Complete About DIP

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