The Dependency Inversion Principle states that high-level modules should not depend on low-level modules, but should depend on abstractions. Both high- and low-level modules should depend on abstractions, not on details. Inversion of Control is an aspect of software design where objects are provided to other objects rather than created by them. Dependency Injection is a design pattern that reduces coupling between components by allowing objects to receive their dependencies from external sources rather than creating them directly.

1. Dependency Inversion
Principle
PRESENTED BY:
M QAMAR UL MUSTAFA

2. Definition:
 High level modules should not depend on low level modules. Both should
depend on abstractions.
 Abstractions should not depend on details. Details should depend on
abstractions.

3. Inversion of control
 In software engineering, Inversion of Control (IoC) is an abstract principle
describing an aspect of some software architecture designs in which the flow of
control of a system is inverted in comparison to procedural programming.

4. Cont.…
 Also known as the Hollywood Principle
 Don’t call us, we’ll call you!
 Objects rely on their environment to provide dependencies rather than actively
obtaining them.
 Inversion of Control can make the difference between a library and a framework.

5. Dependency Injection (DI):
 A design pattern in object-oriented computer programming whose purpose is to
reduce the coupling between software components.
 With DI, the object does not need to know in advance about how the other part
of the system works.

6. The Service Locator Pattern
 A design pattern used in software development to summarize the processes
involved in obtaining a service with a strong abstraction layer. This uses a central
registry known as the "service locator" which on request returns the information
necessary to perform a certain task.

7. DIP Violations:
 Use of “new”

8. DIP Violations (cont…)
 Use of “static”

9. What is a DI (IoC) Container?
 Creates objects that are ready for you to use
 Knows how to create objects and their dependencies
 Knows how to initialize objects when they are created (if necessary)
 Provide lifecycle support
 A container is nothing more than a fancy dictionary of interfaces and their implementing types
 Inversion Of Control containers act like “super factories”

10. DI Containers
 Spring Framework
 Unity (Microsoft)
 Windsor (Castle Project)
 Ninject
 StructureMap

11. Types of Dependency Injection
 Constructor (Most popular)
 Setter
 Method

12. Method Injection

13. Setter Injection

14. Constructor Injection

15. Dependency Injection (Pros):
 Loosely Coupled
 Increases Testability (A LOT!)
 Separates components cleanly
 Allows for use of Inversion of Control Container

16. Dependency Injection (Cons):
 Increases code complexity
 Can Complicate Debugging at First
 Complicates following Code Flow
 Architecture is less straight-forward
 Overkill for smaller or throwaway applications
 Easy to abuse
 Be careful to avoid “XML Hell” in configuration files