Sorting a GridView

Sorting a GridView with a DataSource requires an external storage variable for a the last SortDirection. First, I call the GridViewReport_Sorting in the Sorting event in the GridView. A GridView has e.SortExpression and e.SortDirection. I combine the two to form a unique Session variable and then set the SortDirection to compare at later sorts:

    protected void GridViewReport_Sorting(object sender, GridViewSortEventArgs e)
    {
        DataTable dt;
        DataView dv;
        dt = (DataTable)Cache["dvStocks"];
        dv = new DataView(dt);
        string direction = SortDirection.Descending.ToString();
        string curDirecton = SortDirection.Ascending.ToString(); // set to default
        string key = string.Concat(e.SortExpression, e.SortDirection);
        if(Session[key]!=null) {
            curDirecton = (string)Session[key];
        }
        if (curDirecton.Contains("Ascending"))
        {
            direction = Global.DESC; //DESC
            Session[key] = SortDirection.Descending.ToString();
        }
        else
        {
            direction = Global.ASC; //ASC
            Session[key] = SortDirection.Ascending.ToString();
        }
        dv.Sort = e.SortExpression + " " + direction;
        Cache["dtCalculated"] = dv.ToTable();
        GridViewReport.DataSource = dv;
        GridViewReport.DataBind();
    }

Reference: http://forums.asp.net/t/825118.aspx