How does Visual Studio picks up the current framework?

Question

I started with a net6.0 project. And decided to provide netstandard2.0 as internal nuget output for the older supported builds.

Replaced <TargetFramework>net6.0</TargetFramework> with <TargetFrameworks>net6.0;netstandard2.0</TargetFrameworks> in the .proj file. Now have this

The problem though is usage of the nullable reference types. net6.0 and netstandard2.0 are using different language versions

I understand that I would have to do one of these

• Downgrade the language for net6.0
• Create separate projects with certain common files and other separate files
• Use conditional compilation

And I tried the conditional compilation

And it shows that current active framework is netstandard2.0. I was wondering, how to change that? I added symbols in "Conditional compilation symbols" on the project level, for "Debug and net6.0 Custom symbols". And I was able to switch that way. Now, I set the symbols so that netstandard2.0 is active. I rebuilt and what I see - it compiled for bin\Debug\net6.0 but there is nothing in bin\Debug\netstandard2.0. And also I get error -

Error CS8630 Invalid 'nullable' value: 'Enable' for C# 7.3. Please use language version '8.0' or greater. projectName (net6.0) C:\DEV\Components\projectName\CSC 1 Active

Not a single file has error inside. All references/packages seem resolving fine. I removed all net6.0-specific pieces in code files. Need some advise here. Thanks

Answer 1

In multi-target projects VS allows switching between the targets for intellisense and syntax highlighting - there is dropdown on the top left of the text editor (I use .NET 7 since I don't have .NET 6 installed):

For the JetBrains Rider users the same is possible by selecting the framework at the bottom of text editor:

Also in my reproducer I have added the conditional attribute to the Nullable element in the .csproj:

<PropertyGroup Condition="'$(TargetFramework)' == 'net7.0'">
    <Nullable>enable</Nullable>
</PropertyGroup>

For only nullable you can do it also inline:

<Nullable Condition="'$(TargetFramework)' == 'net7.0'">enable</Nullable>