“IServiceCollection”不包含“AddSpaStaticFiles”的定义

我不明白Startup.cs为什么抛出这个错误。我尝试了建议的解决方案 here (包括重启我的机器和运行dotnet恢复)没有运气。有什么想法吗?

CS1061“IServiceCollection”不包含“AddSpaStaticFiles”的定义,并且找不到接受类型为“IServiceCollection”的第一个参数的可访问扩展方法“AddSpaStaticFiles”(是否缺少using指令或程序集引用?)

使用startup.cs顶部的语句:

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Myproject.Models;

using Microsoft.EntityFrameworkCore;
using Microsoft.AspNetCore.Identity;
using Microsoft.AspNetCore.Authentication.JwtBearer;
using Microsoft.IdentityModel.Tokens;
using System.Text;
//Install-Package Microsoft.AspNetCore.Session
//Install-Package AutoMapper.Extensions.Microsoft.DependencyInjection

  <ItemGroup>
    <PackageReference Include="AutoMapper.Extensions.Microsoft.DependencyInjection" Version="5.0.1" />
    <PackageReference Include="Microsoft.AspNetCore.Session" Version="2.1.1" />
    <PackageReference Include="System.IdentityModel.Tokens.Jwt" Version="5.2.4" />
    <PackageReference Include="Flurl.Http" Version="2.2.1" />
    <PackageReference Include="jQuery" Version="3.3.1" />
    <PackageReference Include="jQuery.Validation" Version="1.17.0" />
    <PackageReference Include="LeanKit.API.Client" Version="1.2.6" />
    <PackageReference Include="Newtonsoft.Json" Version="11.0.2" />

    <PackageReference Include="Microsoft.AspNetCore.All" Version="2.0.5" />
    <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="2.0.2" />
    <PackageReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="2.0.2" />
  </ItemGroup>

  <ItemGroup>
    <DotNetCliToolReference Include="Microsoft.VisualStudio.Web.CodeGeneration.Tools" Version="2.1.0-preview1-final" />
  </ItemGroup>