Topic 6. Dependency injection, configuration, and logging in .NET applications

Goal: become familiar with the dependency inversion principle and the Microsoft.Extensions.DependencyInjection container; learn to register services with different lifetimes, read settings from appsettings.json, environment variables, the command line, and user secrets, and use the options pattern with validation and the ILogger<T> logger; master creating console hosts with background services, dependency injection in Windows Forms, and unit testing of services with fake dependencies.

Lecture contents

1. Dependency injection and the container — Dependencies and their injection · The Microsoft.Extensions.DependencyInjection container · Service lifetimes
2. The host, configuration, and options — The .NET Generic Host · Configuration · User secrets · The options pattern
3. Logging — Logging
4. DI in Windows Forms and testability — Dependency injection in Windows Forms · Testability
5. Common mistakes — Common mistakes

Practice and review

• Practice — 3 worked examples with complete code and output
• Tasks — 30 variants, each with tasks at three difficulty levels
• Summary — conclusions, self-check questions, and useful links