protected void GridView_OnSort(object sender, GridViewSortEventArgs e)
	{
		String sortExpression = e.SortExpression;

		if (GridViewSortDirection == SortDirection.Ascending)
		{
			DataView myDataView = new DataView(mybll.GetItemsOrdered());
			myDataView.Sort = sortExpression + " DESC";
			GridView.DataSource = myDataView;
			GridView.DataBind();
		}
		else
		{
			DataView myDataView = new DataView(mybll.GetItemsOrdered());
			myDataView.Sort = sortExpression + " ASC";
			GridView.DataSource = myDataView;
			GridView.DataBind();
		}
	}

private const string ASCENDING = " ASC";
private const string DESCENDING = " DESC";

public SortDirection GridViewSortDirection
{
    get
    {
        if (ViewState["sortDirection"] == null)
            ViewState["sortDirection"] = SortDirection.Ascending;

        return (SortDirection) ViewState["sortDirection"];
    }
    set { ViewState["sortDirection"] = value; }
}

protected void GridView_Sorting(object sender, GridViewSortEventArgs e)
{
    string sortExpression = e.SortExpression;

    if (GridViewSortDirection == SortDirection.Ascending)
    {
        GridViewSortDirection = SortDirection.Descending;
        SortGridView(sortExpression, DESCENDING);
    }
    else
    {
        GridViewSortDirection = SortDirection.Ascending;
        SortGridView(sortExpression, ASCENDING);
    }

}

private void SortGridView(string sortExpression,string direction)
{
    //  You can cache the DataTable for improving performance
    DataTable dt = GetData().Tables[0];

    DataView dv = new DataView(dt);
    dv.Sort = sortExpression + direction;

    GridView1.DataSource = dv;
    GridView1.DataBind();
}