Dagger 2 Best Practices

Create a perfect Dagger setup with your codebase can become a challenge even with those who are already familiar with Dagger 2. This talk covers some of the problems you would stumble upon when setting up Dagger in a real-world application, give you best practices on the journey with Dagger.

Transcript

1. Dagger 2 Take it to the next level
2. Outline • What’s new • Extend the graph • Dagger in multi-module project • Constructor injection
3. What’s new?
4. @Component( dependencies = [FooComponent!::class], modules = [BarModule!::class] ) interface ActivityComponent { @Component.Builder interface Builder { @BindsInstance fun activity(activity: Activity): Builder fun foo(fooComponent: FooComponent): Builder fun bar(barModule: BarModule): Builder fun create(): ActivityComponent } } Component Factory
5. @Component( dependencies = [FooComponent!::class], modules = [BarModule!::class] ) interface ActivityComponent { @Component.Factory interface Factory { fun create( @BindsInstance activity: Activity, fooComponent: FooComponent, barModule: BarModule ): ActivityComponent } } Component Factory
6. Extend the graph Do it the right way
7. The graph Aka dependency graph Database Api DataRepository ApplicationComponent Context
8. The graph Aka dependency graph Database Api DataRepository ApplicationComponent Context @Component( modules = [FooActivityModule!::class] ) interface ApplicationComponent @Module( subcomponents = [FooActivityComponent!::class] ) interface FooActivityModule @Subcomponent interface FooActivityComponent { @Subcomponent.Factory interface Factory { fun create( @BindsInstance activity: FooActivity ) } }
9. The graph Aka dependency graph Database Api DataRepository ApplicationComponent Context FooActivityComponent FooActivity @Component( modules = [FooActivityModule!::class] ) interface ApplicationComponent @Module( subcomponents = [FooActivityComponent!::class] ) interface FooActivityModule @Subcomponent interface FooActivityComponent { @Subcomponent.Factory interface Factory { fun create( @BindsInstance activity: FooActivity ) } }
10. The graph Aka dependency graph Database Api DataRepository ApplicationComponent Context FooActivityComponent FooActivity FooFragmentComponent FooFragment @Component( modules = [FooActivityModule!::class] ) interface ApplicationComponent @Module( subcomponents = [FooActivityComponent!::class] ) interface FooActivityModule @Subcomponent interface FooActivityComponent { @Subcomponent.Factory interface Factory { fun create( @BindsInstance activity: FooActivity ) } }
11. Dependency Which only available at runtime
12. @Subcomponent.Factory interface Factory { fun create( @BindsInstance activity: FooActivity ) } } Dependency Request @Module object Provision { @Provides fun viewModel(activity: FooActivity): FooViewModel = activity.viewModel @Provides fun args(activity: FooActivity): FooActivityArgs { return FooActivityArgs.fromBundle(activity.intent.extras) } @Provides fun navigator(activity: FooActivity): FooNavigator = FooNavigator(activity) } @Subcomponent(modules = [Provision!::class]) interface FooActivityComponent {
13. @Subcomponent.Factory interface Factory { fun create( @BindsInstance activity: FooActivity ) } } Dependency Request @Module object Provision { @Provides fun viewModel(activity: FooActivity): FooViewModel = activity.viewModel @Provides fun args(activity: FooActivity): FooActivityArgs { return FooActivityArgs.fromBundle(activity.intent.extras) } @Provides fun navigator(activity: FooActivity): FooNavigator = FooNavigator(activity) } Extended dependency @Subcomponent(modules = [Provision!::class]) interface FooActivityComponent {
14. @Subcomponent.Factory interface Factory { fun create( @BindsInstance activity: FooActivity ) } } Dependency Request @Module object Provision { @Provides fun viewModel(activity: FooActivity): FooViewModel = activity.viewModel @Provides fun args(activity: FooActivity): FooActivityArgs { return FooActivityArgs.fromBundle(activity.intent.extras) } @Provides fun navigator(activity: FooActivity): FooNavigator = FooNavigator(activity) } Extended dependency Request Request Request @Subcomponent(modules = [Provision!::class]) interface FooActivityComponent {
15. One time dependency • Variable that only available at runtime • User input • Parameters • Use only 1 time at 1 place
16. One time dependency class DownloadUserInfoWorker @Inject constructor( private val userId: String, private val isSaveToDatabase: Boolean, private val okhttp: OkHttpClient, private val database: Database ) { fun doWork() { !// bla !// bla if (isSaveToDatabase) { !// bla bla } } }
17. One time dependency class DownloadUserInfoWorker @Inject constructor( private val userId: String, private val isSaveToDatabase: Boolean, private val okhttp: OkHttpClient, private val database: Database ) { fun doWork() { !// bla !// bla if (isSaveToDatabase) { !// bla bla } } } Already available 
 in the graph }
18. One time dependency class DownloadUserInfoWorker @Inject constructor( private val userId: String, private val isSaveToDatabase: Boolean, private val okhttp: OkHttpClient, private val database: Database ) { fun doWork() { !// bla !// bla if (isSaveToDatabase) { !// bla bla } } } Not available } Already available 
 in the graph }
19. One time dependency class DownloadUserInfoWorker @Inject constructor( private val userId: String, private val isSaveToDatabase: Boolean, private val okhttp: OkHttpClient, private val database: Database ) { fun doWork() { !// bla !// bla if (isSaveToDatabase) { !// bla bla } } } Not available } Already available 
 in the graph }
20. Setup @Subcomponent interface DownloadSubcomponent { fun worker(): DownloadUserInfoWorker @Subcomponent.Factory interface Factory { fun create( @BindsInstance userId: String, @BindsInstance isSaveToDatabase: Boolean ): DownloadSubcomponent } }
21. Setup @Subcomponent interface DownloadSubcomponent { fun worker(): DownloadUserInfoWorker @Subcomponent.Factory interface Factory { fun create( @BindsInstance userId: String, @BindsInstance isSaveToDatabase: Boolean ): DownloadSubcomponent } } @Module( subcomponents = [ DownloadSubcomponent!::class ] ) interface WorkerModule
22. Setup @Subcomponent interface DownloadSubcomponent { fun worker(): DownloadUserInfoWorker @Subcomponent.Factory interface Factory { fun create( @BindsInstance userId: String, @BindsInstance isSaveToDatabase: Boolean ): DownloadSubcomponent } } @Module( subcomponents = [ DownloadSubcomponent!::class ] ) interface WorkerModule @Component( modules = [ WorkerModule!::class ] ) interface ParentComponent
23. Setup @Subcomponent interface DownloadSubcomponent { fun worker(): DownloadUserInfoWorker @Subcomponent.Factory interface Factory { fun create( @BindsInstance userId: String, @BindsInstance isSaveToDatabase: Boolean ): DownloadSubcomponent } } class Main { fun main() { val isSaveToDatabase: Boolean val userId: String val component = DaggerDownloadSubcomponent .factory() .create(isSaveToDatabase, userId) val worker = component.worker() !// finally! worker.doWork() } } @Module( subcomponents = [ DownloadSubcomponent!::class ] ) interface WorkerModule @Component( modules = [ WorkerModule!::class ] ) interface ParentComponent
24. The right tool for the right job • Subcomponent advantage: • Can request the extended dependencies at
 multiple places
25. The right tool for the right job • Subcomponent advantage: • Can request the extended dependencies at
 multiple places one place
26. One time dependency class DownloadUserInfoWorker private val userId: String, private val isSaveToDatabase: Boolean, private val okhttp: OkHttpClient, private val database: Database ) { fun doWork() { !// bla bla !// bla bla if (isSaveToDatabase) { !// bla bla } } @Inject } constructor(
27. One time dependency class DownloadUserInfoWorker private val userId: String, private val isSaveToDatabase: Boolean, private val okhttp: OkHttpClient, private val database: Database ) { fun doWork() { !// bla bla !// bla bla if (isSaveToDatabase) { !// bla bla } } class Factory constructor( private val okhttp: OkHttpClient, private val database: Database ) { fun create(params: Params, userId: String): DownloadUserInfoWorker { return DownloadUserInfoWorker(params, userId, okhttp, database) } } @Inject } constructor (
28. One time dependency fun main() { val isSaveToDatabase: Boolean val params: Params worker.doWork() } } val component = DaggerDownloadSubcomponent .factory() .create(isSaveToDatabase, params) component.worker() val worker = class Main {
29. One time dependency fun main() { val isSaveToDatabase: Boolean val params: Params worker.doWork() } } val component = DaggerDownloadSubcomponent .factory() .create(isSaveToDatabase, params) component.worker() val worker = class Main {
30. @Inject lateinit var factory: DownloadSubcomponent.Factory One time dependency fun main() { val isSaveToDatabase: Boolean val params: Params worker.doWork() } } val component = DaggerDownloadSubcomponent .factory() .create(isSaveToDatabase, params) component.worker() val worker = class Main { factory.create(params, isSave)
31. OkHttpClient,
 Database class Factory @Inject constructor( private val okhttp: private val database: ) { fun create( params: Params, save: Boolean ): DownloadUserInfoWorker { return DownloadUserInfoWorker( params, save, ) } } Performance matter okhttp, database
32. Provider<OkHttpClient>,
 Provider<Database> OkHttpClient,
 Database class Factory @Inject constructor( private val okhttp: private val database: ) { fun create( params: Params, save: Boolean ): DownloadUserInfoWorker { return DownloadUserInfoWorker( params, save, ) } } Performance matter okhttp, database okhttp.get(), database.get()
33. In a nutshell • When the extended dependencies are request • Multiple time => Subcomponent • One time => Factory
34. Common use cases • Jetpack WorkManager • ViewModel • View
35. Even further beyond • Google AutoFactory • Square AssistedInject
36. assisted-inject class DownloadUserInfoWorker @AssistedInject constructor( @Assisted private val params: Params, @Assisted private val isSaveToDatabase: Boolean, private val okhttp: OkHttpClient, private val database: Database ) { @AssistedInject interface Factory { fun create(params: Params, isSaveToDatabase: Boolean) } } // generate DownloadUserInfoWorker_AssistedFactory // https://github.com/square/AssistedInject
37. auto-factory @AutoFactory class DownloadUserInfoWorker( private val params: Params, private val isSaveToDatabase: Boolean, @Provided private val okhttp: OkHttpClient, @Provided private val database: Database ) // generate DownloadUserInfoWorkerFactory // https://github.com/google/auto/tree/master/factory
38. Multi-module project With component dependency
39. Encapsulation –Edward Aloysius Murphy Jr. “Whatever can go wrong, will go wrong.”
40. –Me “If they can use it, they will use it” Encapsulation
41. DataRepositoryImpl DataRepository DataModule UiModule
42. DataRepositoryImpl DataRepository DataModule UiModule Karen Jim
43. DataRepositoryImpl DataRepository DataModule DataRepository UiModule Karen Jim
44. DataRepositoryImpl DataRepository DataModule DataRepositoryImpl DataRepository UiModule Karen Jim
45. DataRepositoryImpl DataRepository DataModule DataRepositoryImpl DataRepository UiModule AppComponent Karen Jim
46. DataRepositoryImpl DataRepository DataModule DataRepository UiModule AppComponent DataComponent UiSubcomponent Karen Jim
47. DataRepositoryImpl DataRepository DataModule DataRepository UiModule AppComponent DataComponent UiSubcomponent Karen Jim
48. Dynamic Feature Module AppComponent :app :dynamicFeatureA FeatureComponent :feature1 :feature2
49. Dynamic Feature Module @Component(dependencies = [AppComponent::class]) interface FeatureComponent { } class FeatureActivity : AppCompatActivity() { } } @Component interface AppComponent {
50. Dynamic Feature Module @Component(dependencies = [AppComponent::class]) interface FeatureComponent { fun inject(activity: FeatureActivity) @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, appComponent: AppComponent ): FeatureComponent } } class FeatureActivity : AppCompatActivity() { } } @Component interface AppComponent {
51. Dynamic Feature Module @Component(dependencies = [AppComponent::class]) interface FeatureComponent { fun inject(activity: FeatureActivity) @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, appComponent: AppComponent ): FeatureComponent } } class FeatureActivity : AppCompatActivity() { @Inject lateinit var sharePreference: SharePreference } } @Component interface AppComponent {
52. Dynamic Feature Module @Component(dependencies = [AppComponent::class]) interface FeatureComponent { fun inject(activity: FeatureActivity) @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, appComponent: AppComponent ): FeatureComponent } } class FeatureActivity : AppCompatActivity() { @Inject lateinit var sharePreference: SharePreference } fun sharePreference(): SharePreference } @Component interface AppComponent {
53. Dynamic Feature Module @Component(dependencies = [AppComponent::class]) interface FeatureComponent { fun inject(activity: FeatureActivity) @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, appComponent: AppComponent ): FeatureComponent } } class FeatureActivity : AppCompatActivity() { @Inject lateinit var sharePreference: SharePreference @Inject lateinit var repository: Repository } fun sharePreference(): SharePreference } @Component interface AppComponent {
54. Dynamic Feature Module @Component(dependencies = [AppComponent::class]) interface FeatureComponent { fun inject(activity: FeatureActivity) @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, appComponent: AppComponent ): FeatureComponent } } class FeatureActivity : AppCompatActivity() { @Inject lateinit var sharePreference: SharePreference @Inject lateinit var repository: Repository } fun sharePreference(): SharePreference fun repository(): Repository } @Component interface AppComponent {
55. @Component( dependencies = [ ] ) interface FeatureComponent { @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, ): FeatureComponent } }
56. @Component( dependencies = [ ] ) interface FeatureComponent { @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, @Component interface AndroidComponent { fun context(): Context fun sharePreference(): SharePreference } ): FeatureComponent } }
57. @Component( dependencies = [ ] ) interface FeatureComponent { @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, AndroidComponent::class, @Component interface AndroidComponent { fun context(): Context fun sharePreference(): SharePreference } ): FeatureComponent } }
58. @Component( dependencies = [ ] ) interface FeatureComponent { @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, AndroidComponent::class, @Component interface AndroidComponent { fun context(): Context fun sharePreference(): SharePreference } androidComponent: AndroidComponent, ): FeatureComponent } }
59. @Component( dependencies = [ ] ) interface FeatureComponent { @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, AndroidComponent::class, @Component interface DataComponent { fun repository(): Repository } @Component interface AndroidComponent { fun context(): Context fun sharePreference(): SharePreference } androidComponent: AndroidComponent, ): FeatureComponent } }
60. @Component( dependencies = [ ] ) interface FeatureComponent { @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, AndroidComponent::class, DataComponent::class @Component interface DataComponent { fun repository(): Repository } @Component interface AndroidComponent { fun context(): Context fun sharePreference(): SharePreference } androidComponent: AndroidComponent, ): FeatureComponent } }
61. @Component( dependencies = [ ] ) interface FeatureComponent { @Component.Factory interface Factory { fun create( @BindsInstance activity: FeatureActivity, AndroidComponent::class, DataComponent::class @Component interface DataComponent { fun repository(): Repository } @Component interface AndroidComponent { fun context(): Context fun sharePreference(): SharePreference } dataComponent: DataComponent androidComponent: AndroidComponent, ): FeatureComponent } }
62. class FeatureActivity : AppCompatActivity() { fun onCreate() { DaggerFeatureComponent.factory().create( dataComponent = androidComponent = activity = this ) } }
63. class FeatureActivity : AppCompatActivity() { fun onCreate() { class MyApplivation : Application() { lateinit var androidComponent: AndroidComponent lateinit var dataComponent: DataComponent fun onCreate() { androidComponent = TODO() dataComponent = TODO() } } DaggerFeatureComponent.factory().create( dataComponent = androidComponent = activity = this ) } }
64. class FeatureActivity : AppCompatActivity() { fun onCreate() { class MyApplivation : Application() { lateinit var androidComponent: AndroidComponent lateinit var dataComponent: DataComponent fun onCreate() { androidComponent = TODO() dataComponent = TODO() } } DaggerFeatureComponent.factory().create( dataComponent = androidComponent = activity = this ) } } application.dataComponent, application.androidComponent, val application: MyApplivation = applicationContext as MyApplivation
65. @Component interface FeatureComponent { !// bla bla companion object { fun inject(activity: FeatureActivity) { val application = activity.applicationContext as MyApplication DaggerFeatureComponent .factory() .create( activity = activity, androidComponent = application.androidComponent, dataComponent = application.dataComponent ) .inject(activity) } } } class FeatureActivity { fun onCreate() { FeatureComponent.inject(this) } }
66. Tips
67. @Provides @Singleton fun provideLibrary(): SomeLibrary { return SomeLibrary.getInstance() }
68. @Provides @Singleton fun provideLibrary(): SomeLibrary { return SomeLibrary.getInstance() }
69. @Provides @Singleton fun provideLibrary(): SomeLibrary { return SomeLibrary.getInstance() } “You don’t need to scope a dependency that already singleton”
70. class Sample { @Inject lateinit var heavy: HeavyDependency @Inject lateinit var heavyProvider: Provider<HeavyDependency> fun onButtonClick() { heavyProvider.get() // bla bla } }
71. class Sample { @Inject lateinit var heavy: HeavyDependency @Inject lateinit var heavyProvider: Provider<HeavyDependency> fun onButtonClick() { heavyProvider.get() // bla bla } } “Request a provider of a dependency if you don’t need to use it right away”
72. Reference: https://github.com/google/dagger/issues/368
73. Reference: https://github.com/google/dagger/issues/368
74. “Disable format generated code if you don’t need it” // root build.gradle allprojects { tasks.withType(JavaCompile).all { options.compilerArgs += [ '-Adagger.formatGeneratedSource=DISABLED', '-Adagger.gradle.incremental=ENABLED', ] } afterEvaluate { extensions.findByName("kapt")?.arguments { arg("dagger.formatGeneratedSource", "DISABLED") arg("dagger.gradle.incremental", "ENABLED") } } }
75. @Module interface SampleModule { @Provides fun provideLibrary(): SomeLibrary { return SomeLibrary.getInstance() } } Static Provision Method
76. ibrary { nstance() @Module object SampleModule { @Provides @JvmStatic fun provideLibrary(): SomeLibrary { return SomeLibrary.getInstance() } } Static Provision Method 15%-20% faster
 Reference: https://developer.android.com/training/articles/perf-tips
77. Constructor Injection Now with Fragment and View
78. FragmentFactory
79. FragmentFactory class MainActivity : DaggerAppCompatActivity() { @Inject lateinit var fragmentFactory: FragmentFactory override fun onCreate(savedInstanceState: Bundle?) { AndroidInjection.inject(this) supportFragmentManager.fragmentFactory = fragmentFactory } }
80. FragmentFactory class TodoFragmentFactory @Inject constructor() : FragmentFactory() { override fun instantiate( classLoader: ClassLoader, className: String ): Fragment { !// instantiate your fragment here } }
81. Circular dependency @FragmentScope class TaskDetailNavigator @Inject constructor( private val fragment: TaskDetailFragment ) class TaskDetailFragment @Inject constructor( private val navigator: TaskDetailNavigator ) : Fragment()
82. Circular dependency class TaskDetailFragment : Fragment { @Inject lateinit var navigator: TasksNavigator override fun onCreate(savedInstanceState: Bundle?) { !// subcomponent creation time !// !-> got fragment instance AndroidSupportInjection.inject(this) !// use fragment instance to create navigator }
83. Circular dependency @FragmentScope class TaskDetailNavigator @Inject constructor( private val ) class TaskDetailFragment @Inject constructor( private val navigator: TaskDetailNavigator ) : Fragment() fragment: TaskDetailFragment
84. holder: Holder<TaskDetailFragment> Circular dependency @FragmentScope class TaskDetailNavigator @Inject constructor( private val ) class TaskDetailFragment @Inject constructor( private val navigator: TaskDetailNavigator ) : Fragment() class Holder<T : Any> { private var _instance: T? = null var instance: T get() = requireNotNull(_instance) set(value) { require(_instance !== null) _instance = value } }
85. Holder Injection @Module inteface Module { @Provides @FragmentScope fun fragment( holder: Holder<TasksFragment>, navigator: TasksNavigator ) = TasksFragment( navigator = navigator ).also { holder.instance = it } @Provides @FragmentScope fun navigator(holder: Holder<TasksFragment>): TasksNavigator { return TasksNavigator(holder) } @Provides @FragmentScope fun holder() = Holder<TasksFragment>() }
86. Problems • Circular dependency • Maintain scoping • Multi-binding • Dynamic feature module https:!//medium.com/@nlg.tuan.kiet/d9d16c892626
 https:!//github.com/nlgtuankiet/FragmentFactory
87. Constructor Injection • Android View • Jetpack WorkManager • MvRx ViewModel