Can't inject BackgroundService into PageModel - asp.net-core

Question

I am trying to use the BackgroundService is an asp.net core 2.2 project using the Razor page project template, not MVC. This little sample app took me about 1 minute to write so it couldn't be much simpler. Looking at the debugger I know the background service is starting and chugging along just fine. But when I attempt to navigate to a page (path 'Banana') that requires this service as a dependency, I get InvalidOperationException: Unable to resolve service for type 'WebApplication23.DumbService' while attempting to activate 'WebApplication23.Pages.BananaModel'. Why can't I access this service from my page model? The code is at https://github.com/jmagaram/SimpleBackgroundService
I have the following service:
using Microsoft.Extensions.Hosting;
using System.Threading;
using System.Threading.Tasks;
namespace WebApplication23
{
public class DumbService : BackgroundService
{
public DumbService()
{
}
public void QueueWork()
{
}
protected async override Task ExecuteAsync(CancellationToken cancellationToken)
{
while (!cancellationToken.IsCancellationRequested) {
await Task.Delay(TimeSpan.FromSeconds(1));
}
}
}
}
And this is where I register it:
services.AddHostedService<DumbService>();
services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
Here is a page model that uses it:
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;
namespace WebApplication23.Pages
{
public class BananaModel : PageModel
{
private readonly DumbService _service;
public BananaModel(DumbService service)
{
_service = service;
}
public void OnGet()
{
}
}
}

Answer 1

Registering a background service doesn't actually add it to the service collection, mostly because there's no need to. The whole point of a background service is that your app doesn't really need to know about it. It's not clear why you think you need this service injected, but almost certainly you'd be better served by factoring out whatever logic you need in your Razor Page into a separate class that both the service and your Razor page can utilize.
UPDATE
See the documentation on IHostedService where an example of a queue background service is given. You'll notice that the actual hosted service is injected with the task queue. Your app then would also inject just the task queue itself to schedule tasks.