c# - Using Autofac's ReplaceInstance with interface types -

according documentation, can use activating event "switch instance or wrap in proxy," haven't been able work.

here's i've tried:

[testfixture] public class replaceinstancetest {     public interface isample { }     public class sample : isample { }     public class proxiedsample : isample {         private readonly isample _sample;         public proxiedsample(isample sample) {             _sample = sample;         }     }      [test]     public void replaceinstance_can_proxy_for_interface_type()     {         var builder = new containerbuilder();         builder.registertype<sample>()                .as<isample>()                .onactivating(x =>                   x.replaceinstance(new proxiedsample(x.instance)))                .singleinstance();         var container = builder.build();          var sample = container.resolve<isample>();         assert.that(sample, is.instanceof<proxiedsample>());     }  } 

the above results in class cast exception because autofac trying cast proxiedsample sample instance, not.

is possible use replaceinstance on activatingevent proxy object in autofac (2.6 or 3.0)?

i know it's possible use registerdecorator, actual implementation both configures , conditionally proxies, i'd prefer use activating event, if it's possible.

travis responded on autofac list detailing of challenges surrounding this. between comments , nsgaga's suggestions came following workaround:

[test] public void replaceinstance_can_proxy_for_interface_type_when_using_multi_stage_registration() {     var builder = new containerbuilder();     builder.registertype<sample>().asself();     builder.register(c => (isample)c.resolve<sample>())            .onactivating(x => x.replaceinstance(new proxiedsample(x.instance)))            .singleinstance();     var container = builder.build();      var sample = container.resolve<isample>();     assert.that(sample, is.instanceof<proxiedsample>()); } 

it's possible make registration more compact:

builder.register<isample>(c => new sample()).onactivating(/*...*/); 

the downfall of approach if sample constructor changes registration have change well, avoided additional registration of concrete type.