How to resolve package reference issue in NetStandard 2.0 library used by Framework 4.8?

Question

I have the dreaded 'Could not load file or assembly' and this time I ran out of options to fix it, hope you are smarter.

My (simplified) solution is this:

• Winforms.exe, Framework 4.8. This references:
• Client.dll, .Net Standard 2.0 which uses
• IdentityModel.OidcClient 5.0.0 which uses
• System.Text.Json

Since Client.dll is not .Net Core 5.0, I added System.Text.Json as a NuGet package. This leads to the following exception when calling RefreshTokenAsync on OidcClient:

System.IO.FileLoadException: 'Could not load file or assembly 'System.Text.Json, Version=5.0.0.2, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)'

I tried a couple of things but none have worked so far:

1. Add the closest version to 5.0.0.2 of System.Text.Json I could find (5.0.0, 5.0.1) to Client.dll, issue remains.

2. Add the latest version to 5.0.0.2 of System.Text.Json I could find (6.0.1) to Client.dll, issue remains.

3. Add a package redirect to Winforms.exe (even though Generate Auto Redirects = true):

    <dependentAssembly>
        <assemblyIdentity name="System.Text.Json" publicKeyToken="cc7b13ffcd2ddd51" culture="neutral"/>
        <bindingRedirect oldVersion="5.0.0.2" newVersion="6.0.1"/>
    </dependentAssembly>
   

No dice

4. Tried adding the NuGet (all different versions) to WinForms.exe, with or without redirect. Issue remains.

I'm not sure how to fix this anymore, any takers? Thanks so much in advance.

Answer 1

I did something similar with EF Core and EF6. Inside cproj add a condition:

<ItemGroup Condition=" '$(TargetFramework)' == 'net48' ">
    <PackageReference Include="System.Text.Json" Version="5.0.0"></PackageReference>
</ItemGroup>

Then use preprocessor directives to load the assembly:

#if NET48
using System.Text.Json;
#endif