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What is the difference between Singleton, Scoped, and Transient service lifetimes in ASP.NET Core's DI container? What is the Inversion of Control (IoC) principle, and how does dependency injection relate to it as one specific technique? How does constructor injection differ from property (setter) injection, and why is constructor injection generally preferred? What causes a 'captive dependency' bug, and how does ASP.NET Core's DI container detect and prevent it? How do you correctly and safely resolve a Scoped service from within a Singleton service using IServiceScopeFactory, avoiding the captive dependency problem? How would you write a custom IServiceProviderFactory or use a third-party container (like Autofac) to enable advanced DI features not supported by the built-in ASP.NET Core container, like property injection or convention-based registration? How does the DI container resolve a class with MULTIPLE constructors, and how do you influence which one gets chosen?
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How would you implement the Factory pattern using dependency injection to resolve a specific implementation at runtime based on a parameter, when the standard container can't decide statically?

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Answer

Inject a factory delegate (Func<string, IService>) or a dedicated factory interface/class instead of the service directly — the factory itself is registered normally in DI, and its implementation resolves the correct concrete service (often via a keyed lookup among several registered implementations) at the moment it's actually needed, based on runtime information the container itself doesn't have.
public interface IPaymentProcessorFactory { IPaymentProcessor Create(string provider); }

public class PaymentProcessorFactory : IPaymentProcessorFactory {
  private readonly IEnumerable<IPaymentProcessor> _processors;
  public PaymentProcessorFactory(IEnumerable<IPaymentProcessor> processors) { _processors = processors; }
  public IPaymentProcessor Create(string provider) =>
    _processors.First(p => p.ProviderName == provider);
}
Real-world example Selecting between multiple registered payment gateway implementations (Stripe, PayPal, etc.) at runtime based on a user's chosen provider.

Common follow-ups: How does .NET 8's newer KEYED SERVICES feature (AddKeyedSingleton, etc.) simplify this exact pattern natively?

Design Patterns in C#
All 10 Dependency Injection & IoC Principles questions