Private Sub dgvFiles_RowHeaderMouseClick(sender As Object,
          e As DataGridViewCellMouseEventArgs) Handles _
            dgvFiles.RowHeaderMouseClick
 
        'Anzeige einer Textdatei beim Click auf einen Zeilenkopf im Grid mit 
        'den Dateinamen
 
        'an GridView gebundene Bindingsource
        Dim rowview As DataRowView = bsFiles(e.RowIndex)
 
        'Datarelation verwenden
        'Datarowview weist die Datarow der gebundenen Tabelle (row-Eigenschaft)  
        Dim parentrow = rowview.Row.GetParentRow("FoldersFiles")
        Dim subfoldername As String = parentrow("Subfolder")
 
        'Den kompletten Pfad der Datei zusammenstellen
        Dim filename As String = IO.Path.Combine(basefolder, 
                                  subfoldername, rowview.Row( _
                                    "Filename").ToString)
 
        Try
            tboFileContent.Text = IO.File.ReadAllText(filename)
            Me.Text = IO.Path.GetFileName(filename)
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
 
End Sub

Dim subfoldername As String = parentrow("Subfolder")