entity framework - Trying to do sorting when click on asp.net Gridview Header -

i put code steps below. asp.net code

<asp:gridview allowsorting="true" id="grdsolicitacoes" runat="server" gridlines="none" allowpaging="true" pagesize="10" onpageindexchanging="grdsolicitacoes_pageindexchanging" onsorting="gvshows_sorting"> <columns> <asp:boundfield datafield="id" headertext="cód." sortexpression="id </asp:boundfield>  <asp:boundfield datafield="cns" dataformatstring="{0:dd/mm/yyyy}" headertext="cns" sortexpression="cns" ></asp:boundfield> <asp:boundfield datafield="nome" headertext="nome paciente" sortexpression="nome"  ></asp:boundfield> <asp:boundfield datafield="data_nascimento" headertext="data de nascimento" dataformatstring="{0:dd/mm/yyyy}" sortexpression="data_nascimento </asp:boundfield> <asp:boundfield datafield="nome_mae" headertext="nome da mãe" sortexpression="nome_mae"></asp:boundfield> </columns> </asp:gridview> 

c# (backend code) populate gridview below

private void populagrid() { private modeldatacontext mdc; mdc = new modeldatacontext();         try         {             var pacientes = pac in mdc.tbl_pacientes                             select new                             {                                 id = pac.id,                                 cns = pac.cns,                                 nome = pac.nome,                                 data_nascimento = pac.data_nascimento,                                 nome_mae = pac.nome_mae,                                 idatendimento = 0                              };                  grdsolicitacoes.datasource = pacientes;                 grdsolicitacoes.databind();         }         catch (exception ex) { page.clientscript.registerclientscriptblock(gettype(), "alerta", "alert('erro ao consultar')" + ex.message, true); }         { mdc.dispose(); }     } 

onsorting method below

    private string convertsortdirection(sortdirection sortdirection)     {         string newsortdirection = string.empty;         switch (sortdirection)         {             case sortdirection.ascending:                 newsortdirection = "asc";                 break;              case sortdirection.descending:                 newsortdirection = "desc";                 break;         }         return newsortdirection;     }      protected void gvshows_sorting(object sender, gridviewsorteventargs e)     {         debug.writeline("sorting called");         var datatable = session["pacientes"] datatable;          if (datatable != null)         {             var dataview = new dataview(datatable)             {                 sort = e.sortexpression + " " + convertsortdirection(e.sortdirection)             };              grdsolicitacoes.datasource = dataview;             grdsolicitacoes.databind();         }     } 

can please guide me doing wrong ? when click on "onsort" method call function doesn't change anything. checked tutorials discussed here thing doesnt work. sure missing little details plx help.