[RESOLVED] Need help with cross-threading

[adshocker]

hi all,

i have a program with MDI parent and child. initially, the program will call a child e.g. ChildMain. on this child form, 2 processes are run. the 2nd is ran on a backgroundworker. the backgroundworkder in created through code. the process in the background worker is to create another childform but i'm having problem setting the MDIParent of this child form since VS is saying some sort of cross-thread issue.

below are the codes i'm using.

Imports Microsoft.VisualBasic
Imports System.Net.NetworkInformation

Public Class CHILDMAIN
    Dim strRTOTime As String

    Private _Host As String

    Public Delegate Sub setTextCallback(ByVal value As String)

    Public Property Host()
        Get
            Return _Host
        End Get
        Set(ByVal value)
            _Host = value
        End Set
    End Property

    Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
        Try
            Dim strLine As String = String.Empty
            Dim strTime As String = Format(Now, "MM-dd-yyyy hh.mm.ss")

            Dim Ping As New Ping
            Dim PingOptions As New PingOptions

            PingOptions.Ttl = 64

            Dim PingReply As PingReply = Ping.Send(_Host, 500)

            If PingReply.Status = IPStatus.Success Then
                strLine = strTime & " Reply from " & _Host & ": bytes=" & PingReply.Buffer.Length & " time=" & PingReply.RoundtripTime & "ms TTL=" & PingReply.Options.Ttl & vbNewLine
            Else
                strLine = strTime & " Request timed out" & vbNewLine
                strRTOTime = strTime
                Timer1.Stop()

                Dim bgwTemp As New System.ComponentModel.BackgroundWorker

                AddHandler bgwTemp.DoWork, AddressOf DoWork
                AddHandler bgwTemp.RunWorkerCompleted, AddressOf RunWorkerCompleted

                bgwTemp.RunWorkerAsync()
                bgwTemp.Dispose()
            End If

            rtbLog.AppendText(strLine)
        Catch ex As Exception
            MessageBox.Show(ex.Message)
        End Try
    End Sub

    Private Sub DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs)
        Dim LogForm As New LOG
        LogForm.MdiParent = Me.MdiParent
        LogForm.RichTextBox1.AppendText(ReturnShellResults("tracert.exe", _Host))
        LogForm.Show()

        'setText(vbNewLine)
        'setText("Trace Route " & _Host & vbNewLine)
        'setText("--------------------------------------------------" & vbNewLine)
        'setText(ReturnShellResults("tracert.exe", _Host))
        'setText("--------------------------------------------------" & vbNewLine)
        'setText(vbNewLine)
    End Sub

    Private Sub RunWorkerCompleted(ByVal sender As Object, ByVal e As System.ComponentModel.RunWorkerCompletedEventArgs)
        Timer1.Start()
    End Sub

    Private Sub setText(ByVal value As String)
        If rtbLog.InvokeRequired Then
            rtbLog.Invoke(New setTextCallback(AddressOf setText), value)
        Else
            rtbLog.AppendText(value)
        End If
    End Sub

if i use the following codes it works but i need to set the text on a different richtextbox on a different child form.

        setText(vbNewLine)
        setText("Trace Route " & _Host & vbNewLine)
        setText("--------------------------------------------------" & vbNewLine)
        setText(ReturnShellResults("tracert.exe", _Host))
        setText("--------------------------------------------------" & vbNewLine)
        setText(vbNewLine)

please help me.

thanks.

[jmcilhinney]

As the name suggests, the whole point of a BackgroundWorker is to do background work. Anything to do with the UI is inherentlly NOT background work. Anything to do with the UI is, by defeinition, foreground work. You do NOT create a form in the DoWork event handler. If you do, that form's handle will be owned by that background thread. As you know, you cannot access a window handle on any thread other than the one that created it. How could you possibly then have a parent form created on one thread contain a child form created on another? The two would obviously have to communicate in some way, which is not possible across the thread boundary.

You need to stop and think this through and determine exactly what is foreground work and what is background work. If you want to display a form, perform some long-running task and display the results in the form, that's fair enough. Only the long-running task is background work though, so that's the only part that gets done in the DoWork event. Creating and displaying the form is foreground work, so you do it before calling RunWorkerAsync. Displaying the results is foreground work, so you do that in the ProgressChanged and/or RunWorkerCompleted event handlers. The number one rule of using a BackgroundWorker is NEVER do anything relating specifically to the UI in the DoWork event handler.

[adshocker]

thanks for the tip.

i opted to have the background process at form_load instead and it seemed to work.