How do I correctly inject an IHostedService into a Controller?

[stijnherreman]

I'm using ASP.NET Core 2.1 and I'm running into the issue described at https://simpleinjector.readthedocs.io/en/latest/disposabletransientcomponent.html

I have a service implementing BackgroundService. It is registered with services.AddSingleton<IHostedService, ActorSystemBackgroundService>(). When trying to add it to the constructor of a controller, e.g. public AutomatedTestsController(ActorSystemBackgroundService actorSystemBackgroundService), I get the following error:

-[Disposable Transient Component] ActorSystemBackgroundService is registered as transient, but implements IDisposable.

I don't understand why it says ActorSystemBackgroundService is registered as transient, I'm registering it as a singleton. How do I correctly resolve the error in this case?

[dotnetjunkie]

That's because your constructor references ActorSystemBackgroundService instead of IHostedService. Simple Injector tries to cross-wire ActorSystemBackgroundService for you by looking in the IServiceCollection, but it can't find any, because you only registered an IHostedService; this is simply the way the ASP.NET Core DI works.

Because Simple Injector can't find ActorSystemBackgroundService in ASP.NET Core, and since it is a concrete type, Simple Injector will create the type for you. In doing so, however, it creates the type as Transient.

So fix this, you can do 2 things:

• Change your constructor to reference IHostedService
• Register ActorSystemBackgroundService as itself, e.g. services.AddSingleton<ActorSystemBackgroundService>().

[stijnherreman]

Right, it's obvious now that you say it 😄 Thank you!

I've changed the registration as follows, if I understand correctly then the background service must be registered as an IHostedService to work correctly:

services.AddSingleton<ActorSystemBackgroundService>();
services.AddSingleton<IHostedService, ActorSystemBackgroundService>(
	serviceProvider => serviceProvider.GetService<ActorSystemBackgroundService>());

[dotnetjunkie]

So why does your AutomatedTestsController need to depend on ActorSystemBackgroundService instead of IHostedService?

[stijnherreman]

There could be multiple IHostedServices and I need a specific one. Or if you mean to ask why ActorSystemBackgroundService instead of IActorSystemBackgroundService, I'm still in the PoC phase so things will probably still change a bit.

Looking at HostedServiceExecutor, I assume registering it as an IHostedService ensures that ASP.NET Core calls the StartAsync and StopAsync methods at the right time, for all IHostedServices.

[dotnetjunkie]

btw, have you seen this related q/a? https://stackoverflow.com/questions/50394666/injecting-simple-injector-components-into-ihostedservice-with-asp-net-core-2-0

[stijnherreman]

I hadn't seen it yet. I did see you talk somewhere else about creating an adapter, but didn't quite understand it. Thanks for the link, I'll see if I can make it fit with my requirements.

[olegkap]

Or I would suggest this post https://stackoverflow.com/questions/51254053/how-to-inject-a-reference-to-a-specific-ihostedservice-implementation

I have more than one hosted service and followed that post to inject specific hosted service into controller.