inversion of control

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Introduction to the

Inversion of Control

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AgendaWhat is a Dependency?Example Application High Level Architecture Inversion of ControlDependency InjectionService LocatorDependency Injection Pros/Cons Unity ContainerQuestions

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What is a Dependency?Some common dependencies include:

Application Layers Data Access Layer & Databases Business Layer

External services & Components Web Services Third Party Components

.NET Framework Components File Objects (File.Delete(…), Directory.Exists(…)) Web Objects (HttpContext, Session, Request, etc)

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Database

Data Access Layer

Which Depends OnBusiness Logic Layer

Which Depends On

User Interface

Depends on

Dependencies at a Very High Level

CI Server

BROKEN BUILD!

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The problem

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Code is tightly coupledDifficult to isolate when testingDifficult to maintain

If I change ComponentX how do I know what else it will affect? Did I break anything? If tests are in place they can be your safety net

What problems do dependencies create?

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Inversion Of Control

Don’t call me, I’ll call you

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Dependency Injection is an implementation of IoC

The ability to supply (inject) an external dependency into a software component.

Types of Dependency Injection: Constructor (Most popular)Setter Method

What is Dependency Injection?

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What is Dependency Injection?

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Dependency InjectionIn DI we have three ways of implementing

the same:Constructor way Setter wayMethod way

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Constructor Injection

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Setter Way

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Method Way

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DemonstrationLets See Some Code…

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ProsLoosely CoupledIncreases Testability (A LOT!)Separates components cleanlyAllows for use of Inversion of Control Container

ConsIncreases code complexitySome Jr. Developers find it difficult to understand

at FirstCan Complicate Debugging at FirstComplicates following Code Flow

Dependency Injection Pros & Cons

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Service Locator Form of the Inversion of Control pattern It allows classes to locate specific services they

are interested in without needing to know who implements the service.

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Service Locator

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Who will manage the Dependency Injection?

Containers !

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ContainerA container is an abstraction

responsible for object management, instantiation and configuration.

you can configure the objects using the container rather than writing client code like factory patterns to implement object management.  

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Container

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Thanks For Listening. Mail: hasanjaffal@hotmail.com Blog: http://www.jaftalks.com/ Twitter: http://twitter.com/jaftalks

“You should be pragmatic with any pattern,it's not necessary to be applicable for every situation”

Jaffal Hasan

Practical