DIY Dependency Injection with Kotlin @ DevFest Florida 2019

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@HandstandSam #DevFestFL DIY Dependency Injection with Kotlin Sam Edwards -

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@HandstandSam #DevFestFL Why am I talking about DIY Dependency Injection with Kotlin?

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@HandstandSam #DevFestFL Why am I talking about DIY Dependency Injection with Kotlin? ! Share the story of how we implemented DIY

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@HandstandSam #DevFestFL Why am I talking about DIY Dependency Injection with Kotlin? ! Share the story of how we implemented DIY ! Demystify the topic of Dependency Injection

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@HandstandSam #DevFestFL Why am I talking about DIY Dependency Injection with Kotlin? ! Share the story of how we implemented DIY ! Demystify the topic of Dependency Injection ! Show how you can implement DIY, if you choose

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@HandstandSam #DevFestFL Our Story

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@HandstandSam #DevFestFL Our Story ! Our team previously built Capital One Wallet

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@HandstandSam #DevFestFL Our Story ! Our team previously built Capital One Wallet ! We got tasked to build a reusable SDK for Authentication

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@HandstandSam #DevFestFL Our Story ! Our team previously built Capital One Wallet ! We got tasked to build a reusable SDK for Authentication ! This was the first time we were building a complex SDK

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@HandstandSam #DevFestFL Product Requirements

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@HandstandSam #DevFestFL Product Requirements ! SDK will be used by different apps, in different codebases

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@HandstandSam #DevFestFL Product Requirements ! SDK will be used by different apps, in different codebases ! Should not assume clients will be using a 3rd party library

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@HandstandSam #DevFestFL Product Requirements ! SDK will be used by different apps, in different codebases ! Should not assume clients will be using a 3rd party library ! Stay lean and lightweight

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@HandstandSam #DevFestFL Product Requirements ! SDK will be used by different apps, in different codebases ! Should not assume clients will be using a 3rd party library ! Stay lean and lightweight ! Make the SDK configurable

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@HandstandSam #DevFestFL Technical Requirements

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@HandstandSam #DevFestFL Technical Requirements ! Reactive Programming

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@HandstandSam #DevFestFL Technical Requirements ! Reactive Programming ! Immutable Data

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@HandstandSam #DevFestFL Technical Requirements ! Reactive Programming ! Immutable Data ! Modular Code

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@HandstandSam #DevFestFL Technical Requirements ! Reactive Programming ! Immutable Data ! Modular Code ! Single Responsibility Code

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@HandstandSam #DevFestFL Technical Requirements ! Reactive Programming ! Immutable Data ! Modular Code ! Single Responsibility Code ! Well Tested Code

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@HandstandSam #DevFestFL Technical Requirements ! Reactive Programming ! Immutable Data ! Modular Code ! Single Responsibility Code ! Well Tested Code ! Avoid 3rd Party Libraries

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@HandstandSam #DevFestFL Technical Requirements ! Reactive Programming ! Immutable Data ! Modular Code ! Single Responsibility Code ! Well Tested Code ! Avoid 3rd Party Libraries ! 100% Kotlin

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@HandstandSam #DevFestFL Technical Requirements ! Reactive Programming ! Immutable Data ! Modular Code ! Single Responsibility Code ! Well Tested Code ! Avoid 3rd Party Libraries ! 100% Kotlin ! Dependency Injection

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@HandstandSam #DevFestFL Why 100% Kotlin?

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@HandstandSam #DevFestFL Why 100% Kotlin? makes coding easy and concise.

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@HandstandSam #DevFestFL Why 100% Kotlin? makes dependency injection easy and concise.

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@HandstandSam #DevFestFL Why Dependency Injection?

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@HandstandSam #DevFestFL Why Dependency Injection? ! Testing

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@HandstandSam #DevFestFL Why Dependency Injection? ! Testing ! Mock Flavors

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@HandstandSam #DevFestFL Why Dependency Injection? ! Testing ! Mock Flavors ! Custom Debug Features

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@HandstandSam #DevFestFL Why Dependency Injection? ! Testing ! Mock Flavors ! Custom Debug Features ! Environment Switching (Test vs Production Servers)

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@HandstandSam #DevFestFL Why Dependency Injection? ! Testing ! Mock Flavors ! Custom Debug Features ! Environment Switching (Test vs Production Servers) ! Promotes building more reusable code

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@HandstandSam #DevFestFL Why Dependency Injection? ! Testing ! Mock Flavors ! Custom Debug Features ! Environment Switching (Test vs Production Servers) ! Promotes building more reusable code ! Discourages use of static singletons

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@HandstandSam #DevFestFL It Enables Testing DevFest Florida

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@HandstandSam #DevFestFL It Enables Custom Debug Features Droidcon Boston

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@HandstandSam #DevFestFL It Enable Mock Flavors Droidcon NYC

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@HandstandSam #DevFestFL Dependency Injection is Not Magical

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@HandstandSam #DevFestFL Dependency Injection is Not Magical DI !=

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@HandstandSam #DevFestFL Dependency Injection is

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@HandstandSam #DevFestFL Dependency Injection is Inversion of Control

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@HandstandSam #DevFestFL Dependency Injection is Passing in dependencies  instead of pre-defining them. Inversion of Control

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@HandstandSam #DevFestFL Dependency Injection is Inversion of Control Code execute Dependencies ( )

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@HandstandSam #DevFestFL Dependency Injection is Inversion of Control Code execute ( ) Dependencies

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@HandstandSam #DevFestFL Without Dependency Injection class NetworkConfig( val fullUrl = "http://localhost:8080/" val isLocalhostServer = true }

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@HandstandSam #DevFestFL Setter Injection class NetworkConfig( var fullUrl: String, var isLocalhostServer: Boolean ) val config = NetworkConfig() config.fullUrl = “http://localhost:8080/" config.isLocalhostServer = true

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@HandstandSam #DevFestFL Constructor Injection class NetworkConfig( val baseUrl: String, val port: Int ) { val fullUrl = "$baseUrl:$port/" val isLocalhostServer = baseUrl.contains("//localhost") }

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@HandstandSam #DevFestFL Commonalities: Inversion of Control ! Inversion of Control is passing in dependencies instead of pre- defining them.

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@HandstandSam #DevFestFL Aren’t Their Libraries That Do DI for You? ! Yes, let’s take a look.

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@HandstandSam #DevFestFL Open Source DI Libraries ! Dagger ! Toothpick ! Koin ! Kodein

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@HandstandSam #DevFestFL ! Dagger ! Toothpick ! Koin ! Kodein Code Generation YES YES NO NO

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@HandstandSam #DevFestFL ! Dagger ! Toothpick ! Koin ! Kodein Code Generation YES YES NO NO ❌ ❌

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@HandstandSam #DevFestFL ! Dagger ! Toothpick ! Koin ! Kodein Code Generation YES YES NO NO Single  Instance NO NO YES NO ❌ ❌

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@HandstandSam #DevFestFL ! Dagger ! Toothpick ! Koin ! Kodein Code Generation YES YES NO NO Single  Instance NO NO YES NO ❌ ❌ ❌

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@HandstandSam #DevFestFL ! Dagger ! Toothpick ! Koin ! Kodein Code Generation YES YES NO NO Single  Instance NO NO YES NO Available  at the time YES YES YES NO ❌ ❌ ❌

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@HandstandSam #DevFestFL ! Dagger ! Toothpick ! Koin ! Kodein Code Generation YES YES NO NO Single  Instance NO NO YES NO Available  at the time YES YES YES NO ❌ ❌ ❌ ❌

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@HandstandSam #DevFestFL ! Dagger ! Toothpick ! Koin ! Kodein Code Generation YES YES NO NO Single  Instance NO NO YES NO Available  at the time YES YES YES NO Adds dependency on another library YES YES YES YES ❌ ❌ ❌ ❌

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@HandstandSam #DevFestFL So, How Much Work is DIY?

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@HandstandSam #DevFestFL So, How Much Work is DIY? ! Not that much

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@HandstandSam #DevFestFL So, How Much Work is DIY? ! Not that much ! Slightly more verbose

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@HandstandSam #DevFestFL So, How Much Work is DIY? ! Not that much ! Slightly more verbose ! Have to manually build advanced DI features

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@HandstandSam #DevFestFL So, How Much Work is DIY? ! Not that much ! Slightly more verbose ! Have to manually build advanced DI features ! Great for simple use cases when you don’t already know a DI library really well

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@HandstandSam #DevFestFL ShoppingApp - Open Source on GitHub https:/ /github.com/handstandsam/ShoppingApp

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@HandstandSam #DevFestFL Swapping Dependencies on a Graph

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@HandstandSam #DevFestFL Swapping Dependencies on a Graph ! Mock Server vs. Testing Server vs. Live (Production Server)

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@HandstandSam #DevFestFL Swapping Dependencies on a Graph ! Mock Server vs. Testing Server vs. Live (Production Server) ! Graph is where all your dependencies are configured.

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@HandstandSam #DevFestFL Swapping Dependencies on a Graph ! Mock Server vs. Testing Server vs. Live (Production Server) ! Graph is where all your dependencies are configured. ! Just swap out pieces of your graph you need to change.

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@HandstandSam #DevFestFL Network Graph interface NetworkGraph { val categoryRepo: CategoryRepo val itemRepo: ItemRepo val userRepo: UserRepo }

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@HandstandSam #DevFestFL Network Graph interface NetworkGraph { val categoryRepo: CategoryRepo val itemRepo: ItemRepo val userRepo: UserRepo } class NetworkGraphImpl( networkConfig: NetworkConfig ) : NetworkGraph { private val retrofit: Retrofit= Retrofit.Builder() .baseUrl(networkConfig.fullUrl) .addConverterFactory(moshiConverterFactory) .addCallAdapterFactory(rxJava2CallAdapterFactory) .client(okHttpClientBuilder.build()) .build() private val shoppingService: ShoppingService = retrofit.create(ShoppingService::class.java) override val categoryRepo: CategoryRepo = NetworkCategoryRepo(shoppingService) override val itemRepo: ItemRepo = NetworkItemRepo(shoppingService) override val userRepo: UserRepo = NetworkUserRepo(shoppingService) }

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@HandstandSam #DevFestFL Create Graphs of Dependencies • Similar to Dagger @Component OkHttpClient Services Retrofit NetworkGraph Url Repos

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@HandstandSam #DevFestFL Session Graph interface SessionGraph { val sessionManager: SessionManager val checkoutCart: CheckoutCart val userPreferences: UserPreferences }

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@HandstandSam #DevFestFL Session Graph interface SessionGraph { val sessionManager: SessionManager val checkoutCart: CheckoutCart val userPreferences: UserPreferences } class SessionGraphImpl( appContext: Context ) : SessionGraph { override val checkoutCart = CheckoutCart() override val userPreferences = UserPreferences(appContext) override val sessionManager = SessionManager(checkoutCart, userPreferences) }

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@HandstandSam #DevFestFL Multiple or Nested Graphs are AppGraph SessionGraph NetworkGraph

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@HandstandSam #DevFestFL Multiple or Nested Graphs are AppGraph SessionGraph NetworkGraph

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@HandstandSam #DevFestFL Multiple or Nested Graphs are AppGraph SessionGraph NetworkGraph ! Each module project needs their own graph

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@HandstandSam #DevFestFL Multiple or Nested Graphs are AppGraph SessionGraph NetworkGraph ! Each module project needs their own graph ! Each graph is similar to a Dagger @Component

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@HandstandSam #DevFestFL ! Use the `by lazy` language feature of Kotlin to delay initialization, but cache result. Leveraging `by lazy`

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@HandstandSam #DevFestFL ! Use the `by lazy` language feature of Kotlin to delay initialization, but cache result. Leveraging `by lazy` class AppGraph { val networkGraph by lazy NetworkGraph(config = config) }

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@HandstandSam #DevFestFL ! Create a factory with a lambda Factories

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@HandstandSam #DevFestFL ! Create a factory with a lambda Factories class AppGraph { val dbFactory: () -> Database = {Database(logger = logger, utils = utils)} } val db = dbFactory()

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@HandstandSam #DevFestFL Scoping

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@HandstandSam #DevFestFL ! Use a factory, but this is DIY, so you will have to manage scoping yourself. Scoping

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@HandstandSam #DevFestFL Setting up Your Graphs class MyApplication : Application { val graph by lazy { AppGraph(this) } override fun onCreate() { //Access Graph to Instantiate graph } } class MyApplication : Application { lateinit var graph: AppGraph override fun onCreate() { graph = AppGraph(this) } } or ! Create Graph during Application::onCreate() and attach to Application

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@HandstandSam #DevFestFL Supporting Graphs in Modules class AppGraph(context: Context) { init { instance = this } companion object { lateinit var instance: AppGraph } }

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@HandstandSam #DevFestFL ! Create a singleton since the module is unaware of the Application Supporting Graphs in Modules class AppGraph(context: Context) { init { instance = this } companion object { lateinit var instance: AppGraph } }

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@HandstandSam #DevFestFL Dependency Injection on Activities & Fragments

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@HandstandSam #DevFestFL ! Constructors of Application, Fragments, Activities & Services are called by the platform Dependency Injection on Activities & Fragments

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@HandstandSam #DevFestFL ! Constructors of Application, Fragments, Activities & Services are called by the platform ! You have to wait do do any injection until after the `onCreate` lifecycle method Dependency Injection on Activities & Fragments

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@HandstandSam #DevFestFL ! lateinit var, grabbing from Application Accessing Graph in Activities & Fragments class MyActivity : Activity() { lateinit private var graph: AppGraph override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) graph = (application as MyApplication).graph //Access your fields now graph.database } }

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@HandstandSam #DevFestFL ! Simplify using an extension function. Accessing Graph in Activities & Fragments class MyActivity : Activity() { lateinit private var graph: AppGraph override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) graph = application.graph } } fun Application.graph(): AppGraph{ return (this as MyApplication).graph }

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@HandstandSam #DevFestFL ! OR use `by lazy` to defer access until the Activity has been created Accessing Graph in Activities & Fragments class MyActivity : Activity() { private val graph: AppGraph get() = application.graph() private val db: UserRepo by lazy {graph.networkGraph.userRepo} } fun Application.graph(): AppGraph{ return (this as MyApplication).graph }

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@HandstandSam #DevFestFL Accessing Graph in Activities & Fragments class MyActivity : Activity() { private val graph: AppGraph get() = application.graph() private val db: UserRepo get() = graph.networkGraph.userRepo } fun Application.graph(): AppGraph{ return (this as MyApplication).graph }

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@HandstandSam #DevFestFL ! OR use `get() =` to defer access until the Activity has been created Accessing Graph in Activities & Fragments class MyActivity : Activity() { private val graph: AppGraph get() = application.graph() private val db: UserRepo get() = graph.networkGraph.userRepo } fun Application.graph(): AppGraph{ return (this as MyApplication).graph }

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@HandstandSam #DevFestFL Pro Tips

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@HandstandSam #DevFestFL Pro Tips ! Try and avoid `lateinit var` for injected values

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@HandstandSam #DevFestFL Pro Tips ! Try and avoid `lateinit var` for injected values ! `lateinit` can create runtime Exceptions

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@HandstandSam #DevFestFL Pro Tips ! Try and avoid `lateinit var` for injected values ! `lateinit` can create runtime Exceptions ! `var` creates mutable state

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@HandstandSam #DevFestFL Pro Tips ! Try and avoid `lateinit var` for injected values ! `lateinit` can create runtime Exceptions ! `var` creates mutable state ! `by lazy` create an anonymous class

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@HandstandSam #DevFestFL Pro Tips ! Try and avoid `lateinit var` for injected values ! `lateinit` can create runtime Exceptions ! `var` creates mutable state ! `by lazy` create an anonymous class ! You can use `get() =` if your data is an immutable singleton

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@HandstandSam #DevFestFL Accessing Dependencies from the Graph LoginPresenter( view = loginView, sessionManager = appGraph.sessionGraph.sessionManager, userRepo = appGraph.networkGraph.userRepo )

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@HandstandSam #DevFestFL Accessing Dependencies from the Graph private val sessionManager: SessionManager get() = graph.sessionGraph.sessionManager private val userRepo: UserRepo get() = graph.networkGraph.userRepo LoginPresenter( view = loginView, sessionManager = sessionManager, userRepo = userRepo )

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@HandstandSam #DevFestFL Key Takeaways

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@HandstandSam #DevFestFL Key Takeaways ! You don’t HAVE to use a Dependency Injection Library, Dagger

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@HandstandSam #DevFestFL Key Takeaways ! You don’t HAVE to use a Dependency Injection Library, Dagger ! There are no magic annotations. @Inject

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@HandstandSam #DevFestFL Key Takeaways ! You don’t HAVE to use a Dependency Injection Library, Dagger ! There are no magic annotations. @Inject ! Kotlin language features make this concise and straightforward

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@HandstandSam #DevFestFL Thank you. My team is hiring in DC, Richmond & San Francisco.