Loginview is used in the master page, the page control is null, please advice-CodePudding

Such as in the title, use vs2017, this problem bothering me for a long time, suffer from gates, hereby, more kindness, and to give directions, thank you,
Master page:
The

reference

 
& lt; % @ Master Language="c #" AutoEventWireup="true" CodeFile="MasterPage. Master. Cs" Inherits="MasterPage % & gt;" 

& lt; ! DOCTYPE html> 

& lt; html> 
& lt; The head runat="server" & gt; 
& lt; Meta HTTP - equiv="content-type" Content="text/HTML. Charset=utf-8 "/& gt; 
& lt; title> & lt;/title> 
& lt; Asp: ContentPlaceHolder id="head" runat="server" & gt; 
& lt;/asp: ContentPlaceHolder> 
& lt;/head> 
& lt; body> 
& lt; The form id="form1" runat="server" & gt; 
& lt; Asp: LoginView ID="LoginView1" runat="server" & gt; 
& lt; AnonymousTemplate> Hello 
& lt; LoggedInTemplate> 
& lt; Div> 
You have logged 
& lt; Asp: ContentPlaceHolder id="ContentPlaceHolder1" runat="server" & gt; 
& lt;/asp: ContentPlaceHolder> 
& lt;/div> 
& lt;/LoggedInTemplate> 
& lt;/asp: LoginView> 
& lt;/form> 
& lt;/body> 
& lt;/html>

The child page:
The

reference

 
& lt; % @ Page Title="" Language=" c # "MasterPageFile=" ~/MasterPage. Master "AutoEventWireup=" true "CodeFile=" Default2. Aspx. Cs "Inherits=" Default2 % & gt;" 

& lt; Asp: Content ID="Content1" ContentPlaceHolderID="head" Runat="Server" & gt; 
& lt;/asp: Content> 
& lt; Asp: Content ID="Content2 ContentPlaceHolderID"="ContentPlaceHolder1" Runat="Server" & gt; 
& lt; Asp: TextBox ID="TextBox1" runat="server" & gt; & lt;/asp: TextBox> 
& lt;/asp: Content>

A page of cs:
The

reference

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

Public partial class Default2: System. Web. UI. Page 
{
Protected void Page_Load (object sender, EventArgs e) 
{
TextBox1. Text="hello3"; 
} 
}

A running, an error:
The

reference

 
System. NullReferenceException 
HResult=0 x80004003 
Message=the object reference not set to an instance of an object, 
Source=App_Web_basnoeqa 
StackTrace: 
In Default2. Page_Load (Object sender, EventArgs e) in the C: \ WebSite3 \ WebSite3 \ Default2 aspx. Cs: line 12

Kindly advice, thank you,