Dependency injection in .NET and WithParameter goodie

[MartyIX]

Hi,

I would like to port an app using Autofac DI container to use .NET's dependency container because MAUI is using the latter DI library.

One thing that I do not know how to rewrite elegantly¹ is:

_ = builder.RegisterType<DatabaseMain>().WithParameter(new TypedParameter(typeof(string), appDataFolder)).InstancePerLifetimeScope();

where DatabaseMain type is defined in the following way:

public class DatabaseMain
{
    // ...

    public DatabaseMain(string appDataFolder, TypeA typeA, TypeB typeB, TypeC typeC) 
    {
        // ...
    }
}

TypeA, TypeB and TypeC are all registered in DI container but appDataFolder should not be added to the DIC because it might be then assigned somewhere where I don't want it. Registration of string and integral types in DIC seems like a bad idea to me and it's possible only in some scenarios anyway.

Now I know I can write:

Services.AddSingleton((IServiceProvider provider) => new DatabaseMain(
    appDataFolder,
    provider.GetRequiredService<TypeA>(),
    provider.GetRequiredService<TypeB>(),
    provider.GetRequiredService<TypeC>()
);

but it is more verbose than the Autofac's syntax and when I refactor DatabaseMain, I need to fix the DI registration as well.

Obviously, I can create some wrapper type public record AppDataFolder(string dataFolder) just to please the .NET's DIC but I would rather not do that. Also I do not really wish to create AppSettings class with all these parameters as I want DatabaseMain to accept what it needs.

Do you know about another not mentioned solution for this problem?

Thanks!

Footnotes

1. WithParameter is explained here: https://autofac.readthedocs.io/en/latest/register/parameters.html?highlight=WithParameter#parameters-with-reflection-components ↩

[pinkfloydx33]

You can use ActivatorUtilities.CreateInstance to pass in additional, non-DI parameters

services.AddSingleton(sp =>
   ActivatorUtilities.CreateInstance<DatabaseMain>(sp, appDataFolder)
);

There's a few other methods on ActivatorUtilities that can be used to support such scenarios and create factories that are aware of additional parameters.

[MartyIX]

Thank you very much for this. I'll give it a try!