Welcome to the Dependency Injection Fundamentals Course! We are happy to have you join us on this comprehensive course made to teach you the Dependency Injection software design pattern.

Nowadays, the Dependency Injection design pattern is one of the most commonly used design patterns in .NET applications. It is a built-in part of .NET framework so every developer should understand how and why to use Dependency Injection.

What is dependency injection?

Dependency injection is a design pattern - a technique for building software used to implement inversion of control between classes and their dependencies. It helps us write loosely-coupled code that is more modular and achieves increased maintainability and testability of our applications.

Dependency Injection in it's essence is all about creating objects other classes depend on. It helps us deal with dependencies - in this context a dependency is an object another object depends on. Instead of manually new-ing up objects inside classes, we delegate that responsibility to an external container which takes care of creating and disposing of objects. .NET provides us with a built-in container we can use for creation of our class instances.

By using interfaces or base classes we abstract away the concrete implementation of classes. This removes direct dependencies between objects which results in loosely-coupled code. An approach like this allows for easy replacement of implementations without affecting existing classes.

Dependency Injection and SOLID principles

Dependency Injection in .NET primarily addresses three SOLID design principles.

Single Responsibility Principle

• DI helps ensure that a class has only one reason to change by delegating the responsibility of creating dependencies to an external container.
• Without DI, a class might handle both its main functionality and the creation of its dependencies, violating SRP.

Open/Closed Principle

• With DI, classes depend on abstractions (interfaces or abstract classes) rather than concrete implementations, making it easy to extend functionality without modifying existing code.
• You can introduce new implementations of an interface without altering the existing classes.

Dependency Inversion Principle

• DI is a direct implementation of this principle because it ensures that high-level modules depend on abstractions rather than concrete implementations.

Liskov Substitution Principle

• Although DI doesn't directly enforce this, it encourages using interfaces which can help maintain LSP.

Interface Segregation Principle

• DI doesn't enforce how interfaces are designed, but it benefits from well-segregated interfaces.

Dependency Injection covers almost all aspects of SOLID principles without thinking too much about it - simply following the DI techniques gets the job done!

What you'll learn

✅ Injection methods
✅ Service lifetimes
✅ Inversion of Control design pattern
✅ Service resolution
✅ How to use Dependency Injection in console applications
➡️ And more!