Type 'Object' is defined in an assembly that is not referenced (NET Standard 2.0/.NET Framework 4.6.1) [duplicate]

Question

I'm using the .NET Standard 2.0 preview, on which my Class Libraries are based.

After having trouble with a few NuGet packages, especially regarding archive extraction, I decided to migrate my .NET Core 2.0 Console projects back to the .NET Framework 4.6.1.

The .NET Framework 4.6.1 is supposed to implement the .NET Standard 2.0 specification - according to different sources. Especially the dotnet/standard GitHub Repo.

Unfortunately, the migration to the .NET Framework resulted in the following errrors throughout all of .NET Framework Console projects:

Error CS0012 The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51'.

Where Object can be anything: Enum, Task, ...

How would I reference .NET Standard 2.0 class libraries with .NET Framework (4.6.1) without getting such errors?

Answer 1

Try to add a reference to netstandard in web.config as below:

<system.web>     <compilation debug="true" targetFramework="4.7.1">        <assemblies>           <add assembly="netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51"/>        </assemblies>      </compilation>  </system.web> 

Answer 2

I had this problem even after using the latest 2.0, and VS 15.3. However, I think my problem was different. After upgrading from Core 1.1, to 2.0, for some reason, my .web's .csproj had <RuntimeFrameworkVersion>1.1.2</RuntimeFrameworkVersion>. Which prevented the project from targeting the correct 2.0 version.

My class libraries (.Layer) projects had <NetStandardImplicitPackageVersion>1.6.1</NetStandardImplicitPackageVersion>.

I deleted both of them and my project finally started using 2.0 and everything went fine after.