升级到 asp.net core 3.1 后声明逐字变量时出错

问题描述

在将我的 Asp.Net Core MVC Webapp 解决方案从 .Net Core 2.2 迁移到 .Net Core 3.1 后，我遇到了一个奇怪的错误。
我按照官方 docs 中描述的步骤，更新程序、启动、nuget 包...

我正在使用 Syncfusion Essential Studio 2 - 我认为这与此错误无关 - 在许多视图中，我正在声明变量/创建对象，例如创建用于在 Datagrid 中查找的 DropDownList：

@model CultureMultiModel

@{
    var userCultLookupDDL = new Syncfusion.EJ2.DropDowns.DropDownList()
    {
        FilterType = Syncfusion.EJ2.DropDowns.FilterType.Contains,Fields = new Syncfusion.EJ2.DropDowns.DropDownListFieldSettings { Text = "display",Value = "Name",GroupBy = "Parent" }
        ...
    };
    var userCultParams = new { @params = userCultLookupDDL };

这在 2.2 中运行良好，但现在我在 new { @params ...
上遇到错误将鼠标悬停在@params 上时，将显示以下内容：
CS1525：无效的表达式术语“参数”
CS1003: 语法错误，',' 预期

我尝试了很多东西：

使用圆括号@(params) 给出同样的错误
添加 nuget 包 Microsoft.AspNetCore.Mvc.Razor.Extensions，同样的错误
在项目文件中添加了 <AddRazorSupportForMvc>true</AddRazorSupportForMvc>，同样的错误
更改为@Params 或@arams 会出现错误 CS0103：当前上下文中不存在该名称

由于在编辑 cshtml 文件时立即编译/验证期间发生这种情况，我认为这与启动无关，但为了完整性我还是添加了它：

public void ConfigureServices(IServiceCollection services)
        {
            services.AddDbContext<myContext>(options =>
                options.UsesqlServer(
                    Configuration.GetConnectionString("myConnection"),builder => builder.MigrationsAssembly("myDAL")));


            services.AddDefaultIdentity<IdentityUser>()
                .AddRoles<IdentityRole>()
                .AddRoleManager<RoleManager<IdentityRole>>()
                .AddEntityFrameworkStores<ApplicationDbContext>();
            
            services.AddLocalization(options => options.ResourcesPath = "Resources");
            LocalizationSupport localizationSupport = new LocalizationSupport();
            services.Configure<RequestLocalizationoptions>(options =>
            {
                options.DefaultRequestCulture = new RequestCulture(culture: "en",uiCulture: "en");
                options.SupportedCultures = localizationSupport.SupportedCultures;
                options.SupportedUICultures = localizationSupport.SupportedCultures;
            });

            services.AddMemoryCache();

            services
                .AddMvc()
                .AddViewLocalization()
                .AddDataAnnotationsLocalization(options =>
                {
                    options.DataAnnotationLocalizerProvider = (type,factory) =>
                        factory.Create(typeof(SharedModelLocale));
                })
                .AddNewtonsoftJson(options =>
                {
                    options.SerializerSettings.ContractResolver = new DefaultContractResolver();
                });
            ;

            services
                .AddControllersWithViews()
                .AddNewtonsoftJson(
                    options => options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore
                );
            services.AddRazorPages();

            services.Configure<IdentityOptions>(options =>
            ...

            services.AddHttpContextAccessor();
        }

        public void Configure(IApplicationBuilder app,IWebHostEnvironment env)
        {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                app.UseHsts();
            }

            app.UseHttpsRedirection();
            // << Localization           
            LocalizationSupport localizationSupport = new LocalizationSupport();
            var options = new RequestLocalizationoptions
            {
                DefaultRequestCulture = new RequestCulture("en"),SupportedCultures = localizationSupport.SupportedCultures,SupportedUICultures = localizationSupport.SupportedCultures,};
            app.UseRequestLocalization(options);
            // >> Localization
            app.UseStaticFiles();
            app.UseCookiePolicy();

            app.UseRouting();

            app.UseAuthentication();
            app.UseAuthorization();

            app.UseEndpoints(endpoints => {
                endpoints.MapAreaControllerRoute(name: "IdentityRoute",areaName: "Identity",pattern: "{area:exists}/{controller=Home}/{action=Index}");
                endpoints.MapDefaultControllerRoute();
            });
        }

和我的项目文件

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <packagereference Include="markdig" Version="0.22.1" />
    <packagereference Include="Microsoft.AspNetCore.Identity.UI" Version="3.1.15" />
    <packagereference Include="Microsoft.AspNetCore.Mvc.NewtonsoftJson" Version="3.1.1" />
    <packagereference Include="Microsoft.VisualStudio.Web.CodeGeneration.Design" Version="3.1.5" PrivateAssets="All" />
    <packagereference Include="Syncfusion.EJ2.AspNet.Core" Version="19.1.0.59" />
    <packagereference Include="System.ServiceModel.Http" Version="4.5.3" />
  </ItemGroup>

这可能是一件微不足道的事情，但在任何文档中都没有提及此事，我的搜索也没有返回任何内容。

解决方法

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asp.net-core-2.2 asp.net-core-3.1 c#c#migration razor razor razor