Mastering Dependency Injection: Effective Ways to Inject Dependencies in C#

Introduction

Dependency Injection (DI) is a design pattern that helps achieve Inversion of Control (IoC) between classes and their dependencies. It allows objects to receive their dependencies from an external source rather than creating them internally. This leads to loosely coupled code, making it easier to maintain, test, and extend. Imagine a builder constructing a house. Instead of running to buy tools every time he needs to work, someone provides the tools for him—allowing him to focus on construction. Similarly, Dependency Injection provides necessary dependencies to a class, improving efficiency and flexibility.

Modern frameworks like ASP .NET Core heavily rely on DI to manage dependencies effectively. Without DI, tightly coupled code can make maintenance and testing difficult, leading to rigid architectures.

Let's dive in! 🚀

What Are Dependencies in Dependency Injection?

In software development, dependencies are objects or components that a class requires to function properly. Think of dependencies as necessary tools that a class relies on to perform its tasks.

For example:

• A Builder needs tools such as Saw and Hammer to construct something.
• Instead of the Builder creating its own tools, the tools are provided externally, allowing more flexibility.

Example Dependencies

// Dependency
public class Saw
{
    public void Use()
    {
        Console.WriteLine("Sawing Wood!");
    }
}

// Dependency
public class Hammer
{
    public void Use()
    {
        Console.WriteLine("Hammering Nails!");
    }
}

Ways to Inject Dependencies in CSharp

There are four common ways to inject dependencies in C#:

1. Manual Injection (Instance Creation)
2. Constructor Injection (Commonly Used)
3. Setter Injection
4. Interface Injection

Manual Injection

In manual injection, dependencies are explicitly created inside the class itself.

Example:

public class Builder
{
    public void Build()
    {
        // Builder creates its own dependencies
        Saw saw = new();
        Hammer hammer = new();

        saw.Use();
        hammer.Use();

        Console.WriteLine("House Built!");
    }
}

// Usage
Builder builder = new();
builder.Build();

Advantages:

• Simple and easy to implement without additional frameworks.
• Full control over object instantiation and lifecycle.
• No dependency resolution overhead from an IoC container.

Disadvantages:

• Creates tightly coupled code, making future modifications harder.
• Difficult to mock dependencies for unit testing.
• Leads to poor maintainability and scalability in larger applications.

Use Case:

• Best for small applications and one-off scripts where DI is unnecessary.
• Useful in early development stages or proof-of-concept implementations.
• Suitable for standalone utilities with minimal dependency management.

Constructor Injection

Dependencies are provided through the class constructor, ensuring they exist at the time of object instantiation.

Example:

public class BuilderConstructorInjection
{
    private readonly Saw _saw;
    private readonly Hammer _hammer;

    public BuilderConstructorInjection(Saw saw, Hammer hammer)
    {
        _saw = saw;
        _hammer = hammer;
    }

    public void Build()
    {
        _saw.Use();
        _hammer.Use();
        Console.WriteLine("House Built!");
    }
}

// Usage
BuilderConstructorInjection builderCI = new (new Saw(), new Hammer());
builderCI.Build();

Advantages:

• Ensures required dependencies are available when the class is instantiated.
• Makes code loosely coupled and easier to test.
• Works seamlessly with IoC containers for automatic dependency resolution.

Disadvantages:

• Requires dependencies at object creation, which can limit flexibility.
• Can lead to long constructors when many dependencies are required.
• Makes certain patterns (e.g., optional dependencies) harder to implement.

Use Case:

• Ideal for scenarios where dependencies are mandatory and should not be modified after object creation.
• Works well in ASP .NET Core and large-scale applications using DI frameworks.
• Best suited for services, controllers, and core components that rely on stable dependencies.

Setter Injection

Dependencies are injected through public setter methods after the object is created.

Example:

public class BuilderSetterInjection
{
    public Saw? Saw { private get; set; }
    public Hammer? Hammer { private get; set; }

    public void Build()
    {
        Saw!.Use();
        Hammer!.Use();
        Console.WriteLine("House Built!");
    }
}

// Usage
BuilderSetterInjection builderSI = new();
builderSI.Saw = new Saw();
builderSI.Hammer = new Hammer();
builderSI.Build();

Advantages:

• Allows dependencies to be modified after object creation, increasing flexibility.
• Useful for optional or configurable dependencies that change at runtime.
• Provides better control over lifecycle management compared to constructor injection.

Disadvantages:

• Dependencies might be unset initially, leading to incomplete object states.
• Requires additional validation to ensure dependencies are set before usage.
• Can make debugging harder if a required dependency isn’t injected properly.

Use Case:

• Ideal for UI components or dynamic configurations where dependencies may change.
• Works well in scenarios where dependency availability depends on runtime conditions.
• Suitable for factories, dynamically loaded services, and non-critical dependencies.

Interface Injection

Dependencies are provided through an interface that exposes a method for dependency injection.

Example:

public interface IBuilder
{
    void SetDependencies(Saw saw, Hammer hammer);
}

public class BuilderInterfaceInjection : IBuilder
{
    private Saw? _saw;
    private Hammer? _hammer;

    public void SetDependencies(Saw saw, Hammer hammer)
    {
        _saw = saw;
        _hammer = hammer;
    }

    public void Build()
    {
        _saw!.Use();
        _hammer!.Use();
        Console.WriteLine("House Built!");
    }
}

// Usage
BuilderInterfaceInjection builderII = new();
builderII.SetDependencies(new Saw(), new Hammer());
builderII.Build();

Advantages:

• Maximizes flexibility by enforcing dependency provision via an interface.
• Makes code more testable and interchangeable by allowing different implementations.
• Often used in plugin-based architectures or systems requiring dependency swapping.

Disadvantages:

• Requires objects to implement a specific interface, which may add complexity.
• Can make the design more rigid if multiple interfaces must be implemented.
• Overuse can lead to unnecessary abstraction and complexity in simple projects.

Use Case:

• Best for modular applications where dependencies vary dynamically.
• Frequently used in extensible frameworks, plugin-based systems, and middleware.
• Ideal for scenarios requiring dependency injection without tight coupling to concrete classes.

Dependency Injection in ASP .NET Core

ASP .NET Core comes with built-in IoC containers, making DI implementation effortless.

Example:

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddScoped<Saw>();
builder.Services.AddScoped<Hammer>();

This ensures dependencies are automatically provided without manual instantiation.

Why Use Dependency Injection?

Using DI improves software development in the following ways:

• Reduces Coupling: Classes are independent of specific implementations.
• Enhances Testability: Dependencies can be mocked for unit testing.
• Improves Code Maintainability: Changing dependencies does not require modifying the dependent class.
• Boosts Flexibility: Dependency changes can be handled without affecting core logic.

Common Pitfalls to Avoid

When implementing DI, watch out for these mistakes:

1. Overusing Singleton Dependencies – Can cause unintended side effects in multi-threaded applications.
2. Misconfigure IoC Containers – Incorrect service lifetimes (e.g., using Scoped dependencies in Singleton services).
3. Injecting Too Many Dependencies – A class with numerous dependencies may indicate poor design.
4. Using Service Locator Patterns – This can lead to hidden dependencies and make code harder to understand.

Best Practices for Dependency Injection

When implementing DI, follow these best practices:

• Prefer Constructor Injection for mandatory dependencies.
• Use IoC Containers to manage dependencies efficiently (e.g., ASP .NET Core's built-in DI, Autofac, Unity).
• Avoid Service Locator Patterns, which introduce hidden dependencies.
• Ensure Single Responsibility Principle (SRP) when handling dependency management.
• Keep Dependencies Small & Specific, avoiding unnecessary dependency injections.

Performance Considerations

While DI improves maintainability, keep these performance factors in mind:

• Object Creation Cost – Too many transient dependencies may affect performance.
• Garbage Collection Load – Unnecessary object instantiation can increase memory usage.
• Dependency Resolution Overhead – IoC containers add a small processing cost when resolving objects.
• Service Lifetime Management – Ensure proper lifetimes (Transient, Scoped, Singleton) to avoid memory leaks.

This ensures that dependencies are managed and provided automatically without manual instantiation.

Common Misconceptions About Dependency Injection

Many beginners misinterpret Dependency Injection, leading to confusion about its purpose and implementation. Here are some common misconceptions:

DI is only for ASP .NET Core

• DI is a general design pattern that works in any C# application, including console apps, desktop applications, and game development.
• While ASP .NET Core has built-in support, DI can be implemented without a framework using manual or third-party IoC containers.

DI is just about using interfaces

• Many think DI is just about programming to an interface (e.g., IService), but DI is about managing dependencies externally.
• DI can work without interfaces (e.g., injecting concrete classes), although interfaces make swapping dependencies easier.

DI is too complex for small applications

• DI doesn't require advanced frameworks. You can even apply DI principles manually in small projects.
• Even a basic constructor injection approach can improve flexibility, making DI beneficial regardless of project size.

Using DI always improves performance

• While DI improves maintainability, excessive use of IoC containers can introduce performance overhead due to object resolution costs.
• Optimize DI by using scoped and singleton dependencies wisely and avoiding unnecessary object instantiations.

Dependency Injection Beyond ASP .NET Core

While DI is built into ASP .NET Core, it is a general design pattern that can be applied in many types of applications:

• Console Applications: Manage dependencies in command-line tools.
• Windows Forms & WPF Apps: Inject services for UI components.
• Game Development: Manage game objects and services dynamically.
• Microservices & Background Services: Handle dependency lifetimes in distributed or long-running processes.

The concept remains the same: instead of creating dependencies inside a class, you provide them externally to improve flexibility and maintainability.

Conclusion

Dependency Injection is more than just a design pattern. It is a fundamental principle that promotes flexibility, scalability, and maintainability in software development. By injecting dependencies externally, we decouple components, making applications easier to modify, test, and extend.

As applications grow in complexity, managing dependencies manually becomes increasingly impractical, leading to rigid and tightly coupled designs. DI addresses these challenges by allowing developers to swap implementations dynamically, integrate mock dependencies for testing, and manage lifetimes efficiently using IoC containers.

Whether you're building a simple console application, a large-scale ASP .NET Core project, or even game development services, Dependency Injection enhances code reusability, modularity, and testability. The beauty of DI lies in its versatility. It is not confined to a single framework but can be applied across various technologies.

Understanding different injection methods—constructor injection, setter injection, and interface injection—provides developers with the tools to create scalable architectures while avoiding common pitfalls. By following best practices and optimizing dependency lifetimes, developers can strike the perfect balance between maintainability and performance.

At its core, Dependency Injection encourages the principles of clean code and software craftsmanship, empowering developers to write robust, flexible, and future-proof applications. As you continue exploring DI, consider experimenting with different approaches, testing out IoC containers, and refining your implementation strategies to build high-quality, maintainable software.

Key Takeaways

• Prefer constructor injection for required dependencies.
• Use IoC containers to manage dependencies efficiently.
• Avoid service locator patterns and overusing singletons.
• DI is not just for ASP .NET Core—apply it in any C# project.
• Always keep dependencies minimal and focused.

Further Reading

• Microsoft Docs: Dependency injection in .NET
• Dependency Injection Principles, Practices, and Patterns (Book)
• Autofac Documentation
• Ninject Documentation

About the Author

Hi, I’m Jiten Shahani, a passionate developer with a strong background in API development and C# programming. Although I’m new to .NET, my journey into learning ASP .NET Core began in December 2024, driven by a desire to build scalable and maintainable applications.

Through my exploration of dependency injection, I’ve realized how crucial it is for writing flexible, testable, and loosely coupled code. This article is a reflection of my learning process, aimed at helping fellow developers, especially beginners, understand the different ways to inject dependencies effectively in C#.

Feel free to connect with me to exchange ideas and learn together!