Property Injection in Microsoft.Extensions.DependencyInjection

Question

I am relatively new to working with DI containers and have hit a bit of a roadblock.

SimpleInjector has a method with the following signature:

Container.RegisterInitializer<TService>(Action<TService>)

In our code base we do use it like this:

// this is a property injection of the abstract file system
container.RegisterInitializer<IFileSystemInjection>(
    fs => fs.FileSystem = new FileSystem());

I am wondering how I would achieve the same using the IServiceCollection parameter in the ConfigureServices method in the Startup.cs class. So far I have been able to register all my types using the services.AddTransient(); but I am not sure how what the equivalent simpleinjector.RegisterInitializer is within the IServiceCollection.

Answer 1

You'd use the factory overload(s) of AddSingleton, AddScoped, and AddTransient. I'm not sure what scope IFileSystemInjection should be in, but it sounds like something that could be a singleton. If not, change the method you call appropriately:

service.AddSingleton<IFileSystemInjection>(p =>
{
    var fs = new FileSystemInjection();
    fs.FileSystem = new FileSystem();
});

In short, if you provide a factory, then you're responsible for the entire object initialization, hence the new FileSystemInjection(), which I'm subbing as the actual implementation of IFileSystemInjection your using.

If that implementation has dependencies that need to be injected in order to create it, you can pull those from p, which is an instance of IServiceProvider:

var myDep = p.GetRequiredService<MyDep>();
var fs = new FileSystemImplementation(myDep);