Mastering Dependency Injection in ASP.NET Core MVC: Tips, Tricks, and a Real-World Example

Dependency Injection (DI) is a design pattern that allows for the removal of hard-coded dependencies and makes it possible to change them, whether at run-time or compile-time. In this article, we will discuss how to implement dependency injection in an ASP.NET Core MVC application using a custom class called "EmailSender" which is responsible for sending emails.

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What is Dependency Injection?

Dependency injection is a technique where an object receives other objects that it depends on. These other objects are called dependencies. The technique is used to reduce the coupling between objects and make the code more maintainable and testable. In other words, the goal of dependency injection is to achieve loose coupling between objects and classes.

Setting up Dependency Injection in ASP.NET Core

To set up dependency injection in an ASP.NET Core application, you need to configure the built-in dependency injection container by adding services to it. In the Program class, you can use the builder.Services method to register services with the container.

In the above code snippet, we are registering the IEmailSender interface and its implementation EmailSender as a transient service. Also, we are registering the IEmailConfiguration interface and its implementation EmailConfiguration as a transient service. This means that a new instance of EmailSender and EmailConfiguration will be created every time they are requested.

Using Dependency Injection in Controllers

Once you have configured the dependency injection container, you can use it to inject dependencies into controllers. You can do this by adding a constructor to the controller that takes in the required dependency as a parameter.

In the above example, the HomeController is dependent on an IEmailSender. The dependency injection container will automatically provide an instance of IEmailSender to the HomeController when it is created. And the EmailSender class internally uses the IEmailConfiguration interface to send email.

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Tips and Tricks

• Use interfaces for dependency injection: By using interfaces for dependency injection, you can change the implementation of a service without affecting the rest of the application. It also allows for easier testing and more flexible code.
• Use constructor injection: Constructor injection is a preferred way to inject dependencies into a class because it makes the dependencies required for the class to function explicit. This makes it easier to understand the class's dependencies and also makes it more difficult to create an instance of a class in an invalid state.
• Avoid using the service locator pattern: The service locator pattern is an anti-pattern because it makes it harder to understand the dependencies of a class and can make it difficult to change the implementation of a service. Instead, use constructor injection to make the dependencies of a class explicit.
• Use the AddScoped method for services that are scoped to a single request: Use the AddScoped method to register a service that is scoped to a single request. This means that a new instance of the service will be created for each request and the same instance will be used for the duration of the request.
• Use the AddSingleton method for services that are singleton across the application: Use the AddSingleton method to register a service that is a singleton across the application. This means that a single instance of the service will be created and used for the lifetime of the application.
• Use the built-in dependency injection container: ASP.NET Core has a built-in dependency injection container that you can use to register and resolve dependencies. This container is optimized for performance and has many features that make it easy to use.
• Use open generics: You can register open generic types, which allows you to register a single implementation for multiple types. This is useful when you have multiple classes that implement the same interface but have different generic arguments.

By following these tips and tricks, you can use dependency injection to make your code more maintainable and testable.

Conclusion

Dependency injection is a powerful technique that can help you create more maintainable and testable code. By using dependency injection, you can reduce the coupling between objects and make it easier to change the implementation of a service without affecting the rest of the application. In this article, we have discussed how to set up dependency injection in an ASP.NET Core MVC application, and provided some tips and tricks for using dependency injection in your code, using a custom class "EmailSender" as an example.