This document discusses dependency injection and how it can be implemented using Ninject as a dependency injection container. Dependency injection allows removing hard-coded dependencies and making it possible to change dependencies at runtime or compile-time. It describes how a booking class can be decoupled from its dependencies like email and SMS notification classes by injecting them through the constructor instead of creating them internally. Ninject is then introduced as a dependency injection container that can further remove the need to manually inject dependencies and make the code less tightly coupled.

1. Dependency Injection
(Ninject)
Ruchir Shah

2. What is Dependency Injection?
▪ Dependency Injection is a software design pattern that
allows the removal of hard coded dependencies and makes
it possible to change them, whether at run-time or
compile-time.

3. Dependency Injection
▪ One of the requirement was: System should able to book seat. And
after booking confirmation email should go to customer.
▪ To send emails we have created class we have created class Email
Notification with a method SendEmail()

4. Dependency Injection
▪ To send notification; Book() method is calling SendEmail() method of
EmailNotification class.
▪ Here Booking class internally use EmailNotificationclass. Such
classes are said to be tightly coupled

5. Dependency Injection
▪ Booking class can be consumed in application as follow:

6. Dependency Injection
▪ But requirements keep changing…
▪ Now client wanted to send Booking details to cell phone via SMS .

7. Dependency Injection
▪ To fulfill this requirement we need to create new class
SMSNotification with method SendSMS()

8. Dependency Injection
▪ And also need to modify class Booking Booking to use
SMSNotification SMSNotification instead of EmailNotification:

9. Dependency Injection
▪ And System is up again with new changes in place...

10. Dependency Injection
▪ Classes should always communicateWith each other via Interfaces.
▪ Interface INotification with a method declaration SendMessage()

11. Dependency Injection
▪ Implement interface in EmailNotification.

12. Dependency Injection
▪ Call method of EmailNotification from Booking using reference of
INotification interface.

13. Dependency Injection
▪ Using interfaces we have Decoupled Booking and EmailNotification
classes.
▪ Still there is dependency of EmailNotification in Booking class. As we
are creating object of EmailNotification inside Booking class.

14. Dependency Injection
▪ Can we move this dependency out of Booking class?
▪ Yes, with the help of
Inversion of Control (IoC)
or
Dependency Injection

15. Dependency Injection
▪ Instead of creating object of EmailNotification in Booking class we
will pass it via constructor.

16. Dependency Injection
▪ To create Object of Booking class in HomeController, we need to
Inject object of EmailNotification to constructor of Booking.

17. Dependency Injection
▪ To create Object of Booking class in HomeController, we can also
Inject object ofSMSNotification to constructor of Booking.

18. Dependency Injection
We have just achieved
Dependency Injection!

19. Dependency Injection
But there are 2 problems…
1. We are manually injecting dependency into Booking class by
providing the implementation for INotification interface.
2. We are creating EmailNotification or SMSNotification in
HomeController; making HomeController tightly coupled with
these classes.
But there problems can be resolved using…
DI Container

20. Dependency Injection
DI container is about removing need of
this object instantiation from client code.

21. Dependency Injection – Ninject
And to help developers from this situation we have…

22. Get started with Ninject
Install NuGet package for Ninject from Package Manager Console.

23. Get started with Ninject
Configure and setup Ninject to use

24. Modify HomeController to use Dependency
Resolver

25. Dependency Injection – Ninject
▪ And to user SMS Notification, we just have to change binding in
dependency resolver file as:

26. Dependency Injection