After migrating from .NET Core 2.1 to .NET Core 3.1, publish has a problem

Question

After migrating my project from .NET Core 2.1 to .NET Core 3.1, everything works fine but when publishing the project, Iget this error:

System.Runtime.CompilerServices.Unsafe doesn't support netcoreapp3.1. Consider updating your TargetFramework to netcoreapp3.1 or later.

Hadst

Please show your project file. – Supinator

Is the .net core 3.1 there on machine? – Nannettenanni

yes, .net core 3.1 is on machine – Hadst

Answer 1

Try this first!

For anyone suddenly running into this error for seemingly no reason, the error message may be a red herring. You should try deleting all bin and obj folders first before anything else.

1. For each project in your solution, locate and delete the obj and bin folders (don't worry, they will be regenerated automatically).
2. Right-click the solution and click "Clean Solution"
3. Right-click your startup project and click "Rebuild"

For me, the problem occurred while attempting to publish, even though (a) no changes had taken place, (b) it worked the day before, and (c) I was actually using .NET 6.0!

After failing to fix the issue through any recommended solutions, I went ahead and actually removed the warning from the .targets file in the System.Runtime.CompilerServices.Unsafe package folder (i.e., I suppressed the error), but then the next package in the list started complaining about the same thing.

Solution

Deleting the bin/obj folders and cleaning the solution fixed the issue immediately.

Winburn

OMG, cleaning up the bin and obj directories was it for me. Thank you so much! – Longplaying

Answer 2

I resolved the problem after remove the tag <RuntimeIdentifier> from the publish profile.

Meneau

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Answer 3

The root cause of the issue for me is, one of the NuGet packages is referring to "Microsoft.Extensions.DependencyModel" v6.0.0. After downgrading the "Microsoft.Extensions.DependencyModel" NuGet to version 5.0.0 issue is resolved.

Please refer to the link for more info, https://github.com/dotnet/runtime/issues/62561

Taken

Answer 4

@@Morteza install System.Runtime.CompilerServices.Unsafe version 6.0.0 from NuGet into your project.

Install-Package System.Runtime.CompilerServices.Unsafe -Version 6.0.0

Brookes

it does not work – Hadst