Dependency Injection for Kotlin Apps with Koin

The light version of my slides, for my talk at Kotlin Day in London

(https://www.eventbrite.co.uk/e/kotlineverywhere-kotlin-day-london-tickets-74713806005?aff=eemailordconf&utm_campaign=order_confirm&utm_medium=email&ref=eemailordconf&utm_source=eventbrite&utm_term=viewevent#)

Transcript

1. Dependency injection for Kotlin apps with Koin Arnaud Giuliani @arnogiu
2. ! Freelance Software Eng " Mobile First Lead of Koin project Arnaud GIULIANI
3. Why a new dependency injection framework?
4. The CoffeeMaker App ☕ * aka the thermosiphon dagger’s nightmare sample app
5. Pump +pump() Thermosiphon Heater +off() +on() +isHot() ElectricHeater CoffeeMaker +brew()
6. The Heater
7. interface Heater { fun on() fun off() fun isHot() : Boolean }
8. class ElectricHeater : Heater { var heating: Boolean = false override fun on() { println("~ ~ ~ heating ~ ~ ~") heating = true } override fun off() { heating = false } override fun isHot(): Boolean = heating }
9. The Thermosiphon
10. interface Pump { fun pump() }
11. class Thermosiphon(val heater: Heater) : Pump{ override fun pump() { if (heater.isHot()){ println("=> => pumping => =>") } } }
12. The CoffeeMaker
13. class CoffeeMaker(val pump: Pump, val heater: Heater) { fun brew() { heater.on() pump.pump() println(" [_]P coffee! [_]P ") heater.off() } }
14. The CoffeeApp
15. class CoffeeApp { val coffeeMaker: CoffeeMaker fun run() { coffeeMaker.brew() } }
16. Pump +pump() Thermosiphon Heater +off() +on() +isHot() ElectricHeater CoffeeMaker +brew() how to assemble it?
17. class ElectricHeater : Heater class Thermosiphon(val heater: Heater) : Pump class CoffeeMaker(val pump: Pump, val heater: Heater) // bootstrap from an injector // ---- // heater : Heater = ElectricHeater() // pump : Pump = Thermosiphon(heater) // coffeeMaker = CoffeeMaker(heater,pump) val coffeeMaker = Injector.get<CoffeeMaker>()
18. { Thermosiphon(get()) } { ElectricHeater() } Provide Provide
19. Koin
20. - Intuitive DSL to describe it - Lightweight container to run it - Simple API to use it - Pure Kotlin!
21. repositories { jcenter() } dependencies { // Koin for Kotlin implementation ‘org.koin:koin-core:$version’ } Gradle Setup
22. // declare definitions here module { }
23. module { // definition single | factory { instance creation expression } }
24. class ElectricHeater : Heater class Thermosiphon(val heater: Heater) : Pump class CoffeeMaker(val pump: Pump, val heater: Heater)
25. class ElectricHeater : Heater class Thermosiphon(val heater: Heater) : Pump class CoffeeMaker(val pump: Pump, val heater: Heater) val coffeeMakerModule = module { single { CoffeeMaker(get(),get()) } single<Pump>{ Thermosiphon(get()) } single<Heater> { ElectricHeater() } } * also multi modules
26. class ElectricHeater : Heater class Thermosiphon(val heater: Heater) : Pump class CoffeeMaker(val pump: Pump, val heater: Heater) val coffeeMaker = module { single { CoffeeMaker(get(),get()) } } val coffeeParts = module { single<Pump>{ Thermosiphon(get()) } single<Heater> { ElectricHeater() } } * also multi modules
27. Koin Component a class that can use the Koin container
28. ✅ open access to Kotlin extensions: inject(), get() identify a class linked to the Koin API KoinComponent is an interface marker bootstrap & help integrate with runtime (Android…)
29. class CoffeeApp : KoinComponent { val coffeeMaker: CoffeeMaker by inject() fun run() { coffeeMaker.brew() } }
30. The CoffeeApp
31. startKoin to start the Koin container
32. class CoffeeApp : KoinComponent { val coffeeMaker: CoffeeMaker by inject() fun run() { coffeeMaker.brew() } } fun main(vararg args: String) { }
33. fun run() { coffeeMaker.brew() } } fun main(vararg args: String) { startKoin { } }
34. fun run() { coffeeMaker.brew() } } fun main(vararg args: String) { startKoin { modules(coffeeMakerModule) } }
35. fun run() { coffeeMaker.brew() } } fun main(vararg args: String) { startKoin { modules(coffeeMakerModule) } CoffeeApp().run() }
36. ~ ~ ~ heating ~ ~ ~ => => pumping => => [_]P coffee! [_]P
38. Can’t create Android components directly
39. Activity, Fragment, Service … are extended as KoinComponent! out of the box! ✅ Koin extensions for Android
40. repositories { jcenter() } dependencies { // Koin for Android implementation ‘org.koin:koin-android:$version’ } Gradle Setup
41. class MyApplication : Application() { override fun onCreate() { super.onCreate() // Add Android Koin Logger startKoin { androidLogger() modules(coffeeMakerModule) } } }
42. class MyApplication : Application() { override fun onCreate() { super.onCreate() // Reference Android context in Koin startKoin { androidLogger() androidContext(this@MyApplication) modules(coffeeMakerModule) } } }
43. class MyActivity : AppCompatActivity() { val coffeeMaker: CoffeeMaker by inject() }
44. Get the Android context?
45. class MyApplication : Application() { override fun onCreate() { super.onCreate() // Reference Android context in Koin startKoin { androidLogger() androidContext(this@MyApplication) modules(coffeeMakerModule) } } }
46. class MyComponent(val context : Context) val myModule = module { single { MyComponent(androidContext()) } }
47. class MyComponent(val context : Context) val myModule = module { single { MyComponent(get()) } }
48. Dealing with transient components? ie. presenters …
49. class MyPresenter(val coffeeMaker : CoffeeMaker) val myModule = module { // will create MyPresenter on each call factory { MyPresenter(get()) } }
50. class MyPresenter(val coffeeMaker : CoffeeMaker) val myModule = module { // will create MyPresenter on each call factory { MyPresenter(get()) } } class MyActivity : AppCompatActivity() { // new instance on each call val presenter: MyPresenter by inject() }
51. Ready for Android Architecture Components
52. repositories { jcenter() } dependencies { // Koin for Android + ViewModel features implementation ‘org.koin:koin-android-viewmodel:$version’ implementation ‘org.koin:koin-androidx-viewmodel:$version’ } Gradle Setup
53. ✅ Koin extensions for Android ViewModel
54. class MyViewModel(val coffeeMaker : CoffeeMaker) : ViewModel() val coffeeMakerModule = module { viewModel { MyViewModel(get()) } }
55. //... viewModel { MyViewModel(get()) } } class MyActivity : AppCompatActivity() { // inject ViewModel val myViewModel: MyViewModel by viewModel()
56. //... viewModel { MyViewModel(get()) } } class MyFragment : Fragment() { // inject ViewModel val myViewModel: MyViewModel by viewModel()
57. //... viewModel { MyViewModel(get()) } } class MyFragment : Fragment() { // inject ViewModel from parent activity val myViewModel: MyViewModel by sharedViewModel()
58. Injecting Bundle State in ViewModel
59. repositories { jcenter() } dependencies { // Koin for Android Fragments feature implementation ‘org.koin:koin-androidx-viewmodel:$version’ } Gradle Setup 2.1.0-alpha-4
60. // Inject your state class StateViewModel(val state: SavedStateHandle) : ViewModel() // use injection parameter to get state viewModel { (handle: SavedStateHandle, id: String) -> StateViewModel(handle, id, get()) } // Provide initial state as parameter class MVVMActivity : AppCompatActivity() { val mySavedVM: StateViewModel by viewModel { parametersOf(Bundle(), "vm1") } }
61. // Inject your state class StateViewModel( val handle: SavedStateHandle, val id: String, val service: SimpleService) : ViewModel() // use injection parameter to get state viewModel { (handle: SavedStateHandle) -> StateViewModel(handle, id, get()) } // Provide initial state as parameter class MVVMActivity : AppCompatActivity() { val mySavedVM: StateViewModel by viewModel { parametersOf(Bundle(), "vm1") } }
62. // Inject your state class StateViewModel( val handle: SavedStateHandle, val id: String, val service: SimpleService) : ViewModel() // use injection parameter to get state viewModel { (handle: SavedStateHandle, id: String) -> StateViewModel(handle, id, get()) } // Provide initial state as parameter class MVVMActivity : AppCompatActivity() { val mySavedVM: StateViewModel by viewModel { parametersOf(Bundle()) } }
63. Inject your Fragments
64. repositories { jcenter() } dependencies { // Koin for Android Fragments feature implementation ‘org.koin:koin-androidx-fragment:$version’ } Gradle Setup 2.1.0-alpha-4
65. // Use constructor injection :) class MyFragment(val session: Session) : Fragment() // Declare your fragment val module = module { single { Session() } fragment { MyFragment(get()) } } // Setup in Activity class MyMActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { // setup factory setupKoinFragmentFactory() super.onCreate(savedInstanceState)
66. // Use constructor injection :) class MyFragment(val session: Session) : Fragment() // Declare your fragment val module = module { single { Session() } fragment { MyFragment(get()) } } // Setup in Activity class MyMActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { // setup factory setupKoinFragmentFactory() super.onCreate(savedInstanceState)
67. // Setup in Activity class MyMActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { // setup factory setupKoinFragmentFactory() super.onCreate(savedInstanceState) // Call your Fragment supportFragmentManager.beginTransaction() .replace(R.id.fragment, MyFragment::class.java, null, null) .commit() } }
68. // Setup in Activity class MyMActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) { // setup factory setupKoinFragmentFactory() super.onCreate(savedInstanceState) // Call your Fragment supportFragmentManager.beginTransaction() .replace(R.id.fragment, MyFragment::class.java, null, null) .commit() } }
69. Ktor Web Applications
70. repositories { jcenter() } dependencies { // Koin for Ktor compile ‘org.koin:koin-ktor:$version’ // Koin SLF4J Logger compile ‘org.koin:koin-logger-slf4j:$version’ } Gradle Setup
71. fun main(args: Array<String>) { // Start Ktor embeddedServer(Netty, commandLineEnvironment(args)).start() } fun Application.main() { install(DefaultHeaders) install(CallLogging) // Routing section routing { get("/hello") { call.respondText(...) } } }
72. fun main(args: Array<String>) { // Start Ktor embeddedServer(Netty, commandLineEnvironment(args)).start() } fun Application.main() { install(DefaultHeaders) install(CallLogging) // Routing section routing { get("/coffee") { call.respondText(...) } } }
73. fun Application.main() { install(DefaultHeaders) install(CallLogging) install(Koin) { slf4jLogger() modules(coffeeMakerModule) } // Routing section routing { get(“/coffee") { call.respondText(...) } } }
74. fun Application.main() { install(DefaultHeaders) install(CallLogging) install(Koin) { slf4jLogger() modules(coffeeMakerModule) } val coffeeMaker by inject() // Routing section routing { get("/coffee") { call.respondText(...) } } }
75. fun Application.main() { install(DefaultHeaders) install(CallLogging) install(Koin) { slf4jLogger() modules(coffeeMakerModule) } val coffeeMaker by inject() // Routing section routing { get("/coffee") { call.respondText(coffeeMaker.printBrew()) } } }
76. Application, Route, Routing … are extended as KoinComponent! out of the box! ✅ Koin extensions for Ktor
77. class ElectricHeater : Heater class Thermosiphon(val heater: Heater) : Pump class CoffeeMaker(val pump: Pump, val heater: Heater) val coffeeMakerModule = module(createdAtStart = true) { single<CoffeeMaker>() singleBy<Pump,Thermosiphon>() singleBy<Heater,ElectricHeater>() }
78. Testing easily with Koin ✅
79. repositories { jcenter() } dependencies { // Koin for Tests testImplementation ‘org.koin:koin-test:$version’ } Gradle Setup In rewrite!
80. Checking your modules ✔
81. class ModuleTest { @Test fun `check all definitions from coffeeMakerModule`() { startKoin { modules(coffeeMakerModule) }.checkModules() } }
82. ✅ Koin extensions with JUnit & Mockito
83. class CoffeeMakerTest : KoinTest { val coffeeMaker: CoffeeMaker by inject() val heater: Heater by inject() @Test fun testHeaterIsTurnedOnAndThenOff() { startKoin { modules(coffeeMakerModule) } } }
84. class CoffeeMakerTest : KoinTest { val coffeeMaker: CoffeeMaker by inject() val heater: Heater by inject() @Test fun testHeaterIsTurnedOnAndThenOff() { startKoin { modules(coffeeMakerModule) } declareMock<Heater>() } }
85. class CoffeeMakerTest : KoinTest { val coffeeMaker: CoffeeMaker by inject() val heater: Heater by inject() @Test fun testHeaterIsTurnedOnAndThenOff() { startKoin { modules(coffeeMakerModule) } declareMock<Heater>() given(heater.isHot()).will { true } coffeeMaker.brew() verify(heater, times(1)).on() verify(heater, times(1)).off() } }
86. More about Koin✨
87. - Container DSL - Qualifiers (string/type) - Global vs isolated context - Scope API - Android, Scopes & lifecycle - Injection Parameters - AndroidX - Koin for Java - Koin for Ktor
88. Koin 2.0
89. Since first 1.0 version…
90. Simple DSL module, single, factory, get
91. Pragmatic API ✌ KoinComponent, get, inject
94. * startup & Kotlin overhead ** split modules startup if needed
95. Benchmarks https://github.com/InsertKoinIO/thermosiphon_dagger2koin https://github.com/Sloy/android-dependency-injection-performance https://github.com/arnaudgiuliani/android-dependency-injection-performance
96. http://bit.ly/ready4koin
97. - Container DSL - Qualifiers (string/type) - Global vs isolated context - Scope API - Android, Scopes & lifecycle - Injection Parameters - AndroidX - Koin for Java - Koin for Ktor
98. - Container DSL - Qualifiers (string/type) - Global vs isolated context - Scope API - Android, Scopes & lifecycle - Injection Parameters - AndroidX - Koin for Java - Koin for Ktor
99. Dependency injection & Service Locator?
100. Dependency injection & Service Locator
101. class Thermosiphon(val heater : Heater) : Pump class ElectricHeater() : Heater module { single<Pump>{ Thermosiphon(get()) } single<Heater> { ElectricHeater() } } Dependency Injection - Constructor injection configured via Koin DSL - Your classes are not dependant to Koin API - Instances are called by Koin Container - Functional DSL Configuration: parameters, context, scopes…
102. class CoffeeApp : KoinComponent { val coffeeMaker by inject<CoffeeMaker>() } Service Locator - Use the Koin API to retrieve a dependency - “Host” class not created by Koin
103. Is service locator bad?
104. class CoffeeApp : KoinComponent { // Lazily ask for instance val coffeeMaker : CoffeeMaker by inject() } Service Locator class CoffeeApp { lateinit var coffeeMaker : CoffeeMaker init { // ask injection of setters DI.inject(this) } } Setter Injection
105. 0
106. 80% of your Koin usage will be configuration 20% will be platform extensions Limit your dependency to Koin as much as possible
107. The choice between Service Locator and Dependency Injection is less important than the principle of separating service configuration from the use of services within an application. Martin Fowler
108. Functional Dependency Injection
109. Function and Container Context
110. val coffeeMakerModule = module { single { CoffeeMaker(get(),get()) } single<Pump>{ Thermosiphon(get()) } single<Heater> { ElectricHeater() } } typealias Definition<T> = Scope.(DefinitionParameters) -> T
111. Definition Parameters DSL Extension Scope
112. Function to inject parameters
113. class MyPresenter(val id : String) val myModule = module { factory { (id : String) -> MyPresenter(id)} }
114. val myModule = module { factory { (id : String) -> MyPresenter(id)} } class MyActivity : AppCompatActivity(){ val presenter : MyPresenter by inject { parametersOf("42")} }
115. class MyViewModel(val id : String) val myModule = module { viewModel { (id : String) -> MyViewModel(id)} }
116. val myModule = module { viewModel { (id : String) -> MyViewModel(id)} } class MyActivity : AppCompatActivity(){ val presenter : MyViewModel by viewModel { parametersOf("42")} }
117. ✨ Simpler declaration with Reflection ✨
118. A.k.a “Get rid of get() get() get() get() get()”
119. Functional Dependency Injection 0
120. repositories { jcenter() } dependencies { // Koin for Android implementation ‘org.koin:koin-core-ext:$version’ } Gradle Setup
121. class ElectricHeater : Heater class Thermosiphon(val heater: Heater) : Pump class CoffeeMaker(val pump: Pump, val heater: Heater) val coffeeMakerModule = module { single { CoffeeMaker(get(),get()) } single<Pump>{ Thermosiphon(get()) } single<Heater> { ElectricHeater() } }
122. class ElectricHeater : Heater class Thermosiphon(val heater: Heater) : Pump class CoffeeMaker(val pump: Pump, val heater: Heater) val coffeeMakerModule = module { single<CoffeeMaker>() singleBy<Pump,Thermosiphon>() singleBy<Heater,ElectricHeater>() }
123. Available out of the box for pure JVM platforms (Ktor, TornadoFx…)
124. repositories { jcenter() } dependencies { // Koin for Android implementation ‘org.koin:koin-android-ext:$version’ implementation ‘org.koin:koin-androidx-ext:$version’ } Gradle Setup
125. class MyViewModel(val coffeeMaker : CoffeeMaker) : ViewModel() val coffeeMakerModule = module { viewModel<MyViewModel>() }
126. Add following pro guard rules https://insert-koin.io/docs/2.0/quick-references/experimental-features/#proguard-rule
127. Check performances Pure functional DSL declaration is 4x - 10x faster * definition execution time ** depending on devices (< Android 6)
128. Let’s migrate to Koin, what else?
129. Refactoring is not always sustainable
130. « Hard to switch from our current DI » Top #1 issue
132. What if you could… run it easily in a module ✨
133. startKoin { modules(…) } loadKoinModules(…) Definition<Heater> Definition<Pump> Definition<CoffeeMaker> unloadKoinModules(…)
134. Making dynamic modules with Koin - Load dynamic modules/definitions - Change implementation on the fly - Easy to compose step by step
135. Onboarding Wallet Profile Transactions Profile v2 Payments Card Management Onboarding Onboarding v2
136. Dynamic Modules Architecture - Registry / Plugin architecture - Feature <> Libraries isolation (modules) - Navigation, Feature Flagging, A/B testing …
137. What’s next?
139. Tips & Best pratices
140. Try the getting started projects * look at code samples
141. start.insert-koin.io
142. doc.insert-koin.io
143. Add it step by step to your project * start with small components
144. Check your modules ✅
145. Keep it simple
146. and …
147. StackOverflow, Github & Slack for any question
149. @insertkoin_io koin-developers
150. Thank you! All the community…
151. stable_version = “2.0.1" unstable_version = “2.1.0-alpha-4” repositories { jcenter() } dependencies { // Core features compile "org.koin:koin-core:$version" // Ktor compile "org.koin:koin-ktor:$version" compile "org.koin:koin-logger-slf4j:$version" // Android implementation "org.koin:koin-android:$version"
152. dependencies { // Core features compile "org.koin:koin-core:$version" // Ktor compile "org.koin:koin-ktor:$version" compile "org.koin:koin-logger-slf4j:$version" // Android implementation "org.koin:koin-android:$version" // Android + ViewModel implementation "org.koin:koin-android-viewmodel:$version" // JUnit & Mockito testImplementation "org.koin:koin-test:$version" }
153. dependencies { // Core features compile "org.koin:koin-core:$version" // Ktor compile "org.koin:koin-ktor:$version" compile "org.koin:koin-logger-slf4j:$version" // Android implementation "org.koin:koin-android:$version" // Android + ViewModel implementation "org.koin:koin-android-viewmodel:$version" // JUnit & Mockito testImplementation "org.koin:koin-test:$version" }
154. dependencies { // Core features compile "org.koin:koin-core:$version" // Ktor compile "org.koin:koin-ktor:$version" compile "org.koin:koin-logger-slf4j:$version" // Android implementation “org.koin:koin-android:$version” // Android + ViewModel implementation "org.koin:koin-android-viewmodel:$version" // JUnit & Mockito testImplementation "org.koin:koin-test:$version" }
155. dependencies { // Core features compile "org.koin:koin-core:$version" // Ktor compile "org.koin:koin-ktor:$version" compile "org.koin:koin-logger-slf4j:$version" // Android implementation "org.koin:koin-android:$version" // Android + ViewModel implementation "org.koin:koin-android-viewmodel:$version" // JUnit & Mockito testImplementation "org.koin:koin-test:$version" }
156. insert-koin.io
157. Arnaud Giuliani - @arnogiu Thank you!