asp.net using c# gridview sorting
<p>i have a asp.net grid</p>

<pre><code> &lt;asp:GridView ID="GrdUsers" runat="server" AutoGenerateColumns="False" 
                            Width="95%" BorderWidth="1px" BorderColor="Black" PagerStyle-CssClass="pgr" GridLines="Horizontal"
                            CssClass="DataGridStyle" AllowPaging="True" OnRowCommand="GrdUsers_RowCommand"
                            OnRowDeleting="GrdUsers_RowDeleting" OnRowEditing="GrdUsers_RowEditing" AllowSorting="true" OnSorting="gridView_Sorting"
                            OnPageIndexChanging="GrdUsers_PageIndexChanging"&gt;
                            &lt;%--&lt;EmptyDataRowStyle--%&gt;
                            &lt;EmptyDataRowStyle CssClass="pgr" /&gt;
                            &lt;EmptyDataTemplate&gt;
                                &lt;asp:Label ID="lblNorecId" CssClass="notification error" runat="server" Text="No records were found using your search criteria."
                                    Font-Bold="true" ForeColor="Brown" Font-Names="Arial" Font-Size="Medium"&gt;&lt;/asp:Label&gt;
                            &lt;/EmptyDataTemplate&gt;
                            &lt;Columns&gt;
                                &lt;%-- &lt;asp:BoundField HeaderText="Name" DataField="User_Fullname" /&gt;
      &lt;asp:BoundField HeaderText="City" DataField="User_city" /&gt;
      &lt;asp:BoundField HeaderText="State" DataField="User_state" /&gt;
      &lt;asp:BoundField HeaderText="Zip" DataField="User_zip" /&gt;
      &lt;asp:BoundField HeaderText="Joining Date" DataField="User_joiningdate" /&gt;--%&gt;
                                &lt;asp:BoundField DataField="catId" HeaderText="Categery Id" Visible="False" /&gt;
                                &lt;asp:BoundField DataField="MasterCName" HeaderText="Master Categery" /&gt;
                                &lt;asp:BoundField DataField="CatName" HeaderText="Sub Categery" /&gt;
                                &lt;asp:BoundField DataField="GearID" HeaderText="GearID" Visible="False" /&gt;
                                &lt;asp:BoundField DataField="GearName" HeaderText="Gear" /&gt;
                                &lt;asp:TemplateField HeaderText="RentHourly" SortExpression="RentHourly"&gt;

                                    &lt;ItemTemplate&gt;
                                        &lt;asp:Label ID="Label7" runat="server" Text="$"&gt;&lt;/asp:Label&gt;
                                        &lt;asp:Label ID="Label1" runat="server" Text='&lt;%# Bind("RentHourly") %&gt;'&gt;&lt;/asp:Label&gt;

                                    &lt;/ItemTemplate&gt;
                                &lt;/asp:TemplateField&gt;
                                &lt;asp:TemplateField HeaderText="Rentdaily" SortExpression="Rentdaily"&gt;

                                    &lt;ItemTemplate&gt;
                                    &lt;asp:Label ID="Label8" runat="server" Text="$"&gt;&lt;/asp:Label&gt;
                                        &lt;asp:Label ID="Label2" runat="server" Text='&lt;%# Bind("Rentdaily") %&gt;'&gt;&lt;/asp:Label&gt;

                                    &lt;/ItemTemplate&gt;
                                &lt;/asp:TemplateField&gt;
                                &lt;asp:TemplateField HeaderText="RentWeekend" Visible="false"&gt;

                                    &lt;ItemTemplate&gt;
                                    &lt;asp:Label ID="Label9" runat="server" Text="$" Visible="false"&gt;&lt;/asp:Label&gt;
                                        &lt;asp:Label ID="Label3" runat="server" Text='&lt;%# Bind("RentWeekend") %&gt;' Visible="false"&gt;&lt;/asp:Label&gt;

                                    &lt;/ItemTemplate&gt;
                                &lt;/asp:TemplateField&gt;
                                &lt;asp:TemplateField HeaderText="RentWeekly" Visible="false"&gt;

                                    &lt;ItemTemplate&gt;
                                    &lt;asp:Label ID="Label10" runat="server" Text="$" Visible="false"&gt;&lt;/asp:Label&gt;
                                        &lt;asp:Label ID="Label4" runat="server" Text='&lt;%# Bind("RentWeekly") %&gt;' Visible="false"&gt;&lt;/asp:Label&gt;

                                    &lt;/ItemTemplate&gt;
                                &lt;/asp:TemplateField&gt;
                                &lt;asp:TemplateField&gt;
                                    &lt;ItemTemplate&gt;
                                        &lt;asp:ImageButton ID="btnEdit" runat="server" CommandName="edit" CommandArgument='&lt;%# DataBinder.Eval(Container.DataItem, "GearID") %&gt;'
                                            ImageUrl="~/img/icons/16/edit_icon.png" /&gt;
                                    &lt;/ItemTemplate&gt;
                                &lt;/asp:TemplateField&gt;
                                &lt;asp:TemplateField&gt;
                                    &lt;ItemTemplate&gt;
                                        &lt;asp:ImageButton ID="btnDel" runat="server" CommandName="delete" CommandArgument='&lt;%# DataBinder.Eval(Container.DataItem, "GearID") %&gt;'
                                            ImageUrl="~/img/icons/16/cancel.png" /&gt;
                                        &lt;cc1:ConfirmButtonExtender ID="btnDel_ConfirmButtonExtender" runat="server" ConfirmText="Do You  Want To Delete?"
                                            Enabled="True" TargetControlID="btnDel"&gt;
                                        &lt;/cc1:ConfirmButtonExtender&gt;
                                    &lt;/ItemTemplate&gt;
                                &lt;/asp:TemplateField&gt;
                            &lt;/Columns&gt;
                            &lt;PagerSettings Mode="NextPrevious" NextPageText="Next" PreviousPageText="Last" /&gt;
                            &lt;RowStyle HorizontalAlign="Center" /&gt;
                            &lt;AlternatingRowStyle BackColor="#DBDBDB" ForeColor="Black" HorizontalAlign="Center" /&gt;
                        &lt;/asp:GridView&gt;
</code></pre>

<p>now i want to sort them renthourly and rentdaily in ascending and descending order </p>
