Gridview Sorting

<asp:GridView ID="gvDetails" runat="server"
              AutoGenerateColumns="False"  AllowPaging="true"
              onsorting="gvDetails_Sorting" PageSize="6" AllowSorting="True">
<Columns>
<asp:TemplateField HeaderText="EmployeeName" SortExpression="EmployeeName">
<ItemTemplate>
<asp:Label ID="lblFname" runat="server" Text='<%#Eval("EmployeeName")%>'/>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Mobile" SortExpression="Mobile">
<ItemTemplate>
<asp:Label ID="lblLname" runat="server" Text='<%#Eval("Mobile")%>'/>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="BatchCode" SortExpression="BatchCode">
<ItemTemplate>
<asp:Label ID="lblLocation" runat="server" Text='<%#Eval("BatchCode")%>'/>
</ItemTemplate>
</asp:TemplateField>
<asp:TemplateField HeaderText="Created" SortExpression="Created">
<ItemTemplate>
<asp:Label ID="lblLocation" runat="server" Text='<%#Eval("Created")%>'/>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>





 protected void Page_Load(object sender, EventArgs e)
        {
            gvDetails.DataSource = BindGridView();
            gvDetails.DataBind();
        }



 protected void gvDetails_Sorting(object sender, GridViewSortEventArgs e)
        {
            string sortingDirection = string.Empty;
            if (sortProperty == SortDirection.Ascending)
            {
                sortProperty = SortDirection.Descending;
                sortingDirection = "Desc";
            }
            else
            {
                sortProperty = SortDirection.Ascending;
                sortingDirection = "Asc";
            }

            DataView sortedView = new DataView(BindGridView());
            sortedView.Sort = e.SortExpression + " " + sortingDirection;
            gvDetails.DataSource = sortedView;
            gvDetails.DataBind();
        }


     private DataTable BindGridView()
        {
            SPWeb web = SPContext.Current.Web;
            SPList list = web.Lists["Employee Feedback Details"];
            SPListItemCollection item = list.GetItems();


            //foreach (SPListItem items in item) ;
            //{

            //}
            DataTable dt = new DataTable();
            dt = item.GetDataTable();

            return dt;
            //gvDetails.DataSource = dt;
            //gvDetails.DataBind();
        }



        public SortDirection sortProperty
        {
            get
            {
                if (ViewState["SortingState"] == null)
                {
                    ViewState["SortingState"] = SortDirection.Ascending;
                }
                return (SortDirection)ViewState["SortingState"];
            }
            set
            {
                ViewState["SortingState"] = value;
            }
        }