StyleIndex" is "1", because "NumberFormatId=14"
// is in the 2nd item of `CellFormats` array.
cell.StyleIndex = 1;
}
Note that StyleIndex value depends on the order of CellFormat items in the CellFormats array or the Stylesheet object. In this example NumberFormatId = 14 item on the 2nd item in the array.

You have to convert DateTime to double using function ToOADate i.e.:
DateTime dtValue = DateTime.Now;
string strValue = dtValue.ToOADate().ToString(CultureInfo.InvariantCulture);
then set it as CellValue
Cell cell;
cell.DataType = new EnumValue<CellValues>(CellValues.Date);
cell.CellValue = new CellValue(strValue);
Remember to format cell using DateTime formatting, otherwise you will see double value, not date.

There are 2 ways to store dates in OpenXml; by writing a number (using ToOADate) and setting the DataType to Number or by writing an ISO 8601 formatted date and setting the DataType to Date. Note that the default DataType is Number so if you go with the first option you don't have to set the DataType.
Whichever method you choose, you'll need to set the style as Excel displays both methods identically. The following code shows an example of writing a date using the Number format (with and without explicitly setting the DataType) and using the ISO 8601 format.
using (SpreadsheetDocument document = SpreadsheetDocument.Create(filename, SpreadsheetDocumentType.Workbook))
{
//fluff to generate the workbook etc
WorkbookPart workbookPart = document.AddWorkbookPart();
workbookPart.Workbook = new Workbook();
var worksheetPart = workbookPart.AddNewPart<WorksheetPart>();
worksheetPart.Worksheet = new Worksheet();
Sheets sheets = workbookPart.Workbook.AppendChild(new Sheets());
Sheet sheet = new Sheet() { Id = workbookPart.GetIdOfPart(worksheetPart), SheetId = 1, Name = "Sheet" };
sheets.Append(sheet);
workbookPart.Workbook.Save();
var sheetData = worksheetPart.Worksheet.AppendChild(new SheetData());
//add the style
Stylesheet styleSheet = new Stylesheet();
CellFormat cf = new CellFormat();
cf.NumberFormatId = 14;
cf.ApplyNumberFormat = true;
CellFormats cfs = new CellFormats();
cfs.Append(cf);
styleSheet.CellFormats = cfs;
styleSheet.Borders = new Borders();
styleSheet.Borders.Append(new Border());
styleSheet.Fills = new Fills();
styleSheet.Fills.Append(new Fill());
styleSheet.Fonts = new Fonts();
styleSheet.Fonts.Append(new Font());
workbookPart.AddNewPart<WorkbookStylesPart>();
workbookPart.WorkbookStylesPart.Stylesheet = styleSheet;
CellStyles css = new CellStyles();
CellStyle cs = new CellStyle();
cs.FormatId = 0;
cs.BuiltinId = 0;
css.Append(cs);
css.Count = UInt32Value.FromUInt32((uint)css.ChildElements.Count);
styleSheet.Append(css);
Row row = new Row();
DateTime date = new DateTime(2017, 6, 24);
/*** Date code here ***/
//write an OADate with type of Number
Cell cell1 = new Cell();
cell1.CellReference = "A1";
cell1.CellValue = new CellValue(date.ToOADate().ToString());
cell1.DataType = new EnumValue<CellValues>(CellValues.Number);
cell1.StyleIndex = 0;
row.Append(cell1);
//write an OADate with no type (defaults to Number)
Cell cell2 = new Cell();
cell2.CellReference = "B1";
cell2.CellValue = new CellValue(date.ToOADate().ToString());
cell1.StyleIndex = 0;
row.Append(cell2);
//write an ISO 8601 date with type of Date
Cell cell3 = new Cell();
cell3.CellReference = "C1";
cell3.CellValue = new CellValue(date.ToString("yyyy-MM-dd"));
cell3.DataType = new EnumValue<CellValues>(CellValues.Date);
cell1.StyleIndex = 0;
row.Append(cell3);
sheetData.AppendChild(row);
worksheetPart.Worksheet.Save();
}

Use Shared String:
// assuming it's the first item in the shared string table
SharedStringItem sharedStringItem = new SharedStringItem();
Text text = new Text();
text.Text = DateTime.Today.ToString("MM/dd/yyyy hh:mm");
sharedStringTable1.Append(sharedStringItem);
Then later in code:
// assuming it's the first item in the shared string table
var cell = new Cell {CellReference = "A1", DataType = CellValues.SharedString};
var cellValue = new CellValue("0");
cell.Append(cellValue);

The following worked for us:
c.CellValue = new CellValue(datetimeValue).ToOADate().ToString());
c.DataType = CellValues.Number;
c.StyleIndex = StyleDate;
Set the DataType to CellValues.Number and then be sure to format the cell with the appropriate style index from the CellFormats. In our case we build a stylesheet within the worksheet, and StyleDate is an index into the CellFormats in the stylesheet.

a) Get compatibility with Excel 2007, Excel 2007 Viewer etc.
b) DateTime before 1.1.1900 write as string.
DateTime dat = (DateTime)dr[dc.ColumnName];
//Not working with Excel 2007
//cell.DataType = CellValues.Date;
//cell.CellValue = new CellValue(dat.ToString("s"));
double diff = (dat - new DateTime(1899, 12, 30)).TotalSeconds / 86400.0;
if (diff > 1)
{
cell.DataType = CellValues.Number;
cell.CellValue = new CellValue(diff.ToString().Replace(",", "."));
if (dat.TimeOfDay == new TimeSpan(0))
{
cell.StyleIndex = 2; //Custom Style NumberFormatId = 14 ( d/m/yyyy)
}
else
{
cell.StyleIndex = 1; //Custom Style NumberFormatId = 22 (m/d/yyyy H:mm)
}
}
else
{
cell.DataType = CellValues.String;
cell.CellValue = new CellValue(dat.ToString());
}