Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click

        For Each f As Form In Me.MdiChildren
            If CStr(f.Tag) = "ListView" Then
                f.BringToFront()
                Exit Sub
            End If
        Next 'f

        ListViewxxx.Tag = "ListView" 'you get the idea: each type of form will get its own tag
        ListViewxxx.MdiParent = Me
        ListViewxxx.Show()
        AddHandler ListViewxxx.FormClosing, AddressOf ListViewxxx_FormClosing
    End Sub

    Private Sub ListViewxxx_FormClosing(ByVal sender As Object, ByVal e As FormClosingEventArgs)
        If e.CloseReason <> CloseReason.MdiFormClosing Then
            e.Cancel = True
            ' Nascondo il form
            CType(sender, ListView).Visible = False
            ListViewxxx.MinimizeBox = True
        End If
    End Sub