Question

I have a search function in my program that uses a background worker in order to get the results. The Progress changed event is used to update the listview with the new item.

Private Sub SearchWorker_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles SearchWorker.ProgressChanged
    Dim itmX As ListViewItem
    Dim tmpCustomer As CustomerItem

    If e.UserState.ToString = "New" Then
        lstResults.Items.Clear()
    Else
        Try
            tmpCustomer = e.UserState
            itmX = lstResults.Items.Add(tmpCustomer.CustomerName) ' <-- Error here
            itmX.Tag = tmpCustomer.CustomerID
            itmX.Name = tmpCustomer.CustomerID
            itmX.SubItems.Add(tmpCustomer.City)
            itmX.SubItems.Add(tmpCustomer.State)
            itmX.SubItems.Add(tmpCustomer.Zip)
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End If

    progBar.Value = e.ProgressPercentage

    Application.DoEvents()
End Sub

And I get this error

An unhandled exception of type 'System.StackOverflowException' occurred in System.Windows.Forms.dll

I’ve tried this, but it doesn’t make a difference

Private Sub SearchWorker_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles SearchWorker.ProgressChanged

    If e.UserState.ToString = "New" Then
        lstResults.Items.Clear()
    Else
        Try
            itmX = lstResults.Items.Add("Test")
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End If

    progBar.Value = e.ProgressPercentage

    Application.DoEvents()
End Sub

Edit:
Oh, and if I just step through the code, it doesn’t have any problems.

Edit 2:
Here is the backgroundworker DoWork event:

Sub doSearch(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles SearchWorker.DoWork
    canceled = False
    If curSearch = doSearchText Then
        canceled = True
        Exit Sub
    End If
    curSearch = doSearchText

    SearchWorker.ReportProgress(0, "New")
    Dim rSelect As New ADODB.Recordset
    Dim CustomerID As Integer = MakeNumeric(doSearchText)
    Dim sSql As String = "SELECT DISTINCT CustomerID, CustomerName, City, State, Zip FROM qrySearchFieldsQuick WHERE "
    Dim sWhere As String = "CustomerID = " & CustomerID & " OR CustomerName Like '" & doSearchText & "%'"
    If Not doSearchText.Contains(" ") Then
        sWhere &= " OR FirstName Like '" & doSearchText & "%' OR LastName Like '" & doSearchText & "%'"
    Else
        Dim str() As String = doSearchText.Split(" ")
        sWhere &= " OR (FirstName Like '" & str(0) & "%' AND LastName Like '" & str(1) & "%')"
    End If

    Dim i As Integer = 0
    Dim tmpCustomer As CustomerItem

    With rSelect
        .Open(sSql & sWhere & " ORDER BY CustomerName", MyCn, ADODB.CursorTypeEnum.adOpenStatic, ADODB.LockTypeEnum.adLockReadOnly)
        Do While Not .EOF
            If SearchWorker.CancellationPending Then
                canceled = True
                Exit Do
            End If

            Do While IsDBNull(.Fields("CustomerID").Value)
                .MoveNext()
            Loop

            tmpCustomer.CustomerID = "c" & .Fields("CustomerID").Value
            tmpCustomer.CustomerName = NZ(.Fields("CustomerName").Value, "").ToString.Trim
            tmpCustomer.City = Trim(NZ(.Fields("City").Value, ""))
            tmpCustomer.State = Replace(Trim(NZ(.Fields("State").Value, "")), ",", "")
            tmpCustomer.Zip = Trim(NZ(.Fields("Zip").Value, ""))

            SearchWorker.ReportProgress((i / .RecordCount) * 100, tmpCustomer)
            i += 1
            Application.DoEvents()
aMoveNext:

            .MoveNext()
        Loop
        .Close()
    End With
End Sub

Answer 1

I think the problem is likely this line:

Application.DoEvents()

If your BackgroundWorker is queueing up ProgressChanged events fast enough, each call to Application.DoEvents() will work through the message queue, come to a ProgressChanged event, update the progress, call Application.DoEvents(), work through the message queue, come to a ProgressChanged event, etc.. essentually causing a recursive behavior in your code.

Try removing that call and see if the problem goes away.