Visual Studio Intellisense 无法识别动态关键字，即使项目已构建。我试图添加对 System.Core 的引用来解决问题。我收到此错误:

A reference to 'System.Core' could not be added. This component is already automatically referenced by the build system.

我注意到我的其他项目引用了 System.Core。我的修复是通过直接编辑 csproj 来添加它，这修复了 Intellisense。是什么赋予了？为什么 VS 不让我通过 UI 来做？

最佳答案

在做了一些研究之后，我能找到的只是以前的 SO 票和一些博客，最终他们都使用了与您相同的解决方法。然后我发现有人在 2011 年在 Microsoft Connect 上提交的错误报告(现在仅在 Wayback Machine 上可用，或者在 my blog 上以更易读的格式提供)，最终在一年或所以后来由 MSFT 员工 Chuck England 提供。

TL;DR - 由于 multi-targeting，团队做出了一个有意识的决定添加到 VS2008 的功能(能够更改项目的 .NET Framework 目标)。

由于目标框架需要“System.Core”，删除它会阻止构建(据我所知查克的回答)，他们决定强制引用它，即使你实际上并没有在引用列表中看到它。

有点“安全”黑客，你可能会说，有一个不良的副作用，当你试图再次将它添加到引用时它会抛出该错误，并且你最终需要直接编辑项目文件。

Microsoft Connect 已于 2018 年停用，但这里是原始线程的相关部分:

Yes, the experience is not great. Since System.Core is required, you should never remove it. We fixed this by adding it for you even if you remove the reference. [A]s the message you saw indicates, System.Core is implicitly referenced. So, the fact that you have removed it, other than physically removing a line from the project file, has not changed the build in any way.

There are legitimate scenarios where you might want to be able to do this, but it is a very edgy corner case. However, we should blindly ignore the fact that when you add it back an error is generated. A lot of this was imposed on us by previous versions which did not understand multi-targeting, and simply did not get cleaned up.

[Y]ou can manually add it back by right-clicking on the project node and selecting Unload. Right-click on the project node again and select Edit. In the editor, copy another reference line (for example, the one for "System") and paste it below the original reference inside the same ItemGroup. Change the reference name to "System.Core". Right-click on the project node and select Reload. Choose "yes" for question to save and reload.

VS2008 did not handle multi-targeting correctly. It would allow you to build things that were not legitimate. With VS2010, we have tried very hard to make sure that if it builds for the target framework, then it will run on the target framework. I can't say I know of any places where this is not true.

We can't go back to the VS2008 way, as it does not understand multi-targeting. Nor did it understand true "profiles", like the Client Profile of the .NET 4.0 framework. In fact, the issue you are seeing is because the VS2008 system was upgraded to handle multi-targeting, and it is the new set of rules that are rejecting the reference.

In this case, we build even though you removed a reference. You might say, but it should not have built. But, it will run on the targeted framework, and hence should have built. The fact that we have added a "required" refererence for you is somewhat of a broken experience in how it was developed.

We really just did not catch this early enough, and with a really solid understanding of how we could fix it to get a fix prior to our release. But, the fact that you should always reference, and hence never remove "System.Core", made this a Won't Fix, since this is not something that 99% of customers would ever do.

关于c# - 在构建系统已引用 System.Core 时添加对它的引用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25394979/