SimpleInjector and custom WebViewPage

Question

I have a custom WebViewPage, and I would like SimpleInjector to resolve some dependencies in it. It seems like I can't use constructor injection due to the way MVC instantiates this class.

I've enabled explicity property injection as described in the SimpleInjector documentation. But the properties are not getting injected - they're always null.

custom WebViewPage class:

public abstract class CustomWebViewPage<T> : WebViewPage<T>
{
   [Import]
   public IMyDependency Dependency { get; set; }

   public void UseDependency()
   {
      Dependency.DoStuff(); // Dependency is null
   }
}

IOC setup:

var container = new Container();
container.Options.DefaultScopedLifestyle = new WebRequestLifestyle();
container.Options.PropertySelectionBehavior = new ImportPropertySelectionBehavior();

container.RegisterMvcControllers(Assembly.GetExecutingAssembly());

container.Register<IMyDependency, MyDependency>();

Do I need to wire anything else up to get this working? I've tried registering the custom WebViewPage with SimpleInjector (mapping WebViewPage<> to CustomWebViewPage<> and making my class non-abstract), but that didn't work either.

Just to be clear, all other property and constructor dependency injection is working in the application - just not for this particular class.

Answer 1

I agree with Remo Gloor's answer and the statement from Stefan:

But as the others said you shouldn't do view injection anyway. Your view should be dumb and just render the view model to HTML. Anything requiring a dependency should be done in the controller or a service.

That said, in case you really, really, really need this (which you shouldn't), I think it's a matter of creating a custom IViewEngine.

WARNING: The code below is NOT!!! tested AT ALL*

internal class PropertyInjectionViewEngineDecorator : IViewEngine
{
    private readonly ConcurrentDictionary<Type, Registration> registrations = new ConcurrentDictionary<Type, Registration>();

    private readonly IViewEngine decoratee;
    private readonly Func<Type, Registration> createRegistration;

    public PropertyInjectionViewEngineDecorator(IViewEngine decoratee, Container container)
    {
        this.decoratee = decoratee;
        this.createRegistration = type => Lifestyle.Transient.CreateRegistration(type, container);
    }

    public ViewEngineResult FindPartialView(ControllerContext context, string partialViewName, bool useCache) =>
        this.InitializeView(this.decoratee.FindPartialView(context, partialViewName, useCache));

    public ViewEngineResult FindView(ControllerContext context, string viewName, string masterName, bool useCache) =>
        this.InitializeView(this.decoratee.FindView(context, viewName, masterName, useCache));

    public void ReleaseView(ControllerContext controllerContext, IView view) =>
        this.decoratee.ReleaseView(controllerContext, view);

    private ViewEngineResult InitializeView(ViewEngineResult result)
    {
        if (result.View != null)
        {
            Registration registration = this.registrations.GetOrAdd(result.View.GetType(), this.createRegistration);
            registration.InitializeInstance(result.View);
        }

        return result;
    }
}

You can hook this custom PropertyInjectionViewEngineDecorator into the MVC pipeline as follows:

var razor = ViewEngines.Engines.Single(e => e.GetType() == typeof(RazorViewEngine));
ViewEngines.Engines.Remove(razor);
ViewEngines.Engines.Add(new PropertyInjectionViewEngineDecorator(razor, container));