Koin - следующий шаг на пути становления проектов полностью на Kotlin. Что внутри Koin? Только DSL и магия Kotlin. Давайте выясним правда ли Dependency Injection + Kotlin + Easy of Use == Koin?

1. Kiev 2018
Absolute Mobile Fest
Kirill Rozov
Android Developer

2. Kiev 2018Insert Koin
Dependency Injection

3. Kiev 2018Insert Koin
Inversion of Control (IoC) is a design
principle in which custom-written portions
of a computer program receive the flow of
control from a generic framework
wikipedia.org/wiki/Inversion_of_control

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Inversion of Control
CLIENT
CLIENT
CLIENT
DEPENDENCY 1
DEPENDENCY 2
DEPENDENCY 3
DEPENDENCY 4

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Inversion of Control
DEPENDENCY 1
DEPENDENCY 2
DEPENDENCY 3
DEPENDENCY 4
IoC CONTAINER
CLIENT
CLIENT
CLIENT

6. Kiev 2018Insert Koin
Inversion of Control
DEPENDENCY 1
DEPENDENCY 2
DEPENDENCY 3
DEPENDENCY 4
IoC CONTAINER
CLIENT
CLIENT
CLIENT

7. Kiev 2018Insert Koin
Popular DI
• Guice
• Spring DI
• Square Dagger
• Google Dagger 2
• Java EE CDI
• PicoContainer
• Kodein
• Koin

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insert-Koin.io

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10. Kiev 2018Insert Koin
Sample
val sampleModule = applicationContext {
bean { ComponentA() }
}

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Sample
val sampleModule = applicationContext {
bean { ComponentA() }
}

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Sample
val sampleModule = applicationContext {
bean { ComponentA() }
}
class Application : KoinComponent {
val component by inject<ComponentA>()
}

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Sample
val sampleModule = applicationContext {
bean { ComponentA() }
}
class Application : KoinComponent {
val component by inject<ComponentA>()
}

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Sample
val sampleModule = applicationContext {
bean { ComponentA() }
}
class Application : KoinComponent {
val component by inject<ComponentA>()
}
fun main(vararg args: String) {
startKoin(listOf(sampleModule))
}

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Init
class SampleApplication : Application() {
override fun onCreate() {
startKoin(this, listOf(sampleModule))
}
}
fun main(vararg args: String) {
start(listOf(sampleModule)) { … }
}
fun main(vararg args: String) {
startKoin(listOf(sampleModule))
}

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KoinComponent
fun <T> KoinComponent.inject(name: String) : Lazy<T>
fun <T> KoinComponent.inject(name: String, paras: Parameters) : Lazy<T>
fun <T> KoinComponent.property(key: String) : T
fun <T> KoinComponent.property(key: String, defaultValue: T) : T
fun <T> KoinComponent.get(name: String) : T
fun <T> KoinComponent.get(name: String, params: Parameters) : T
fun KoinComponent.setProperty(key: String, value: Any)
fun KoinComponent.releaseContext(name: String)
fun KoinComponent.releaseProperties(vararg keys: String)
interface KoinComponent

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KoinComponent
fun <T> KoinComponent.inject(name: String) : Lazy<T>
fun <T> KoinComponent.inject(name: String, paras: Parameters) : Lazy<T>
fun <T> KoinComponent.property(key: String) : T
fun <T> KoinComponent.property(key: String, defaultValue: T) : T
fun <T> KoinComponent.get(name: String) : T
fun <T> KoinComponent.get(name: String, params: Parameters) : T
fun KoinComponent.setProperty(key: String, value: Any)
fun KoinComponent.releaseContext(name: String)
fun KoinComponent.releaseProperties(vararg keys: String)

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KoinComponent
fun <T> ComponentCallbacks.inject(name: String) : Lazy<T>
fun <T> ComponentCallbacks.inject(name: String, paras: Parameters) : Lazy<T>
fun <T> ComponentCallbacks.property(key: String) : T
fun <T> ComponentCallbacks.property(key: String, defaultValue: T) : T
fun <T> ComponentCallbacks.get(name: String) : T
fun <T> ComponentCallbacks.get(name: String, params: Parameters) : T
fun ComponentCallbacks.setProperty(key: String, value: Any)
fun ComponentCallbacks.releaseContext(name: String)
fun ComponentCallbacks.releaseProperties(vararg keys: String)

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Provide dependencies
applicationContext {
bean { ComponentA() }
factory { ComponentB() }
}

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Provide dependencies
applicationContext {
bean { ComponentA() }
factory { ComponentB() }
}

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Provide dependencies
class ComponentA(c : ComponentB)

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Provide dependencies
applicationContext {
bean { ComponentB() }
bean { ComponentA(get<ComponentB>()) }
}
class ComponentA(c : ComponentB)

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Named dependencies
applicationContext {
bean { ComponentB(…) }
bean { ComponentB(…) }
}

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Named dependencies
applicationContext {
bean(“debug”) { ComponentB(…) }
bean(“prod”) { ComponentB(…) }
}

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Named dependencies
applicationContext {
bean(“debug”) { ComponentB(…) }
bean(“prod”) { ComponentB(…) }
bean { ComponentA(get(“debug”)) }
}

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Named dependencies
applicationContext {
bean(“debug”) { ComponentB() }
bean(“prod”) { ComponentB() }
bean { ComponentA(get(“debug”)) }
}
class Application : KoinComponent {
val componentProd by inject<ComponentB>(“prod”)
val componentDebug by inject<ComponentB>(“debug”)
}

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Type binding
applicationContext {
bean { ComponentImpl() }
bean { ComponentImpl() as Component }
bean { ComponentImpl() } bind Component::class
}

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Dependency Parameters

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Properties
class RestService(url: String)

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Properties
applicationContext {
bean { RestService(getProperty(“url”)) }
}
class RestService(url: String)

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Properties
applicationContext {
bean { RestService(getProperty(“url”)) }
}
class RestService(url: String)
applicationContext {
bean { RestService(getProperty(“url”, “http://localhost”)) }
}

32. Kiev 2018Insert Koin
Properties
applicationContext {
bean { RestService(getProperty(“url”)) }
}
class RestService(url: String)
applicationContext {
bean { RestService(getProperty(“url”, “http://localhost”)) }
}
val key1Property: String by property(“key1”)

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Properties
startKoin(properties: Map<String, Any> = mapOf(“key” to 1))

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Properties Sources
• koin.properties in JAR resources
• koin.properties in assets
• Environment properties

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Environment variables
startKoin(useEnvironmentProperties = true)
// Get user name from properties
val key1Property: String by property(“USER”)

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Problem
class NewsDetailPresenter(newsId : String)

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Parameters
val presenter: NewsDetailPresenter
by inject { mapOf(NEWS_ID to "sample") }

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Parameters
applicationContext {
factory { params: ParametersProvider ->
NewsDetailsPresenter(params[NEWS_ID])
}
}
val presenter: NewsDetailPresenter
by inject { mapOf(NEWS_ID to "sample") }

39. Kiev 2018Insert Koin
Parameters
applicationContext {
factory { params: ParametersProvider ->
NewsDetailsPresenter(params[NEWS_ID])
}
}
val presenter: NewsDetailPresenter
by inject { mapOf(NEWS_ID to "sample") }
interface ParametersProvider {
operator fun <T> get(key: String): T
fun <T> getOrNull(key: String): T?
}

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Contexts

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Contexts
applicationContext {
context("main") {
bean { ComponentA() }
bean { ComponentB() }
}
}

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Contexts
applicationContext {
context("main") {
bean { ComponentA() }
bean { ComponentB() }
}
}
class MainActivity : Activity() {
override fun onStop() {
releaseContext("main")
}
}

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Context isolation
applicationContext {
context("A") {
bean { ComponentA() }
context("B") {
bean { ComponentB() }
}
}
context("C") {
bean { ComponentС() }
}
}

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Context isolation
applicationContext {
context("A") {
bean { ComponentA() }
context("B") {
bean { ComponentB() }
}
}
context("C") {
bean { ComponentС() }
}
}

45. Kiev 2018Insert Koin
Context isolation
applicationContext {
context("A") {
bean { ComponentA() }
context("B") {
bean { ComponentB() }
}
}
context("C") {
bean { ComponentС() }
}
}

46. Kiev 2018Insert Koin
Context isolation
applicationContext {
context("A") {
bean { ComponentA() }
context("B") {
bean { ComponentB() }
}
}
context("C") {
bean { ComponentС() }
}
}

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Logging

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class Presenter(repository: Repository)
class Repository(dateSource: DateSource)
interface DateSource
class DebugDataSource() : DateSource

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applicationContext {
factory { Presenter(get()) }
bean { Repository(get()) }
bean { DebugDataSource() } bind DateSource::class
}
class Presenter(repository: Repository)
class Repository(dateSource: DateSource)
interface DateSource
class DebugDataSource() : DateSource

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applicationContext {
factory { Presenter(get()) }
bean { Repository(get()) }
bean { DebugDataSource() } bind DateSource::class
}
get<Presenter>()
get<Presenter>()
class Presenter(repository: Repository)
class Repository(dateSource: DateSource)
interface DateSource
class DebugDataSource() : DateSource

51. Kiev 2018Insert Koin
applicationContext {
factory { Presenter(get()) }
bean { Repository(get()) }
bean { DebugDataSource() } bind DateSource::class
}
get<Presenter>()
get<Presenter>()
(KOIN) :: Resolve [Presenter] ~ Factory[class=Presenter]
(KOIN) :: Resolve [Repository] ~ Bean[class=Repository]
(KOIN) :: Resolve [Datasource] ~ Bean[class=DebugDatasource, binds~(Datasource)]
(KOIN) :: (*) Created
(KOIN) :: (*) Created
(KOIN) :: (*) Created
(KOIN) :: Resolve [Repository] ~ Factory[class=Repository]
(KOIN) :: Resolve [DebugDatasource] ~ Bean[class=DebugDatasource, binds~(Datasource)]
(KOIN) :: (*) Created
class Presenter(repository: Repository)
class Repository(dateSource: DateSource)
interface DateSource
class DebugDataSource() : DateSource

52. Kiev 2018Insert Koin
Missing dependency
applicationContext {
bean { ComponentA(get()) }
bean { ComponentB(get()) }
}
class ComponentA(component: ComponentB)
class ComponentB(component: ComponentA)
get<ComponentC>()

53. Kiev 2018Insert Koin
Missing dependency
applicationContext {
bean { ComponentA(get()) }
bean { ComponentB(get()) }
}
class ComponentA(component: ComponentB)
class ComponentB(component: ComponentA)
org.koin.error.DependencyResolutionException:
No definition found for ComponentC - Check your definitions and contexts visibility
get<ComponentC>()

54. Kiev 2018Insert Koin
Cyclic dependencies
class ComponentA(component: ComponentB)
class ComponentB(component: ComponentA)

55. Kiev 2018Insert Koin
Cyclic dependencies
applicationContext {
bean { ComponentA(get()) }
bean { ComponentB(get()) }
}
class ComponentA(component: ComponentB)
class ComponentB(component: ComponentA)

56. Kiev 2018Insert Koin
Cyclic dependencies
get<ComponentA>()
applicationContext {
bean { ComponentA(get()) }
bean { ComponentB(get()) }
}
class ComponentA(component: ComponentB)
class ComponentB(component: ComponentA)

57. Kiev 2018Insert Koin
Cyclic dependencies
org.koin.error.BeanInstanceCreationException: Can't create bean Bean[class=ComponentA] due to error :
BeanInstanceCreationException: Can't create bean Bean[class=ComponentB] due to error :
BeanInstanceCreationException: Can't create bean Bean[class=ComponentA] due to error :
DependencyResolutionException: Cyclic dependency detected while resolving class ComponentA
applicationContext {
bean { ComponentA(get()) }
bean { ComponentB(get()) }
}
class ComponentA(component: ComponentB)
class ComponentB(component: ComponentA)
get<ComponentA>()

58. Kiev 2018Insert Koin
Tests

59. Kiev 2018Insert Koin
Tests
class SampleTest : KoinTest {
val presenter : MyPresenter by inject()
val repository : Repository by inject()
@Before
fun before(){
startKoin(listOf(myModule))
}
@Test
fun testSayHello() {
val hello = repository.giveHello()
assertEquals(hello, presenter.sayHello())
}
@After
fun after(){
closeKoin()
}
}

60. Kiev 2018Insert Koin
Tests
class SampleTest : KoinTest {
val presenter : MyPresenter by inject()
val repository : Repository by inject()
@Before
fun before(){
startKoin(listOf(myModule))
}
@Test
fun testSayHello() {
val hello = repository.giveHello()
assertEquals(hello, presenter.sayHello())
}
@After
fun after(){
closeKoin()
}
}

61. Kiev 2018Insert Koin
Tests
class SampleTest : KoinTest {
val presenter : MyPresenter by inject()
val repository : Repository by inject()
@Before
fun before(){
startKoin(listOf(myModule))
}
@Test
fun testSayHello() {
val hello = repository.giveHello()
assertEquals(hello, presenter.sayHello())
}
@After
fun after(){
closeKoin()
}
}

62. Kiev 2018Insert Koin
Tests
class SampleTest : KoinTest {
val presenter : MyPresenter by inject()
val repository : Repository by inject()
@Before
fun before(){
startKoin(listOf(myModule))
}
@Test
fun testSayHello() {
val hello = repository.giveHello()
assertEquals(hello, presenter.sayHello())
}
@After
fun after(){
closeKoin()
}
}

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Graph validation

64. Kiev 2018Insert Koin
Graph validation
class ComponentA(component: ComponentB)
class ComponentB(component: ComponentC)
class ComponentC()

65. Kiev 2018Insert Koin
Graph validation
class ComponentA(component: ComponentB)
class ComponentB(component: ComponentC)
class ComponentC()
val sampleModule = applicationContext {
bean { ComponentA(get()) }
factory { ComponentB(get()) }
}

66. Kiev 2018Insert Koin
Graph validation
class ComponentA(component: ComponentB)
class ComponentB(component: ComponentC)
class ComponentC()
val sampleModule = applicationContext {
bean { ComponentA(get()) }
factory { ComponentB(get()) }
}
class DryRunTest : KoinTest {
@Test
fun dryRunTest() {
startKoin(listOf(sampleModule))
dryRun()
}
}

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Android Arch Components

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Default Way
class ListFragment : Fragment() {
val listViewModel =
ViewModelProviders.of(this).get(ListViewModel::class.java)
}

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Simpler with Kotlin
class ListFragment : Fragment() {
val listViewModel = getViewModel<ListViewModel>()
}
inline fun <reified VM : ViewModel> Fragment.getViewModel():VM {
return viewModelProvider.get(VM::class.java)
}

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ViewModel with arguments
class DetailViewModel(id: String) : ViewModel()

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ViewModel with arguments
class DetailViewModel(id: String) : ViewModel()
class DetailFactory(val id: String) : ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
if (modelClass == DetailViewModel::class.java) {
return DetailViewModel(id) as T
}
error("Can't create ViewModel for class='$modelClass'")
}
}

72. Kiev 2018Insert Koin
ViewModel with arguments
class DetailViewModel(id: String) : ViewModel()
class DetailFactory(val id: String) : ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>): T {
if (modelClass == DetailViewModel::class.java) {
return DetailViewModel(id) as T
}
error("Can't create ViewModel for class='$modelClass'")
}
}
class ListFragment : Fragment() {
val listViewModel = provideViewModel<DetailViewModel>(DetailFactory(id))
}

73. Kiev 2018Insert Koin
Koin Way
applicationContext {
viewModel { params -> DetailViewModel(params["id"]) }
}

74. Kiev 2018Insert Koin
Koin Way
applicationContext {
viewModel { params -> DetailViewModel(params["id"]) }
}
class ListFragment : Fragment() {
val listViewModel
by viewModel<ListViewModel> { mapOf("id" to "sample") }
}

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Koin vs Dagger 2

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What missed from Dagger 2?
• Compile time validation
• Features
• Multibindings
• Async Injection
• Reusable scope

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Why use Koin?
• Dagger 2 is too complex for start with DI
• No need Dagger 2 advanced features
• Single place of dependencies declaration
• DSL is amazing for dependencies declaration
• Support Kotlin Multiplatform projects
• Faster build time
• Pure Kotlin code

78. Kiev 2018Insert Koin
Thanks insert-Koin.io
kiryl.rozau@apalon.com
krlrozov