'Could not load type 'Microsoft.AspNetCore.Mvc.MvcJsonOptions' from assembly 'Microsoft.AspNetCore.Mvc.Formatters.Json, Version=3.0.0.0

user_10851213 0
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I'm using netstandard2.1 library in my netcoreapp3.0 web application. When adding my service in Startup, I'm getting the below error:

'Could not load type 'Microsoft.AspNetCore.Mvc.MvcJsonOptions' from assembly 'Microsoft.AspNetCore.Mvc.Formatters.Json, Version=3.0.0.0

I'm also using some features from Microsoft.AspNetCore.Mvc 2.2.0 package in my class library.

Here is my library .csproj,

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

  <PropertyGroup>
    <TargetFramework>netstandard2.1</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.Mvc" Version="2.2.0" />
  </ItemGroup>

</Project>

Here is my ServiceExtensions class from my library,

public static class ServiceExtensions
{
    public static IMvcBuilder AddMyLibrary(this IMvcBuilder builder)
    {
        builder.Services.TryAddSingleton<IHttpContextAccessor, HttpContextAccessor>();
        builder.AddJsonOptions(options =>
        {
            options.SerializerSettings.ContractResolver = new DefaultContractResolver();
        });
        builder.Services.ConfigureOptions<ConfigureLibraryOptions>();

        return builder;
    }
}

Here is my ConfigureLibraryOptions class,

public class ConfigureLibraryOptions : IConfigureOptions<MvcOptions>
{
    public void Configure(MvcOptions options)
    {
        options.ModelBinderProviders.Insert(0, new CustomBinderProvider());
    }
}

Here is the ConfigureServices from Startup,

services.AddControllersWithViews().AddMyLibrary();

Please help on why I'm getting this error and assist on how to solve this?

.net-standard-2.1 asp.net-core-3.0 asp.net-core-mvc json.net c#
6 Answers

I'm not sure if this solves OP's problem, but this error also occurs when you use Swashbuckle 4 in .Net Core 3. The solution is to use Swashbuckle 5. (use command install-package Swashbuckle.AspNetCore) to have in .csproj

<PackageReference Include="Swashbuckle.AspNetCore" Version="5.0.0" />

Then you'll need to upgrade it in Startup.cs. Generally that involves prefixing classes that don't compile with OpenApi e.g.

options.SwaggerDoc("v1" new Info ...

becomes

options.SwaggerDoc("v1", OpenApiInfo

Also OpenApiSecurityScheme becomes ApiKeyScheme

See also docs at https://github.com/domaindrivendev/Swashbuckle.AspNetCore

user_407830

netstandard2.1 to netcoreapp3.0 MvcJsonOptions -> MvcNewtonsoftJsonOptions

public IServiceProvider ConfigureServices(IServiceCollection services)
{
            //MVC
            services.AddControllersWithViews(options =>
            {
            }).AddNewtonsoftJson();

            services.PostConfigure<MvcNewtonsoftJsonOptions>(options => {
                options.SerializerSettings.ContractResolver = new MyCustomContractResolver()
                {
                    NamingStrategy = new CamelCaseNamingStrategy()
                };
                options.SerializerSettings.ReferenceLoopHandling = Newtonsoft.Json.ReferenceLoopHandling.Ignore;
            });
}
user_51375590

The reason why you're getting the error is because MvcJsonOptions was removed in .NET Core 3.0; you can read more about the breaking changes here.

user_6330980
user_134665850

When you config "Swashbuckle.AspNetCore", needed for configuring ApiKeyScheme become to OpenApiSecurityScheme it is changing the scheme from

 c.AddSecurityDefinition("Bearer", new ApiKeyScheme { In = "header", Description = 
 "Please enter JWT with Bearer into field", Name = "Authorization", Type = "apiKey" 
 });
 c.AddSecurityRequirement(new Dictionary<string, IEnumerable<string>> {
 { "Bearer", Enumerable.Empty<string>() }, });

To

    c.AddSecurityDefinition("Bearer", new OpenApiSecurityScheme
{
    Description =
        "JWT Authorization header using the Bearer scheme. \r\n\r\n Enter 'Bearer' [space] and then your token in the text input below.\r\n\r\nExample: \"Bearer 12345abcdef\"",
    Name = "Authorization",
    In = ParameterLocation.Header,
    Type = SecuritySchemeType.ApiKey,
    Scheme = "Bearer"
});

c.AddSecurityRequirement(new OpenApiSecurityRequirement()
{
    {
        new OpenApiSecurityScheme
        {
            Reference = new OpenApiReference
            {
                Type = ReferenceType.SecurityScheme,
                Id = "Bearer"
            },
            Scheme = "oauth2",
            Name = "Bearer",
            In = ParameterLocation.Header,

        },
        new List<string>()
    }
});
user_100631520
user_55360060
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