Error CS0579 Duplicate 'global::System.Runtime.Versioning.TargetFrameworkAttribute'

Question

When I build my application I get the following error

 Error  CS0579  Duplicate 'global::System.Runtime.Versioning.TargetFrameworkAttribute' attribute    MyUIApp
D:\MyUIApp\obj\Debug\netcoreapp3.1\.NETCoreApp,Version=v3.1.AssemblyAttributes.cs   4   Active

The following code is autogenerated in the obj/Debug/netcoreapp3.1 folder

// using System; using System.Reflection; [assembly: global::System.Runtime.Versioning.TargetFrameworkAttribute(".NETCoreApp,Version=v3.1", FrameworkDisplayName = "")]

I have a project file starting with

<Project Sdk="Microsoft.NET.Sdk.WindowsDesktop">
  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <OutputType>Library</OutputType>
    <SolutionDir Condition="$(SolutionDir) == '' Or $(SolutionDir) == '*Undefined*'">..\</SolutionDir>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
    <RestorePackages>true</RestorePackages>
    <UseWindowsForms>true</UseWindowsForms>
  </PropertyGroup>
  <PropertyGroup>

I can work around the issue by commenting out the contents of the file, but not by deleting the file.

Answer 1

The problem was about my folder structure : the test project was in the main project folder. Passing each side by side in the same repo solved the problem

MyProject
   src/MyProject.csproj
   tests/MyTestProject.csproj

Taken from Github issue : https://github.com/dotnet/core/issues/4837

Answer 2

I fixed this by deleting the obj and bin folders in each project directory. I then cleaned the solution and rebuilt. The rebuild succeeded.

Answer 3

This error can also happen if you accidentally copied an project file into another projects folder.

Answer 4

in my case (.NET 6.0); I just exclude the Properties folder from the project/solution.

Answer 5

I was able to solve this issue by getting a new clone of the project.

Answer 6

Add the following two lines to the <PropertyGroup>. This fixed it for me.

<PropertyGroup>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
    <GenerateTargetFrameworkAttribute>false</GenerateTargetFrameworkAttribute>    
</PropertyGroup>

Answer 7

Encountered this issue when working with AWS Lambda. Turns out I was switching branches, and some auto-generated folders did not get cleared after switching to new branch, and dotnet was picking them up for some reason. The easiest solution is to delete all local project folders, and check out clean version of the code again.

Answer 8

Try to delete obj folder from Project, delete it from SolutionExplorer instead of WindowExplorer.

Answer 9

From the many different kind of answers, it's clear that there could be different reasons for the same issue. In my case the solution definition file was the cause. I decided to delete and create a clean solution file.

1. Delete the .sln file
2. Create a blank .sln file, in the root of your project/solution:

dotnet new sln

3. For every C# project file in your solution, add it with the following command, for example:

dotnet add MyApplication.csproj

and for example:

dotnet add CustomPackages/MyLibrary.csproj

Then to make sure all previous build artefacts are cleaned up

dotnet clean

Answer 10

I had this kind of Errors in my Blazor Server project when I tried to add .NET Standard Class Library project in Visual Studio 2019.

Errors:

To fix this i tried following ways.

.csproj file Before

.csproj file After

Answer 11

Came across this problem dealing with MAUI. In my case, it was definitely caused by the folder organization. If the second project gets created inside the first one, everything breaks. Can't really think of a reason, I would say that it doesn't matter with regular Xamarin/Xamarin.Forms, but here we are.

Having each csproj + files in different folders does the trick.

Answer 12

Way down here, if you are like me and changing the project structure is not realistic you can use a variation of this:

https://helloglenn.me/blog/dotnet-clean-bin-obj/

insert this node into the xml of your csproj file

 <Target Name="SpicNSpan" AfterTargets="Test">
    <RemoveDir Directories="$(BaseOutputPath)" />
    <RemoveDir Directories="$(BaseIntermediateOutputPath)" /> 
  </Target>

I included it in both my normal csproj and test csproj to be safe, seems like it could just be in the test one though.

Answer 13

So i did encounter the same on a .NET 4.7 based solution, spent hours, only to find out a colleague of mine did include the obj and bin folders in the project! excluding them fixed the issue and that error went away.

hope this save someone a couple of hours.

Answer 14

I had this when my folder structure got messed up. I'm using Visual Studio 2019 and switched branches that has different folder structure. Some folders got added up in the file explorer and didn't get deleted even if I switched branches. All I did was to delete those folders that weren't part of my current branch and it worked.

Answer 15

I am having the same problem. As far as I can tell, the flag should prevent the auto-generation of assembly info. However, I can see this file in my obj directory:

.NETStandard,Version=v2.1.AssemblyAttributes.cs

It only contains the target version attribute. Maybe there is some other way of suppressing this attribute?

It seems like this might be a regression in .NET core 3.1.300. I was building with .NET core 3.1.200 and I didn't see this issue until I upgraded.

Answer 16

I encountered that issue, what I did is I deleted the .NETCoreApp,Version=v3.1.AssemblyAttributes.cs and then I ran VSCode as an administrator.

Answer 17

You just need to exclude the obj folder from the project/solution. If you don't know how to do this, add this to your .csproj or .vbproj or .whateverproj:

  <ItemGroup>
    <Compile Remove="obj\**" />
    <Content Remove="obj\**" />
    <EmbeddedResource Remove="obj\**" />
    <None Remove="obj\**" />
  </ItemGroup>

Answer 18

I would like to mention a different case here which causes the issue because nothing from the solutions worked in my case. When I clicked on the error, it took me to a file. This file was inside a folder, which was mistakenly moved from another project. I reverted it back to original position and it fixed the issue.

Answer 19

In my case the culprit was my test project so I had to go to my test folder > obj > Debug/net6.0 > .NETCoreApp,Version=v6.0.AssemblyAttributes.cs

and then commented this line

[assembly:global::System.Runtime.Versioning.TargetFrameworkAttribute(".NETCoreApp,Version=v6.0", FrameworkDisplayName = "")]

Answer 20

In my case I had a temp copy of folder with duplicated bin and obj directories... The solution was to remove the temp bin and obj that were duplicated.

Answer 21

This is an ancient topic, but I found it happens when I incorrectly setup my folders for Docker as well.

I needed to make sure that each project exists in the its own folder when building the Dockerfile or the same error occurs.

FROM mcr.microsoft.com/dotnet/sdk:7.0 AS build

WORKDIR /app

COPY ./ReferenceProject1/*.csproj /app/ReferenceProject1/
RUN dotnet restore /app/ReferenceProject1/ReferenceProject1.csproj

COPY ./MainProject/*.csproj /app/MainProject/
RUN dotnet restore /app/MainProject/MainProject.csproj

COPY . ./

WORKDIR /app/MainProject
RUN dotnet publish -c Release -o out

container
FROM mcr.microsoft.com/dotnet/aspnet:7.0

COPY --from=build /app/MainProject/out ./

EXPOSE 5000
EXPOSE 5001

ENTRYPOINT ["dotnet", "MainProject.dll"]

Answer 22

DELETE [assembly: global::System.Runtime.Versioning.TargetFrameworkAttribute(".NETCoreApp,Version=v6.0", FrameworkDisplayName = "")]

Answer 23

I was facing the same issue in my asp.net core 3.1 application right after I add the xUnit project to the solution. Ultimately, the main issue was because of that I selected the check box Place solution and project in the same directory as shown in the preceding image.

This should work in normal cases, and you will just consider this root directory as the Git repository (the .sln file and the .csproj will be in the same folder). But you will not be able to add a new project to this directory as you will get the error "Error CS0579 Duplicate 'global::System.Runtime.Versioning.TargetFrameworkAttribute'". So, to fix this error, we just have to follow the preceding steps.

1. Create a folder with the same name in the .sln file
2. Move all the project-related files to that directory
3. Open your .sln file with any code editor
4. Edit the Project references.
5. Make sure that your .sln file is in the root directory

This is how your project file references may look like now.

Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "WebApplication2", "WebApplication2\WebApplication2.csproj", "{027937D8-D0E6-45A4-8846-C2E28DA102E6}"
EndProject 

Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "WebApplication2.Tests", "WebApplication2.Tests\WebApplication2.Tests.csproj", "{AD4C6C31-F617-4E76-985A-32B0E3104004}" 
EndProject

That's it. Just reload your solution and happy coding!.

Answer 24

I was also getting this error in VS Code and the following fixed it.

I have a project/solution with three projects within in.

• netstandard2.1
• netstandard2.1
• netcoreapp3.1

I added the following line to each of the *.csproj files within the <PropertyGroup> section:

<GenerateTargetFrameworkAttribute>false</GenerateTargetFrameworkAttribute>

Full example

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

  <PropertyGroup>
    <TargetFramework>netstandard2.1</TargetFramework>
    <GenerateTargetFrameworkAttribute>false</GenerateTargetFrameworkAttribute>
    <GenerateAssemblyInfo>false</GenerateAssemblyInfo>
  </PropertyGroup>

</Project>

After doing the above you might need to clean /bin and /obj folders for each project.

This article pointed me in the right direction though nothing online that I found mentioned the attribute above. I just guessed and it worked!

Answer 25

I commented out the offending attribute

// obj/Debug/netcoreapp3.1/.NETCoreApp,Version=v3.1.AssemblyAttributes.cs

using System;
using System.Reflection;
//[assembly: global::System.Runtime.Versioning.TargetFrameworkAttribute(".NETCoreApp,Version=v3.1", FrameworkDisplayName = "")]

Answer 26

I experienced this on a build pipeline in Azure Devops. I was using a local agent to run the pipeline on (my own machine). It appears that there was code in the working directory that was causing this conflict, and by default, the agent doesn't clean the working directory before starting the pipeline process.

The fix was to delete the contents of the working directory on the agent. I did this by selecting the option to clean the working directory: