Visual Studio 2012 new ASP Web Forms Application can't access textboxes from aspx file

问题

i just created a new Web Forms application in VS 2012, i'm trying to get the value of the "UserName" textbox located in the Login.aspx page, all im getting is "the name UserName does not exist in the currect context" when trying to access it in the login.aspx.cs file...

the ASPX file:

    <%@ Page Title="Log in" Language="C#" MasterPageFile="~/Site.Master" AutoEventWireup="true" CodeBehind="Login.aspx.cs" Inherits="WebApplication1.Account.Login" %>
<%@ Register Src="~/Account/OpenAuthProviders.ascx" TagPrefix="uc" TagName="OpenAuthProviders" %>

<asp:Content runat="server" ID="BodyContent" ContentPlaceHolderID="MainContent">
    <hgroup class="title">
        <h1><%: Title %>.</h1>
    </hgroup>
    <section id="loginForm">
        <h2>Use a local account to log in.</h2>
        <asp:Login runat="server" ViewStateMode="Disabled" RenderOuterTable="false">
            <LayoutTemplate>
                <p class="validation-summary-errors">
                    <asp:Literal runat="server" ID="FailureText" />
                </p>
                <fieldset>
                    <legend>Log in Form</legend>
                    <ol>
                        <li>
                            <asp:Label runat="server" AssociatedControlID="UserName">User name</asp:Label>
                            <asp:TextBox runat="server" ID="UserName" />
                            <asp:RequiredFieldValidator runat="server" ControlToValidate="UserName" CssClass="field-validation-error" ErrorMessage="The user name field is required." />
                        </li>
                        <li>
                            <asp:Label runat="server" AssociatedControlID="Password">Password</asp:Label>
                            <asp:TextBox runat="server" ID="Password" TextMode="Password" />
                            <asp:RequiredFieldValidator runat="server" ControlToValidate="Password" CssClass="field-validation-error" ErrorMessage="The password field is required." />
                        </li>
                        <li>
                            <asp:CheckBox runat="server" ID="RememberMe" />
                            <asp:Label runat="server" AssociatedControlID="RememberMe" CssClass="checkbox">Remember me?</asp:Label>
                        </li>
                    </ol>
                    <asp:Button runat="server" CommandName="Login" Text="Log in" />
                </fieldset>
            </LayoutTemplate>
        </asp:Login>
        <p>
            <asp:HyperLink runat="server" ID="RegisterHyperLink" ViewStateMode="Disabled">Register</asp:HyperLink>
            if you don't have an account.
        </p>
    </section>

    <section id="socialLoginForm">
        <h2>Use another service to log in.</h2>
        <uc:OpenAuthProviders runat="server" ID="OpenAuthLogin" />
    </section>
</asp:Content>

the CS file:

    using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace WebApplication1.Account
{
    public partial class Login : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            string id = UserName.Text;
        }
    }
}

EDIT: added the auto-generated aspx.designer.cs file:

    //------------------------------------------------------------------------------
// <auto-generated>
//     This code was generated by a tool.
//
//     Changes to this file may cause incorrect behavior and will be lost if
//     the code is regenerated. 
// </auto-generated>
//------------------------------------------------------------------------------

namespace WebApplication1.Account
{


    public partial class Login
    {

        /// <summary>
        /// RegisterHyperLink control.
        /// </summary>
        /// <remarks>
        /// Auto-generated field.
        /// To modify move field declaration from designer file to code-behind file.
        /// </remarks>
        protected global::System.Web.UI.WebControls.HyperLink RegisterHyperLink;

        /// <summary>
        /// OpenAuthLogin control.
        /// </summary>
        /// <remarks>
        /// Auto-generated field.
        /// To modify move field declaration from designer file to code-behind file.
        /// </remarks>
        protected global::WebApplication1.Account.OpenAuthProviders OpenAuthLogin;
    }
}

any help would be greatly appreciated.

回答1:

(Commented converted to an answer at the OP's request)

Ah, I see UserName is contained within a <LayoutTemplate>. That messes-up control generation by the designer. If you move your textbox outside then it will work, but if you're using <asp:Login> (which I don't recommend you do) you're not meant to access controls directly from your code-behind.

回答2:

For one, you should name your Login control (e.g. Login1). Then reference it as so:

    protected void Page_Load(object sender, EventArgs e)
    {
        string id = Login1.UserName;
    }

回答3:

Because you use LoginControl. try this :

TextBox tb = (TextBox)Login1.FindControl("UserName");

来源：https://stackoverflow.com/questions/17889692/visual-studio-2012-new-asp-web-forms-application-cant-access-textboxes-from-asp