VB2008.NETのListViewにおけるItemSelectionChangedイベントで質問です。

ListView.SelectedIndexChanged イベント

上記リンクのＶＢサンプル中のSelectedIndexChangedイベントの記述にある通り、選択された複数行をコレクションとして取得可能な様です。

Private Sub ListView1_SelectedIndexChanged_UsingItems _
    (ByVal sender As Object, ByVal e As System.EventArgs) _
    Handles ListView1.SelectedIndexChanged

    Dim breakfast As ListView.SelectedListViewItemCollection = _
        Me.ListView1.SelectedItems
    Dim item As ListViewItem
    Dim price As Double = 0.0
    For Each item In breakfast
        price += Double.Parse(item.SubItems(1).Text)
    Next

    ' Output the price to TextBox1.
    TextBox1.Text = CType(price, String)
End Sub

内容は確かではありませんが、こんな感じでしょうか。

順番が期待通りでなければ、ＳＯＲＴの処理を入れることになります。

Private Sub ListView1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListView1.SelectedIndexChanged

    Dim myitems As ListView.SelectedListViewItemCollection = Me.ListView1.SelectedItems
    If myitems.Count = 0 Then Exit Sub

    Dim strMakerComment() As String = New String(myitems.Count) {}
    Dim i As Integer

    i = 0
    For Each datItem As ListViewItem In myitems
        strMakerComment(i) = "X = " & datItem.SubItems(enmListView1.X).Text & " Y = " & datItem.SubItems(enmListView1.X).Text & vbCrLf
        i += 1
    Next
    Array.Resize(strMakerComment, i + 1)

    If strMakerComment.Length > 0 Then
        vidFileReflesh(strMakerComment) ' ここでファイル書き出し
    End If

End Sub