首先在Program.cs中，注册

builder.Services.AddHttpContextAccessor();

Program.cs完整代码：

using Microsoft.AspNetCore.Mvc.Filters;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using System.Text.Encodings.Web;
using System.Text.Unicode;
using WebReportInfoNetCore7;
using WebReportInfoNetCore7.DataBaseEntity;
using WebReportInfoNetCore7.IBLL;
using WebReportInfoNetCore7.IBLL_impl;
using WebReportInfoNetCore7.IDAO;
using WebReportInfoNetCore7.IDAO_impl;var builder = WebApplication.CreateBuilder(args);//依赖注入
builder.Services.AddSingleton<IAh_userDao, Ah_userDao>();
builder.Services.AddSingleton<IUserBll, UserBll>();// Add services to the container.
builder.Services.AddControllersWithViews(ops => {//全局异常过滤器，注册ops.Filters.Add<ExceptionFilter>();
})//Microsoft.AspNetCore.Mvc.NewtonsoftJson
.AddNewtonsoftJson(options =>
{options.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver();
});builder.Services.AddSession();//IHttpContextAccessor 在其他程序集中获取HttpContext
builder.Services.AddHttpContextAccessor();//解决输入页面中文被编码了
builder.Services.AddSingleton(HtmlEncoder.Create(UnicodeRanges.All));var app = builder.Build();// Configure the HTTP request pipeline.
if (!app.Environment.IsDevelopment())
{app.UseExceptionHandler("/Home/Error");
}
app.UseStaticFiles();app.UseRouting();app.UseAuthorization();
app.UseSession();app.MapControllerRoute(name: "default",pattern: "{controller=Home}/{action=Index}/{id?}");AppServicesHelpter.App = app;//Microsoft.AspNetCore.Session.ISessionStore
//IHttpContextAccessor Accessor = app.Services.GetService<IHttpContextAccessor>();app.Run();

其他程序集中获取,其他程序集需要引用文件：Microsoft.AspNetCore.Http.Abstractions.dll
文件位置：
C:\Program Files\dotnet\packs\Microsoft.AspNetCore.App.Ref\7.0.5\ref\net7.0

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;using Microsoft.AspNetCore.Builder;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.AspNetCore.Http;
using WebReportInfoNetCore7.ViewEntity;
using System.Net.Http;
using System.Runtime.CompilerServices;namespace WebReportInfoNetCore7.DataBaseEntity
{/// <summary>/// 依赖注册，获取接口实例/// </summary>/// 创建时间：2023-10-8 16:03:39 public sealed class AppServicesHelpter{/// <summary>/// 程序/// </summary>public static Microsoft.AspNetCore.Builder.WebApplication App { get; set; }/// <summary>/// 获取接口实例/// </summary>/// <typeparam name="T"></typeparam>/// <returns></returns>public static T GetServices<T>() where T : notnull{T instance = App.Services.GetRequiredService<T>();return instance;}/// <summary>/// 获取当前登录用户/// </summary>/// <returns></returns>/// 创建时间：2023-10-10 14:48:23， public static Ah_userView CurrentLoginUser(){Microsoft.AspNetCore.Http.IHttpContextAccessor accessor = App.Services.GetService<Microsoft.AspNetCore.Http.IHttpContextAccessor>();string json = accessor.HttpContext.Session.GetString("userLogin");return Newtonsoft.Json.JsonConvert.DeserializeObject<Ah_userView>(json);}}
}

微软文档：
https://learn.microsoft.com/zh-cn/aspnet/core/fundamentals/http-context?view=aspnetcore-7.0