Why installation of .NET SDK 5.0 (after SDK 2.1 was installed) affected my solution with only netstandard2.0 or netcoreapp2.1 projects?

Question

Why installation of additional .NET SDK 5.0 (after SDK 2.1 was installed already) affected my solution, all projects of which have TargetFramework either netstandard2.0 or netcoreapp2.1? I expected, that I need only SDK 2.1. And installation of SDK 5.0 (I thought) should not affect this solution.

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Below I will say about all effects that appeared in my solution after I installed .NET SDK 5.0

1. Projects appearance
So, as I said, I have a Visual Studio solution with some projects in it. All the projects have a TargetFramework either netstandard2.0 or netcoreapp2.1. I installed .NET SDK 2.1.818 (from here) (it was the only installed SDK at that moment).

1.a) When I opened the solution all dependencies had yellow warning sign. But it was no warnings in an "Error list":

Then I installed one more SDK: .NET SDK 5.0.408 (from here)
And all this signs are gone.

1.b) Also projects properties was displayed different:
Left - only SDK 2.1 is installed, Right - both 2.1 & 5.0 are installed

My question is - Why installing of SDK 5 affects the solution, all projects of which have a TargetFramework either netstandard2.0 or netcoreapp2.1?
May be it's caused somehow by the fact, (f.e.) that one of the nuGet-dependencies - Microsoft.CSharp (4.7.0) has one of it's dependencies - .NETCore 5.0:

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2. Builds difference
But the main question is that build artifacts are not equal when I built the solution while only SDK 2.1 was installed compared with another build after SDK 5.0 was installed also. I compared build artifacts and the main differences are (I will call these two builds "2.1 build" and "5.0 build":

2.a) deps.jsons:

• All assemblies deps.jsons had runtimeTarget->signature:
  -2.1 build: NOT empty
  -5.0 build: empty
• One of my assemblies deps.json had additional block about a couple of its dependency projects in "targets"->".NETCoreApp,Version=v2.1" and in "libraries" sections in 2.1 build, but had NOT this block at 5.0 build
  !!: And in my case this difference caused another behaviour of the program

2.b) All jsons in projects obj folders (e.g. project.assets.json) had different:

• addersses of nuget:
  -2.1 build: www.nuget.org/api/v2
  -5.0 build: api.nuget.org/v3/index.json
• • And different "project"->"frameworks"->"netcoreapp2.1"->"imports" and "runtimeIdentifierGraphPath" sections:
    Left - 2.1 build (only SDK 2.1 is installed), Right - 5.0 build (both 2.1 & 5.0 are installed)
    

I'll repeat my question:
So, help me please to understand, why installation of additional SDK 5.0 had such effect? I expected, as all projects of solution have TargetFramework either netstandard2.0 or netcoreapp2.1, I need only SDK 2.1. And installation of SDK 5.0 (I expected) should not affect this solution.

Answer 1

Hi @SaShka-K1 ,

In previous versions, .NET Core was the framework for building cross-platform applications, while .NET Standard was the specification for sharing code. Developers need to choose to use . NET Core as the runtime framework for your application and choose a . The NET Standard version serves as the target framework for shared code.

However, starting with .NET 5, Microsoft decided to merge .NET Core and .NET Standard into a single .NET platform. This way, you can use it simultaneously in a single project. .NET all the features, and no longer need to choose different target frameworks for applications and shared code.

So installing the .NET 5 SDK will affect both of your projects.

And the .NET 5 SDK is forward compatible with some .NET Framework versions, enabling you to work in the . These versions of class libraries and applications are used in the NET 5 development environment.

Best Regards.

Jiachen Li

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