Autofac: After inactivity I get "Object reference not set to an instance of an object"

Question

I have two projects in my solution: BusinessLibrary and Web (asp.net MVC 4). I'm using autofac for DI and it seems that after some inactivity, the injected object in the controller becomes null. Am I doing something wrong the lifecycle configuration in autofac?

Web project

AccountController references a service class from BusinessLibrary like this:

public class AccountController : Controller
{
    private readonly IAccountService accountService;

    public AccountController(){}

    public AccountController(IAccountService accountService)
    {
        this.accountService = accountService;
    }

    [HttpPost]
    public ActionResult Logon(User model)
    {
        if (accountService.AuthenticateUser(model.Username, model.Password))
        {
            //... some logic here
        }
    }
}

This is Global.asax.cs:

public class MvcApplication : System.Web.HttpApplication
{
    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();
        //some other logic here
        IoCConfig.RegisterDependencies();
    }
}

Finally, autofac configuration in IoCConfig:

    public static void RegisterDependencies()
    {
        var builder = new ContainerBuilder();

        // register services
        builder.RegisterAssemblyTypes(AppDomain.CurrentDomain.GetAssemblies())
            .Where(t => t.Name.EndsWith("Service"))
            .AsImplementedInterfaces()
            .InstancePerHttpRequest();

        // register controllers
        builder.RegisterControllers(typeof(MvcApplication).Assembly).InstancePerHttpRequest();

        var container = builder.Build();
        DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
    }

BusinessLibrary project

AccountService class:

public interface IAccountService
{
    bool AuthenticateUser(string username, string password);
}

public class AccountService : IAccountService
{
    private readonly IAuthenticationService authenticationService;

    public AccountService(IAuthenticationService authenticationService)
    {
        this.authenticationService = authenticationService;
    }

    public bool AuthenticateUser(string username, string password)
    {
        //some logic that uses authenticationService
    }
}

AccountService accepts an instance of IAuthenticationService which I get from a referenced dll, which does some AD authentication logic.

Problem

When I run it on my local machine (IIS 7.5) after rebuilding in VS2012, I am able to login and everything works fine. Now, if I leave the tab open and do something else, after I come page to the page and try to do any action, I get an exception: Object reference not set to an instance of an object. The accountService is null in the controller here:

public class AccountController : Controller
{
    // constructors...
    [HttpPost]
    public ActionResult Logon(User model)
    {
        if (accountService.AuthenticateUser(model.Username, model.Password)) // accountService is null

Any help would be greatly appreciated.

PS. I checked similar problems on SO, but those were around private constructors or double autofac configuration in web.config files.

Answer 1

According to your last comment, your web project need to reference all Service Projects.

Basically, you should be able to register like this -

builder.RegisterType<AccountService>().As<IAccountService>()
   .InstancePerHttpReq‌​uest();
builder.RegisterType<AuthenticationService>().As<IAuthenticationService>()
   .InstancePerHttpReq‌​uest();