accesing controls from a thread (safely)

**jim@satcomtechnology** · Oct 17th, 2008, 10:31 AM

Hi,

In short this is what I have 2 forms formA and formB. Button on formA opens formB. FormB has a progress bar and a thread. The thread runs some code that creates a report. That code must access controls on formA e.g.

Code:

if formA.checkbox1.checked then
..
end if

In VB6 this was simply but I can't seem to figure out how to use invoke to do this.

I would greatly appreciate a detailed answer as I'm under pressure to get this work done.

Jim

**kleinma** · Oct 17th, 2008, 10:37 AM

You didn't state the version of .NET you use, so its hard to give you a solid answer.

You could read over this
http://msdn.microsoft.com/en-us/libr...28(VS.80).aspx

If you are using .NET 2.0 or above, then you could also look at using the BackgroundWorker, which automatically handles marshalling between threads.

Also, just a side note, but using your email address as your user name is probably just asking to get tons of spam as bots crawl these pages looking for email addresses.

**jim@satcomtechnology** · Oct 17th, 2008, 10:48 AM

Hi,

First yep probably wasn't a good idea to use my email but its incomplete anyways.

I use .NET 2. I have tried the back ground worker but as soon as I call the my class that refers to my main form I get the thread error at formA.checkbox1.checked

Jim

**kleinma** · Oct 17th, 2008, 10:51 AM

when using the BGW, where are you trying to access your control from? Which routine? You can't access controls in the DoWork routine, that routine is ONLY for the background thread. However from that routine you can call reportprogress on the BGW, which will fire an event in the main UI thread, and there you CAN access UI controls like checkboxes.

**jim@satcomtechnology** · Oct 17th, 2008, 11:10 AM

Hi,

This is my do work

Code:

Private Sub bgwProcessingReport_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgwProcessingReport.DoWork
        ' Run report function
        ProcessReport()
End Sub

In side the Process Report I have

Code:

                With Me
                    Select Case True
                        Case .rbReportJourneySummary.Checked
                            ' I get the error here.
                            frmActiveReportViewer.FillTreeView(mySQLDataSet) 
                            JourneySummarySetup(mySQLDataSet)

Also in journey summary setup, I have

Code:

            With frmDiscoveryII ' I get the error here as well
                Select Case True
                    Case .rbDateToday.Checked
                        With CType(ShowReport, rptJourneySummary)
                            .txtStartRange.Text = Format(Now(), "dddd, dd MMMM yyyy").ToString
                            .txtEndRange.Text = Format(Now(), "dddd, dd MMMM yyyy").ToString
                        End With
                    Case .rbDateYesterday.Checked
                        With CType(ShowReport, rptJourneySummary)
                            .txtStartRange.Text = Format(DateAdd(DateInterval.Day, -1, Now()), "dddd, dd MMMM yyyy").ToString
                            .txtEndRange.Text = Format(DateAdd(DateInterval.Day, -1, Now()), "dddd, dd MMMM yyyy").ToString
                        End With

This is the error.

An error occurred creating the form. See Exception.InnerException for details. The error is: ActiveX control '35f36212-43a6-48fa-8a6a-af558abe7030' cannot be instantiated because the current thread is not in a single-threaded apartment.

Thanks,
Jim

**michaelerice** · Oct 17th, 2008, 01:13 PM

Try creating a delegate and call 'Invoke'...

Code:

'This goes outside at the top of your form class code
Public Delegate Sub InvokeFillTreeViewDelgate(ByVal o As Object)
...

With Me
    Select Case True
        Case .rbReportJourneySummary.Checked
            ''replace frmActiveReportViewer.FillTreeView(mySQLDataSet) with
            Invoke(New InvokeFillTreeViewDelgate(AddressOf FillTreeView), mySQLDataSet)

**jim@satcomtechnology** · Oct 20th, 2008, 03:55 AM

Hi Michael,

That didn't work for me I still got the following error.

An error occurred creating the form. See Exception.InnerException for details. The error is: ActiveX control '35f36212-43a6-48fa-8a6a-af558abe7030' cannot be instantiated because the current thread is not in a single-threaded apartment.

I had to make a couple of changes to your code as the compiler were reporting an error.

Code:

Public Delegate Sub InvokeFillTreeViewDelgate(ByVal objD As DataSet)

Code:

                    Select Case True
                        Case .rbReportJourneySummary.Checked
                            ' Fill Tree View
                            Invoke(New InvokeFillTreeViewDelgate(AddressOf frmActiveReportViewer.FillTreeView), mySQLDataSet)
                            'frmActiveReportViewer.FillTreeView(mySQLDataSet)
                            JourneySummarySetup(mySQLDataSet)

This is the code for Fill Tree View.

Code:

Friend Sub FillTreeView(ByVal MySQLDataReader As DataSet)
        Dim tvAsset As TreeNode = Nothing, tvDate As TreeNode = Nothing
        Dim intX As Integer
        Try
            If tcReport.TabPages.Count = 1 Then Exit Try

            With MySQLDataReader.Tables(0)
                tvReports.Nodes.Clear()
                For intX = 0 To .Rows.Count - 1
                    ' If Journey is Private and either Private or Limited Private is ticked then do not show
                    If MySQLDataReader.Tables(0).Rows(intX).Item("Type") = "P" And (LoginUsername.JourneyType(1) = "0" Or LoginUsername.JourneyType(2) = "1") Then
                        ' do not show
                    Else
                        If tvReports.Nodes.Count = 0 Then
                            tvAsset = tvReports.Nodes.Add(.Rows(intX).Item("Primary Asset"))
                            tvDate = tvAsset.Nodes.Add(Format(GMTtoUserLocalTime(.Rows(intX).Item("Start")), "dddd, dd MMM, HH:mm") & " - " & Format(GMTtoUserLocalTime(.Rows(intX).Item("End")), "dddd, dd MMM, HH:mm") & " (" & ConvertSeconds(DateDiff(DateInterval.Second, GMTtoUserLocalTime(.Rows(intX).Item("Start")), GMTtoUserLocalTime(.Rows(intX).Item("End")))) & ")")
                            tvDate.Tag = .Rows(intX).Item("JourneyID")
                        Else
                            If tvAsset.Text.ToString = MySQLDataReader.Tables(0).Rows(intX).Item("Primary Asset").ToString Then
                                tvDate = tvAsset.Nodes.Add(Format(GMTtoUserLocalTime(.Rows(intX).Item("Start")), "dddd, dd MMM, HH:mm") & " - " & Format(GMTtoUserLocalTime(.Rows(intX).Item("End")), "dddd, dd MMM, HH:mm") & " (" & ConvertSeconds(DateDiff(DateInterval.Second, GMTtoUserLocalTime(.Rows(intX).Item("Start")), GMTtoUserLocalTime(.Rows(intX).Item("End")))) & ")")
                                tvDate.Tag = .Rows(intX).Item("JourneyID")
                            Else
                                tvAsset = tvReports.Nodes.Add(.Rows(intX).Item("Primary Asset").ToString)
                                tvDate = tvAsset.Nodes.Add(Format(GMTtoUserLocalTime(.Rows(intX).Item("Start")), "dddd, dd MMM, HH:mm") & " - " & Format(GMTtoUserLocalTime(.Rows(intX).Item("End")), "dddd, dd MMM, HH:mm") & " (" & ConvertSeconds(DateDiff(DateInterval.Second, GMTtoUserLocalTime(.Rows(intX).Item("Start")), GMTtoUserLocalTime(.Rows(intX).Item("End")))) & ")")
                                tvDate.Tag = .Rows(intX).Item("JourneyID")
                            End If
                        End If
                    End If
                Next
                tvReports.ExpandAll()
            End With
        Catch ex As Exception
            MsgBox("Error generating Map Replay list", MsgBoxStyle.Exclamation, "Error")
        End Try
    End Sub

I'm not to worried about this part, I can make the mySQLDataSet a public variable and access it once the form opens up later on.

My main problem comes from this code which is called via ProcessReport

Code:

            With frmDiscoveryII
                Select Case True
                    Case .rbDateToday.Checked
                        With CType(ShowReport, rptJourneySummary)
                            .txtStartRange.Text = Format(Now(), "dddd, dd MMMM yyyy").ToString
                            .txtEndRange.Text = Format(Now(), "dddd, dd MMMM yyyy").ToString
                        End With

I know accessing forms from other forms in VB6 was not "safe" but it was a lot easier then this!

Thanks for all the help.

Jim

**jim@satcomtechnology** · Oct 20th, 2008, 03:55 AM

Hi Michael,

That didn't work for me I still got the following error.

An error occurred creating the form. See Exception.InnerException for details. The error is: ActiveX control '35f36212-43a6-48fa-8a6a-af558abe7030' cannot be instantiated because the current thread is not in a single-threaded apartment.

I had to make a couple of changes to your code as the compiler were reporting an error.

Code:

Public Delegate Sub InvokeFillTreeViewDelgate(ByVal objD As DataSet)

Code:

                    Select Case True
                        Case .rbReportJourneySummary.Checked
                            ' Fill Tree View
                            Invoke(New InvokeFillTreeViewDelgate(AddressOf frmActiveReportViewer.FillTreeView), mySQLDataSet)
                            'frmActiveReportViewer.FillTreeView(mySQLDataSet)
                            JourneySummarySetup(mySQLDataSet)

This is the code for Fill Tree View.

Code:

Friend Sub FillTreeView(ByVal MySQLDataReader As DataSet)
        Dim tvAsset As TreeNode = Nothing, tvDate As TreeNode = Nothing
        Dim intX As Integer
        Try
            If tcReport.TabPages.Count = 1 Then Exit Try

            With MySQLDataReader.Tables(0)
                tvReports.Nodes.Clear()
                For intX = 0 To .Rows.Count - 1
                    ' If Journey is Private and either Private or Limited Private is ticked then do not show
                    If MySQLDataReader.Tables(0).Rows(intX).Item("Type") = "P" And (LoginUsername.JourneyType(1) = "0" Or LoginUsername.JourneyType(2) = "1") Then
                        ' do not show
                    Else
                        If tvReports.Nodes.Count = 0 Then
                            tvAsset = tvReports.Nodes.Add(.Rows(intX).Item("Primary Asset"))
                            tvDate = tvAsset.Nodes.Add(Format(GMTtoUserLocalTime(.Rows(intX).Item("Start")), "dddd, dd MMM, HH:mm") & " - " & Format(GMTtoUserLocalTime(.Rows(intX).Item("End")), "dddd, dd MMM, HH:mm") & " (" & ConvertSeconds(DateDiff(DateInterval.Second, GMTtoUserLocalTime(.Rows(intX).Item("Start")), GMTtoUserLocalTime(.Rows(intX).Item("End")))) & ")")
                            tvDate.Tag = .Rows(intX).Item("JourneyID")
                        Else
                            If tvAsset.Text.ToString = MySQLDataReader.Tables(0).Rows(intX).Item("Primary Asset").ToString Then
                                tvDate = tvAsset.Nodes.Add(Format(GMTtoUserLocalTime(.Rows(intX).Item("Start")), "dddd, dd MMM, HH:mm") & " - " & Format(GMTtoUserLocalTime(.Rows(intX).Item("End")), "dddd, dd MMM, HH:mm") & " (" & ConvertSeconds(DateDiff(DateInterval.Second, GMTtoUserLocalTime(.Rows(intX).Item("Start")), GMTtoUserLocalTime(.Rows(intX).Item("End")))) & ")")
                                tvDate.Tag = .Rows(intX).Item("JourneyID")
                            Else
                                tvAsset = tvReports.Nodes.Add(.Rows(intX).Item("Primary Asset").ToString)
                                tvDate = tvAsset.Nodes.Add(Format(GMTtoUserLocalTime(.Rows(intX).Item("Start")), "dddd, dd MMM, HH:mm") & " - " & Format(GMTtoUserLocalTime(.Rows(intX).Item("End")), "dddd, dd MMM, HH:mm") & " (" & ConvertSeconds(DateDiff(DateInterval.Second, GMTtoUserLocalTime(.Rows(intX).Item("Start")), GMTtoUserLocalTime(.Rows(intX).Item("End")))) & ")")
                                tvDate.Tag = .Rows(intX).Item("JourneyID")
                            End If
                        End If
                    End If
                Next
                tvReports.ExpandAll()
            End With
        Catch ex As Exception
            MsgBox("Error generating Map Replay list", MsgBoxStyle.Exclamation, "Error")
        End Try
    End Sub

I'm not to worried about this part, I can make the mySQLDataSet a public variable and access it once the form opens up later on.

My main problem comes from this code which is called via ProcessReport

Code:

            With frmDiscoveryII
                Select Case True
                    Case .rbDateToday.Checked
                        With CType(ShowReport, rptJourneySummary)
                            .txtStartRange.Text = Format(Now(), "dddd, dd MMMM yyyy").ToString
                            .txtEndRange.Text = Format(Now(), "dddd, dd MMMM yyyy").ToString
                        End With

I know accessing forms from other forms in VB6 was not "safe" but it was a lot easier then this!

Thanks for all the help.

Jim

**Atheist** · Oct 20th, 2008, 04:14 AM

Have you tried calling the backgroundworders ReportProgress method, which raises the ProgressChanged event, and execute the code that accesses the controls in its eventhandler? Thats how it should be done using BackgroundWorkers, which kleinma pointed out.

**jim@satcomtechnology** · Oct 20th, 2008, 04:35 AM

Hi,

I have tried doing this.

Code:

    Private Sub bgwProcessingReport_DoWork(ByVal sender As Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles bgwProcessingReport.DoWork
        bgwProcessingReport.ReportProgress(1)
    End Sub

    Private Sub bgwProcessingReport_ProgressChanged(ByVal sender As Object, ByVal e As System.ComponentModel.ProgressChangedEventArgs) Handles bgwProcessingReport.ProgressChanged
        ' Run report function
        ProcessReport()
    End Sub

The reason I want to run Process Report in a back ground thread is that it can cause the form to go "WHITE". If I do Process Report in Progress Changed event then it results in the same issue as it seems that event is ran in the main thread of the form which is basically the same as running it without any threads.

I should add that I've tried

Code:

Dim f As Form1 = My.Application.OpenForms("Form1")

But my tree view selected node throws up the same error - single threading etc.

Thanks,
Jim

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