Everything you need to know about Dagger 2

Dagger v2.2 presentation I gave to internal teams @CapitalOne

Tips and tricks I have learnt over time.

Transcript

1. Everything you need to know about Dagger 2 Mayank Mehta
2. Agenda • Overview • Key Concepts • Quiz
3. Inversion Of Control Pic courtesy history.com Hollywood Principle - “Don’t call us, we’ll call you!”
4. What is Dependency Injection? “The Dependency Injection pattern is a specialized version of the Inversion of Control pattern where the concern being inverted is the process of obtaining the needed dependency.” - Microsoft Dagger is Dependency Injection Framework!
5. What’s in name? Trip CloudDataStore GoogleAPI Retrofit Mapper Realm Context
6. Without Dependency Injection public LaunchActivityViewModel() { this.tripRepository = new TripRepositoryImpl(new CloudTripDataStore(new ModelMapper(), new LogExporter()); }
7. Using Dependency Injection public LaunchActivityViewModel(TripRepository tripRepository) { this.tripRepository = tripRepository; } public LaunchActivityViewModel() { this.tripRepository = new TripRepositoryImpl(new CloudTripDataStore(new ModelMapper(), new LogExporter()); }
8. Pros – Dependency Injection • Clean and modular code. • Makes code more readable. • Easier to write tests.
9. Pros – Dagger 2 • Compile time code generation and validation (easier to follow through). • No use of reflection as a result code is easy to trace and better performance almost 13% compared to Dagger 1 (according to Google’s benchmark).
10. How to include Dagger 2 library? // Android Gradle plugin < 2.2 apply plugin: 'com.neenbedankt.android-apt' // Dagger 2 compile 'com.google.dagger:dagger:2.2' apt 'com.google.dagger:dagger-compiler:2.2' provided 'javax.annotation:jsr250-api:1.0'
11. Gratis Pilot • Our team created a separate android application to evaluate location vendors, to see how accurately they can identify a store when user walks into it. • Code snippets in this presentation are from that application. • Code - https://github.kdc.capitalone.com/android-wallet/GratisPilot
12. Agenda • Overview • Key Concepts • Quiz
13. Key concepts • @Inject • @Module • @Scope • @Lazy • @Named & @Qualifier • @Component • @Subcomponent
14. @Inject • Annotated constructor tells dagger how to create instance of that class and requests to resolve it’s dependency.
15. Constructor Injection public class DemoClass { private DummyExporter dummyExporter; @Inject public DemoClass(DummyExporter dummyExporter) { this.dummyExporter = dummyExporter; } }
16. Field Injection public class DemoClass { @Inject StatusValidator statusValidator; private DummyExporter dummyExporter; @Inject public DemoClass(DummyExporter dummyExporter) { this.dummyExporter = dummyExporter; } }
17. @Inject • Annotated constructor tells dagger how to create instance of that class and requests to resolve it’s dependency. • Can only be applied to Field (non-private & non-static), Constructor and Method. • Injection order : Constructor, Field and Method. • Only one constructor of the class can be annotated.
18. When @Inject doesn’t work • Interfaces • Libraries • Objects that you would like to mock for testing.
19. Key concepts • @Inject • @Module • @Scope • @Lazy • @Named & @Qualifier • @Component • @Subcomponent
20. @Module • Provides dependency for the graph. • Annotate method with @Provides to create provider method binding.
21. @Module - Remember • Don’t pollute your modules. • Organize your modules. • Publish binding – functionality used across the app. • Internal binding – all that are not-publish binding or dependency use to construct publish binding.
22. Published Binding @Module public class TripModule { @Provides TripRepository providesTripRepository(Realm realm, CloudTripDataStore cloudTripDataStore) { return new TripRepositoryImpl(realm, cloudTripDataStore); } }
23. Internal Binding @Module public class TripModule { @Provides TripRepository providesTripRepository(Realm realm, CloudTripDataStore cloudTripDataStore) { return new TripRepositoryImpl(realm, cloudTripDataStore); } } Dagger will resolve CloudTripDataStore.
24. Internal Binding public class CloudTripDataStore { @Inject public CloudTripDataStore(…) { } }
25. Compose Modules @Module(includes = {DependentModuleOne.class,DependentModuleTwo.class}) public class ModuleOne { }
26. @Module + Member injection public class DemoClass { @Inject StatusValidator statusValidator; @Inject public DemoClass() { } } @Module public class ApplicationModule { @Provides DemoClass demoClass() { return new DemoClass(); } } statusValidator will be null
27. Key concepts • @Inject • @Module • @Scope • @Lazy • @Named & @Qualifier • @Component • @Subcomponent
28. @Scope • Dagger control creation of scoped instance.
29. @Scope – Custom Annotation @Scope @Retention(RetentionPolicy.RUNTIME) public @interface PerApplication { } @Scope @Retention(RetentionPolicy.RUNTIME) public @interface TripScope { } @Scope @Retention(RetentionPolicy.RUNTIME) public @interface PerActivity { }
30. Granular Scopes Fragment 1 List View Fragment 2 Detail View Thank You Activity Scope Application Scope Confirmation Activity Scope Trip Scope Launch Activity Scope Activity Scope Activity Scope
31. @Scope - Example • @PerApplication – Context – SharedPreference • @TripScope – TripRepository - DAOs, Services • @PerActivity – ViewModels or Presenters
32. @Scope • Dagger control creation of scoped instance. • Scope can be added to @Provides in @Module, @Component and class instance.
33. Add Scope to Module @Module public class ApplicationModule { private final GratisPilotApplication application; public ApplicationModule(GratisPilotApplication application) { this.application = application; } @Provides @PerApplication Realm providesRealm() { RealmConfiguration config = new RealmConfiguration.Builder(application).build(); Realm.setDefaultConfiguration(config); return Realm.getDefaultInstance(); } }
34. Add Scope to Class @PerApplication public class DemoClass { @Inject public DemoClass() { } }
35. ScopedProvider.java – Dagger @SuppressWarnings("unchecked") // cast only happens when result comes from the factory @Override public T get() { // double-check idiom from EJ2: Item 71 Object result = instance; if (result == UNINITIALIZED) { synchronized (this) { result = instance; if (result == UNINITIALIZED) { instance = result = factory.get(); } } } return (T) result; }
36. @Scope • Dagger control creation of scoped instance. • Scope can be added to @Provides in @Module, @Component and class instance. • @Singleton is part of javax.inject package
37. Key concepts • @Inject • @Module • @Scope • @Lazy • @Named & @Qualifier • @Component • @Subcomponent
38. @Lazy • Defer object creation. @Inject Lazy<DemoClass> demoClassLazy; // Object created only post following code demoClassLazy.get();
39. Key concepts • @Inject • @Module • @Scope • @Lazy • @Named & @Qualifier • @Component • @Subcomponent
40. Resolving Dependency Conflict • When you have multiple implementation of an interface and you have it injected via dagger, let it know which interface you are interested in.
41. Resolving Dependency Conflict //In Module @Provides public OkHttpClient providesOkHttpClient() { //Regular } @Provides public OkHttpClient providesFactualOkHttpClient(String factual_key) { // OAuth } Unsatisfied dependencies for type [OkHttpClient] with qualifiers… // In class @Inject OkHttpClient regularOkHttp;
42. @Named // Default - Regular Client @Provides @Named("regular_okhttp") public OkHttpClient providesOkHttpClient() { } // Explicit – OAuth Client @Provides @Named("oauth_okhttp") public OkHttpClient providesFactualOkHttpClient(@Named("factual_key") String) { } // In Class @Inject @Named("oauth_okhttp") OkHttpClient oauthOkHttp;
43. @Named • Provide string value to binding conflict • Un named binding becomes default. • Refactoring is difficult L
44. @Qualifier • Need to create custom interface for each Implementation • Refactoring is easy.
45. How to declare @Qualifier @java.lang.annotation.Documented @java.lang.annotation.Retention(RetentionPolicy.RUNTIME) @javax.inject.Qualifier public @interface OAuthOkHttp { }
46. How to consume @Qualifier @Provides @OAuthOkHttp public OkHttpClient providesFactualOkHttpClient() { } @Inject @OAuthOkHttp OkHttpClient oauthOkHttp;
47. @Named Vs @Qualifier • If Object is being injected at many places or it’s “name” might change prefer @Qualifier.
48. Key concepts • @Inject • @Module • @Lazy • @Scope • @Named & @Qualifier • @Component • @Subcomponent
49. Dagger Graph Creation • Component • Subcomponent
50. @Component • Interface that allows accessing objects specified in modules included with component.
51. @Component @PerApplication @Component(modules = { ApplicationModule.class, LocationVendorModule.class, NetworkModule.class }) public interface ApplicationComponent { // Members-injection void inject (GratisPilotApplication gratisPilotApplication); // Provision methods Context context(); Realm realm(); }
52. Component Implementation @PerApplication @Component(modules = { ApplicationModule.class, LocationVendorModule.class, NetworkModule.class }) public interface ApplicationComponent { // Members-injection void inject (GratisPilotApplication gratisPilotApplication); // Provision methods Context context(); Realm realm(); } • Included modules will resolve each others dependencies.
53. Component – Member Injection @PerApplication @Component(modules = { ApplicationModule.class, LocationVendorModule.class, NetworkModule.class }) public interface ApplicationComponent { // Members-injection void inject (GratisPilotApplication gratisPilotApplication); // Provision methods Context context(); Realm realm(); } • Allows Dagger to inject and resolve dependency of that class. • Generally class that you don’t control creation like Application, Activity will declared here.
54. Component – Provision Methods @PerApplication @Component(modules = { ApplicationModule.class, LocationVendorModule.class, NetworkModule.class }) public interface ApplicationComponent { // Members-injection void inject (GratisPilotApplication gratisPilotApplication); // Provision methods Context context(); Realm realm(); } • Expose dependency, needed by child component.
55. Component – Provision Methods • Allows component to expose dependency to child component • Dependencies are needed to be exposed in component hierarchy for child component to consume. • It increases overall method count
56. Scoped Component @PerApplication @Component(modules = { ApplicationModule.class, LocationVendorModule.class, NetworkModule.class }) public interface ApplicationComponent { // Members-injection void inject (GratisPilotApplication gratisPilotApplication); // Provision methods Context context(); Realm realm(); } • Scoped component forces @Modules and dependencies with @Inject to have same scope or no scope. • Unscoped components can not depend on scoped components.
57. Child Component @TripScope @Component(dependencies = ApplicationComponent.class, modules = TripModule.class ) public interface TripComponent { TripRepository tripRepository(); } • Child component cannot have same scope as its parent.
58. @Component – How to build? DaggerApplicationComponent.builder() .applicationModule(new ApplicationModule(this)).build(); • Component will be gc’d if references to it is removed, that is how you can manage scope.
59. Key concepts • @Inject • @Module • @Scope • @Lazy • @Named & @Qualifier • @Component • @Subcomponent
60. @Subcomponent – Subcomponent behaves exactly like component, but implementation is different. – No need to explicitly expose dependency for child components.
61. @Component @PerApplication @Component(modules = { ApplicationModule.class, LocationVendorModule.class, NetworkModule.class }) public interface ApplicationComponent { TripComponent plus(TripModule module); GratisPilotApplication inject(GratisPilotApplication gratisPilotApplication); }
62. Declare child component @PerApplication @Component(modules = { ApplicationModule.class, LocationVendorModule.class, NetworkModule.class }) public interface ApplicationComponent { TripComponent plus(TripModule module); GratisPilotApplication inject(GratisPilotApplication gratisPilotApplication); }
63. @Subcomponent @TripScope @Subcomponent( modules = {TripModule.class} ) public interface TripComponent { TripActivityComponent plus(TripActivityModule module); LaunchActivityComponent plus(LaunchActivityModule module); }
64. @Component vs @Subcomponent • @Component – Prefer strict control over dependencies exposed to child components. • @Subcomponent – Loosely coupled. – Method count is a problem. – Easy to setup.
65. Testing • Unit test • Functional / Integration test
66. Unit tests with Dagger • Test piece of code while all it’s dependencies are mocked. • Mockito + JUnit +AssertJ to resuce
67. Class under test public class LaunchActivityViewModel extends AbstractBaseViewModel { private final TripRepository tripRepository; public PublishRelay<String> createTrip = PublishRelay.create(); private BehaviorSubject<Trip> tripIdSubject = BehaviorSubject.create(); @Inject public LaunchActivityViewModel(TripRepository tripRepository) { this.tripRepository = tripRepository; initializeCommands(); } @Override public void initializeCommands() { createTrip .map(trip -> tripRepository.createTrip(trip)) .subscribe(tripIdSubject::onNext); } }
68. Identify dependencies public class LaunchActivityViewModel extends AbstractBaseViewModel { private final TripRepository tripRepository; public PublishRelay<String> createTrip = PublishRelay.create(); private BehaviorSubject<Trip> tripIdSubject = BehaviorSubject.create(); @Inject public LaunchActivityViewModel(TripRepository tripRepository) { this.tripRepository = tripRepository; initializeCommands(); } @Override public void initializeCommands() { createTrip .map(trip -> tripRepository.createTrip(trip)) .subscribe(tripIdSubject::onNext); } }
69. Mock dependencies @RunWith(JUnit4.class) public class LaunchActivityViewModelTest { @Mock TripRepository tripRepository; LaunchActivityViewModel launchActivityViewModel; @Before public void setUp() { MockitoAnnotations.initMocks(this); launchActivityViewModel = new LaunchActivityViewModel(tripRepository); } @Test public void testTripSubscriber() { … } }
70. Functional/Integration Tests with Dagger • Create graph for each flavor and add modules with real or mock objects as needed. • Define a common interface without component annotation.
71. Common Interface public interface GratisPilotComponent { void inject(GratisPilotApplication gratisPilotApplication); }
72. Functional/Integration Tests with Dagger? • Create graph for each flavor and add modules with real or mock objects as needed. • Define a common interface without component annotation. • Build flavor specific components extending common interface.
73. Flavor - Prod @PerApplication @Component(modules = { ApplicationModule.class, LocationVendorModule.class, NetworkModule.class }) public interface ApplicationComponent extends GratisPilotComponent { Context context(); Realm realm(); }
74. Flavor - Mock @PerApplication @Component(modules = {MockApplicationModule.class, MockLocationVendorModule.class}) public interface TestApplicationComponent extends GratisPilotComponent { Context context(); StatusValidator statusValidator(); }
75. Flavor - Mock @PerApplication @Component(modules = {MockApplicationModule.class, MockLocationVendorModule.class}) public interface TestApplicationComponent extends GratisPilotComponent { Context context(); StatusValidator statusValidator(); }
76. Functional/Integration Tests with Dagger? • Create graph for each flavor and add modules with real or mock objects as needed. • Define a common interface without component annotation. • Build flavor specific components extending common interface. • Build flavor specific modules.
77. Prod Flavor - Module @Module public class LocationVendorModule { @Provides @PerApplication GoogleApiClient providesGoogleApiClient(Context context) { return new GoogleApiClient .Builder(context) .addApi(Places.GEO_DATA_API) .addApi(Places.PLACE_DETECTION_API) .build(); } }
78. Mock Flavor - Module @Module public class MockLocationVendorModule { @Provides @PerApplication GoogleApiClient providesGoogleApiClient() { return mock(GoogleApiClient.class); } }
79. Functional/Integration Tests with Dagger? • Create graph for each flavor and add modules with real or mock objects as needed. • Define a common interface without component annotation. • Create flavor specific components extending common interface. • Create flavor specific modules. • Extend main application class for your flavor and overwrite method to build graph.
80. Prod Flavor – Application Class public class GratisPilotApplication extends Application { private final GratisPilotComponent component = createComponent(); @Override protected GratisPilotComponent createComponent() { return DaggerApplicationComponent.builder() .applicationModule(new ApplicationModule(this)).build(); } }
81. Prod Flavor – Application Class public class GratisPilotApplication extends Application { private final GratisPilotComponent component = createComponent(); @Override protected GratisPilotComponent createComponent() { return DaggerApplicationComponent.builder() .applicationModule(new ApplicationModule(this)).build(); } }
82. Mock Flavor - Application Class public class MockApplication extends GratisPilotApplication { @Override protected GratisPilotComponent createComponent() { return DaggerTestApplicationComponent.builder(). mockApplicationModule(new MockApplicationModule(this)).build(); } }
83. Mock Flavor - Application Class public class MockApplication extends GratisPilotApplication { @Override protected GratisPilotComponent createComponent() { return DaggerTestApplicationComponent.builder(). mockApplicationModule(new MockApplicationModule(this)).build(); } }
84. What NOT to do? • Extending module and overriding the binding method to return mock.
85. Why NOT? • It force dagger to resolve the parameters and it’s dependencies even though your method returns mock. • Binding methods cannot be static.
86. Agenda • Overview • Key Concepts • Quiz
87. Fun With Dagger 2! J
88. No scope on class, not defined in module public class classA { @Inject DemoClass demoClassInClassA; } public class classB { @Inject DemoClass demoClassInClassB; } public class DemoClass { @Inject public DemoClass() { } } How many instance of DemoClass will be created? 2 Why? - Since the binding is not scoped, dagger will generate simple factory for this class that will return new object for every injection.
89. Class is scoped, not defined in module @PerApplication public class DemoClass { @Inject public DemoClass() { } } public class classA { @Inject DemoClass demoClassInClassA; } public class classB { @Inject DemoClass demoClassInClassB; } How many instance of DemoClass will be created? 1 Why? Dagger creates ScopedProvider.create(DemoClass_Factory.create()); which will maintain scope as long as new component is not created.
90. Class not scoped, not scoped in module public class DemoClass { @Inject public DemoClass() { } } //Module @Provides DemoClass demoClass() { return new DemoClass(); } public class classA { @Inject DemoClass demoClass; } public class classB { @Inject DemoClass demoClass; } How many instance of DemoClass will be created? 2
91. Class scoped, not scoped in module @PerApplication public class DemoClass { @Inject public DemoClass() { } } //Module @Provides DemoClass demoClass() { return new DemoClass(); } How many instance of DemoClass will be created? 2 Tip: Binding provided by @Module takes precedence. public class classA { @Inject DemoClass demoClass; } public class classB { @Inject DemoClass demoClass; }
92. Class not scoped, scoped in module //@PerApplication public class DemoClass { @Inject public DemoClass() { } } //Module @Provides @PerApplication DemoClass demoClass() { return new DemoClass(); } How many instance of DemoClass will be created? 1 public class classA { @Inject DemoClass demoClass; } public class classB { @Inject DemoClass demoClass; } Given - @Component is scoped with @PerApplication
93. Class scoped & scoped in module @PerApplication public class DemoClass { @Inject public DemoClass() { } } //Module @Provides @PerApplication DemoClass demoClass() { return new DemoClass(); } How many instance of DemoClass will be created? 1 public class classA { @Inject DemoClass demoClass; } public class classB { @Inject DemoClass demoClass; } Given - @Component is scoped with @PerApplication
94. Class scoped & scoped in module @PerApplication public class DemoClass { @Inject public DemoClass() { } } //Module @Provides @PerActivity DemoClass demoClass() { return new DemoClass(); } How many instance of DemoClass will be created? public class classA { @Inject DemoClass demoClass; } public class classB { @Inject DemoClass demoClass; } Error – Binding in module can be without scope or same scope as Component. So here it can only be @PerApplication or nothing. Given - @Component is scoped with @PerApplication
95. Not specified in module public final class LogExporter { private Context context; //@Inject public LogExporter(Context context) { this.context = context; } } How many instance of LogExporter will be created? Error - Cannot be provided without an @Inject constructor or from an @Provides- annotated method.
96. Questions ?
97. Appendix
98. History • Build on JSR 330 – October 09 • Google Guice 3.0 – March 11 • Dagger 1 – May 2013 • Dagger 2 – Apr 2015