迁移到.NET Core 3后，出现“项目'Web'必须提供配置值”错误

Question

我已经将ASP.NET Core 2.2项目迁移到Core 3.0，并且收到错误消息：

项目[项目位置]必须为Configuration提供一个值。

该错误消息并没有太多处理，有人知道如何解决该错误吗？

This looks like it could be similar to this issue on the dotnet cli github repo.

Answer 1

The issue turned out to be that I was still referencing Microsoft.AspNetCore.Razor.Design Version="2.2.0" in the .proj file's package references. Deleting that reference (which isn't needed at all as Razor.Design is now part of AspNetCore library) fixed the issue.

Once I'd done that, I then got hundreds of errors about nullable objects being a new feature not compatible with razor. That was because I had <LangVersion>Latest</LangVersion> in my .proj file. Removing that line fixed that issue and got the project running again.

(In some cases you might need to clean and rebuild and/or restart VS too, according to comments on the github thread)

如果仍不能解决问题，则可能是项目使用的NuGet软件包之一。尝试删除依赖项以查看是否可以解决问题，然后一次重新添加一个以找出是哪个NuGet软件包引起的。

Answer 2

我遇到了同样的问题，通过删除以下引用解决了这个问题：

"Microsoft.AspNetCore.Mvc" Version="2.2.0"

"Microsoft.AspNetCore.Mvc.Razor.ViewCompilation" Version="2.2.0"

Answer 3

MS 文档标题为“ Migrate from ASP.NET Core 2.2 to 3.0 ”。在“更新项目文件”下，它指出，

“大量 NuGet 包不是为 ASP.NET Core 3.0 生成的。应从项目文件中删除此类包引用”

作为例子给出的两个是：

• 微软.AspNetCore.App
• Microsoft.AspNetCore.Razor.Design

在其下方，您可以展开以查看所有不再生产的包：

• 微软.AspNetCore
• 微软.AspNetCore.All
• 微软.AspNetCore.App
• Microsoft.AspNetCore.Antiforgery
• Microsoft.AspNetCore.Authentication
• Microsoft.AspNetCore.Authentication.Abstractions
• Microsoft.AspNetCore.Authentication.Cookies
• Microsoft.AspNetCore.Authentication.Core
• Microsoft.AspNetCore.Authentication.OAuth
• Microsoft.AspNetCore.Authorization.Policy
• Microsoft.AspNetCore.CookiePolicy
• 微软.AspNetCore.Cors
• Microsoft.AspNetCore.Diagnostics
• Microsoft.AspNetCore.Diagnostics.HealthChecks
• Microsoft.AspNetCore.HostFiltering
• Microsoft.AspNetCore.Hosting
• Microsoft.AspNetCore.Hosting.Abstractions
• Microsoft.AspNetCore.Hosting.Server.Abstractions
• 微软.AspNetCore.Http
• Microsoft.AspNetCore.Http.Abstractions
• Microsoft.AspNetCore.Http.Connections
• Microsoft.AspNetCore.Http.Extensions
• Microsoft.AspNetCore.HttpOverrides
• Microsoft.AspNetCore.HttpsPolicy
• Microsoft.AspNetCore.Identity
• Microsoft.AspNetCore.Localization
• Microsoft.AspNetCore.Localization.Routing
• 微软.AspNetCore.Mvc
• Microsoft.AspNetCore.Mvc.Abstractions
• Microsoft.AspNetCore.Mvc.Analyzers
• Microsoft.AspNetCore.Mvc.ApiExplorer
• Microsoft.AspNetCore.Mvc.Api.Analyzers
• Microsoft.AspNetCore.Mvc.Core
• Microsoft.AspNetCore.Mvc.Cors
• Microsoft.AspNetCore.Mvc.DataAnnotations
• Microsoft.AspNetCore.Mvc.Formatters.Json
• Microsoft.AspNetCore.Mvc.Formatters.Xml
• Microsoft.AspNetCore.Mvc.Localization
• Microsoft.AspNetCore.Mvc.Razor
• Microsoft.AspNetCore.Mvc.Razor.ViewCompilation
• Microsoft.AspNetCore.Mvc.RazorPages
• Microsoft.AspNetCore.Mvc.TagHelpers
• Microsoft.AspNetCore.Mvc.ViewFeatures
• 微软.AspNetCore.Razor
• Microsoft.AspNetCore.Razor.Runtime
• Microsoft.AspNetCore.Razor.Design
• Microsoft.AspNetCore.ResponseCaching
• Microsoft.AspNetCore.ResponseCaching.Abstractions
• Microsoft.AspNetCore.ResponseCompression
• Microsoft.AspNetCore.Rewrite
• Microsoft.AspNetCore.Routing
• Microsoft.AspNetCore.Routing.Abstractions
• Microsoft.AspNetCore.Server.HttpSys
• 微软.AspNetCore.Server.IIS
• Microsoft.AspNetCore.Server.IISIntegration
• Microsoft.AspNetCore.Server.Kestrel
• Microsoft.AspNetCore.Server.Kestrel.Core
• Microsoft.AspNetCore.Server.Kestrel.Https
• Microsoft.AspNetCore.Server.Kestrel.Transport.Abstractions
• Microsoft.AspNetCore.Server.Kestrel.Transport.Sockets
• Microsoft.AspNetCore.Session
• Microsoft.AspNetCore.SignalR
• Microsoft.AspNetCore.SignalR.Core
• Microsoft.AspNetCore.StaticFiles
• Microsoft.AspNetCore.WebSockets
• Microsoft.AspNetCore.WebUtilities
• Microsoft.Net.Http.Headers

Answer 4

这有点奇怪。

对我来说，问题是因为“Microsoft.AspNetCore.Mvc”包。

我卸载了它并安装了“Microsoft.AspNetCore.Mvc.Core”。

我需要补充一点，我也安装了“Microsoft.AspNetCore.Mvc.Razor.RuntimeCompilation”。