Configuration pattern and ConfigureServices

ServiceWithOptionsExample.cs

// I have a service that needs to be initialized with a FooOptions and then added to the DI container.
// I also want to have IOptions<FooOptions> in the DI container to allow injection in other methods.
// How should I write my AddFoo extension method to support this?

public void ConfigureServices(IServiceCollection services)
{
    services.AddFoo(fooOptions => 
    {
        configuration.GetSection("FooOptions").Bind(fooOptions)
        fooOptions.param = "override";
    });
}

namespace Microsoft.Extensions.DependencyInjection
{
    public static class MyFooExtensions
    {
        public static IServiceCollection AddFoo(this IServiceCollection services,
          Action<FooOptions> setupOptions)
        {
            services.Configure<FooOptions>(setupOptions);
            services.AddSingleton<IFoo>(sp =>
            {
                var options = sp.GetRequiredService<IOptions<FooOptions>>();
                return new FooFactory(options.Value);
            };
            return services;
        }
    }
}

Yeah, unfortunately, you're kinda screwed in that case 🙁

Basically, requiring concrete IOptions<> in the AddFoo() method is not the recommended pattern, for exactly this reason! But if that's what it is, there's not a lot you can do...

In the few cases I've run into this I have just manually bound the configuration instead. It's not ideal, and means you can't use the full options pattern, but it may do:

public void ConfigureServices(IServiceCollection services)
{
    var fooOptions = new FooOptions();
    Configuration.Bind("FooOptions", fooOptions);

    services.AddFoo(fooOptions);
}

Rich Strahl has a nice post about this here: https://weblog.west-wind.com/posts/2017/dec/12/easy-configuration-binding-in-aspnet-core-revisited

@andrewlock, argh I'm an idiot. The signature is FooFactory(FooOptions options), not an IOptions<FooOptions>, if that helps.

I think I've revised the AddFoo() code in a way that should work now?? Or not...
I found a helpful blog post from @TsuyoshiUshio that gave me the idea:
https://medium.com/@tsuyoshiushio/servicecollection-di-with-optional-settings-fc4ee46984d1

@ericsampson That looks very similar to my suggestion, with a slight tweak. I don't think your suggestion will quite work though. Try this instead:

public void ConfigureServices(IServiceCollection services)
{
    services.AddFoo(fooOptions => 
    {
        configuration.GetSection("FooOptions").Bind(fooOptions)
        fooOptions.param = "override";
    });
}

Thanks again @andrewlock, I'll give this all a go. Really appreciate the help :)