DI friendly factory pattern.

gistfile1.txt

// this is how we want to consume the factory, here in the context of a razor page:
public class IndexModel : PageModel
{
    
    private readonly IShapeRendererFactory _shapeRendererFactory;

    public IndexModel( IShapeRendererFactory shapeRendererFactory)
    {
        _shapeRendererFactory = shapeRendererFactory;
    }

    public void OnGet()
    {
        var render = _shapeRendererFactory.Create<CircleRenderer>();
        render.RenderMe();
    }
}


// this is how we can make the DI registrations:
 builder.Services.AddSingleton<OtherDep>();
        builder.Services.AddSingleton<IShapeRenderer, CircleRenderer>();
        builder.Services.AddSingleton<IShapeRenderer, TriangleRenderer>();
        builder.Services.AddSingleton<IShapeRenderer, SquareRenderer>();
        builder.Services.AddSingleton<IShapeRendererFactory>(ctx =>
        {
            var shapeRendererImplementations = ctx.GetServices<IShapeRenderer>();

            var factories = new Dictionary<Type, Func<IShapeRenderer>>();

            foreach (var item in shapeRendererImplementations)
            {
                factories.Add(item.GetType(), () => item);

            }

            return new ShapeRendererFactory(factories);
        });


public interface IShapeRendererFactory
{
    IShapeRenderer Create<T>() where T : class, IShapeRenderer;
}
public interface IShapeRenderer
{
    public void RenderMe();
}

public class OtherDep { }
public class CircleRenderer : IShapeRenderer
{
    private readonly OtherDep otherDep;

    public CircleRenderer(OtherDep otherDep)
    {
        this.otherDep = otherDep;
    }
    public void RenderMe()
    {
        Console.WriteLine("I'm a circle");
    }
}
public class TriangleRenderer : IShapeRenderer
{
    public void RenderMe()
    {
        Console.WriteLine("I'm a triangle");
    }
}
public class SquareRenderer : IShapeRenderer
{
    public void RenderMe()
    {
        Console.WriteLine("I'm a square");
    }
}
public class ShapeRendererFactory : IShapeRendererFactory
{
    private readonly Dictionary<Type, Func<IShapeRenderer>> _factories;

    public ShapeRendererFactory(Dictionary<Type, Func<IShapeRenderer>> factories)
    {
        _factories = factories;
    }
    public IShapeRenderer Create<T>() where T : class, IShapeRenderer
    {
        if (!_factories.TryGetValue(typeof(T), out var factory))
        {
            throw new ArgumentOutOfRangeException($"{typeof(T).Name} is not Registered");
        }
        return factory();
    }
}