How to resolve interface based on service where it's passed to

Question

I have an interface.

public interface ISomeInterface {...}

and two implementations (SomeImpl1 and SomeImpl2):

public class         


        

Answer 1

Autofac supports identification of services by name. Using this, you can register your implementations with a name (using the Named extension method). You can then resolve them by name in the IServiceX registration delegates, using the ResolveNamed extension method. The following code demonstrates this.

var cb = new ContainerBuilder();
cb.Register(c => new SomeImpl1()).Named("impl1");
cb.Register(c => new SomeImpl2()).Named("impl2");
cb.Register(c => new Service1(c.ResolveNamed("impl1"))).As();
cb.Register(c => new Service2(c.ResolveNamed("impl2"))).As();
var container = cb.Build();

var s1 = container.Resolve();//Contains impl1
var s2 = container.Resolve();//Contains impl2

Alternative using RegisterType (as opposed to Register)

You can achieve the same result using the RegisterType extension method in combination with WithParameter and ResolvedParameter. This is useful if the constructor taking a named parameter also takes other non-named parameters that you don't care to specify in a registration delegate:

var cb = new ContainerBuilder();
cb.RegisterType().Named("impl1");
cb.RegisterType().Named("impl2");
cb.RegisterType().As().WithParameter(ResolvedParameter.ForNamed("impl1"));
cb.RegisterType().As().WithParameter(ResolvedParameter.ForNamed("impl2"));
var container = cb.Build();

var s1 = container.Resolve();//Contains impl1
var s2 = container.Resolve();//Contains impl2