Dependency Injection & Inversion of Control Unity Application Block vs. Spring.NET Dennis Loktionov [email_address] February 2009

Agenda What is a Dependency? Dependency Injection Pattern Injection Types Dependency Injection Pros & Cons Spring.NET vs. MS Unity Application Block References Questions

What is a Dependency?

Dependency Injection Pattern

Injection Types

Dependency Injection Pros & Cons

Spring.NET vs. MS Unity Application Block

References

Questions

What is a Dependency? Common Dependencies Application Layers -- Data Access Layer -- Business Layer -- Presentation Layer External Services -- Web Services -- WCF Services External Components -- Frameworks & Libraries -- 3 rd Party Components

Common Dependencies

Application Layers

-- Data Access Layer

-- Business Layer

-- Presentation Layer

External Services

-- Web Services

-- WCF Services

External Components

-- Frameworks & Libraries

-- 3 rd Party Components

Application Layers Dependencies

Why dependencies are evil? Problems that dependencies create Tight coupling of software components Software becomes hard to maintain Difficult to isolate when testing

Problems that dependencies create

Tight coupling of software components

Software becomes hard to maintain

Difficult to isolate when testing

Dependency Injection Pattern WHAT Dependency Injection (DI) in computer programming refers to the process of supplying an external dependency to a software component or service. WHY Ability to specify component dependencies at run time Simplified management of cross-cutting concerns Increased testability of individual components Need for pluggable architecture

WHAT

Dependency Injection (DI) in computer programming refers to the process of supplying an external dependency to a software component or service.

WHY

Ability to specify component dependencies at run time

Simplified management of cross-cutting concerns

Increased testability of individual components

Need for pluggable architecture

Dependency Injection Types Types of Dependency Injection Constructor Injection Property (Setter) Injection Method Call Injection

Types of Dependency Injection

Constructor Injection

Property (Setter) Injection

Method Call Injection

Dependency Injection Types Constructor Injection

Constructor Injection

Dependency Injection Types Property (Setter) Injection

Property (Setter) Injection

Dependency Injection Types Method Call Injection

Method Call Injection

Dependency Injection Pros & Cons Pros Loosely Coupled & Highly Cohesive Increased Testability & Maintainability Flexibility of run time configuration Inversion of Control containers do the wiring for you Cons Increased code complexity Can complicate debugging during the learning curve Code flow becomes not trivial

Pros

Loosely Coupled & Highly Cohesive

Increased Testability & Maintainability

Flexibility of run time configuration

Inversion of Control containers do the wiring for you

Cons

Increased code complexity

Can complicate debugging during the learning curve

Code flow becomes not trivial

Inversion of Control Dependency Inversion Principle (DIP) The principle states that high level or low level modules should not depend upon each other, instead they should depend upon abstractions. Specific implementation (object instances) are deferred to a higher level of abstraction control. Parent Classes Container

Dependency Inversion Principle (DIP)

The principle states that high level or low level modules should not depend upon each other, instead they should depend upon abstractions.

Specific implementation (object instances) are deferred to a higher level of abstraction control.

Parent Classes

Container

Frameworks Frameworks Spring.NET MS Unity Application Block Castle Windsor StructureMap Ninject PicoContainer.NET … and many more

Frameworks

Spring.NET

MS Unity Application Block

Castle Windsor

StructureMap

Ninject

PicoContainer.NET

… and many more

Spring.NET Spring.NET Architecture

Spring.NET Architecture

Spring.NET Inversion of Control Container in Action

Inversion of Control Container in Action

Spring.NET: code samples Movie Lister example

Movie Lister example

MS Unity Application Block Unity Application Block Architecture

Unity Application Block Architecture

Unity: code samples Movie Lister example Quick start web example

Movie Lister example

Quick start web example

Dependency Injection Pitfalls Circular References Objects generated though constructor injection that reference each other in their constructor parameters Objects generated though constructor injection that pass a reference of their type in constructor Objects generated though method call injection that reference each other Objects generated though property injection that reference each other Partial Trust Environment Limitations

Circular References

Objects generated though constructor injection that reference each other in their constructor parameters

Objects generated though constructor injection that pass a reference of their type in constructor

Objects generated though method call injection that reference each other

Objects generated though property injection that reference each other

Partial Trust Environment Limitations

References Useful links: http://martinfowler.com/articles/injection.html http://www.springframework.net/ http://www.codeplex.com/unity

Useful links:

http://martinfowler.com/articles/injection.html

http://www.springframework.net/

http://www.codeplex.com/unity

THANKS

Questions ? Dennis Loktionov [email_address] 604-628-5100 ext .356