Question

I have an action filter in an ASP.NET MVC 3 app that needs some dependencies injected into it. I am using Autofac.Mvc3 as the dependency injector.

According to the autofac wiki I just have to register the types that I want to inject, call RegisterFilterProvider, and put a public property on my action filter, and then autofac will fill the property with the right object during filter instantiation.

Here is a part of my action filter:

Public Class LogActionAttribute
    Inherits ActionFilterAttribute

    Property tracer As TraceSource

    Public Overrides Sub OnActionExecuting(filterContext As System.Web.Mvc.ActionExecutingContext)
        ...
        tracer.TraceData(...)
        ...
    End Sub
End Class

Here is a part of my global.asax:

Public Class MvcApplication
    Inherits System.Web.HttpApplication

    Shared Sub RegisterGlobalFilters(ByVal filters As GlobalFilterCollection)
        filters.Add(New MyHandleErrorAttribute)
        filters.Add(New LogActionAttribute)
    End Sub

    Sub Application_Start()
        InitSettingRepoEtc()
        ...
    End Sub

    Protected Shared Sub InitSettingRepoEtc()
        ...
        Dim builder = New ContainerBuilder
        builder.RegisterControllers(Reflection.Assembly.GetExecutingAssembly)
        ...
        builder.Register(Of TraceSource)(
            Function(x) New TraceSource("requests", SourceLevels.All)).InstancePerHttpRequest()
        ...
        builder.RegisterFilterProvider()
        Dim container = builder.Build
        DependencyResolver.SetResolver(New AutofacDependencyResolver(container))
        ...
    End Sub
End Class

I have put breakpoint right after SetResolver and in the immediate window tried:

DependencyResolver.Current.GetService(Of TraceSource)

And I successfully got a TraceSource object from autofac, so the registration seems to be OK.

But during OnActionExecuting my tracer property is empty.

What did I miss?

Answer 1

IIRC the provider doesn’t work with ‘global’ filters.

Remove this function:

Shared Sub RegisterGlobalFilters(ByVal filters As GlobalFilterCollection)
    filters.Add(New MyHandleErrorAttribute)
    filters.Add(New LogActionAttribute)
End Sub

And instead, register the global filters with Autofac directly:

 builder.Register(Of MyHandleErrorAttribute)
     .As(Of IActionFilter)
     .PropertiesAutowired()
     .SingleInstance();

 builder.Register(Of LogActionAttribute)
     .As(Of IActionFilter)
     .PropertiesAutowired()
     .SingleInstance();

Autofac will create the filters and include them appropriately. The advantage of this approach is that you can refactor so the filters are not attribute-derived, and then use constructor rather than property injection.