c# - Create instance using ctor injection and ServiceProvider -

i know there iservicecollection interface can register services , iserviceprovider can instantiate services.

how instantiate class, based on specified type, uses registered services?

class myclass {     public myclass(isomeservice someservice) { } }  var servicecollection = new servicecollection(); servicecollection.addsingleton<isomeservice, someservice>()  myclass instance = createinstance(typeof(myclass));  object createintance(type type) {    ??? } 

for example, how asp.net core creates controller instances?

i've made naive implementation of activator isn't there in .net core already?

private static object createinstance(type type, iserviceprovider serviceprovider) {     var ctor = type.getconstructors()         .where(c => c.ispublic)         .orderbydescending(c => c.getparameters().length)         .firstordefault()         ?? throw new invalidoperationexception($"no suitable contructor found on type '{type}'");      var injectionservices = ctor.getparameters()         .select(p => serviceprovider.getrequiredservice(p.parametertype))         .toarray();      return ctor.invoke(injectionservices); } 

}

edit: scenario. i've refactored legacy code implements interface.

public interface ieventdispatcher {     void registerhandler(type handler);     void dispatch(domainevent @event); } 

in dispatch method implementation create instances of handlers:

public class inmemorybus : ieventdispatcher {     private readonly list<type> _handlers = new list<type>();     private readonly func<type, object> activator;      /// <param name="activator">used create instance of message handlers</param>     public inmemorybus(func<type, object> activator)     {         this.activator = activator;     }      public void dispatch(domainevent @event)     {         type messagetype = message.gettype();         var openinterface = typeof(ihandlemessages<>);         var closedinterface = openinterface.makegenerictype(messagetype);          var handlerstonotify = h in _handlers                                closedinterface.gettypeinfo().isassignablefrom(h.gettypeinfo())                                select h;         foreach (type h in _handlerstonotify)         {             //this tricky part             var handlerinstance = activator(h);             closedinterface.gettypeinfo()                 .getmethod(nameof(ihandlemessages<t>.handle))                 .invoke(handlerinstance, new[] { message });         }     }      public void registerhandler(type type) => _handlers.add(type); } 

given

public class myclass {     public myclass(isomeservice someservice) {          //...     } } 

you need build entire object graph provider knows can create

var servicecollection = new servicecollection(); servicecollection.addsingleton<isomeservice, someservice>() servicecollection.addtransient<myclass>();  iserviceprovider provider = servicecollection.buildserviceprovider();  myclass instance = provider.getservice<myclass>(); 

when provider.getservice<myclass>() called provider initialize myclass, resolving dependencies in process.

reference introduction dependency injection in asp.net core