GridView Sort Direction Images issue

Question

Hello,

I have a Gridview in my aspx page and I have the following code for Sorting. Though the records are getting sorted for some reason the image is always showing Up arrow.

I don't know what is the problem.

Thanks in advance for your help.

    protected void GridView_Sorting(object sender, GridViewSortEventArgs e)
        {
            try
            {
                GridView GridViewSender = sender as GridView;

                DataTable dataTable = ViewState["dt"] as DataTable;

                if (dataTable != null)
                {
                    DataView dataView = new DataView(dataTable);
                    dataView.Sort = e.SortExpression + " " + ConvertSortDirectionToSql(e);

                    GridViewSender.DataSource = dataView;
                    GridViewSender.DataBind();
                }
            }
            catch (Exception ex)
            {
            }
        }

private string ConvertSortDirectionToSql(GridViewSortEventArgs e)
    {

        string newSortDirection = String.Empty;
        if (ViewState["sortColumn"] == null)
        {
            ViewState["sortColumn"] = "";
        }

        if (ViewState["sortColumn"].ToString() == e.SortExpression.ToString())
        {
            if ("ASC" == ViewState["sortDirection"].ToString())
            {
                ViewState["sortDirection"] = "DESC";
                newSortDirection = "DESC";
            }
            else
            {
                ViewState["sortDirection"] = "ASC";
                newSortDirection = "ASC";
            }
        }
        else
        {
            ViewState["sortColumn"] = e.SortExpression.ToString();
            ViewState["sortDirection"] = "ASC";
            newSortDirection = "ASC";
        }
        return newSortDirection;

    }



private string ConvertSortDirectionToSql(GridViewSortEventArgs e)
    {

        string newSortDirection = String.Empty;
        if (ViewState["sortColumn"] == null)
        {
            ViewState["sortColumn"] = "";
        }

        if (ViewState["sortColumn"].ToString() == e.SortExpression.ToString())
        {
            if ("ASC" == ViewState["sortDirection"].ToString())
            {
                ViewState["sortDirection"] = "DESC";
                newSortDirection = "DESC";
            }
            else
            {
                ViewState["sortDirection"] = "ASC";
                newSortDirection = "ASC";
            }
        }
        else
        {
            ViewState["sortColumn"] = e.SortExpression.ToString();
            ViewState["sortDirection"] = "ASC";
            newSortDirection = "ASC";
        }
        return newSortDirection;

    }