Question

I am very new with Background worker control. I have an existing project that builds file but throughout my project while building files I get the deadlock error.
I am trying to solve it by creating another project that will only consist out of the background worker. I will then merge them.

My problem is I don’t know where it will be more effective for my background worker to be implemented and also the main problem is how can I use the SaveDialog with my background worker? I need to send a parameter to my background worker project telling it when my file is being build en when it is done.

This is where my file is being build:

  srOutputFile = New System.IO.StreamWriter(strFile, False) 'Create File

  For iSeqNo = 0 To iPrintSeqNo
    ' Loop through al the record types
    For Each oRecord As stFileRecord In pFileFormat
      If dsFile.Tables.Contains(oRecord.strRecordName) Then
        ' Loop through al the records
        For Each row As DataRow In dsFile.Tables(oRecord.strRecordName).Rows
          ' Check record id
          If oRecord.strRecordId.Length = 0 Then
            bMatched = True
          Else
            bMatched = (CInt(oRecord.strRecordId) = CInt(row.Item(1)))
          End If

          ' Match records
          If iSeqNo = CInt(row.Item(0)) And bMatched Then
            strRecord = ""
            ' Loop through al the fields
            For iLoop = 0 To UBound(oRecord.stField)
              ' Format field
              If oRecord.stField(iLoop).iFieldLength = -1 Then
                If strRecord.Length = 0 Then
                  strTmp = row.Item(iLoop + 1).ToString
                Else
                  strTmp = strDelimiter & row.Item(iLoop + 1).ToString
                End If
              ElseIf oRecord.stField(iLoop).eFieldType = enumFieldType.TYPE_VALUE Or _
                     oRecord.stField(iLoop).eFieldType = enumFieldType.TYPE_AMOUNT_CENT Then

                strTmp = row.Item(iLoop + 1).ToString.Replace(".", "").PadLeft(oRecord.stField(iLoop).iFieldLength, "0")
                strTmp = strTmp.Substring(strTmp.Length - oRecord.stField(iLoop).iFieldLength)
              Else
                strTmp = row.Item(iLoop + 1).ToString.PadRight(oRecord.stField(iLoop).iFieldLength, " ").Substring(0, oRecord.stField(iLoop).iFieldLength)
              End If

              If oRecord.stField(iLoop).iFieldLength > -1 And (bForceDelimiter) And strRecord.Length > 0 Then
                strTmp = strDelimiter & strTmp
              End If

              strRecord = strRecord & strTmp
            Next

            ' Final delimiter
            If (bForceDelimiter) Then
              strRecord = strRecord & strDelimiter
            End If

            srOutputFile.WriteLine(strRecord)
          End If
        Next
      End If
    Next
  Next

Answer 1

You could try this:

Private locker1 As ManualResetEvent = New System.Threading.ManualResetEvent(False)
Private locker2 As ManualResetEvent = New System.Threading.ManualResetEvent(False)
Dim bOpenFileOK As Boolean
Dim myOpenFile As OpenFileDialog = New OpenFileDialog()

Private Sub FileOpener()
    While Not bTerminado
        If myOpenFile.ShowDialog() = System.Windows.Forms.DialogResult.OK Then
            bOpenFileOK = True
        Else
            bOpenFileOK = False
        End If

        locker2.Set()
        locker1.WaitOne()
    End While
End Sub

' Detonator of the action
Private Sub Button1_Click(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Button1.Click
    Dim tFileOp As Thread = New Thread(AddressOf FileOpener)
    tFileOp.SetApartmentState(ApartmentState.STA)
    tFileOp.Start()

    ' Start BackgroundWorker
    BW1.RunWorkerAsync()
End Sub

Private Sub AsyncFunctionForBW(ByVal args As ArrayList)
    '[...]

    'Change options dinamically for the OpenFileDialog
    myOpenFile.Filter = ""
    myOpenFile.MultiSelect = True

    'Calling the FileDialog
    locker1.Set()
    locker2.WaitOne()
    locker1.Reset()
    locker2.Reset()

    If bOpenFileOK Then
        myStream = myOpenFile.OpenFile()

        '[...]
    End If
End Sub

It’s a little bit complicated but it works.

ManualResetEvents interrupt the execution of code (if they are told to stop) when reached until you use .Set(). If you use .WaitOne() you set it in stop mode, so it will stop again when reached.

This code defines two ManualResetEvents. When you click the Button1 starts the function FileOpener() in a new Thread, and then starts the BackgroundWorker. The FileOpener() function shows a FileOpenDialog and waits in the locker1 so when you use locker1.Set() the function shows the file dialog.

As the myOpenFile is a “global” variable (as well as bOpenFileOK), once the user select the file (or not) you could detect the dialog result (bOpenFileOK) and the selected file.