Is there any extensibility point in Asp.Net core to register services anywhere other than startup.cs?

Question

Basically in Asp.Net Core we register services inside startups.cs file. Now the question is , is there any extensibility point in Asp.Net Core giving us the chance to hook into some kind of registrar method (by implementing a specific interface for example) and don't mess up with startup.cs ?

Answer 1

Avoid making a mess of Startup

If you just want to avoid making a mess in Startup.cs just delegate the service registration logic to another method, perhaps in another static class.

ServiceRegistry.RegisterAllServices(services);

Hooking into ASP.Net Startup pipeline

If you really want to hack your way into startup logic of ASP.Net I'm afraid you're out if luck. The build up of the ServicesCollection takes place in the BuildCommonServices method. As you can see there is no easy way to hook into the logic here.

In short what happens when an ASP.Net app start is the following:

1. In .Net core there is only one app model - Console Apps; so Main is called.
2. Some magic happens and we arrive at StartupLoader.LoadMethods .
3. Three methods are located Configure , ConfigureContainer and ConfigureServices .
4. All three lookups are passed to FindMethod which always looks up in the startupType and the startupType only. ( REF )

How to register services post startup

Registering additional services into the IOC Container that comes with ASP.Net Core is not trivial.

The DI Framework itself is very basic and if you find yourself trying to do something that is not trivial you probably should upgrade yourself to a more mature and feature complete IOC Container .

You can find some links in the README file on the aspnet/DependencyInjection repository on GitHub.

I have to note though, registering services after the container is created is considered a bad practice.

Answer 2

Good answer here already, but just to add my 2c.

I think what you are essentially looking for is something like "Profiles" or "Modules" and the IOC does an assembly scan. You can do this already, but you would need to create your own interface/reflection code.

Another option is to use the ServiceCollection Extension pattern which seems to be the default way to add "services".

For example take this code :

public static class ServicesConfiguration
{
    public static void AddCustomServices(this IServiceCollection services)
    {
        services.AddTransient<IMyService, MyService>();
    }
}

Then your Configure Services method would look more like :

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();
    services.AddCustomServices();
}

In some ways I prefer this as you can still at a glance see what is being loaded in and follow the trail rather than having some mystery reflection going on.

Further reading : http://dotnetcoretutorials.com/2017/01/24/servicecollection-extension-pattern/