Autofac Parameter injection

Question

I am misunderstanding the Autofac documentation on passing parameters to a Resolve method. The following is a minimalistic example of what I mean:

Example

https://dotnetfiddle.net/fz5eTp

public static void Main()
{
  var cb = new ContainerBuilder();
  cb.RegisterType<A>();
  cb.Register<B>((c, p) => new B(p.TypedAs<C>()));
  using (var c = cb.Build())
  {
    // works
    c.Resolve<B>(TypedParameter.From(new C()));
    // fails
    c.Resolve<A>(TypedParameter.From(new C()));
  }
}
public class A { public A(B b) { } }
public class B { public B(C c) { } }
public class C { }

Expected

I expected the TypedParameter to get passed down to B class.

Unfortunately the Exception message "Sequence contains no elements" suggests that no parameter was passed down.

Question

How can I pass parameters (only known at Resolve time) down to lower level constructors? Or in this specific example, how do I pass a C parameter down to B, when resolving a A.

Answer 1

Option1

The simplest way I can think of is to divide the resolving process into two steps:

First you can resolve the B by the specified known C value on run time, store it in a myB reference value:

B myB = c.Resolve<B>(TypedParameter.From(new C()));

And then pass myB value to the A resolver:

A myA = c.Resolve<A>(TypedParameter.From(myB));

You can find a full working example in my GitHub (with output).

Option2

If you like to write a one line of code on resolve time you will need to modify the register of A and B with:

cb.Register<A>((c, p) =>
{
    B myB = c.Resolve<B>(p);
    return new A(myB);
});
cb.Register<B>((c, p) => {
    C myC = p.Named<C>("myC");
    return new B(myC);
});

And then:

A myA = c.Resolve<A>(new NamedParameter("myC", new C()));

Again, you can find a full working example in my GitHub (with output).