NU1202: Package 与 netcoreapp2.0 (.NETCoreApp,Version=v3.0) 不兼容

Question

I have created a new Solution where I have added a few projects. They are either ASP.NET Core, Class Libraries or NUnit Test projects. Both the ASP.NET and test projects experience the same errors, where I cannot add packages to the projects. The error I get is NU1202, a few examples:

Error   NU1202  Package Newtonsoft.Json 10.0.1 is not compatible with netcoreapp3.0 (.NETCoreApp,Version=v3.0). 
Package Newtonsoft.Json 10.0.1 does not support any target frameworks.  

Error   NU1202  Package System.AppContext 4.1.0 is not compatible with netcoreapp3.0 (.NETCoreApp,Version=v3.0). 
Package System.AppContext 4.1.0 supports:
  - monoandroid10 (MonoAndroid,Version=v1.0)
  - monotouch10 (MonoTouch,Version=v1.0)
  - netstandard (.NETStandard,Version=v0.0)
  - xamarinios10 (Xamarin.iOS,Version=v1.0)
  - xamarinmac20 (Xamarin.Mac,Version=v2.0)
  - xamarintvos10 (Xamarin.TVOS,Version=v1.0)
  - xamarinwatchos10 (Xamarin.WatchOS,Version=v1.0)

These errors comes after I've tried to add Swashbuckle.AspNetCore to my ASP.NET project.

I have tried to clear the caches, checked that the NuGet version is up to date (it is 5.3). I don't know what else I can do. Any suggestions?

Edit: I have tried downgrading, even to netcoreapp2.0. But this does not solve the problem

To be clear, I have only added Swashbuckle.AspNetCore, not Newtonsoft.Json or or System.AppContext, however that is still the error messages i get

Answer 1

You have two options:

1. Use Swashbuckle.AspNetCore

or

2. Downgrade your project from .NET Core 3.0

Option 1: Use Swashbuckle.AspNetCore

Since you're using a .NET Core 3.0 project, you can use the Swashbuckle NuGet Package that is specifically designed for .NET Core, Swashbuckle.AspNetCore .

Option 2: Downgrade Project

You'll need to downgrade your project from .NET Core 3.0 to .NET Core 2.2.

In the csproj file, change the TargetFramework version from netcoreapp3.0 to netcoreapp2.2 .

Here's an example csproj file that uses .NET Core 2.2:

<Project Sdk="Microsoft.NET.Sdk.Web">
    <PropertyGroup>
        <TargetFramework>netcoreapp2.2</TargetFramework>
    </PropertyGroup>
</Project>

Answer 2

If you are installing from NuGet Packages, choose the latest stable version from the version dropdown and then install. It worked for me:)