Question

I created a custom controller factory to be able to inject service instances to my controllers using StructureMap.

Everything works fine with the exception that with every request the controller factory is called a first time in which it resolves the controller properly and a second time in which the controllerType parameter is null and so StructureMap’s GetInstance method throws an ArgumentNullException: Value cannot be null. Parameter name: key.

The application actually does not crash but if I’m debugging it always stops there and I have to manually continue the execution so the view gets displayed.

Could anyone please explain why this is happening and how could I solve it.

Here is the code from both my Global.asax and the controller factory:

Controller Factory:

public class IocControllerFactory : DefaultControllerFactory
{
    private readonly IContainer container;

    public IocControllerFactory(IContainer container)
    {
        if(container == null) throw new ArgumentNullException("container");
        this.container = container;
    }

    protected override IController GetControllerInstance(RequestContext requestContext, Type controllerType)
    {
        return this.container.GetInstance(controllerType) as IController;
    }
}

Global.asax

private void RegisterControllerFactory()
{
    var ioc = new Container();

    var controllerFactory = new IocControllerFactory(ioc);
    ControllerBuilder.Current.SetControllerFactory(controllerFactory);

    ioc.Configure(r => 
        r.Scan(x =>
        {
            x.AssemblyContainingType<UserAccountController>();
            x.AddAllTypesOf<IController>();
            x.Include(t => typeof(IController).IsAssignableFrom(t));
        }
    ));

    ioc.Configure(r => r
        .For<IUserAccountService>()
        .Use<UserAccountService>());
}

Thank you so much for any help.

Answer 1

Remember that ASP.NET MVC punches every request that does not map to a file through the controller factory with the default configurations. And most browsers request a favicon.ico file by default. So, what is happening is your favicon is getting called but that don’t map to a type so StructureMap is getting a null type and erroring out.

Easiest fixes are to add a favicon.ico file or to add an ignore for the route.