Android Dagger Therapy Session

Android, Dagger, and Mangroves.

Slides from talk at GDG Boulder Jan 11, 2018.

1. Android Dagger Therapy Session Joshua Jamison
2. Meet Josh
3. Story Time Josh wrote an app.
4. Well… better at least. More organized, less spaghetti. But this time he’s going to do it “right”… Josh decides to write a new app from scratch. Story Time Mangrove
5. Josh likes this Separation of Concerns and Inversion of Control stuff Josh decides to use Dagger Dagger
6. Dagger Dependency Injection framework Separates object creation from business logic Reusability Testability
7. Josh starts a new application. New App Stuff
8. Updating build.gradle Time for Dagger apply plugin: ‘kotlin-kapt' … dependencies { ... // Dagger implementation "com.google.dagger:dagger:2.13" kapt "com.google.dagger:dagger-compiler:2.13" ... }
9. Defines a root “Application” Component and stores an instance of it on the Application @Component @Component interface MangroveComponent class MangroveApplication : Application() { val component: MangroveComponent by lazy { DaggerMangroveComponent.create() } }
10. Component? Component is one-half of an Object Graph. Defines graph relationships Defines injectable targets
11. Serve as the “root node” for the object graph. Application Component Root Node Child A Child A-A Child B Child C Child A-A-A Child A-A-B
12. Adding an injection target to your component @Component @Component interface MangroveComponent { fun inject(target: MangroveApplication) }
13. Also be sure to call inject @Component class MangroveApplication : Application() { val component: MangroveComponent by lazy { DaggerMangroveComponent.create() } override fun onCreate() { super.onCreate() component.inject(this) } }
14. Update the component with a Module Adding Modules @Module class MangroveModule @Component(modules = [MangroveModule::class]) interface MangroveComponent { fun inject(target: MangroveApplication) }
15. Module? Modules serve as the other half of the object graph Defines how dependencies are created Not necessary to be 1-1 with Component
16. Providing dependencies from a Module Providing dependencies @Module class MangroveModule { @Provides fun provideApiKey(): String = "110b1a3cd59a299dc8a1f14" }
17. Injecting into the target from the component Injecting class MangroveApplication : Application() { … @Inject lateinit var cacheFileName: String override fun onCreate() { super.onCreate() component.inject(this) } }
18. Sometimes you need to provide two different objects of the same type Qualifiers @Provides fun provideApiKey(): String = "110b1a3cd59a299dc8a1f14" @Provides fun provideCacheFileName(): String = "mangrove-cache" e: /Users/joshuajamison/Projects/personal/Mangrove/app/build/tmp/kapt3/ stubs/debug/com/codeundone/mangrove/MangroveComponent.java:7: error: java.lang.String is bound multiple times:
19. Qualifier? Uniqueness identifier for providing an object Usually used for primitive and common types
20. Providing multiple, separate dependencies of the same Type Qualifiers @Qualifier @Retention(AnnotationRetention.RUNTIME) annotation class CacheFile @Qualifier @Retention(AnnotationRetention.RUNTIME) annotation class ApiKey
21. Sometimes you need to provide two different objects of the same type Qualifiers @Provides @ApiKey fun provideApiKey(): String = "110b1a3cd59a299dc8a1f14" @Provides @CacheFile fun provideCacheFileName(): String = "mangrove-cache"
22. Providing multiple, separate dependencies of the same Type Qualifiers class MangroveApplication : Application() { … @Inject @CacheFile lateinit var cacheFileName: String override fun onCreate() { super.onCreate() component.inject(this) } }
23. Including a DataModule with MangroveModule Adding more Modules @Module(includes = [DataModule::class]) class MangroveModule
24. Sometimes modules have dependencies of their own Module Dependencies @Module class DataModule { @Provides fun provideSharedPreferences(context: Context): SharedPreferences { return PreferenceManager.getDefaultSharedPreferences(context) } }
25. Use @BindsInstance to provide Application instance in @Component.Builder Module Dependencies @Component(modules = [DataModule::class]) interface MangroveComponent { … @Component.Builder interface Builder { @BindsInstance fun appContext(context: Context): Builder fun build(): MangroveComponent } }
26. Update the Application to use the builder and supply the dependency Module Dependencies private val component by lazy { DaggerMangroveComponent.builder() .appContext(applicationContext) .build() }
27. Mangrove Break
28. Extending the object graph with Subcomponents Subcomponents @Subcomponent interface UserComponent
29. Subcomponent? Inherit and extend the object graph of a parent component. Useful for splitting object graph into smaller subgraphs.
30. Multiple ways to connect a Subcomponent to a parent Component. Can be done from a module included by the parent Component, or by the Subcomponent’s dependencies parameter. Module defined subcomponents are general recommended. Subcomponents
31. Module referenced subcomponents Subcomponents @Module(includes = [DataModule::class], subcomponents = [UserComponent::class]) class MangroveModule @Subcomponent interface UserComponent { @Subcomponent.Builder interface Builder { fun build(): UserComponent } }
32. Module referenced subcomponents Subcomponents @Module class UserModule @Subcomponent(modules = [UserModule::class]) interface UserComponent { ... }
33. Using the subcomponent Subcomponents @Component(modules = [MangroveModule::class]) interface MangroveComponent {A fun inject(target: MangroveApplication) fun userComponentBuilder(): UserComponent.Builder @Component.Builder interface Builder { @BindsInstance fun appContext(context: Context): Builder fun build(): MangroveComponent } }A
34. @Component(modules = [MangroveModule::class]) interface MangroveComponent {A … fun userComponentBuilder(): UserComponent.Builder … }A Using the subcomponent Subcomponents
35. Using the subcomponent Subcomponents val app: MangroveApplication = (application as MangroveApplication) app.component .userComponentBuilder() .build() .inject(this)
36. Reusing injection objects with scopes Scope
37. Scope? Without Scope a new instance is created for each injection Scopes persist injected object Inject same instance for lifetime of scope
38. Singleton Scope Scope /** * Identifies a type that the injector only instantiates once. Not inherited. * * @see javax.inject.Scope @Scope */ @Scope @Documented @Retention(RUNTIME) public @interface Singleton {}
39. Scope Using a scope @Singleton @Component(modules = [MangroveModule::class]) interface MangroveComponent … @Module class DataModule { @Provides @Singleton fun provideSharedPreferences(context: Context): SharedPreferences { return PreferenceManager.getDefaultSharedPreferences(context) } }
40. Scopes can be helpful, but be careful Scoped injections are thread safe, but this means more overhead in the generated code Slower than a scope-less injection Use scopes for providing stateful objects Scope
41. Making a Custom Scope Scope @Scope @Retention(RUNTIME) annotation class User
42. Custom Scope with arguments Scope @Scope @Retention(AnnotationRetention.RUNTIME) annotation class Per(val value: KClass<*>) @Module class UserModule { @Provides @Per(UserComponent::class) fun provideUserModel(userManager: UserManager): UserModel = return userManager.currentUserModel }
43. Activity specific scopes Scope @Per(MainComponent::class) @Subcomponent(modules = [MainModule::class]) interface MainComponent { fun inject(target: MainActivity) @Subcomponent.Builder interface Builder { @BindsInstance fun activity(activity: MainActivity): Builder fun build(): MainComponent } }
44. MVP implementation example Scope interface Contract { abstract class Presenter(val view: View) { ... } interface View { ... } } class MainPresenter(view: MainContract.View): MainContract.Presenter(view) { ... }
45. MVP implementation example Scope @Module abstract class MainModule { @Binds @Per(MainComponent::class) abstract fun provideView( activity: MainActivity): MainContract.View @Binds @Per(MainComponent::class) abstract fun providePresenter( presenter: MainPresenter): MainContract.Presenter }
46. MVP implementation example Scope class MainActivity : AppCompatActivity(), MainContract.View { @Inject lateinit var presenter: MainContract.Presenter override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) val app: MangroveApplication = (application as MangroveApplication) app.component.mainComponentBuilder() .activity(this) .build() .inject(this) } }
47. Dagger & Android // Dagger … implementation "com.google.dagger:dagger-android:2.13" implementation “com.google.dagger:dagger-android-support:2.13" … Alternate way using Dagger’s new Android specific features First update build.gradle with dagger’s Android dependencies
48. Install AndroidInjectionModule in the Application Component Dagger Android @Singleton @Component(modules = [ AndroidSupportInjectionModule::class, MangroveModule::class ]) interface MangroveComponent { ... }
49. Update Application to implement HasActivityInjector and inject a DispatchingAndroidInjector Dagger Android class MangroveApp : Application(), HasActivityInjector { ... @Inject lateinit var activityInjector: DispatchingAndroidInjector<Activity> ... override fun activityInjector(): AndroidInjector<Activity> { return activityInjector } }
50. Update activity Subcomponents and Builders to extend AndroidInjector Dagger Android @Subcomponent(modules = [LauncherModule::class]) @Per(LauncherComponent::class) interface LauncherComponent : AndroidInjector<LauncherActivity> { @Subcomponent.Builder abstract class Builder : AndroidInjector.Builder<LauncherActivity>() }
51. Activity Module multibinding into ActivityKey map Dagger Android @Module(subcomponents = [MainComponent::class]) abstract class MangroveModule { … @Binds @IntoMap @ActivityKey(MainActivity::class) abstract fun bindLauncher(builder: MainComponent.Builder): AndroidInjector.Factory<out Activity> }
52. Multibinding? Provide multiple objects of type T to a single Set<T> or Map<T> @IntoMap binding requires a Key argument The Map/Set is then injected instead of individual objects
53. Simplify Activity injection Dagger Android class MainActivity: Activity() { … override fun onCreate(Bundle savedInstanceState) { AndroidInjection.inject(this) super.onCreate(savedInstanceState) } }
54. Subcomponent Builder parameters (MVP)? Activity already provided, just inject where needed. Dagger Android @Binds abstract fun view(activity: MainActivity): MainContract.View
55. Subcomponent Builder parameters (MVP)? Others can be provided using Activity members Dagger Android @Provides fun provideIntent(activity: MainActivity): Intent { return activity.intent }
56. Lifecycle
57. Let’s review how a scope works. Scoped objects bound to lifecycle of scoped component. Activity scoped components stored on an Activity inherit same lifecycle. Activity lifecycle → destroyed and recreated from system events: eg. rotation, phone call. Lifecycle Concerns
58. An Activity Scope isn’t persisted thru standard lifecycle events. Lifecycle Concerns Tread lightly. Don’t leak Context. Can lead to ANR/Crashes. Don’t use previous MVP implementation with this unless you drop the scope.
59. Android Architecture Components → solution to lifecycle issues with new Lifecycle aware components. Architecture Components LifecycleObserver → Handles disconnecting from a LifecycleOwner when the lifecycle is ending. LifecycleOwner → Free with Support activities and fragments.
60. Add dependencies Architecture Components // Android Architecture Components implementation "android.arch.lifecycle:extensions:1.0.0" annotationProcessor "android.arch.lifecycle:compiler:1.0.0"
61. New ViewModel classes useful with MVVM pattern Architecture Components @Per(UserComponent::class) class UserViewModel @Inject constructor(val userModel: UserModel) : ViewModel() { fun loadUserData(): Observable<UserData> { … } }
62. Inject ViewModel Provider in Activity class MainActivity: Activity { @Inject lateinit var viewModelFactory: ViewModelProvider.Factory lateinit var userViewModel: UserViewModel override fun onCreate(Bundle savedInstanceState) { … userViewModel = ViewModelProviders.of(this, viewModelFactory) .get(UserViewModel::class) userViewModel.loadUserData().subscribe { ... } } }
63. Probably better to inject a custom ViewModelProvider.Factory Architecture Components @Singleton class MangroveViewModelFactory: ViewModelProvider.Factory { private val creators: Map<Class<out ViewModel>, Provider<ViewModel>> … }
64. Review Joshua is a great artist. Dagger is neat. Review slides are pointless great. Mangroves are pretty cool.
65. Links https://github.com/google/dagger https://developer.android.com/topic/ libraries/architecture/index.html https://github.com/googlesamples/ android-architecture-components Mangrove https://twitter.com/cephus +JoshuaJamison Joshua links