Visual Studio 2017 不会在 .NET Standard 库中加载 .NET Framework 引用

Question

I've installed Visual Studio 2017. I have a class library in the new .NET Standard format, which is able to be used by both .NET Framework and .NET Core. But when I go to Add… Reference… Assemblies Framework , Visual Studio spins for a long time and then says,

No Framework assemblies were found on the machine.

(This machine also has Visual Studio 2015 installed, as well as .NET 4.6.1.)

How do I resolve this?

My .csproj file currently looks like this:

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

  <PropertyGroup>
    <TargetFrameworks>net461;netstandard2.0</TargetFrameworks>
  </PropertyGroup>

  <ItemGroup>
    <Compile Remove="Utility\EncryptionUtility.cs" />
  </ItemGroup>

  <ItemGroup>
    <Folder Include="Utility\" />
  </ItemGroup>

  <ItemGroup>
    <Reference Include="System.Runtime.Caching" />
  </ItemGroup>

</Project>

Changing the target framework from:

<TargetFramework>netstandard2.0</TargetFramework>

to

<TargetFrameworks>net461;netstandard2.0</TargetFrameworks>

Allows me to finally add a reference to System.Runtime.Caching , but it has a yellow warning icon in the IDE when expanding the references. It is included under both .NET 4.6.1 and .NET Standard in the collapsible sections, with the reference under Standard also shows the warning icon. Builds fail because the IDE claims that the reference is still missing.

Answer 1

When multi-targeting both .NET Framework and .NET Core/.NET Standard you will almost certainly need to use MSBuild Conditions to prevent .NET Framework references from bleeding over into .NET Core/.NET Standard.

MSBuild conditions have been around for quite some time, but there is no support in Visual Studio to add them, you have to manually edit your .csproj file.

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

  <PropertyGroup>
    <TargetFrameworks>net461;netstandard2.0</TargetFrameworks>
  </PropertyGroup>

  <ItemGroup>
    <Compile Remove="Utility\EncryptionUtility.cs" />
  </ItemGroup>

  <ItemGroup>
    <Folder Include="Utility\" />
  </ItemGroup>

  <ItemGroup Condition=" '$(TargetFramework)' == 'net461' ">
    <Reference Include="System.Runtime.Caching" />
  </ItemGroup>

</Project>

Also note that once you do this, there are no guarantees it will work right to add a NuGet or other assembly reference using Visual Studio - you may need to do manual cleanup every time in the .csproj file to ensure the reference is added to the right conditional section. You are probably better off adding references by hand-editing the file every time.

Answer 2

On my side, I've tried all the solution presented before but the solution was simply install NuGet package for Microsoft.CSharp.

After installation just clean the project and restart your IDE.

Answer 3

Try to change order of TargetFrameworks inside your .csproj.

From

<TargetFrameworks>netstandard2.0;net461</TargetFrameworks>

To

<TargetFrameworks>net461;netstandard2.0</TargetFrameworks>

Answer 4

当我在仅存在 4.7.2 的全新安装 PC 上打开针对 4.7.1 的解决方案时，这发生在我身上

Answer 5

As an alternative, you can use the .NET Standard Library from Nuget Package Manager to handle this issue:

The message in the Add Reference window for .NET Framework is expected. When you create a .NET Standard library, the NETStandard.Library metapackage is automatically referenced during project creation. It is a set of standard .NET APIs that are recommended to be used and supported together. This includes all of the APIs in the NETStandard.Platform package, plus additional libraries that are core to .NET, but built on top of NETStandard.Platform .

This means we don't need to need add references individually.

Answer 6

只需为相应的框架安装 .NET Framework 开发人员包，它就可以正常工作。