Gridview sort in vb.net

Hi Expert,

I have Gridview sorting work for Boundfield and not work for template field? How I can sort in template field? The header is link for Student_number

<asp:GridView ID="gdView" runat="server" AllowSorting="True" 
                                 AutoGenerateColumns="False" AllowPaging="True"
                           OnSorting="_Sorting">
                            <Columns>
                                 <asp:TemplateField HeaderText="Student Number" HeaderStyle-Wrap="false" >
                                    <HeaderTemplate>
                                    <asp:LinkButton ID="lnkStudentNumberHeader" runat="server" Text="Student Number"   CommandName="Sort" CommandArgument='<%# Eval("Student_Number") %>'>
                                    </asp:LinkButton>
                                    </HeaderTemplate>
                                    <ItemTemplate>
                                                                              <asp:LinkButton runat="server" ID="lblStudentNumber" VerticalAlign="Top" Text='<%# Eval("Student_Number") %>'
                                            OnClick="lnkStudentNumber_click" CommandName="Select" ></asp:LinkButton>
                                    </ItemTemplate>
                                                                       <ItemStyle CssClass="leftalign" VerticalAlign="Top" />
                                </asp:TemplateField>
                                <asp:BoundField DataField="First_NAME" HeaderText="First Name" ReadOnly="True" 
                                    SortExpression="First_NAME" />


Code behind:

Public Property SortDirection() As SortDirection

            Get
                If ViewState("SortDirection") Is Nothing Then
                    ViewState("SortDirection") = SortDirection.Ascending
                End If

                Return DirectCast(ViewState("SortDirection"), SortDirection)

            End Get

            Set(ByVal value As SortDirection)

                ViewState("SortDirection") = value

            End Set

        End Property

        

        Protected Sub gdView_Sorting(ByVal sender As Object, ByVal e As GridViewSortEventArgs)

            Dim sortExpression As String = e.SortExpression
            Dim direction As String = String.Empty
            If SortDirection = SortDirection.Ascending Then
                SortDirection = SortDirection.Descending
                direction = " DESC"
            Else
                SortDirection = SortDirection.Ascending
                direction = " ASC"
            End If

            Dim dt As DataTable = Me.GetDataFromdatabase.Tables(0)
            dt.DefaultView.Sort = sortExpression & direction
            gdView.DataSource = dt
            gdView.DataBind()


        End Sub

Select allOpen in new window

Thanks in advance.