I have an application that makes use of excel Interop

I’m using Microsoft Excel Object Library 10

The application does the following:
•    Loads an existing analysis spreadsheet
•    Sets Calculation mode to Manual (to prepare for efficient data import)
•    Clears the first worksheet (of previous input data)
•    Imports the text file into the first worksheet
•    Set Calculation mode back to automatic  
•    Parses a field cells on a results Worksheet

I noticed while testing the application that the cells appear to
(re)calculate much faster when the objApp.Visible = true.  (Improving
calculation speed from several minutes to ~ 25 seconds)  This doesn’t make
sense to me.  My only thought is that excel is throwing up a prompt when my
spreadsheet is running invisibly and that this prompt eventually times out
allowing my method to eventually complete.  I have already set DisplayAlerts
to false. The Analysis spreadsheet does not contain any macros so I wouldn’t
have expected this to be a privilege issue.

I prefer never to display the spreadsheet.  

If anyone has any suggestions I would greatly appreciate them

Thanks,

Jeff
‘############################################
‘code that opens the spreadsheet
 objApp = New Excel.Application
 objApp.DisplayAlerts = False
 objApp.UserControl = False
 objApp.Visible = False ‘True
           
 objBooks = objApp.Workbooks

‘objBooks.Open(FileName, UpdateLinks, ReadOnly, Format, Password,
WriteResPassword, IgnoreReadOnlyRecommended, Origin, Delimiter, Editable,
Notify, Converter, AddToMRU)

 objBook = objBooks.Open(FilePath, 0, True, 5, String.Empty, String.Empty,
True, Excel.XlPlatform.xlWindows, ",", True, False, 0, True)
‘##########################################

‘public method that imports the text file
   Public Sub importDataFromFile(ByVal FilePath As String)
       Me.CalculationMode = Excel.XlCalculation.xlCalculationManual  
'Import CSV file into data worksheet
       importDataFromFile(FilePath, Sheets.Data)      
       Me.CalculationMode = Excel.XlCalculation.xlCalculationAutomatic
       m_Calculating = False
     
   End Sub

‘##############################################

‘ method that imports the text file into the WorkSheet
Protected Sub ImportDataFromFile(ByVal FilePath As String, ByVal
WorkSheetIndex As Integer)
       Dim dataSheet As Excel._Worksheet =
CType(Me.objSheets(WorkSheetIndex), Excel._Worksheet) '
       dataSheet.Activate()
       ClearWorksheet(dataSheet)  'Must clear otherwise old data will just
be shifted to the right of new data

       dataSheet.Range("A1").Select()
 With dataSheet.QueryTables.Add(Connection:=String.Format("TEXT;{0}",
FilePath), _
           Destination:=dataSheet.Range("A1"))
           .Name = "Test_1"
           .FieldNames = True
           .RowNumbers = False
           .FillAdjacentFormulas = False
           .PreserveFormatting = True
           .RefreshOnFileOpen = False
           .AdjustColumnWidth = True
           .RefreshPeriod = 0
           .TextFilePromptOnRefresh = False
           .TextFilePlatform = 437
           .TextFileStartRow = 1
           .TextFileParseType = Excel.XlTextParsingType.xlDelimited
           .TextFileTextQualifier =                                        
Excel.XlTextQualifier.xlTextQualifierDoubleQuote
           .TextFileConsecutiveDelimiter = False
           .TextFileTabDelimiter = False
           .TextFileSemicolonDelimiter = False
           .TextFileCommaDelimiter = True
           .TextFileSpaceDelimiter = False
           .TextFileTrailingMinusNumbers = True
           .Refresh(BackgroundQuery:=False)
       End With

   End Sub