Question

I have the following code:

_container = new UnityContainer();
_container.RegisterType<IDownloader, Downloader>();
_container.RegisterType<INewObject, NewObject>();
_container.RegisterType<SearchViewModel>();

SearchViewModel class with constructor injection:

class SearchViewModel
{
    private readonly Func<IDownloader> _downloaderFactory;
    private readonly INewObject _newObject;
    private IDownloader _downloader;

    public SearchViewModel(Func<IDownloader> downloaderFactory, INewObject newObject)
    {
        _downloaderFactory = downloaderFactory;
        _newObject = newObject;
    }        
}

The question: How to register SearchViewModel that has Fun<> as parameter?

_container.RegisterType<SearchViewModel>(new InjectionConstructor(DownloaderFactory()));

The code above works only without INewObject.

The goal: Resolve factory with InjectionConstructor and resolve INewObject, INewObject2, INewObject3 automatically (like without parameters: RegisterType<SearchViewModel>()).

Is it possible? Maybe alternates?

Answer 1

I have solved the problem:

_container.RegisterType<Func<IDownloader>>(new InjectionFactory(i => 
            new Func<IDownloader> (() => _container.Resolve<IDownloader>())));
_container.RegisterType<SearchViewModel>();

new Func is a key, because before I tried:

_container.RegisterType<Func<IDownloader>>(new InjectionFactory(i => 
            _container.Resolve<IDownloader>()));

Also the better way to use IDownloaderFactory instead of Func<IDownloader> downloaderFactory. IDownloaderFactory can encapsulate the delegate.

Also I think that using a delegate as dependency inside factory is better solution than broken Composition Root.