Could not load file or assembly 'System.Runtime.Loader' for adding application parts into MVC

Question

I'm trying to load application parts into an ASP.NET Core 2.0 MVC appication by using the System.Runtime.Loader package but it won't let me.

The error message says:

FileNotFoundException: Could not load file or assembly 'System.Runtime.Loader, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.

In the Startup.cs I use it like this (it should just be proof of concept that this works so I can move it into a dedicated class or an extension):

services
    .AddMvc()
    .ConfigureApplicationPartManager(apm =>
    {
        var parts = Directory.GetFiles(_rootPath, "*.Part.*");
        foreach (var part in parts)
        {
            apm.ApplicationParts.Add(new AssemblyPart(AssemblyLoadContext.Default.LoadFromAssemblyPath(part)));
        }
    });

The package I installed has the version 4.3.0 and I'm using it in an ASP.NET Core 2.0 with .NET 4.6.2 project.

I thought maybe assembly-binding would help so I added a runtime configuration to the app.config

  <runtime>
    <gcServer enabled="true"/>
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <dependentAssembly>
        <publisherPolicy apply="no"/>
        <assemblyIdentity name="System.Runtime.Loader" publicKeyToken="b03f5f7f11d50a3a" culture="en-US"/>
        <bindingRedirect oldVersion="4.3.0.0" newVersion="4.0.0.0"/>
      </dependentAssembly>
    </assemblyBinding>
  </runtime>

but this didn't help. I also specified a range like 1.0.0.0-5.0.0.0 but this didn't work either.

The stack trace that IE ouputs is this:

WebApiProject.Startup.<ConfigureServices>b__8_1(ApplicationPartManager apm)
Microsoft.Extensions.DependencyInjection.MvcCoreMvcBuilderExtensions.ConfigureApplicationPartManager(IMvcBuilder builder, Action<ApplicationPartManager> setupAction)

WebApiProject.Startup.ConfigureServices(IServiceCollection services) in Startup.cs
- 
38.        public IHostingEnvironment Environment { get; }
39.
40.        // This method gets called by the runtime. Use this method to add services to the container.
41.        public void ConfigureServices(IServiceCollection services)
42.        {
43.            // Add framework services.
44.            services
45.                .AddMvc()
...
50.                .ConfigureApplicationPartManager(apm =>


System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()

Microsoft.AspNetCore.Hosting.ConventionBasedStartup.ConfigureServices(IServiceColection services)

Microsoft.AspNetCore.Hosting.Internal.WebHost.EnsureApplicationServices()

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

In the output folder there are a lot of different System.Runtime.* files but none of them is named System.Runtime.Loader. Maybe this is the problem but where is this file? I searched the packages but there is no such .dll so why is VS trying to load it?

---

Update

Oh, great. I found the package. NuGet did not install it as usual into the packages folder of the soulution but instead it was here:

c:\Users\%USER%\.nuget\packages\system.runtime.loader\4.3.0\lib\

Sadly there is no version net462. The folder contains an empty file named: _

There are couple of other folders but there is only one .dll there:

MonoAndroid10\
MonoTouch10\
net462\
netstandard1.5\ <-- System.Runtime.Loader.dll
xamarinios10\
xamarinmac20\
xamarintvos10\
xamarinwatchos10\

Why does this even install? How is it possible that I can use the types in code but the *.dll fails to load even if I copy it to the output folder? Is this even supposed to work in a project that mixes .net core and the old framework?

---

Is there anything else I can do?

Answer 1

See https://github.com/dotnet/corefx/issues/22142

The TLDR is that System.Runtime.Loader is not supported for .Net Framework

You will have to use Assembly.Load() instead