Clean Apps with Dagger 2

Dagger 2 is a fast dependency injector for both Java and Android. This talk explores using Dagger 2 to enable clean, lean and maintainable Android apps.

Demo App: https://github.com/alexrwegener/dagger2-scopes
Video link to follow.

Clean Apps with Dagger 2 was presented on June 16th, 2015 at the Indy GDG.

Transcript

1. Alex Wegener Clean Apps with Dagger 2
2. • Design Pattern • Facilitates Single Responsiblity Principle • Simple unit tests • Cleaner code Dependency Injection
3. public final class GDG { private final Devs devs; private final Location location; private final Speaker speaker; public GDG() { this.location = new DeveloperTown(); this.speaker = new BillMote(); this.devs = new RandomPeopleFromTheirHut(); } public void meetup() { location.host(); do { speaker.present(); } while (devs.areEatingPizza()); } }
4. public final class GDG { private final Devs devs; private final Location location; private final Speaker speaker; public GDG(Devs devs, Location location, Speaker speaker) { this.devs = devs; this.location = location; this.speaker = speaker; } public void meetup() { location.host(); do { speaker.present(); } while (devs.areEatingPizza()); } }
5. public static void main(String[] args) { final GDG gdg = new GDG(new AndroidEnthusiasts(), new DeveloperTown(), new AlexWegener()); gdg.meetup(); } public static void main(String[] args) { final GDG gdg = new GDG(); gdg.meetup(); }
6. InjectConstructorValidator injectConstructorValidator = new InjectConstructorValidator(); InjectFieldValidator injectFieldValidator = new InjectFieldValidator(); InjectMethodValidator injectMethodValidator = new InjectMethodValidator(); ModuleValidator moduleValidator = new ModuleValidator(types, elements, methodSignatureFormatter, Module.class, Provides.class); ProvidesMethodValidator providesMethodValidator = new ProvidesMethodValidator(elements); BuilderValidator componentBuilderValidator = new BuilderValidator(elements, types, ComponentDescriptor.Kind. COMPONENT); BuilderValidator subcomponentBuilderValidator = new BuilderValidator(elements, types, ComponentDescriptor.Kind. SUBCOMPONENT); ComponentValidator subcomponentValidator = ComponentValidator.createForSubcomponent(elements, types, moduleValidator, subcomponentBuilderValidator); ComponentValidator componentValidator = ComponentValidator.createForComponent(elements, types, moduleValidator, subcomponentValidator, subcomponentBuilderValidator); MapKeyValidator mapKeyValidator = new MapKeyValidator(); ModuleValidator producerModuleValidator = new ModuleValidator(types, elements, methodSignatureFormatter, ProducerModule.class, Produces.class); ProducesMethodValidator producesMethodValidator = new ProducesMethodValidator(elements); ProductionComponentValidator productionComponentValidator = new ProductionComponentValidator();
7. Why Dagger 2? • Extremely fast • Proguard friendly • Generated code is human readable • Compile time validation errors • Clean stack traces • Scopes
8. Dagger 2 as a Marketplace • Buyers / Consumers • Sellers / Producer
9. Tools of a Seller • @Inject • @Component • @Module + @Provides
10. Tools of a Buyer • @Inject
11. #AndroidDevProblems • Component.inject(Activity/Fragment)
12. #MoreAndroidDevProblems • Giant ball of mud • Vast amount of managed state • Historically hard to unit / ui test • Humans are bad at testing
13. Giant ball of mud
14. Android View Android Java Presenter Java Interactor Store Api Intent Owner Toolbar Key Interface Connection Owner
15. Managing State
16. Scopes • Create your own lifecycle • @Scope • Demo
18. @Application @Activity @User @Screen App Lifecycle
19. AppComponent AuthInteractor AppStore OkHttp AuthService Application
20. @ApplicationScope @Component(modules = AppModule.class) public interface AppComponent { Application application(); AuthInteractor authInteractor(); }
21. AppComponent AuthInteractor AppStore OkHttp ActivityComponent Application AuthInteractor AppComponent NavigationOwner AuthService Application
22. @ActivityScope @Component(dependencies = AppComponent.class, modules = ActivityModule.class) public interface ActivityComponent { void inject(MainActivity activity); AuthInteractor authInteractor(); NavigationOwner navigationOwner(); Application application(); }
23. AppComponent AuthInteractor AppStore OkHttp ActivityComponent Application AuthInteractor AppComponent NavigationOwner UserComponent AuthService Application ActivityComponent NavigationOwner UserInteractor UserStore
24. @UserScope @Component(dependencies = ActivityComponent.class, modules = UserModule.class) public interface UserComponent { NavigationOwner navigationOwner(); UserInteractor userInteractor(); }
25. AppComponent AuthInteractor AppStore OkHttp ActivityComponent Application AuthInteractor AppComponent NavigationOwner UserComponent AuthService Application ActivityComponent NavigationOwner UserInteractor UserStore
26. Unit Tests
27. • Accountability • Quality • Documentation • Maintainability Why unit test?
28. Types of unit tests • State • Collaboration • Contract
29. Collaborator / Contract Relationship UserInteractor UserStore Find the authenticated user’s pref? Can I find the authenticated user’s pref? I can return a user’s pref or an error Can I handle a user’s pref and an error?
30. Collaborator / Contract Relationship UserInteractor UserStore Expectations Actions Assertions Answers
31. Android View Android Java Presenter Java Interactor Store Api Intent Owner Toolbar Key Interface Connection Owner
32. Android View Android Java Presenter Java Interactor Store Api Intent Owner Toolbar Key Interface Connection Owner
33. UI & Manual Tests
34. • Happy path vital functionality • Provide a mock mode Effective UI and human tests
36. Miscellaneous
37. Dagger Tips • Favor constructor injection • Use custom qualifiers
38. Scopes vs Subcomponents • Same purpose • Subcomponents are tightly coupled
39. AppComponent AuthInteractor AppStore OkHttp ActivityComponent Application AuthInteractor AppComponent NavigationOwner AuthService Application
40. AppComponent AuthInteractor AppStore OkHttp ActivitySubComponent AppComponent NavigationOwner AuthService Application
41. Dagger 2 Cons • Reference generated code • Cognitive overhead
42. Questions?
43. References Tools: • Mockito: http://mockito.org/ • Google Truth: https://github.com/google/truth • Dagger 2 documentation: http://google.github.io/dagger/ • APT: https://bitbucket.org/hvisser/android-apt
44. References Samples: • Scopes demo: https://github.com/alexrwegener/dagger2-scopes • CGruber on Dagger 2 + u2020: https://github. com/cgruber/u2020
45. References Blogs / Articles: • Martin Fowler on DI: http://martinfowler.com/articles/injection.html • SOLID Principles: http://en.wikipedia.org/wiki/SOLID_%28object- oriented_design%29 • Fernando Cejas on clean architecture: http: //fernandocejas.com/2014/09/03/architecting-android-the-clean-way/ • Uncle Bob on Clean Architecture: http://blog.8thlight. com/uncle-bob/2012/08/13/the-clean-architecture.html
46. References Talks: • JW on Dagger 1: https://www.parleys.com/tutorial/architecting-android- applications-dagger • JW on Dagger 2: https://www.parleys.com/tutorial/the-future-dependency- injection-dagger-2 • Greg Kick on Dagger 2: https://www.youtube.com/watch? v=oK_XtfXPkqw
47. References Talks: • Pierre-Yves on Mortar & Flow: https://www.youtube.com/watch? v=R8NbpkpSuw8 • JBrains on unit / integration tests: https://vimeo. com/80533536