ASP.NET Core 3.1“‘用户’不包含‘FindFirstValue’的定义”

在尝试从这里实现答案时>ASP.NET Core中如何获取当前登录的用户Id用户将我重定向到这里>https://github.com/dotnet/aspnetcore/issues/18348

var UserId = User.FindFirstValue(ClaimTypes.Name);

^ 这不起作用，并打印以下错误'User' does not contain a definition for 'FindFirstValue'

编辑：添加控制器片段

我的控制器的完整片段...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Logging;
using ProjectName.Processing;
using ProjectName.Repository;
using Newtonsoft.Json;

namespace ProjectName.Controllers
{
    [ApiController]
    [Route("api/[controller]/[action]")]
    public class ClassNameController : ControllerBase
    {
        private readonly ILogger<ClassNameController> _logger;
        private OtherClassNameProcessing proc = new OtherClassNameProcessing();

        public ClassNameController(ILogger<ClassNameController> logger)
        {
            _logger = logger;
        }

        [HttpGet]
        [ProducesResponseType(typeof(List<2ndOtherClassNameRepository>), StatusCodes.Status200OK)]
        public IActionResult GetUserName()
        {
            var data = proc.GetUserName();
            return Ok(data.Result);
        }
    }
}

我的控制器正在调用的完整片段...

using Microsoft.EntityFrameworkCore;
using ProjectName.Data;
using ProjectName.Repo;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
//using System.Web;
using System.Threading.Tasks;
using System.Security.Claims;
using Microsoft.AspNetCore.Http;
using System.Web.Providers.Entities;

namespace ProjectName.Processing
{
    public class OtherClassNameProcessing
    {
        private readonly ProjName_DevelContext _context = new ProjName_DevelContext();
        private async Task<List<2ndOtherClassNameRepository>> GetNameFromRepo()
        {
            List<2ndOtherClassNameRepository> repoList = new List<2ndOtherClassNameRepository>();
            var Temp = await _context.tablename.ToListAsync();
            /* Working Test
            2ndOtherClassNameRepository repo = new 2ndOtherClassNameRepository();
            repo.UserName = "JohnDoe";
            repoList.Add(repo);
            return repoList;
            */
            2ndOtherClassNameRepository repo = new 2ndOtherClassNameRepository();
            // repo.UserName = "JohnDoe";
            var userId = User.FindFirstValue(ClaimTypes.Name);
            repo.UserName = userId;
            repoList.Add(repo);
            return repoList;
        }
        internal async Task<List<2ndOtherClassNameRepository>> GetUserName()
        {
            return await GetNameFromRepo();
        }
    }
}

知道为什么我会收到此错误吗？

您可能遇到的问题是缺少合适的软件包。

安装这个：Microsoft.Extensions.Identity.Core

然后，一旦包含 using 语句，它就应该开始工作。