You don't need DI - Sebastian Świerczek Dagger vs. Koin

1. Neversettle
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_You don’t need DI

2. Neversettle
intive.com
_DI and Service Locator
_Dagger vs. Koin
_Testing with Koin
_Summary
You don’t need DI
!2

3. Neversettle
intive.com
_DI and Service Locator

4. Neversettle
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!4
_Providing services to classes
DI and Service Locator

5. „
Neversettle
intive.com
As a result I think we need a more specific name
for this pattern. Inversion of Control is too
generic a term, and thus people find it confusing.
As a result with a lot of discussion with various
IoC advocates we settled on the
name Dependency Injection.
-Martin Fowler
DI and Service Locator

6. Neversettle
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_DI
_Logic in two sets
!6Source: https://www.techyourchance.com/dependency-injection-android/
DI and Service Locator

7. Neversettle
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_DI
_Logic in two sets, integration with Pure Dependency injection or frameworks
!7Source: https://www.techyourchance.com/dependency-injection-android/
DI and Service Locator

8. Neversettle
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_DI
_Logic in two sets, integration with Pure Dependency injection or frameworks
_Common techniques:
_constructor injection
_method/setter injection
_field injection
!8
DI and Service Locator

9. Neversettle
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_Service Locator
_Object which holds services that an application might need
!9Source: https://martinfowler.com/articles/injection.html#ServiceLocatorVsDependencyInjection
DI and Service Locator

10. Neversettle
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_Service Locator
class ServiceLocator {
private Map services = new HashMap();
public Object getService(String key){
return services.get(key);
}
public void loadService(String key, Object service) {
services.put(key, service);
}
}
!10
DI and Service Locator

11. „
Neversettle
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With service locator the application class asks for it
explicitly by a message to the locator. With injection
there is no explicit request, the service appears in the
application class - hence the inversion of control.
- Martin Fowler
DI and Service Locator

12. Neversettle
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_Dagger vs. Koin

13. Neversettle
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_Dagger
_Compile-time dependency injection framework
_Based on annotations and code generation
_1.0.0 version in 2013, current version is 2.16
_Works in Java and Kotlin
_Generates Java classes
Dagger vs. Koin
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14. Neversettle
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_Koin
_Runtime, lightweight service locator
_No code generation
_Based on Kotlin features
_0.2.0 version in 2017, current version is 0.9.3
_Written fully in Kotlin and works in Kotlin classes only
Dagger vs. Koin
!14

15. Neversettle
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_Field injection (Dagger)
class SearchActivity : AppCompatActivity() {
@Inject
lateinit var viewModel: SearchViewModel
override fun onCreate(savedInstanceState: Bundle?) {
AndroidInjection.inject(this)
(...)
}
}
Dagger vs. Koin
!15

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_Field injection (Koin)
class SearchActivity : AppCompatActivity() {
val viewModel: SearchViewModel by inject()
(...)
}
Dagger vs. Koin
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_Reified trick (Koin)
inline fun <reified T> ComponentCallbacks.inject(
name: String = ""
): Lazy<T> = lazy { get<T>(name, emptyParameters()) }
Dagger vs. Koin
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18. Neversettle
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_Modules (Dagger)
@Module
class NetworkModule {
@Provides
fun provideOkHttp(): OkHttpClient {
return OkHttpClient.Builder().build()
}
@Provides
@Singleton
fun provideRetrofit(okClient: OkHttpClient,
networkConfig: NetworkConfig): Retrofit {
return RetrofitFactory.create(okClient, networkConfig)
}
}
Dagger vs. Koin
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19. Neversettle
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_Modules (Dagger)
@Singleton
@Component(
modules = arrayOf(
AppModule::class,
NetworkModule::class
)
)
interface SampleAppComponent {
fun inject(application: SampleApp): SampleApp
}
Dagger vs. Koin
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20. Neversettle
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_Modules (Dagger)
class SampleApp : Application() {
override fun onCreate() {
super.onCreate()
DaggerSampleAppComponent.builder()
.appModule(AppModule(this))
.build()
.inject(this)
}
}
Dagger vs. Koin
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21. Neversettle
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_Modules (Koin)
val networkModule = applicationContext {
factory { OkHttpClient.Builder().build() }
bean { RetrofitFactory(get(), get()).create() }
}
Dagger vs. Koin
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22. Neversettle
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_Modules (Koin)
class SampleApp : Application() {
override fun onCreate() {
super.onCreate()
startKoin(this, listOf(
appModule(),
networkModule())
)
}
}
Dagger vs. Koin
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23. Neversettle
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_Scoping (Dagger)
@Module
class SearchActivityModule {
@ActivityScope
@Provides
fun providesSearchViewModel(): SearchViewModel {
return SearchViewModel()
}
}
Dagger vs. Koin
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24. Neversettle
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_Scoping (Dagger)
@ActivityScope
@Subcomponent(
modules = arrayOf(
SearchActivityModule::class
)
)
interface SearchActivityComponent : AndroidInjector<SearchActivity> {
@Subcomponent.Builder
abstract class Builder : AndroidInjector.Builder<SearchActivity>()
}
Dagger vs. Koin
!24

25. Neversettle
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_Scoping (Dagger)
@Module(subcomponents = arrayOf(SearchActivityComponent::class))
internal abstract class SearchActivityBinder {
@Binds
@IntoMap
@ActivityKey(SearchActivity::class)
internal abstract fun bindYourActivityInjectorFactory(
builder: SearchActivityComponent.Builder
):AndroidInjector.Factory<out Activity>
}
Dagger vs. Koin
!25

26. Neversettle
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_Scoping (Dagger)
class SearchActivity : AppCompatActivity() {
@Inject
lateinit var viewModel: SearchViewModel
override fun onCreate(savedInstanceState: Bundle?) {
AndroidInjection.inject(this)
(...)
}
}
Dagger vs. Koin
!26

27. Neversettle
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_Scoping (Koin)
val searchActivityModule = applicationContext {
context(SearchActivity.SCOPE_CONTEXT_NAME) {
bean { SearchViewModel(get(), get()) }
}
}
Dagger vs. Koin
!27

28. Neversettle
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_Scoping (Koin)
class SearchActivity : AppCompatActivity() {
companion object {
const val SCOPE_CONTEXT_NAME = "SearchActivityScopeContext"
}
val SearchViewModel: SearchViewModel by inject()
override fun onStop() {
super.onStop()
if (isFinishing) {
releaseContext(SCOPE_CONTEXT_NAME)
}
}
}
Dagger vs. Koin
!28

29. Neversettle
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_ViewModel support (Dagger)
@Module
class SearchActivityModule {
@ActivityScope
@Provides
fun providesSearchViewModel(
activity: SearchActivity,
factory: SearchViewModelFactory
): SearchViewModel {
return ViewModelProviders.of(activity, factory)
.get(SearchViewModel::class.java)
}
}
Dagger vs. Koin
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30. Neversettle
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_ViewModel support (Dagger)
class SearchActivity : AppCompatActivity() {
@Inject
lateinit var viewModel: SearchViewModel
override fun onCreate(savedInstanceState: Bundle?) {
AndroidInjection.inject(this)
(...)
}
}
Dagger vs. Koin
!30

31. Neversettle
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_ViewModel support (Koin)
val searchActivityModule = applicationContext {
viewModel { SearchViewModel(get(), get()) }
}
Dagger vs. Koin
!31

32. Neversettle
intive.com
_ViewModel support (Koin)
class SearchActivity : AppCompatActivity() {
val viewModel: SearchViewModel by viewModel()
}
Dagger vs. Koin
!32

33. Neversettle
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_Testing with Koin

34. Neversettle
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_Activity test
class SearchActivityTest : AutoCloseKoinTest() {
val tested = SearchActivity().testable()
val viewModel = mock<SearchViewModel>()
@BeforeEach
fun beforeEach() {
val testModule = applicationContext {
bean { viewModel }
}
loadKoinModules(testModule)
}
@Test
fun `should test something very important here`() {
tested.onCreate(mock())
tested.dataAdapter.itemCount `should equal` 0
}
}
Testing with Koin
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35. Neversettle
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Testing with Koin
!35
_dryRun
class KoinDryRunTest : AutoCloseKoinTest() {
@Test
fun `should have all dependencies injectable`() {
dryRun()
}
}

36. Neversettle
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_Summary

37. Neversettle
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_Pros
_Scales better (when using constructor annotations)
_Implementation of Dependency Injection
_Errors reported on build time
_Well known
_Cons
_Slow build time (code generation)
_Relatively hard to implement and understand
_Quite a lot initial boilerplate
Summary
!37
_Dagger

38. Neversettle
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_Pros
_Very simple to use and easy to debug
_Almost no initial boilerplate
_No code generation (reified trick)
_Cons
_Errors on runtime (dryRun could help)
_Pollutes app classes with by inject() (Service Locator)
_Kind of weird scoping but flexible
_Works only in Activities/Fragments written in Kotlin (by inject())
Summary
!38
_Koin
Bonus
Supports ViewModel
out of the box

39. Neversettle
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Questions?
@sswierczek_
sebastian.swierczek@intive.com