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Answer: .NET supports the dependency injection (DI) software design pattern, which is a technique for achieving Inversion of Control (IoC) between classes and their dependencies. Dependency injection in .NET is a built-in part of the framework, along with configuration, logging, and the options pattern. (S1)

The problem it solves

• A dependency is an object that another object depends on. (S1)
• When a Worker class creates and directly depends on a MessageWriter class, replacing MessageWriter with a different implementation means you must modify the Worker class. (S1)
• In a large project with multiple classes depending on MessageWriter, the configuration code becomes scattered across the app. (S1)
• Dependency injection is a design pattern that you can use to remove hard-coded dependencies and make your application more maintainable and testable. (S2)

The moving parts

• IServiceCollection defines a contract for a collection of service descriptors. (S2)
• IServiceProvider defines a mechanism for retrieving a service object. (S2)
• ServiceDescriptor describes a service with its service type, implementation, and lifetime. (S2)
• Services are typically registered at the app's start-up and appended to an IServiceCollection. (S1)
• After you register services, call the BuildServiceProvider method to build an IServiceProvider instance, which acts as a container for all the registered services. (S2)
• The AddSingleton method registers the service with a singleton lifetime, which means it isn't disposed until the app shuts down. (S2)

Claims

• id: C1 claim: DI is a technique for achieving Inversion of Control. source: S1 evidence: "which is a technique for achieving Inversion of Control (IoC) between classes and their dependencies."
• id: C2 claim: A dependency is an object another object depends on. source: S1 evidence: "A dependency is an object that another object depends on."
• id: C3 claim: IServiceProvider retrieves service objects. source: S2 evidence: "IServiceProvider: Defines a mechanism for retrieving a service object."
• id: C4 claim: BuildServiceProvider builds an IServiceProvider. source: S2 evidence: "call the BuildServiceProvider method to build an IServiceProvider instance."

Sources

• [S1] Dependency injection - .NET. Microsoft Learn (.NET docs). https://learn.microsoft.com/en-us/dotnet/core/extensions/dependency-injection . License: CC BY 4.0 (dotnet/docs). Accessed 2026-11-04.
• [S2] Dependency injection basics quickstart - .NET. Microsoft Learn (.NET docs). https://learn.microsoft.com/en-us/dotnet/core/extensions/dependency-injection-basics . License: CC BY 4.0 (dotnet/docs). Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_ejjyzwz7,
  author = {{iinventedlight}},
  title = {{Dependency injection in .NET}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/dotnet-dependency-injection/},
  note = {Permanent ID iil:note:ejjyzwz7. License: CC-BY-4.0.},
}

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