Unhandled Exception in Background Worker - vb.net

Question

Hi there I am carrying out some integration testing in an application I am developing. The specific element that is causing an issue is a call to a background worker which interrogates an Oracle database. When an error is encountered in the query I want the exception detail to percolate up the call stack to the application level and at that point provide an appropriate user compatible message. In the example test there is a syntax error in the underlying SQL which results in an OraEx Exception:
Oracle.DataAccess.Client.OracleException ORA-00907: missing right parenthesis
Unfortunately the code generates the following exception:
System.Reflection.TargetInvocationException was unhandled
Message: An unhandled exception of type
'System.Reflection.TargetInvocationException' occurred in mscorlib.dll
Additional information: Exception has been thrown by the target of an
invocation.
in the DoWork sub of the backgroundworker, despite my belief that I am handling the exception correctly. Its pretty obvious that I am missing something fundamental here, can someone suggest a solution please.
Thanks in Advance
Paul J.
Here is the code that makes the call to the background worker:
Private Sub EventSearch(ByVal mySQL As String)
Const procName As String = "EventSearch"
Try
_eventMngr = New ScadaEventManager(_CurrentDB, _userName, _myPwd)
_eventMngr.SQL = mySQL
'Set the flag and stop query tool status accordingly
_Stopped = False
uxStopQueryTool.Enabled = True
'activate the timer object to ensure that the execute query menu
'and tool remain disabled until all background processing is complete
uxBackWorkTimer.Enabled = True
_logger.SendLog(Me.Name & "." & procName & " - Scanning for data.", NLog.LogLevel.Trace)
ReviseStatus(2, "Scanning for data. Please wait...", Color.Black, True, True)
'Force the thread to sleep for half a second so the user can see the scanning state taking place
Threading.Thread.Sleep(500)
'Launch the background worker to retrieve the required data from the database
uxBWScan.RunWorkerAsync(_eventMngr)
Catch ex As Exception
MsgBox(ex.Message, MsgBoxStyle.Exclamation, My.Application.Info.ProductName)
_logger.SendLog(ex.Message & ". Thrown in module " & Me.Name.ToString & "." & procName, NLog.LogLevel.Error, ex)
Call ResetStatus()
Finally
End Try
End Sub
And here is the code executed by the background worker:
Private Sub uxBWScan_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles uxBWScan.DoWork
Const procName As String = "uxBWScan_DoWork"
Try
e.Argument.CountRecords(_queryTypeID)
e.Result = e.Argument.RecordCount
Catch NullEx As NullReferenceException
_logger.SendLog(NullEx.Message & ". Thrown in module " & Me.Name.ToString & "." & procName, NLog.LogLevel.Error, NullEx)
Throw
Catch OraEx As OracleException
_logger.SendLog(OraEx.Message & ". Thrown in module " & Me.Name.ToString & "." & procName, NLog.LogLevel.Error, OraEx)
Throw
Finally
End Try
End Sub
And here is the low level code that generates the error:
Public Sub CountRecords(ByVal queryType As Integer)
_myDataset = New DataSet
Try
_myDataset = _myScadaEventDB.CountRecords(_sqlText)
If _myDataset.Tables(0).Rows.Count > 0 Then
If queryType = Enums.QueryType.General Or queryType = Enums.QueryType.KeyPerformanceIndicators Or queryType = Enums.QueryType.TelecontroAnalysis Then
_recordCount = _myDataset.Tables(0).Rows(0).Item("RecordCount")
Else
'The query is grouped therefore count the number of records in the table
_recordCount = _myDataset.Tables(0).Rows.Count
End If
Else
_recordCount = 0
End If
Catch ex As Exception
Throw
Finally
End Try
End Sub

Answer 1

Ok, problem solved. Removed the try catch block from DoWork and moved my exception handling into 'RunWorkerCompleted' using e.error. Some reading of the documentation (RTFM...), highlighted the fact that using Try/Catch in the worker thread interferes with the native functionality of the BackgroundWorker. Thanks again everyone for your input.
Paul,