Question 1

How do the Transient, Scoped, and Singleton service lifetimes differ in .NET?

Accepted Answer

Transient creates a new instance on each injection, Scoped creates one instance per HTTP request shared by its components, and Singleton creates one instance shared for the process lifetime.

Question 2

What is Captive Dependency in the .NET DI container, and how do you detect and prevent it?

Accepted Answer

It happens when a shorter-lived service (such as Scoped) is injected into a longer-lived service (such as Singleton), keeping the Scoped instance in memory forever and preventing cleanup.

Question 3

How do Keyed Services added in .NET 8 work, and how do they address multiple implementations?

Accepted Answer

They let you register multiple implementations of the same interface with explicit keys and request a specific one with [FromKeyedServices("key")] without a custom factory.

Question 4

Who calls Dispose() on services implementing IDisposable when using the .NET DI container?

Accepted Answer

The DI container is responsible for automatically calling Dispose() on services it creates when their Scope ends or when the application shuts down for Singletons.

Question 5

How does Scrutor use Assembly Scanning to register services automatically with Convention-over-Configuration?

Accepted Answer

It scans project classes and registers those implementing matching interfaces with specified lifetimes in one line, instead of writing hundreds of AddScoped calls manually.

Question 6

Why is the Service Locator pattern (injecting IServiceProvider directly) an Anti-pattern in C#?

Accepted Answer

It hides a class's real dependencies, bypasses static compiler checks, complicates unit testing, and can cause runtime errors when requested services are not registered.

Question 7

How do you register and resolve Open Generics such as IRepository<> in the .NET container?

Accepted Answer

Register the open interface type and open implementation without specifying a type argument, with typeof(IRepository<>) and typeof(Repository<>), so the container can construct closed types automatically.

Question 8

What does the [FromServices] Attribute do, and when would you inject a service into an Action method instead of the constructor?

Accepted Answer

It injects a dependency directly into a specific Action method parameter; prefer it for an expensive service used only on one route and not elsewhere in the Controller.

Question 9

What happens when multiple classes implementing the same interface are registered in the .NET container, and how do you resolve them all?

Accepted Answer

Resolving one IService returns only the last registered class, while injecting IEnumerable<IService> returns every registered implementation in order.

Question 10

When should you replace .NET's built-in container with an advanced container such as Autofac?

Accepted Answer

When you need advanced features that are not supported natively, such as Property Injection, Interception for aspect-oriented programming (AOP), or complex custom scopes.