c# code for sorting data in gridview

<asp:GridView ID="gridUserMaster" runat="server" AllowSorting="True" OnSorting="CustomersGridView_Sorting" 

protected void CustomersGridView_Sorting(Object sender, GridViewSortEventArgs e)
    {
        try
        {
            DataTable datatable = (DataTable)ViewState["gridview_datasource"];
            if (datatable != null)
            {
                DataView dataview = new DataView(datatable);
                if ((ViewState["sortdirection"] == null || (SortDirection)ViewState["sortdirection"] == SortDirection.Descending))
                    ViewState["sortdirection"] = SortDirection.Ascending;
                else
                    ViewState["sortdirection"] = SortDirection.Descending;
                dataview.Sort = e.SortExpression + " " + convertsortdirection((SortDirection)ViewState["sortdirection"]);
                gridUserMaster.DataSource = dataview;
                gridUserMaster.DataBind();
            }
        }
        catch (Exception ex)
        {
            Err.ErrorLog(Server.MapPath("Logs/ErrorLog"), ex.Message);
            ClientScript.RegisterStartupScript(this.GetType(), "msg", "alert('" + ex.Message.ToString() + "');", true);
        }
    }