how to find out whether the file write or export is completed

See more:

VB

Dim exportOpts As ExportOptions = RptObj.ExportOptions

   If strRepFormate = "PDF" Then
  exportOpts.ExportFormatType = ExportFormatType.PortableDocFormat
                                Else
  exportOpts.ExportFormatType = ExportFormatType.Excel

Dim objExcelOptions As ExcelFormatOptions = New ExcelFormatOptions
                                    objExcelOptions.ExcelUseConstantColumnWidth = False
RptObj.ExportOptions.FormatOptions = objExcelOptions

End If

exportOpts.ExportDestinationType = ExportDestinationType.DiskFile
exportOpts.DestinationOptions = New DiskFileDestinationOptions
Dim diskOpts As DiskFileDestinationOptions = New DiskFileDestinationOptions

In the above I am exporting an report to an mail scheduler, here I need to find whether the file write to PDF or excel format is being completed. How to find that. The code is not accurate. I need this because I am getting the error that the file is being used by another process cannot access it like that.