C# Dependency Injection: Everything You Need to Know About Dependency Injection In C#

Last updated on July 16th, 2023 at 07:13 pm

Dependency Injection (DI) is a software design pattern that helps developers to build high-quality software.

It reduces tight coupling between software components and allows us to develop loosely-coupled code, which is easier to maintain and offers greater flexibility and testability.

The fundamental principle behind Dependency Injection is to minimize hard-coded dependencies among classes by dynamically injecting them during runtime instead of design time. 

This approach ensures that the dependencies of a class are provided from external sources, typically through constructor parameters or property setters, rather than being directly instantiated within the class itself.

A dependency is an object that another object depends on.

Understanding the Problem:

Let’s imagine a situation where we have two classes, ClassA and ClassB. ClassA relies on ClassB to carry out specific tasks.

In the traditional approach, ClassA would create an instance of ClassB internally, leading to tight coupling between the two classes. This tight coupling causes various problems, such as making it challenging to modify or test ClassA independently.

Code Example:

Let’s illustrate the traditional approach with a code example:

public class ClassA
{
    private ClassB dependency;  // ClassA has a dependency on ClassB

    public ClassA()
    {
        dependency = new ClassB();  // ClassA creates an instance of ClassB internally
    }

    // ClassA methods and operations
}

public class ClassB
{
    // ClassB methods and operations
}

In the above example, ClassA creates an instance of ClassB internally using the new keyword. This approach makes ClassA tightly coupled with ClassB, making it challenging to modify or test ClassA independently.

Different ways to achieve Dependency Injection in C#

There are three different ways to achieve dependency injection in C#: 

• Constructor injection. 
• Method injection.
• Property injection.

Constructor Injection in C#

Constructor injection is a technique in software development where dependencies are provided to a class through its constructor. It involves passing the required dependencies as parameters when creating an instance of the class. It enables loose coupling and makes the class more flexible and testable.

The following is an example of Constructor Injection in C#:

using System;

// Interface for the dependency
public interface IMessageService
{
    void SendMessage(string message);
}

// Implementation of the dependency
public class EmailService : IMessageService
{
    public void SendMessage(string message)
    {
        Console.WriteLine($"Sending email: {message}");
    }
}

// Class that requires the dependency
public class NotificationService
{
    private readonly IMessageService messageService;

    // Constructor injection
    public NotificationService(IMessageService messageService)
    {
        this.messageService = messageService;
    }

    // Method that uses the dependency
    public void NotifyUser(string userName)
    {
        string message = $"Hello, {userName}! You have a new notification.";
        messageService.SendMessage(message);
    }
}

// Main class to run the code
class Program
{
    static void Main(string[] args)
    {
        // Create an instance of the dependency
        IMessageService emailService = new EmailService();

        // Create an instance of the class with the dependency injected
        NotificationService notificationService = new NotificationService(emailService);

        // Use the class with the injected dependency
        notificationService.NotifyUser("Roman");
    }
}

Output:

Property Injection in C#

Property injection in C# is a technique where public properties provide dependencies to a class. Instead of passing dependencies through the constructor, the class exposes properties that can be set with the required dependencies from an external source. 

It allows for flexibility in injecting dependencies after the object is created. Property injection promotes loose coupling and enhances the testability and modifiability of the code.

The following is an example of Property Injection in C#:

using System;

// Interface for the dependency
public interface IMessageService
{
    void SendMessage(string message);
}

// Implementation of the dependency
public class EmailService : IMessageService
{
    public void SendMessage(string message)
    {
        Console.WriteLine($"Sending email: {message}");
    }
}

// Class that requires the dependency
public class NotificationService
{
    // Property to inject the dependency
    public IMessageService MessageService { get; set; }

    // Method that uses the dependency
    public void NotifyUser(string userName)
    {
        string message = $"Hello, {userName}! You have a new notification.";
        MessageService.SendMessage(message);
    }
}

// Main class to run the code
class Program
{
    static void Main(string[] args)
    {
        // Create an instance of the dependency
        IMessageService emailService = new EmailService();

        // Create an instance of the class
        NotificationService notificationService = new NotificationService();

        // Inject the dependency through the property
        notificationService.MessageService = emailService;

        // Use the class with the injected dependency
        notificationService.NotifyUser("Roman");
    }
}

Output:

Sending email: Hello, Roman! You have a new notification.

Method Injection in C#

Method injection in C# is a technique that provides a method with a dependency as a parameter. Instead of injecting the dependency through the constructor or as a property, it is passed explicitly when calling the method. 

This allows for flexibility in injecting different dependencies for specific method invocations, promoting loose coupling and enhancing the modifiability and testability of the code.

The following is an example of Method Injection in C#:

using System;

// Interface for the dependency
public interface ILogger
{
    void Log(string message);
}

// Implementation of the dependency
public class ConsoleLogger : ILogger
{
    public void Log(string message)
    {
        Console.WriteLine($"Logging: {message}");
    }
}

// Class that requires the dependency
public class PaymentService
{
    // Method with the dependency parameter
    public void ProcessPayment(decimal amount, ILogger logger)
    {
        // Perform payment processing logic
        // ...

        // Log the payment transaction
        logger.Log($"Payment processed: {amount}$");
    }
}

// Main class to run the code
class Program
{
    static void Main(string[] args)
    {
        // Create an instance of the dependency
        ILogger consoleLogger = new ConsoleLogger();

        // Create an instance of the class
        PaymentService paymentService = new PaymentService();

        // Use the class with the injected dependency through method injection
        paymentService.ProcessPayment(100.50m, consoleLogger);
    }
}

Output:

Logging: Payment processed: 100.50$

FAQs

References: MSDN-DI in .NET

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Shekh Ali

Meet Sheikh Ali, a skilled Software engineer and passionate a blogger. He enjoys sharing his expertise in C#, Java, SQL, Design Patterns, and other related topics through his writing. When he's not coding, Sheikh Ali can often indulge in his passions for reading books and fitness training.

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