MEF part unable to import Autofac autogenerated factory
Question
This is a (to me) pretty weird problem, because it was already running perfectly but went completely south after some unrelated changes.
I've got a Repository
which imports in its constructor a list of IExtensions
via Autofacs MEF integration. One of these extensions contains a backreference to the Repository
as Lazy(Of IRepository)
(lazy because of the circular reference that would occur).
But as soon as I try to use the repository, Autofac throws a ComponentNotRegisteredException
with the message "The requested service 'ContractName=Assembly.IRepository()' has not been registered."
That is, however, not really correct, because when I break right after the container-build and explore the list of services, it's there - Exported() and with the correct ContractName.
I'd appreciate any help on this...
Michael
[Edit] Here's a thinned-out version of the code:
Repository
Public Class DocumentRepository Implements IDocumentRepository Private _extensions As IEnumerable(Of IRepositoryExtension) Public Sub New(ByVal extensions As IEnumerable(Of IRepositoryExtension)) _extensions = extensions End Sub Public Sub AddDocument(ByVal document As Contracts.IDocument) Implements Contracts.IDocumentRepository.AddDocument For Each extension In _extensions extension.OnAdded(document.Id) Next End Sub End Class
Plugin
<Export(GetType(IRepositoryExtension))> <PartCreationPolicy(ComponentModel.Composition.CreationPolicy.Shared)> Public Class PdfGenerator Implements IRepositoryExtension Private _repositoryFactory As Lazy(Of IDocumentRepository) Public Sub New(ByVal repositoryFactory As Lazy(Of IDocumentRepository)) _repositoryFactory = repositoryFactory End Sub Public Sub CreatePdf(ByVal id As Guid) Implements Contracts.IRepositoryExtension.OnAdded Dim document = _repositoryFactory.Value.GetDocumentById(id) End Sub End Class
Bootstrapper
Public Class EditorApplication Inherits System.Web.HttpApplication Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs) Dim builder As New ContainerBuilder() Dim catalog1 As New TypeCatalog(GetType(DataRepositoryScheme)) Dim catalog2 As New DirectoryCatalog(HttpContext.Current.Server.MapPath("/Plugins")) builder.RegisterComposablePartCatalog(New AggregateCatalog(catalog1, catalog2)) builder.RegisterType(Of DocumentRepository).As(Of IDocumentRepository).SingleInstance().Exported(Function(x) x.As(Of IDocumentRepository)()) AutofacServiceHostFactory.Container = builder.Build() End Sub End Class
Solution
Ah immediately after I posted that last comment I think I figured it out:
The requested service 'ContractName=ConsoleApplication7.IDocumentRepository()'
has not been registered.
Note that there is a pair of parentheses after the contract name - this is because the contract is a function, i.e., this message was produced by the following constructor, which is slightly different from the one in your sample:
Public Sub New(ByVal repositoryFactory As Func(Of IDocumentRepository))
_repositoryFactory = repositoryFactory
End Sub
Note the 'Func' in there. MEF, unlike Autofac, does not regard Func as a special type and so will not translate this into the same contract as for Lazy.
If you want to provide a Func to a MEF component, you need to export it as a Func from Autofac. This is a bit tricky:
builder.RegisterType(Of DocumentRepository).As(Of IDocumentRepository)
builder.Register(Function(c) c.Resolve(Of Func(Of IDocumentRepository))) _
.As(New UniqueService()) _
.Exported(Function(x) x.As(Of Func(Of IDocumentRepository))
You may need to play with the syntax a bit, my VB.NET is fairly shaky.
My guess is that there are stale binaries in your /Extensions directory that are interfering with debugging this.
Hope this is on the mark!
Nick