AutoFac - Instantiating an unregistered service with known services - ioc-container

Question

Instantiating an unregistered service with known services (injecting them via ctr).
I want to avoid container pollution.

Answer 1

Here is another way to resolve unregistered concrete types from container. Note that all autofac constructor finding and selecting logic, all registration event handlers remain in force.
First, you define this method:
public static object ResolveUnregistered(this IComponentContext context, Type serviceType, IEnumerable<Parameter> parameters)
{
var scope = context.Resolve<ILifetimeScope>();
using (var innerScope = scope.BeginLifetimeScope(b => b.RegisterType(serviceType)))
{
IComponentRegistration reg;
innerScope.ComponentRegistry.TryGetRegistration(new TypedService(serviceType), out reg);
return context.ResolveComponent(reg, parameters);
}
}
The idea is that you get component registration from derived context and resolve it in the current context.
Then you can create some handy overloads:
public static object ResolveUnregistered(this IComponentContext context, Type serviceType)
{
return ResolveUnregistered(context, serviceType, Enumerable.Empty<Parameter>());
}
public static object ResolveUnregistered(this IComponentContext context, Type serviceType, params Parameter[] parameters)
{
return ResolveUnregistered(context, serviceType, (IEnumerable<Parameter>)parameters);
}
public static TService ResolveUnregistered<TService>(this IComponentContext context)
{
return (TService)ResolveUnregistered(context, typeof(TService), Enumerable.Empty<Parameter>());
}
public static TService ResolveUnregistered<TService>(this IComponentContext context, params Parameter[] parameters)
{
return (TService)ResolveUnregistered(context, typeof(TService), (IEnumerable<Parameter>)parameters);
}

Answer 2

I found a solution that required some custom code. Somethings are specific to my app, but I think you can get the picture.
Resolve(parameter.ParameterType) would be a call to your container.
public object ResolveUnregistered(Type type)
{
var constructors = type.GetConstructors();
foreach (var constructor in constructors)
{
try
{
var parameters = constructor.GetParameters();
var parameterInstances = new List<object>();
foreach (var parameter in parameters)
{
var service = Resolve(parameter.ParameterType);
if (service == null) throw new NopException("Unkown dependency");
parameterInstances.Add(service);
}
return Activator.CreateInstance(type, parameterInstances.ToArray());
}
catch (NopException)
{
}
}
throw new NopException("No contructor was found that had all the dependencies satisfied.");
}

Answer 3

Here is a way to resolve an unregistered type with know constructor (ctor) properties. This is based on a previous great post: https://stackoverflow.com/a/6994144/2641447.
In this solution, it is absolutely great that constructor finding and selecting logic is handled by Autofac.
The comment is referred to dispose issues what I have solved with the 'ExternallyOwned()' wich configure the component so that instances are never disposed by the container.
I think that an improvement of the solution may be the following:
public static object ResolveUnregistered(this IComponentContext context, Type serviceType, IEnumerable<Parameter> parameters)
{
var scope = context.Resolve<ILifetimeScope>();
using (var innerScope = scope.BeginLifetimeScope(b => b.RegisterType(serviceType).ExternallyOwned()))
return innerScope.Resolve(serviceType, parameters);
}
The usings:
using Autofac;
using Autofac.Core;
using System;
using System.Collections.Generic;