Delegate Sub setTextCallback(ByVal [text] As String)
 
    Private Sub setText(ByVal [text] As String)
 
        If Me.TextBox1.InvokeRequired Then
            Dim d As New setTextCallback(AddressOf SetText)
            Me.Invoke(d, New Object() {[text]})
        Else
            Me.TextBox1.Text = [text]
        End If
    End Sub

Me.TextBox1.Text += [text]