Public Class Form1

    Private Delegate Sub StampaDelegato(ByVal val As String)

    Dim PuntatoreFunzione As StampaDelegato


    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        PuntatoreFunzione = New StampaDelegato(AddressOf Stampa)
    End Sub



    Private Sub Stampa(ByVal val As String)
        If Me.InvokeRequired Then
            Me.Invoke(PuntatoreFunzione, val)
        Else
            ListBox1.Items.Add(val)
        End If
    End Sub


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



    Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
        'Fai conto che al posto del for cicli sul file
        For i As Integer = 0 To 100
            Stampa(i)
        Next
    End Sub
    
End Class