CODEWITHSUNDEEP
vb.netcombobox
Alek
Alek

Reputation: 35

combobox multiple thread error

I have a problem with my code. I keep getting Multiple thread Error with backgroundworker, because of the combobox item display. Please look at my code below its a very simple code which I am planning to use on big scale, all I want it to do is "If item "1" selected show item "1" in label1. I can only assume that problem exists because Combobox runs in different thread.... 

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    BackgroundWorker1.runworkerasync()
    BackgroundWorker1.WorkerReportsProgress = True
    Me.Cursor = Cursors.WaitCursor 'Cursor changes to wait
End Sub
Public Structure controlwithtext
    Public controlname As Control
    Public text As String
    Public Sub New(ByVal ctrl As Control, ByVal text As String)
        Me.controlname = ctrl
        Me.text = text

    End Sub
End Structure

Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork

If comboBox1.SelectedItem = "1" then
        BackgroundWorker1.ReportProgress(5, New controlwithtext(Label1, ComboBox1.SelectedItem))

End If

End Sub

Private Sub SetBackgroundWorker_ProgressChanged(ByVal sender As Object, 
            ByVal e As ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged

    If TypeOf e.UserState Is controlwithtext Then
        Dim cwt As controlwithtext = CType(e.UserState, controlwithtext)
        cwt.controlname.Text = cwt.text
    End If

End Sub

Upvotes: 0

Views: 655

Answers (1)

Idle_Mind
Idle_Mind

Reputation: 39132

Here's an example of how to read from and write to controls from the BackgroundWorker thread:

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    BackgroundWorker1.RunWorkerAsync()
End Sub

Private Sub BackgroundWorker1_DoWork(sender As Object, e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork
    While True
        System.Threading.Thread.Sleep(250)

        Dim selection As String = Me.Invoke(Function()
                                                If Not IsNothing(ComboBox1.SelectedItem) Then
                                                    Return ComboBox1.SelectedItem.ToString
                                                Else
                                                    Return String.Empty
                                                End If
                                            End Function).ToString

        If selection = "1" Then
            Me.Invoke(Sub()
                          Label1.Text = ComboBox1.SelectedItem.ToString
                      End Sub)
        Else
            Me.Invoke(Sub()
                          Label1.Text = "something else"
                      End Sub)
        End If
    End While
End Sub

Upvotes: 2

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