Dagger and Koin

Dagger, Koin, Dependency Injection, Service Locator

Transcript

1. Dagger and Koin @_modge_ Eoin Fogarty
2. # Introduction - Eoin Fogarty - Ex-Engineer at Cyberagent. - Android and Flutter developer @_modge_ https://github.com/eoinfogarty
3. # What? - Dependency Injection? - Service Locator? - Manual Injection?
4. # But First... Whats is the aim of us doing this? - Dependency Inversion - Inversion of Control
5. # Dependency Inversion The D in SOLID. High-level modules should not depend on low-level modules. Both should depend on abstractions (e.g. interfaces).
6. # Inversion of Control Remove dependencies from your code. https://stackoverflow.com/a/3140 class TextEditor { private val checker: SpellChecker init { // this is not testable! this.checker = SpellChecker() } }
7. # Inversion of Control Remove dependencies from your code. https://stackoverflow.com/a/3140 class TextEditor( // control over implementation has be inverted and is not outside the class val checker: IocSpellChecker )
8. # Inversion of Control Remove dependencies from your code. https://stackoverflow.com/a/3140 class SpellChecker : IocSpellChecker { ... } val spellChecker = SpellChecker() // dependency val textEditor = TextEditor(spellChecker)
9. # Providing Field Dependencies • Service Locator val spellChecker = Locator.get(SpellChecker::class) • Dependency Injection @Inject lateinit var spellChecker: SpellChecker
10. # Service Locator have an object that knows how to get hold of all of the services that an application might need
11. # Dependency Injection an assembler, that populates a field in the lister class with an appropriate implementation for the finder interface
12. # Both.. - Provide fundamental decoupling - Application code is independent of the concrete implementation. The differences is how the implementation is provided. - Service Locator: the class asks for it. - Every class has a dependency to the locator. - Injection: there is no explicit request.
13. # So .. .. the decision between locator and injector depends on whether that dependency is a problem. https://martinfowler.com/articles/injection.html
14. # Implementation Koin vs Dagger Fields // with Koin private val viewModel: MainViewModel by inject() // with Dagger @Inject lateinit var viewModel: MainViewModel With dagger there explicit request, so we cannot declare it a val Since it is provided from outside, it cannot be private.
15. # Implementation Koin vs Dagger Constructors // with Koin class DiskCacheImpl(gson: Gson) : DiskCache // with Dagger class DiskCacheImpl @Inject constructor(gson: Gson) : DiskCache @Inject violates separation of concerns. Impl should not know its being injected.
16. # Other Downsides of Dagger - Steep learning curve for beginners. - Complicated, especially wanting to read generated code. - Annotation Processing increasing build times. - Lots of boiler plate code setting up components and modules and binder factories. - Setting up graphs for testing is difficult.
17. # So Koin! Probably not… Dagger2: - Very fast at runtime. - Compile time validation. - Benefits increase with scale. - A lot of daggers problems (complexity, learning curve) are daggers and not the pattern it implements.
18. # In Conclusion Probably … Koin is good if you are new or are learning. Koin is good to get started quickly. As you scale, Dagger is technically the better choice..