ASP.NET

[WebMethod]
       public static string UpdateContent()
        {
            Page page = HttpContext.Current.Handler as Page;
            TextBox tb = (TextBox)page.FindControl("txt");
            tb.Text = "some string here";
            //others coding here//
            if (db.UpdateTable()){return "success";}
            else { return "failed"; }
        }

<asp:GridView ID="myGridView" runat="server" AutoGenerateColumns="False" GridLines="Horizontal"
                onrowediting="myGridView_RowEditing" HorizontalAlign="Center"  
                 onrowcommand="myGridView_RowCommand" CellSpacing="4" forecolor="Black"
                onrowcreated="myGridView_RowCreated">
                
                <RowStyle BorderStyle="Outset" />
                <Columns>
                    <asp:TemplateField>
                        <ItemTemplate>
                            <asp:Button ID="selectButton2" runat="server" Text="Add" CausesValidation="false"
                                OnClick=" AddItemToCart" UseSubmitBehavior="True" 
                                CommandName="selectButton2" oncommand="selectButton2_Command" />
                        </ItemTemplate>
                    </asp:TemplateField>
                    <asp:BoundField DataField ="ItemID"  HeaderText="Item ID"/>
                    
                </Columns>
            </asp:GridView>