Can I add a new scoped service within a custom middleware?

问题

I'm using WebApi in Asp .Net Core and I'm wondering if/how I can add a new scoped service that all following middleware and controllers can get access to through dependency injection? Or should I share state with HttpContext.Items instead? That doesn't seem to be what it is intended for since HttpContext isn't available at all in a WebApi-controller?

If neither HttpContext or DI is the right tool for this, then how can I propagate state in the request-pipeline without having it already created from the beginning?

回答1:

First add your scoped service in your ConfigureServices(IServiceCollection services)

services.AddScoped<IMyService, MyService>();

Then, the only way I know of to get a scoped service injected into your middleware is to inject it into the Invoke method of your Middlware

public class MyMiddleware
{
    private readonly RequestDelegate _next;

    public MyMiddleware(RequestDelegate next)
    {
        _next = next;
    }

    public async Task Invoke(HttpContext httpContext, IMyService service)
    {
        service.DoSomething();
        await _next(httpContext);
    }
}

Injecting in the constructor of MyMiddleware will make it a singleton by default as it's only called on startup. Invoke is called every time and dependency injection will grab the scoped object.

来源：https://stackoverflow.com/questions/42984052/can-i-add-a-new-scoped-service-within-a-custom-middleware