[c#]
    private void InitFlyGrid()
    {
      //...do something...
      // connect to ColumnSortOrderChanging event handler
      this.flyGrid.ColumnSortOrderChanging += new ColumnSortOrderChangingHandler(flyGrid_ColumnSortOrderChanging);
    }

    //custom comparer
    public class NodesComparer : IComparer
    {
      private SortOrder order;
      private Column col;
      public NodesComparer(Column col, SortOrder order)
      {
        this.col = col;
        this.order = order;
      }
      #region IComparer Members
      public int Compare(object x, object y)
      {
        Node xnode = x as Node;
        Node ynode = y as Node;
        int result = 0 ;
        object xobj = xnode.GetCellValue(col);
        object yobj = ynode.GetCellValue(col);
        IComparable xvalue = xobj as IComparable;
        IComparable yvalue = yobj as IComparable;
        if (xvalue != null && order == SortOrder.Ascending)
        {
          result = xvalue.CompareTo(yvalue);
        }
        else if (yvalue != null && order == SortOrder.Descending)
        {
          result = yvalue.CompareTo(xvalue);
        }
        return result;
      }
      #endregion
    }
    
    //ColumnSortOrderChanging event handler
    private void flyGrid_ColumnSortOrderChanging(object sender, Column column, SortOrder value, ref bool sorted)
    {
      if (column is HierachyColumn)
      {
        FlyGrid fg = sender as FlyGrid;
        fg.Rows.Items.Sort(new NodesComparer(column, value));
        fg.Rows.RefreshNodes();
        sorted = true;
      }
    }

[c#]
Random rnd = new Random();
for(int i=0; i < count; i++)
{  
   flyGrid.Rows.Items.Add(new TreeViewNode(new object[]{rnd.NextDouble()}));
}

public int Compare(object x, object y)
{
  Node xnode = x as Node;
  Node ynode = y as Node;
  int result = 0 ;
  object xobj = xnode.GetCellValue(col);
  object yobj = ynode.GetCellValue(col);
  IComparable xvalue = xobj as IComparable;
  IComparable yvalue = yobj as IComparable;
  if (order == SortOrder.Ascending)
  {
    result = xvalue == null ? yvalue == null ? 0 : -1 : xvalue.CompareTo(yvalue);
  }
  else if (order == SortOrder.Descending)
  {
    result = yvalue == null ? xvalue == null ? 0 : -1 : yvalue.CompareTo(xvalue);
  }
  return result;
}