Thread safe Events

Hej ...

jeg vil gerne lave en class der laver nået i mange Thread og når de har nået at melde vil jeg gerne Raise en Event

men så vil jeg gerne fange denne event i min windows form, så får jeg fejlen
"Cross-thread operation not valid: Control 'RichTextBox1' accessed from a thread other than the thread it was created on."

så kan man lave en invoke og så virker det, men jeg vil gerne løse problemet i min class og ikke i min windows form, kan man lave det ?

/jens

sample kode
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Public Class Form1
    Dim WithEvents tester As New ClassTester

    Sub tester_event_handler(ByVal _s As String) Handles tester.NewData
        Me.RichTextBox1.Text = Me.RichTextBox1.Text & System.Environment.NewLine & _s
    End Sub

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        tester.SimEvent()
    End Sub

    Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load

    End Sub
End Class

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Public Class ClassTester

    Public Shared Event NewData(ByVal _string As String)

    Public Sub SimEvent()
        Dim i As New Threading.Thread(AddressOf simHandler)
        i.Start()

        Dim ii As New Threading.Thread(AddressOf simHandler)
        ii.Start()

        Dim iii As New Threading.Thread(AddressOf simHandler)
        iii.Start()
    End Sub


    Sub simHandler()
        Dim b As New Random(System.DateTime.Now.Millisecond)
        Dim Sleeptime As Integer = b.Next(1000, 3000)
        System.Threading.Thread.Sleep(Sleeptime)
        RaiseEvent NewData("Done : " & Sleeptime)

    End Sub

End Class
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