Ciklum & GDG Dnipro - Dagger 2

Talk about Dagger 2 basics, dependency injection basics and alternative tools, and best practices of using Dagger 2 for Android Java projects, Dagger and Koin for Kotlin

1. Dagger 2 Manage dependencies in Google style Royce Mars Tech Lead @ DataArt
2. What is dependency injection?
3. Composition != inheritance Member variables need to be initialized
4. Creating objects with “new” keyword
5. Initializing new objects Via constructor parameters
6. Composition. The simplest example
7. Applying inheritance and composition When creating new objects
8. See dependencies in code • Car depends on Engine. • Engines may vary. • Need different engines for testing and production
9. Dagger and JSR-330
10. Evolution of Dagger • Dagger 2 - Google, Greg Kick • Dagger - Square, Jake Wharton • Guice - Google, Jesse Wilson
11. Inversion of control
12. Reflection vs Compile time Dagger 2 vs Dagger 1
13. JSR-330
14. Simple piece of magic...
15. Default constructor injection
16. Injection through parameters
17. So, how to make it work?
18. How does injection work?
19. Components & Modules Pic. by Miroslaw Stanek from Azimo http://frogermcs.github.io/dagger-graph-creation-performance/
20. Module declaration
21. Module annotations
22. Component declaration
23. Component annotations
24. Component initialization
25. Injection
26. Adding modules
27. Custom scopes
28. Objects lifecycle Pic. by Miroslaw Stanek from Azimo http://frogermcs.github.io/dagger-graph-creation-performance/
29. And again - Components & Modules Pic. by Miroslaw Stanek from Azimo http://frogermcs.github.io/dagger-graph-creation-performance/
30. This mysterious “plus”...
31. Declaring Subcomponent
32. Adding Module instance
33. Adding subcomponent
34. Managing subcomponents lifetime
35. Scope
36. @ActivityScope
37. @ActivityScope
38. Custom scope
39. Custom scope
40. Custom scope
41. So… what should we inject? • Demo data sources / modules • Presenters • Singletons • Test implementations • All other dependencies :)
42. Best practices
43. New Android Injector
44. New Android Injector
45. Favor constructor injection over field injection • Field injection requires non final and non private fields • Forget an @Inject - get NullPointerException on a field • Constructor injection = immutable and thread safe objects. Protect from partially constructed state • For objects, constructed by the system (Activities, Fragments) - still use field injection
46. Favor constructor injection over field injection BAD:
47. Favor constructor injection over field injection BETTER:
48. Favor @Inject over @Provides • @Provides methods should not duplicate the constructor boilerplate • Code is easier to understand when coupled concerns are in one place
49. Favor @Inject over @Provides - no need in provides method in Module
50. Singletons should be extremely rare • Singletons are useful when we need a centralized access to a mutable state • Immutable objects doesn’t need to be a singleton
51. Singletons should be extremely rare BAD: GOOD:
52. Favor static @Provides methods • The generated code can directly invoke the method instead of having to create a module instance. That method call can be inlined by the compiler • All bindings being static will result in a sizable performance increase • Make your modules abstract and Dagger will fail at compile time if one of the @Provides methods isn’t static
53. Favor static @Provides methods BAD:
54. Favor static @Provides methods
55. Use Kotlin, insert Koin :)
56. Home readings for Java • Py “Keeping the Daggers Sharp” • Mert Simsek “New Android Injector with Dagger 2” • James Shvarts “Demystifying the new Dagger Android Injection API” • Fernando Cejas “Tasting Dagger 2 on Android” • Miroslaw Stanek “Dagger2 - graph creation performance” • CodePath’s guide to Dagger2 • Xoxol_89 @ Habrahabr “Dagger 2. Часть третья. Новые грани возможного” • Dagger2 official page
57. Home readings for Kotlin Mobile Architecture Club • Juan Ignacio Saravia, Keddit https://android.jlelse.eu/keddit-part-10-kotlin-dagger- 2-dependency-injection-a620052a7384 • Antonio Leiva https://antonioleiva.com/dagger-android-kotlin/ • Koin https://github.com/Ekito/koin
58. Thank you! :) @RoyceMars @DataArt