This document discusses the differences between dependency injection and service locator patterns for inversion of control. It recommends that constructor injection generally be used except for facade classes, loops, base classes, and unknown types, where a service locator may be preferable. An inversion of control container can also automatically manage object creation and dependencies.

1. Dependency Injection vs. Service Locator
- Best Practice
Lars-Erik Kindblad
Senior Consultant
Blog: kindblad.com

2. Agenda
 Intro
• Inversion of Control
• Dependency Injection Patterns
• Service Locator Patterns
• Inversion of Control Containers
 Best Practice
• What patterns to use
• When to use the patterns
 Summary
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3. Inversion of Control
 Inversion of Control = IOC
 Make code loosely coupled
 Make unit testing possible
 How? Move creation of dependencies outside the class they are
being used in
 A better name - Inversion of Dependency Creation
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4. Traditional Code
Inversion of Control
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5. Traditional Code
Inversion of Control Code
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6. Traditional Code
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7. Dependency Injection - Constructor Injection
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8. Dependency Injection - Interface Injection
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9. Dependency Injection - Setter Injection
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10. Static Service Locator
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11. Injected Service Locator
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12. Inversion of Control Container
 A framework that can automatically create a given type with all the
required dependencies
 Popular frameworks
• Unity
• Castle Windsor
• Ninject
• StructureMap
• etc.
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13. Inversion of Control Container
Manual approach
Using an IOC Container
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15. Which patterns to use

16. Traditional Code
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17. Dependency Injection - Constructor Injection
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18. Dependency Injection - Interface Injection
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19. Dependency Injection - Setter Injection
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20. Static Service Locator
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21. Injected Service Locator
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22. When to use which patterns
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23. Always use Dependency Injection – Constructor Injection
...except
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24. FACADE CLASSES
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25. Facade Classes
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26. Dependency Injection
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27. Service Locator
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28. LOOPS
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29. Loops
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30. Dependency Injection
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31. Service Locator
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32. Dependency Injection using Func<>
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33. BASE CLASSES
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34. Base Classes
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35. Dependency Injection
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36. Service Locator
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37. UNKNOWN TYPES AT COMPILE TIME
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38. Unknown types at compile time
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39. Service Locator
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40. Summary
Constructor Injection Injected Service Locator
Facade classes X
(WCF Services,
MVC Controllers)
Loops X (Func<>) X
Base classes X
Unknown types at X
compile time
All other scenarios X
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41. QUESTIONS?
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