Question

Here’s the situation: on a certain page within SharePoint, a user clicks a button in a webpart to create a report based on data in SharePoint. This report is an Excel document that is created through C# code. When the report is created, it will be uploaded to SharePoint. When the upload is done, the file will be automatically opened for the user so the file can be saved locally or printed or some other action.

Here’s a simplified version of how my code works:

//Prepare the data in a table
//Normally there are multiple rows and columns here
var fileName = "Report.xlsx";
var table = new System.Web.UI.WebControls.Table();
table.Rows.Add(new TableRow());
table.Rows[0].Cells.Add(new TableCell());
table.Rows[0].Cells[0].Text = "Some cell value";
CreateWorkbook("My Report", fileName, table);

private void CreateWorkbook(string name, string fileName, Table table)
{
    using (var doc = SpreadsheetDocument.Create(_tempfolder + fileName, SpreadsheetDocumentType.Workbook))
    {
        var sheetData = new SheetData();
        var excelRow = new Row { RowIndex = 1 };

        sheetData .AppendChild(excelRow);

        //Normally there's a loop here going over all the rows and columns
        var tableCellValue = table.Rows[0].Cells[0].Text;
        var excelCell = CreateTextCell("A", 1, tableCellValue);
        excelRow.AppendChild(excelCell);

        doc.AddWorkbookPart().AddNewPart<WorksheetPart>().Worksheet = new Worksheet(sheetData);
        doc.WorkbookPart.Workbook = new Workbook(
            new Sheets(
                new Sheet
                {
                    Id = doc.WorkbookPart.GetIdOfPart(doc.WorkbookPart.WorksheetParts.First()),                    
                    SheetId = 1,
                    Name = name
                }));
        doc.WorkbookPart.Workbook.Save();
        doc.Close();

        //Upload the file to SharePoint
        //Omitted as this is not the issue here
    }
}

private static Cell CreateTextCell(string col, int row, string cellValue)
{
    var cell = new Cell { DataType = new EnumValue<CellValues>(CellValues.InlineString), CellReference = col + row };
    var inlineString = new InlineString();
    var text = new Text { Text = value };

    inlineString.Append(l_objText);
    cell.Append(inlineString);

    return cell;
}

Everything in the code works fine and the Excel-file is succesfully created and uploaded and after all this Excel opens up and then I get following message:

Excel found unreadable content in ‘…’. Do you want to recover the contents of this workbook? If you trust the source of this workbook, click Yes.

When I click Yes, Excel magically repairs and opens the content and everything is shown as normal. But where does this error come from? I have looked on the internet for this problem and in almost all the cases the source of this problem are macros, formulas and other exotic Excel-stuff. But in this case, only one cell is added with just a string-value.

Does anyone know how to solve this issue?

Edit:

Opening the file in Notepad is not a solution as this gives output like this:

PK ©QiAÙ9
1A A xl/workbook.xml ¢ (  í½I–%&/mÊ{JõJ×àt¡€$Ø@ìÁˆÍæ’ìiG#)«ÊeVe]f@Ìí¼÷Þ{ï½÷Þ{ï½÷º;N’÷ßÿ?\fdlöÎJÚÉž!€ªÈ?~|?”þÇ¿÷|ü{¼[”ée^7Eµüì£ÝñÎGi¾œV³byñÙGëö|ûà£ßãèñ»GWUývRUoSj¿l½ûì£yۮݽÛLçù”kÆÕ_ÒwçU½ÈZú³¾¸Û¬ê<›5óš·íêÑÝ»Ítž/²f\­ò%}w^Õ‹¬

The error “sneaks” into the file upon creation. When I create the file I save it in a temporary folder and from there I upload the file to SharePoint. Both the temp-file and the SharePoint-file contain the error, so the error must occur upon creation of the file. How is it possible that even adding a single text value to one single cell creates a corrupted document?

Answer 1

Thanks to this article I found the problem. With the OpenXmlValidator class you can easily find errors in a created file. In my case the problem was that the title/name of one of my sheets was longer than 31 characters and 31 seems to be the limit. Problem solved, so for anyone with a similar issue, I strongly recommend the use of the validator! 😉