Injecting Simple Injector components into IHostedService with ASP.NET Core 2.0

Question

In ASP.NET Core 2.0, there is a way to add background tasks by implementing the IHostedService interface (see https://docs.microsoft.com/en-us/aspnet/core/funda

Answer 1

I would hook onto the ConfigureContainer method of the HostBuilder and setup simpleinjectore there like this:

                   IHostBuilder()
                   .ConfigureContainer((builder, services) =>
                   {
                       var container = new Container();

                       container.RegisterSingleton();
                       services.AddTransient();

                   })
                   .ConfigureServices((hostContext, services) =>
                   {
                       // Originally we would have done this
                       //services.AddHostedService();
                   })
                   .Build();

        using (host)
        {
            await host.StartAsync();
            await host.WaitForShutdownAsync();
        }

While you could use your IHostedService implementation indeed I think it may hide what is going on. I believe the infrastructure bootstrapping should be done in one place or orchestrated at least in one place. I consider the container to be infrastructure and would set it all up with the rest of the app via the HostBuilder methods.

An added advantage may also be that you do not entirely replace the ServiceCollection as it works well with doing other framework related things. An example of some stuff I would still do with the ServiceCollection:

                   IHostBuilder()
                   .ConfigureServices((hostContext, services) =>
                   {
                       services.AddLogging();
                       services.AddOptions();
                   })

This is in line with what is stated in the simpleinjector docs about setting the container up with ASP.NET Core:

The practice with Simple Injector is to use Simple Injector to build up object graphs of your application components and let the built-in container build framework and third-party components,The practice with Simple Injector is to use Simple Injector to build up object graphs of your application components and let the built-in container build framework and third-party components

The same should apply with just .net core and the generic HostBuilder.