Office.Interop.Excel - Why do I need to have Excel open on the server?

Question

I have been given a legacy project which uses Microsoft.Office.Interop.Excel[11.0.0.0] to import and export files. On the server MS Excel has to be running for the import/exports to work. By running I mean someone has to log on the server and open Excel via start menu (yes it's that bad!). Does anyone know why it needs to be kept open? The import/export is extremely flakey and requires a close and re-open twice a day as it keeps crashing.

Here is the code, be warned...it's horrible!

 objExcelApp = New Excel.Application()
            objExcelApp.DisplayAlerts = False
            objExcelBook = objExcelApp.Workbooks.Open(strExcelFileName, Password:="")
            If objExcelBook.Sheets.Count > 0 Then
                objExcelWorkSheet = CType(objExcelBook.Sheets(1), Excel.Worksheet)
                objExcelWorkSheet.Name = gstrDEFAULTSHEETNAME 'Rename the sheet
                objExcelRangeHeader = CType(objExcelWorkSheet.Rows(1), Excel.Range)
                objExcelWorkSheet.Cells.Interior.ColorIndex = Excel.XlColorIndex.xlColorIndexNone

                objExcelRangeFormat = objExcelWorkSheet.UsedRange
                intColumn = objExcelRangeFormat.Columns.Count

                For intColumnCount = 1 To intColumn
                    objColumnRange = CType(objExcelRangeHeader.Columns(intColumnCount), Excel.Range)
                    objColumnRange.EntireColumn.Interior.Color = System.Drawing.ColorTranslator.ToOle(System.Drawing.Color.White)
                    objColumnRange.EntireColumn.ClearFormats()
                    objColumnRange.EntireRow.ClearFormats()
                Next
                With objExcelWorkSheet
                    .Name = gstrSHEET_EXCEL
                    .Rows.Range("1:1").Font.Bold = True
                    .Rows.Range("1:1").Font.Color = RGB(0, 0, 255)
                    .StandardWidth = 50
                    .Cells.WrapText = True                    
                    .EnableOutlining = True
                End With

            End If


            objCountLink = CType(objExcelBook.LinkSources(), Object)
            If Not IsNothing(objCountLink) Then
                If (objCountLink.ToString.Length > 0) Then
                    lblErrorMessage.Visible = True
                    lblErrorMessage.InnerHtml = "<li> The spreadsheet you trying to import contains external links. Please ensure all links have been removed before attempting to import </li>"
                    objExcelBook.Close()
                    objExcelApp.Workbooks.Close()
                    objExcelApp.Quit()
                    objExcelApp = Nothing
                    Exit Sub
                End If
            End If
            objExcelBook.Save() 'Save the excel
            objExcelBook.Close()
            objExcelApp.Workbooks.Close()
            objExcelApp.Quit()
            objExcelApp = Nothing

Answer 1

Consider using Open XML SDK if you deal with open XML files only. Or you may consider using any other commercial components designed for the server-side execution.

Microsoft does not currently recommend, and does not support, Automation of Microsoft Office applications from any unattended, non-interactive client application or component (including ASP, ASP.NET, DCOM, and NT Services), because Office may exhibit unstable behavior and/or deadlock when Office is run in this environment.

If you are building a solution that runs in a server-side context, you should try to use components that have been made safe for unattended execution. Or, you should try to find alternatives that allow at least part of the code to run client-side. If you use an Office application from a server-side solution, the application will lack many of the necessary capabilities to run successfully. Additionally, you will be taking risks with the stability of your overall solution.

You can read more about that in the Considerations for server-side Automation of Office article.