Could not load type 'Microsoft.AspNetCore.Mvc.MvcJsonOptions' from assembly 'Microsoft.AspNetCore.Mvc.Formatters.Json while updgrading .net core 2.2 to 8.0 or 3.1

Question

Hi All While upgrading .Net core 2.2 project to .Net 8.0. I am getting below error. I am using upgrade assistant from Visual studio 2022.

(Same issue if I am upgrading to 3.2 version)

Application startup exception: System.TypeLoadException: Could not load type 'Microsoft.AspNetCore.Mvc.MvcJsonOptions' from assembly 'Microsoft.AspNetCore.Mvc.Formatters.Json, Version=8.0.0.0, Culture=neutral, PublicKeyToken=adb9793829ddae60'.

at System.Signature.GetSignature(Void* pCorSig, Int32 cCorSig, RuntimeFieldHandleInternal fieldHandle, IRuntimeMethodInfo methodHandle, RuntimeType declaringType)

at System.Reflection.RuntimeConstructorInfo.<get_Signature>g__LazyCreateSignature|21_0()

at System.Reflection.RuntimeConstructorInfo.GetParametersNoCopy()

at System.Reflection.RuntimeConstructorInfo.GetParameters()

at Microsoft.Extensions.Internal.ActivatorUtilities.CreateInstance(IServiceProvider provider, Type instanceType, Object[] parameters)

at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.ReflectionMiddlewareBinder.CreateMiddleware(RequestDelegate next)

at Microsoft.AspNetCore.Builder.ApplicationBuilder.Build()

at Microsoft.AspNetCore.Hosting.WebHost.BuildApplication()

I have upgraded to nuget package Microsoft.AspNetCore.Mvc.NewtonsoftJson - 8.0.2

Also tried adding below code in startup.cs  services.AddMvc(options => options.EnableEndpointRouting = false)

 .AddNewtonsoftJson();

and

       services.AddControllers()

  .AddNewtonsoftJson();  I am not sure why it is still looking for 2.2 version old nuget package and assembly Microsoft.AspNetCore.Mvc.MvcJsonOptions.

When I tried searching old Microsoft.AspNetCore.Mvc.MvcJsonOptions assembly in project folder, I found in test project in bin\Debug\net8.0\refs folder. Tried to delete it but it is adding it again on build.

Answer 1

the Microsoft.AspNetCore.Mvc.Formatters.Json is deprecated, and should not be used with .net 8 applications. remove the package from the project file. You may have another obsolete package that uses it.