Visual Studio 2017找不到命名空间系统

Question

In one of my projects, Visual Studio says it can't find namespace System and similar Microsoft standard assemblies. It also can't load other projects in the other solution that it depends on.

To clarify, it DOES build, but pretty much every line in that project which references another project has a squiggly red "error" underlining.

When loading this solution, or when trying to add a dependency to this project (by right clicking Dependencies and selecting 'Add Reference...', I get this message:

An element with the same key but a different value already exists. Key: Microsoft.CodeAnalysis.CSharp

The top of the csproj file is:

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

 <PropertyGroup>
    <TargetFramework>net462</TargetFramework>
    <NoWarn>$(NoWarn)</NoWarn>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
    <TypeScriptCompileBlocked>true</TypeScriptCompileBlocked>
  </PropertyGroup>

Answer 1

事实证明，在.csproj中两次引用了Microsoft.CodeAnalysis.CSharp程序集，并删除了重复项，从而解决了该问题。

Answer 2

I had this same problem few days back. Actually this problem occurs when you upgrade to Visual Studio 2017 and you try to run projects created on older version of VS.

1) First you have make the Target Framework equal for every module in the project.

2) Then you might have to upgrade Nuget packages with latest version for all modules.

3) Add missing references.

4) run VS as administrator, clean and build it again.

You will get the solution.