How can Autofac and an Options pattern be used in a .NET 5 console application?

Question

I am trying to use an option pattern with Autofac and every attempt has just resulted in errors.

What I've tried:

1. Using the ConfigurationBuilder to retrieve an IConfiguration/IConfigurationRoot.
2. Register an instance of TestSectionOptions using the IConfiguration/IConfigurationRoot that was created before: builder.Register(c => config.GetSection("TestSection").Get<TestSectionOptions>());
3. Trying to inject it via constructor injection:

private readonly TestSectionOptions _options;
    
public DemoClass(IOptions<TestSectionOptions> options)
{
    _options = options.Value;
}

I'm getting following error:

DependencyResolutionException: None of the constructors found with 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type 'DemoApp.DemoClass' can be invoked with the available services and parameters: Cannot resolve parameter 'Microsoft.Extensions.Options.IOptions1[DemoApp.TestSectionOptions] options' of constructor 'Void .ctor(Microsoft.Extensions.Options.IOptions1

Of course I tried other types of registration, but none of them worked. I also know that I can simply bind the configuration file to a class, which I then register and inject without the IOptions<> part. But that would no longer correspond exactly to the option pattern, would it? Even if it doesn't make a big difference, I'd still like to know why it doesn't work and how I could get it to work.

Answer 1

The problem is that this IOptions type should be registerd somewhere.

You can see e.g. this article. There is an example

public void ConfigureServices(IServiceCollection services)
{
    services.Configure<PositionOptions>(Configuration.GetSection(
                                        PositionOptions.Position));
    services.AddRazorPages();
}

So, somewhere inside Configure extension method it registers types for options, among others IOptions<>.

So, in your case you either have to do this explicitly, like

builder.Register(c => Options.Create(config.GetSection("TestSection").Get<TestSectionOptions>()))

This will register IOptions

or, you can create an empty service collection, then call Configure method on it, and then copy all registrations to autofac builder - there is Populate method from the package "Autofac.Extensions.DependencyInjection"

https://autofac.org/apidoc/html/B3162450.htm