Question

I have a Presenter that takes a Service and a View Contract as parameters in its constructor:

public FooPresenter : IFooPresenter {
    private IFooView view;
    private readonly IFooService service;

    public FooPresenter(IFooView view, IFooService service) {
        this.view = view;
        this.service = service;
    }
}

I resolve my service with Autofac:

private ContainerProvider BuildDependencies() {
    var builder = new ContainerBuilder();
    builder.Register<FooService>().As<IFooService>().FactoryScoped();  

    return new ContainerProvider(builder.Build());  
}

In my ASPX page (View implementation):

public partial class Foo : Page, IFooView {
    private FooPresenter presenter;

    public Foo() {
        // this is straightforward but not really ideal
        // (IoCResolve is a holder for how I hit the container in global.asax)
        this.presenter = new FooPresenter(this, IoCResolve<IFooService>());

        // I would rather have an interface IFooPresenter so I can do
        this.presenter = IoCResolve<IFooPresenter>();
        // this allows me to add more services as needed without having to 
        // come back and manually update this constructor call here
    }
}

The issue is FooPresenter’s constructor expects the specific Page, not for the container to create a new one.

Can I supply a specific instance of the view, the current page, to the container for just this resolution? Does that make sense to do, or should I do this another way?

Answer 1

The way to solve passing what I like to call data parameters when resolving dependencies in Autofac is by using generated factories.

(Update: this question discusses the same problem and my article shows how you can avoid large amounts of factory delegates).

The solution to your problem will look something like this:

First, declare a factory delegate thath only accepts the data parameters:

public delegate IFooPresenter FooPresenterFactory(IFooView view);

Your presenter goes unchanged:

public FooPresenter : IFooPresenter {
    private IFooView view;
    private readonly IFooService service;

    public FooPresenter(IFooView view, IFooService service) {
        this.view = view;
        this.service = service;
    }
}

Next the Autofac container setup:

var builder = new ContainerBuilder();
builder.Register<FooService>().As<IFooService>().FactoryScoped();  
builder.Register<FooPresenter>().As<IFooPresenter>().FactoryScoped();  
builder.RegisterGeneratedFactory<FooPresenterFactory>();

Now in your page you can in two lines of code resolve the presenter by first getting the factory and then calling the factory to do the resolution for you:

public partial class Foo : Page, IFooView {
    private FooPresenter presenter;

    public Foo() {
        var factory = IoCResolve<FooPresenterFactory>();
        this.presenter = factory(this);
    }
}