5 Ways Injecting Multiple Instances of Same Interface on ASP.NET Core

01-feed-reader.cs

public interface IFeedReader
{
    string Name { get; }
    string GetSingleFeedTitle();
}

public class BlogFeedReader : IFeedReader
{
    public BlogFeedReader()
    {
        this.Name = "Blog";
    }

    public string Name { get; }

    public string GetSingleFeedTitle()
    {
        return "This is blog item 1";
    }
}

public class PodcastFeedReader : IFeedReader
{
    public PodcastFeedReader()
    {
        this.Name = "Podcast";
    }

    public string Name { get; }

    public string GetSingleFeedTitle()
    {
        return "This is audio item 1";
    }
}

public class YouTubeFeedReader : IFeedReader
{
    public YouTubeFeedReader()
    {
        this.Name = "YouTube";
    }

    public string Name { get; }

    public string GetSingleFeedTitle()
    {
        return "This is video item 1";
    }
}

02-configure-services.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<IFeedReader, BlogFeedReader>();
    services.AddTransient<IFeedReader, PodcastFeedReader>();
    services.AddTransient<IFeedReader, YouTubeFeedReader>();
}

03-feed-service.cs

public class BlogFeedService
{
    private readonly IFeedReader _reader;

    public BlogFeedService(IEnumerable<IFeedReader> readers)
    {
        this._reader = readers.SingleOrDefault(p => p.Name == "Blog");
    }

    public string GetTitle()
    {
        return this._reader.GetSingleFeedTitle();
    }
}

04-feed-service.cs

public class BlogFeedService
{
    private readonly IEnumerable<IFeedReader> _readers;

    public BlogFeedService(IEnumerable<IFeedReader> readers)
    {
        this._readers = readers;
    }

    public string GetTitle()
    {
        foreach (reader in this._readers)
        {
            if (reader.Name != "Blog")
            {
                continue;
            }

            return reader.GetSingleFeedTitle();
        }
    }
}

05-feed-reader-resolver.cs

public interface IFeedReaderResolver
{
    IFeedReader Resolve(string name);
}

public class FeedReaderResolver : IFeedReaderResolver
{
    private readonly IServiceProvider _provider;

    public FeedReaderResolver(IServiceProvider provider)
    {
        this._provider = provider;
    }

    public IFeedReader Resolve(string name)
    {
        var type = Assembly.GetAssembly(typeof(FeedReaderResolver)).GetType($"{name}FeedReader");
        var instance = this._provider.GetService(type);

        return instance as IFeedReader;
    }
}

06-configure-services.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<BlogFeedReader>();
    services.AddTransient<PodcastFeedReader>();
    services.AddTransient<YouTubeFeedReader>();

    services.AddTransient<IFeedReaderResolver, FeedReaderResolver>();
}

07-feed-service.cs

public class BlogFeedService
{
    private readonly IFeedReader _reader;

    public BlogFeedService(IFeedReaderResolver resolver)
    {
        this._reader = resolver.Resolve("Blog");
    }

    public string GetTitle()
    {
        return this._reader.GetSingleFeedTitle();
    }
}

08-feed-reader-resolver.cs

public class FeedReaderResolver : IFeedReaderResolver
{
    public IFeedReader Resolve(string name)
    {
        var type = Assembly.GetAssembly(typeof(FeedReaderResolver)).GetType($"{name}FeedReader");
        var instance = Activator.CreateInstance(type);

        return instance as IFeedReader;
    }
}

09-configure-services.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<IFeedReaderResolver, FeedReaderResolver>();
}

10-feed-reader-delegate.cs

public delegate IFeedReader FeedReaderDelegate(string name);

11-configure-services.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<BlogFeedReader>();
    services.AddTransient<PodcastFeedReader>();
    services.AddTransient<YouTubeFeedReader>();

    services.AddTransient<FeedReaderDelegate>(provider => name =>
    {
        var type = Assembly.GetAssembly(typeof(FeedReaderResolver)).GetType($"FeedReaders.{name}FeedReader");
        var instance = provider.GetService(type);

        return instance as IFeedReader;
    });
}

12-feed-service.cs

public class BlogFeedService
{
    private readonly FeedReaderDelegate _delegate;

    public BlogFeedService(FeedReaderDelegate @delegate)
    {
        this._delegate = @delegate;
    }

    public string GetTitle()
    {
        return this._delegate("Blog").GetSingleFeedTitle();
    }
}

13-configure-services.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<BlogFeedReader>();
    services.AddTransient<PodcastFeedReader>();
    services.AddTransient<YouTubeFeedReader>();

    services.AddTransient<Func<string, IFeedReader>>(provider => name =>
    {
        var type = Assembly.GetAssembly(typeof(FeedReaderResolver)).GetType($"FeedReaders.{name}FeedReader");
        var instance = provider.GetService(type);

        return instance as IFeedReader;
    });
}

14-feed-service.cs

public class BlogFeedService
{
    private readonly Func<string, IFeedReader> _func;

    public BlogFeedService(Func<string, IFeedReader> func)
    {
        this._func = func;
    }

    public string GetTitle()
    {
        return this._func("Blog").GetSingleFeedTitle();
    }
}