private ResetViewPortRows(FlyGrid flyGrid, int rowIndex)
{
  NestedGridNode nestedParent = flyGrid.Rows.Items[rowIndex] as NestedGridNode;
  if (nestedParent != null)
  {
    FlyGridViewPort port = nestedParent.NestedInternal;
    if (port != null)
    {
      port.Rows.BeginUpdate();
      try
      {
        port.Rows.RootNode = null;
      }
      finally
      {
        port.Rows.EndUpdate();
        port.Rows.OnChanged();
      }
    }
  }
}