Change the Gridview SortDirection on Header Click

  protected void grd_SearchQueryBuilder_Sorting(object sender, GridViewSortEventArgs e)
    {
        string Direction =GetSortDirection(e.SortExpression);
        string  expre = e.SortExpression;       
        Sortgridview(expre,Direction);

    }


 public string GetSortDirection(string SortExpression)
    {
        if (ViewState[SortExpression] == null)
            ViewState[SortExpression] = "Desc";
        else
            ViewState[SortExpression] = ViewState[SortExpression].ToString() == "Desc" ? "Asc" : "Desc";

        return ViewState[SortExpression].ToString();
    }