文本框在当前上下文中不存在

代码中的问题

2 个文件：注册.aspx注册.aspx.cs

注册.aspx：

    <%@ Page Title="Register" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
    CodeBehind="Register.aspx.cs" Inherits="HSE_Monitoring_Application.Account.Register" %>
<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
    <asp:CreateUserWizard ID="RegisterUser" runat="server" EnableViewState="false" OnCreatedUser="RegisterUser_CreatedUser">
        <LayoutTemplate>
            <asp:PlaceHolder ID="wizardStepPlaceholder" runat="server"></asp:PlaceHolder>
            <asp:PlaceHolder ID="navigationPlaceholder" runat="server"></asp:PlaceHolder>
        </LayoutTemplate>
        <WizardSteps>
            <asp:CreateUserWizardStep ID="RegisterUserWizardStep" runat="server">
                <ContentTemplate>
                    <h2>
                        Create a New Account
                    </h2>
                    <p>
                        Use the form below to create a new account.
                    </p>
                    <p>
                        Passwords are required to be a minimum of <%= Membership.MinRequiredPasswordLength %> characters in length.
                    </p>
                    <span class="failureNotification">
                        <asp:Literal ID="ErrorMessage" runat="server"></asp:Literal>
                    </span>
                    <asp:ValidationSummary ID="RegisterUserValidationSummary" runat="server" CssClass="failureNotification" 
                         ValidationGroup="RegisterUserValidationGroup"/>
                    <div class="accountInfo">
                        <fieldset class="register">
                            <legend>Account Information</legend>
                            <p>
                                <asp:Label ID="UserNameLabel" runat="server" AssociatedControlID="UserName">User Name:</asp:Label>
                                <asp:TextBox ID="UserName" runat="server" CssClass="textEntry"></asp:TextBox>
                                <asp:RequiredFieldValidator ID="UserNameRequired" runat="server" ControlToValidate="UserName" 
                                     CssClass="failureNotification" ErrorMessage="User Name is required." ToolTip="User Name is required." 
                                     ValidationGroup="RegisterUserValidationGroup">*</asp:RequiredFieldValidator>
                            </p>
                            <p>
                                <asp:Label ID="PasswordLabel" runat="server" AssociatedControlID="Password">Password:</asp:Label>
                                <asp:TextBox ID="Password" runat="server" CssClass="passwordEntry" TextMode="Password"></asp:TextBox>
                                <asp:RequiredFieldValidator ID="PasswordRequired" runat="server" ControlToValidate="Password" 
                                     CssClass="failureNotification" ErrorMessage="Password is required." ToolTip="Password is required." 
                                     ValidationGroup="RegisterUserValidationGroup">*</asp:RequiredFieldValidator>
                            </p>
                            <p>
                                <asp:Label ID="ConfirmPasswordLabel" runat="server" AssociatedControlID="ConfirmPassword">Confirm Password:</asp:Label>
                                <asp:TextBox ID="ConfirmPassword" runat="server" CssClass="passwordEntry" TextMode="Password"></asp:TextBox>
                                <asp:RequiredFieldValidator ControlToValidate="ConfirmPassword" CssClass="failureNotification" Display="Dynamic" 
                                     ErrorMessage="Confirm Password is required." ID="ConfirmPasswordRequired" runat="server" 
                                     ToolTip="Confirm Password is required." ValidationGroup="RegisterUserValidationGroup">*</asp:RequiredFieldValidator>
                                <asp:CompareValidator ID="PasswordCompare" runat="server" ControlToCompare="Password" ControlToValidate="ConfirmPassword" 
                                     CssClass="failureNotification" Display="Dynamic" ErrorMessage="The Password and Confirmation Password must match."
                                     ValidationGroup="RegisterUserValidationGroup">*</asp:CompareValidator>
                            </p>
                        </fieldset>
                        <p class="submitButton">
                            <asp:Button ID="CreateUserButton" runat="server" CommandName="MoveNext" Text="Create User" 
                                 ValidationGroup="RegisterUserValidationGroup" OnClick="onSubmitNewUser"/>
                        </p>
                    </div>
                </ContentTemplate>
                <CustomNavigationTemplate>
                </CustomNavigationTemplate>
            </asp:CreateUserWizardStep>
        </WizardSteps>
    </asp:CreateUserWizard>
</asp:Content>

问题：无法从注册中看到文本框"用户名".aspx.cs类：

void onSubmitNewUser(Object sender, EventArgs e)
        {
            string strcon = "connect_information";
            SqlConnection con = new SqlConnection(strcon);
            SqlCommand com = new SqlCommand("storelogin", con);
            com.CommandType = CommandType.StoredProcedure;
            SqlParameter p1 = new SqlParameter("username",  UserName.Text);
            SqlParameter p3 = new SqlParameter("password", ConfirmPassword.Text);
            com.Parameters.Add(p1);
            com.Parameters.Add(p3);
            con.Open();
            com.ExecuteNonQuery();
            Labelinfo.Text = "registered successful";
        }

    TextBox  UserName= (TextBox)CreateUserWizard.FindControl("UserName");