The document compares Dagger and Koin dependency injection frameworks for Android. It discusses that Dagger uses compile-time code generation while Koin is runtime without code generation. It provides examples of implementing dependency injection with field injection, modules, and scoping for both frameworks. It also covers testing dependency injection with Koin. In summary, the document notes that Dagger scales better but has slower build times while Koin is simpler to use but errors occur at runtime.

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_You don’t need DI

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

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_DI and Service Locator

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!4
_Providing services to classes
DI and Service Locator

5. „
Neversettle
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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

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

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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

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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

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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

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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

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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

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_Dagger vs. Koin

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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
!13

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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

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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
!17

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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
!18

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_Modules (Dagger)
@Singleton
@Component(
modules = arrayOf(
AppModule::class,
NetworkModule::class
)
)
interface SampleAppComponent {
fun inject(application: SampleApp): SampleApp
}
Dagger vs. Koin
!19

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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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_Modules (Koin)
val networkModule = applicationContext {
factory { OkHttpClient.Builder().build() }
bean { RetrofitFactory(get(), get()).create() }
}
Dagger vs. Koin
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_Modules (Koin)
class SampleApp : Application() {
override fun onCreate() {
super.onCreate()
startKoin(this, listOf(
appModule(),
networkModule())
)
}
}
Dagger vs. Koin
!22

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_Scoping (Dagger)
@Module
class SearchActivityModule {
@ActivityScope
@Provides
fun providesSearchViewModel(): SearchViewModel {
return SearchViewModel()
}
}
Dagger vs. Koin
!23

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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

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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

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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

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

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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

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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
!29

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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

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

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

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_Testing with Koin

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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
!34

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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

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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

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Questions?
@sswierczek_
sebastian.swierczek@intive.com