Sharpen your Code with Dagger

Slides from my talk at DevFest Yangon 2017

References I studied for this talk
- Future of Dependency Injection by Jake Wharton (https://www.youtube.com/watch?v=plK0zyRLIP8)
- Dependency Injection in Android with Dagger 2 from RayWenderLich blog
(https://www.raywenderlich.com/146804/dependency-injection-dagger-2)
- Keeping the Dagger sharp By Py
(https://medium.com/square-corner-blog/keeping-the-daggers-sharp-%EF%B8%8F-230b3191c3f)
- That Missing Guide: How to use Dagger2 by Zhuinden (https://medium.com/@Zhuinden/that-missing-guide-how-to-use-dagger2-ef116fbea97)

1. Sharpen your code with Dagger Aung Kyaw Paing
2. Dependency? public class A { B b; public A() { this.b = new B(); } }
3. creates public class A { B b; public A() { this.b = new B(); } } A B
4. Dependency Injection public class A { B b; public A(B b) { this.b = b; } }
5. public class A { B b; public A(B b) { this.b = b; } } Injected into A B
6. S.O.L.I.D Principle • Single Responsibility Principle • Open/Closed Principle • Liskov Substitution Principle • Interface Segregation Principle • Dependency Inversion Principle
7. S.O.L.I.D Principle • Single Responsibility Principle • Open/Closed Principle • Liskov Substitution Principle • Interface Segregation Principle • Dependency Inversion Principle
8. Dependency Inversion Principle • Depend on abstractions. Do not depend on concretions.
9. Network Abstraction Retrofit Volley Mock App
10. Dependency Injection -A pattern
11. public class FacebookService { public void postStatus(String status) { InterfaceFacebookApi apiInterface= RetrofitProvider.createFacebookApi(); apiInterface.postStatus(status); } }
12. public class PostStatus { public void execute(String status) { FacebookService service = new FacebookService(); service.postStatus(status); } } public class FacebookService { public void postStatus(String status) { InterfaceFacebookApi apiInterface= RetrofitProvider.createFacebookApi(); apiInterface.postStatus(status); } }
13. PostStatus postStatus = new PostStatus(); postStatus.execute("Hello DevFest Yangon 2017"); postStatus.execute("Nice to Meet you All");
14. public class FacebookService { public void postStatus(String status) { InterfaceFacebookApi apiInterface= RetrofitProvider.createFacebookApi(); apiInterface.postStatus(status); } }
15. public class FacebookService { InterfaceFacebookApi apiInterface = RetrofitProvider.createFacebookApi(); public void postStatus(String status) { apiInterface.postStatus(status); } }
16. public class FacebookService { InterfaceFacebookApi apiInterface; public FacebookService(InterfaceFacebookApi apiInterface) { this.apiInterface = apiInterface; } public void postStatus(String status) { apiInterface.postStatus(status); } }
17. public class PostStatus { public void execute(String status) { FacebookService service = new FacebookService(); service.postStatus(status); } }
18. public class PostStatus { public void execute(String status) { FacebookService service = new FacebookService(RetrofitProvider.createFacebookApi()); service.postStatus(status); } }
19. public class PostStatus { FacebookService service = new FacebookService(RetrofitProvider.createFacebookApi()); public void execute(String status) { service.postStatus(status); } }
20. PostStatus postStatus = new PostStatus(); postStatus.execute("Hello DevFest Yangon 2017"); postStatus.execute("Nice to Meet you All");
21. PostStatus Facebook Service Retrofit
22. PostStatus postStatus = new PostStatus(); postStatus.execute("Hello DevFest Yangon 2017"); postStatus.execute("Nice to Meet you All");
23. PostStatus postStatus = new PostStatus(); postStatus.execute("Hello DevFest Yangon 2017"); postStatus.execute("Nice to Meet you All"); PostImage postImage = new PostImage(); postImage.execute("www.example.com/boston.jpg"); postImage.execute("www.example.com/paris.jpg");
24. public class FacebookService { InterfaceFacebookApi apiInterface; public FacebookService(InterfaceFacebookApi apiInterface) { this.apiInterface = apiInterface; } public void postStatus(String status) { apiInterface.postStatus(status); } }
25. public class FacebookService { InterfaceFacebookApi apiInterface; public FacebookService(InterfaceFacebookApi apiInterface) { this.apiInterface = apiInterface; } public void postStatus(String status) { apiInterface.postStatus(status); } public void postImage(String imageLink) { apiInterface.postImage(imageLink); } }
26. public class PostImage { FacebookService service = new FacebookService(RetrofitProvider.createFacebookApi()); public void execute(String imageUrl) { service.postImage(imageUrl); } }
27. public class PostImage { FacebookService service = new FacebookService(RetrofitProvider.createFacebookApi()); public void execute(String imageUrl) { service.postImage(imageUrl); } } public class PostStatus { FacebookService service = new FacebookService(RetrofitProvider.createFacebookApi()); public void execute(String status) { service.postStatus(status); } }
28. public class PostImage { FacebookService service = new FacebookService(RetrofitProvider.createFacebookApi()); public void execute(String imageUrl) { service.postImage(imageUrl); } } public class PostStatus { FacebookService service = new FacebookService(RetrofitProvider.createFacebookApi()); public void execute(String status) { service.postStatus(status); } }
29. public class PostImage { FacebookService service; public PostImage(FacebookService service) { this.service = service; } public void execute(String imageUrl) { service.postImage(imageUrl); } } public class PostStatus { FacebookService service; public PostStatus(FacebookService service) { this.service = service; } public void execute(String status) { service.postStatus(status); } }
30. PostStatus postStatus = new PostStatus(); postStatus.execute("Hello DevFest Yangon 2017"); postStatus.execute("Nice to Meet you All"); PostImage postImage = new PostImage(); postImage.execute("www.example.com/boston.jpg"); postImage.execute("www.example.com/paris.jpg");
31. InterfaceFacebookApi apiInterface = RetrofitProvider.createFacebookApi(); FacebookService service = new FacebookService(apiInterface); PostStatus postStatus = new PostStatus(service); postStatus.execute("Hello DevFest Yangon 2017"); postStatus.execute("Nice to Meet you All"); PostImage postImage = new PostImage(service); postImage.execute("www.example.com/boston.jpg"); postImage.execute("www.example.com/paris.jpg");
32. PostStatus Facebook Service Retrofit
33. PostStatus Facebook Service Retrofit PostImage
34. DI comes at the cost of boilerplate
35. Spring DI Framework
36. - Developed by Pivotal Software - Written in XML - Runtime crashes - Untraceable Spring
37. Spring Guice DI Framework
38. - Developed at Google by Bob Lee, Jessie Wilson and others - Maintained by Java Core Lib team - Written in Java - Heavy Initialization - Untraceable - Runtime crashes Guice
39. DI Framework Spring Guice Dagger 1
40. - Developed by Jessie Wilson(Square) - Advised By Bob Lee - Written in Java - Targeted for resource limited environment - Uses reflection - Runtime crashes - No scoping Dagger 1
41. DI Framework Spring Guice Dagger 1 Dagger 2
42. - Developed by Java Core Lib Team - Written with Java - Compile time crashes - Eliminated overheads - Support Scoping Dagger 2
43. Dagger 2 API @Module / @Provides - Provide dependencies
44. Dagger 2 API @Module / @Provides - Provide dependencies @Inject - Request dependencies
45. Dagger 2 API @Module / @Provides - Provide dependencies @Inject - Request dependencies @Component - Bridge modules and injections
46. -@Module is a class that holds related dependencies -@Provides is the method of module classes Dagger 2 API
47. @Module public class NetworkModule { @Provides @Singleton Retrofit providesRetrofit() { return new Retrofit.Builder().build(); } @Provides @Singleton FacebookService providesFacebookService(Retrofit retrofit) { return new FacebookService(retrofit.create(InterfaceFacebookApi.class)); } }
48. FacebookService NetworkModule#providesRetrofit NetworkModule#providesFacebookService Retrofit
49. NetworkModule#providesRetrofit Retrofit @Provides @Singleton FacebookService providesFacebookService(Retrofit retrofit) { return new FacebookService(retrofit.create(InterfaceFacebookApi.class)); } FacebookService NetworkModule#providesFacebookService
50. NetworkModule#providesRetrofit Retrofit FacebookService NetworkModule#providesFacebookService @Provides @Singleton FacebookService providesFacebookService(Retrofit retrofit) { return new FacebookService(retrofit.create(InterfaceFacebookApi.class)); }
51. @Module public class NetworkModule { @Provides @Singleton Retrofit providesRetrofit() { return new Retrofit.Builder().build(); } @Provides @Singleton FacebookService providesFacebookService(Retrofit retrofit) { return new FacebookService(retrofit.create(InterfaceFacebookApi.class)); } }
52. @Module public class NetworkModule { @Provides @Singleton OkHttpClient providesOkHttpClient() { return new OkHttpClient.Builder().build(); } @Provides @Singleton Retrofit providesRetrofit(OkHttpClient okHttpClient) { return new Retrofit.Builder().client(okHttpClient) .build(); } @Provides @Singleton FacebookService providesFacebookService(Retrofit retrofit) { return new FacebookService(retrofit.create(InterfaceFacebookApi.class)); } }
53. NetworkModule#providesRetrofit Retrofit NetworkModule#providesOkHttpClient OkHttpClient FacebookService NetworkModule#providesFacebookService
54. -@Module(s) can be used together Dagger 2 API
55. @Module public class FacebookModule { }
56. @Module public class FacebookModule { @Provides @Singleton PostStatus providesPostStatus(FacebookService facebookService) { return new PostStatus(facebookService); } }
57. NetworkModule#providesRetrofit Retrofit FacebookService NetworkModule#providesFacebookService PostStatus FacebookModule#providesPostStatus
58. @Provides @Singleton PostStatus providesPostStatus(FacebookService facebookService) { return new PostStatus(facebookService); } NetworkModule#providesRetrofit Retrofit FacebookService NetworkModule#providesFacebookService PostStatus FacebookModule#providesPostStatus
59. NetworkModule#providesRetrofit Retrofit FacebookService NetworkModule#providesFacebookService PostStatus FacebookModule#providesPostStatus @Provides @Singleton PostStatus providesPostStatus(FacebookService facebookService) { return new PostStatus(facebookService); }
60. @Module public class FacebookModule { @Provides @Singleton PostStatus providesPostStatus(FacebookService facebookService) { return new PostStatus(facebookService); } }
61. @Module public class FacebookModule { @Provides @Singleton PostStatus providesPostStatus(FacebookService facebookService) { return new PostStatus(facebookService); } @Provides @Singleton PostImage providesPostImage(FacebookService facebookService) { return new PostImage(facebookService); } }
62. PostImage FacebookModule#providesPostImage NetworkModule#providesRetrofit Retrofit FacebookService NetworkModule#providesFacebookService PostStatus FacebookModule#providesPostStatus
63. NetworkModule#providesRetrofit Retrofit FacebookService NetworkModule#providesFacebookService PostStatus FacebookModule#providesPostStatus PostImage FacebookModule#providesPostImage @Provides @Singleton PostImage providesPostImage(FacebookService facebookService) { return new PostImage(facebookService); }
64. NetworkModule#providesRetrofit Retrofit FacebookService NetworkModule#providesFacebookService PostStatus FacebookModule#providesPostStatus PostImage FacebookModule#providesPostImage
65. -@Inject requests dependencies -Constructor/Method/Field Injection Dagger 2 API
66. -@Inject on one constructor -Constructor parameters = dependencies -Can store dependencies as immutable -Can use for downstream injection Constructor Injection
67. @Module public class NetworkModule { @Provides @Singleton Retrofit providesRetrofit() { return new Retrofit.Builder().build(); } @Provides @Singleton FacebookService providesFacebookService(Retrofit retrofit) { return new FacebookService(retrofit.create(InterfaceFacebookApi.class)); } }
68. @Module public class NetworkModule { @Provides @Singleton Retrofit providesRetrofit() { return new Retrofit.Builder().build(); } @Provides @Singleton FacebookService providesFacebookService(Retrofit retrofit) { return new FacebookService(retrofit.create(InterfaceFacebookApi.class)); } }
69. public class FacebookService { private final InterfaceFacebookApi apiInterface; public FacebookService(InterfaceFacebookApi apiInterface) { this.apiInterface = apiInterface; } public void postStatus(String status) { apiInterface.postStatus(status); } public void postImage(String imageLink) { apiInterface.postImage(imageLink); } } Constructor Injection
70. public class FacebookService { private final InterfaceFacebookApi apiInterface; @Inject public FacebookService(Retrofit retrofit) { this.apiInterface = retrofit.create(InterfaceFacebookApi.class); } public void postStatus(String status) { apiInterface.postStatus(status); } public void postImage(String imageLink) { apiInterface.postImage(imageLink); } } Constructor Injection
71. @Singleton public class FacebookService { private final InterfaceFacebookApi apiInterface; @Inject public FacebookService(Retrofit retrofit) { this.apiInterface = retrofit.create(InterfaceFacebookApi.class); } public void postStatus(String status) { apiInterface.postStatus(status); } public void postImage(String imageLink) { apiInterface.postImage(imageLink); } } Constructor Injection
72. Method Injection -@Inject on methods -Method parameters = dependencies -Injection after object is fully instantiated -Use when you need to pass an instance of itself into dependency
73. Method Injection public class MapActivity extends AppCompatActivity { @Inject void subscribeGPSChange(LocationCallback locationCallback) { locationCallback.subscribe(this); } }
74. Field Injection -@Inject on fields -Fields = dependencies -Injection after object is fully instantiated -Risk of Mutability -Use in System objects
75. Field Injection public class MainActivity extends AppCompatActivity { @Inject PostStatus postStatus; @Inject PostImage postImage; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { //Inject here super.onCreate(savedInstanceState); } }
76. -@Components bridges @Inject and @Module/ @Provide Dagger 2 API
77. Components @Component public interface FacebookComponent { }
78. Components @Component(modules = { NetworkModule.class, FacebookModule.class }) public interface FacebookComponent { }
79. Components @Component(modules = { NetworkModule.class, FacebookModule.class }) public interface FacebookComponent { PostStatus postStatus(); PostImage postImage(); }
80. Components @Singleton @Component(modules = { NetworkModule.class, FacebookModule.class }) public interface FacebookComponent { PostStatus postStatus(); PostImage postImage(); }
81. Retrofit retrofit = RetrofitProvider.get(); FacebookService service = new FacebookService(retrofit); PostStatus postStatus = new PostStatus(service); postStatus.execute("Hello DevFest Yangon 2017"); postStatus.execute("Nice to Meet you All"); PostImage postImage = new PostImage(service); postImage.execute("www.example.com/boston.jpg"); postImage.execute("www.example.com/paris.jpg");
82. FacebookComponent facebookComponent = DaggerFacebookComponent.builder() .facebookModule(new FacebookModule()) .networkModule(new NetworkModule()) .build(); PostStatus postStatus = facebookComponent.postStatus(); postStatus.execute("Hello DevFest Yangon 2017"); postStatus.execute("Nice to Meet you All"); PostImage postImage = facebookComponent.postImage(); postImage.execute("www.example.com/boston.jpg"); postImage.execute("www.example.com/paris.jpg");
83. class FacebookActivity extends AppCompatActivity { PostStatus postStatus; PostImage postImage; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); FacebookComponent facebookComponent = DaggerFacebookComponent.builder() .facebookModule(new FacebookModule()) .networkModule(new NetworkModule()) .build(); this.postStatus = facebookComponent.postStatus(); this.postImage = facebookComponent.postImage(); } }
84. Components @Component(modules = { NetworkModule.class, FacebookModule.class }) public interface FacebookComponent { PostStatus postStatus(); PostImage postImage(); }
85. Components @Singleton @Component(modules = { NetworkModule.class, FacebookModule.class }) public interface FacebookComponent { void inject(Activity activity); }
86. class FacebookActivity extends AppCompatActivity { PostStatus postStatus; PostImage postImage; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); FacebookComponent facebookComponent = DaggerFacebookComponent.builder() .facebookModule(new FacebookModule()) .networkModule(new NetworkModule()) .build(); this.postStatus = facebookComponent.postStatus(); this.postImage = facebookComponent.postImage(); } }
87. class FacebookActivity extends AppCompatActivity { @Inject PostStatus postStatus; @Inject PostImage postImage; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); DaggerFacebookComponent.builder() .facebookModule(new FacebookModule()) .networkModule(new NetworkModule()) .build() .inject(this); } }
88. Scoping @Singleton @Component(modules = { NetworkModule.class, FacebookModule.class }) public interface FacebookComponent { void inject(Activity activity); }
89. Scoping @Singleton @Component(modules = { NetworkModule.class, FacebookModule.class }) public interface FacebookComponent { void inject(Activity activity); } @Component(modules = { NetworkModule.class }) @Singleton public class NetworkComponent { }
90. @Singleton @Component( dependencies = { NetworkComponent.class }, modules = { FacebookModule.class } ) public interface FacebookComponent { void inject(Activity activity); } @Component(modules = { NetworkModule.class }) @Singleton public class NetworkComponent { } Scoping
91. @Singleton @Component( dependencies = { NetworkComponent.class }, modules = { FacebookModule.class } ) public interface FacebookComponent { void inject(Activity activity); } @Component(modules = { NetworkModule.class }) @Singleton public interface NetworkComponent { FacebookService facebookService(); } Scoping
92. @Singleton @Component( dependencies = { NetworkComponent.class }, modules = { FacebookModule.class } ) public interface FacebookComponent { void inject(Activity activity); } @Component(modules = { NetworkModule.class }) @Singleton public interface NetworkComponent { FacebookService facebookService(); } Scoping
93. @Component( dependencies = { NetworkComponent.class }, modules = { FacebookModule.class } ) public interface FacebookComponent { void inject(Activity activity); } @Component(modules = { NetworkModule.class }) @Singleton public interface NetworkComponent { FacebookService facebookService(); } Scoping
94. @Component( dependencies = { NetworkComponent.class }, modules = { FacebookModule.class } ) public interface FacebookComponent { void inject(Activity activity); } @Module public class FacebookModule { @Provides @Singleton PostStatus providesPostStatus(FacebookService facebookService) { return new PostStatus(facebookService); } @Provides @Singleton PostImage providesPostImage(FacebookService facebookService) { return new PostImage(facebookService); } } Scoping
95. @Component( dependencies = { NetworkComponent.class }, modules = { FacebookModule.class } ) public interface FacebookComponent { void inject(Activity activity); } @Module public class FacebookModule { @Provides PostStatus providesPostStatus(FacebookService facebookService) { return new PostStatus(facebookService); } @Provides PostImage providesPostImage(FacebookService facebookService) { return new PostImage(facebookService); } } Scoping
96. Scoping @Scope public @interface StatusUpdateScreen { }
97. Scoping @StatusUpdateScreen @Component( dependencies = { NetworkComponent.class }, modules = { FacebookModule.class } ) public interface FacebookComponent { void inject(Activity activity); }
98. Scoping @Module public class FacebookModule { @Provides PostStatus providesPostStatus(FacebookService facebookService) { return new PostStatus(facebookService); } @Provides PostImage providesPostImage(FacebookService facebookService) { return new PostImage(facebookService); } }
99. Scoping @Module public class FacebookModule { @Provides @StatusUpdateScreen PostStatus providesPostStatus(FacebookService facebookService) { return new PostStatus(facebookService); } @Provides @StatusUpdateScreen PostImage providesPostImage(FacebookService facebookService) { return new PostImage(facebookService); } }
100. Scoping class StatusUpdateActivity extends AppCompatActivity { @Inject PostStatus postStatus; @Inject PostImage postImage; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); NetworkComponent daggerNetworkComponent = DaggerNetworkComponent.create(); DaggerStatusUpdateComponent.builder() .networkComponent(daggerNetworkComponent) .facebookModule(new FacebookModule()) .build() .inject(this); } }
101. Network Component
102. Network Component Network Module Retrofit Facebook Service
103. Network Component Network Module Retrofit Facebook Service Facebook Service
104. Network Component Network Module Retrofit Facebook Service Facebook Service Post Status Component
105. Network Component Network Module Retrofit Facebook Service Facebook Service Post Status Component FacebookModule PostStatus PostImage
106. Network Component Network Module Retrofit Facebook Service Facebook Service
107. Generated Code Under The Hood @Module public class NetworkModule { @Provides @Singleton OkHttpClient providesOkHttpClient() { return new OkHttpClient.Builder().build(); } @Provides @Singleton Retrofit providesRetrofit(OkHttpClient okHttpClient) { return new Retrofit.Builder().client(okHttpClient) .build(); } @Provides @Singleton FacebookService providesFaceookService(Retrofit retrofit) { return new FacebookService(retrofit); } }
108. Generated Code Under The Hood @Module public class NetworkModule { @Provides @Singleton OkHttpClient providesOkHttpClient() { return new OkHttpClient.Builder().build(); } @Provides @Singleton Retrofit providesRetrofit(OkHttpClient okHttpClient) { return new Retrofit.Builder().client(okHttpClient) .build(); } @Provides @Singleton FacebookService providesFaceookService(Retrofit retrofit) { return new FacebookService(retrofit); } }
109. Generated Code Under The Hood public final class NetworkModule_ProvidesOkHttpClientFactory implements Factory<OkHttpClient> { private final NetworkModule module; public NetworkModule_ProvidesOkHttpClientFactory(NetworkModule module) { assert module != null; this.module = module; } @Override public OkHttpClient get() { return Preconditions.checkNotNull(module.providesOkHttpClient(), "Cannot return null from a non-@Nullable @Provides method"); } public static Factory<OkHttpClient> create(NetworkModule module) { return new NetworkModule_ProvidesOkHttpClientFactory(module); } }
110. Generated Code Under The Hood public final class NetworkModule_ProvidesOkHttpClientFactory implements Factory<OkHttpClient> { private final NetworkModule module; public NetworkModule_ProvidesOkHttpClientFactory(NetworkModule module) { assert module != null; this.module = module; } @Override public OkHttpClient get() { return Preconditions.checkNotNull(module.providesOkHttpClient(), "Cannot return null from a non-@Nullable @Provides method"); } public static Factory<OkHttpClient> create(NetworkModule module) { return new NetworkModule_ProvidesOkHttpClientFactory(module); } }
111. Generated Code Under The Hood public final class NetworkModule_ProvidesOkHttpClientFactory implements Factory<OkHttpClient> { private final NetworkModule module; public NetworkModule_ProvidesOkHttpClientFactory(NetworkModule module) { assert module != null; this.module = module; } @Override public OkHttpClient get() { return Preconditions.checkNotNull(module.providesOkHttpClient(), "Cannot return null from a non-@Nullable @Provides method"); } public static Factory<OkHttpClient> create(NetworkModule module) { return new NetworkModule_ProvidesOkHttpClientFactory(module); } }
112. Generated Code Under The Hood public final class NetworkModule_ProvidesRetrofitFactory implements Factory<Retrofit> { private final NetworkModule module; private final Provider<OkHttpClient> okHttpClientProvider; public NetworkModule_ProvidesRetrofitFactory( NetworkModule module, Provider<OkHttpClient> okHttpClientProvider) { assert module != null; this.module = module; assert okHttpClientProvider != null; this.okHttpClientProvider = okHttpClientProvider; } @Override public Retrofit get() { return Preconditions.checkNotNull( module.providesRetrofit(okHttpClientProvider.get()), "Cannot return null from a non-@Nullable @Provides method"); } public static Factory<Retrofit> create( NetworkModule module, Provider<OkHttpClient> okHttpClientProvider) { return new NetworkModule_ProvidesRetrofitFactory(module, okHttpClientProvider); } }
113. Generated Code Under The Hood public final class NetworkModule_ProvidesRetrofitFactory implements Factory<Retrofit> { private final NetworkModule module; private final Provider<OkHttpClient> okHttpClientProvider; public NetworkModule_ProvidesRetrofitFactory( NetworkModule module, Provider<OkHttpClient> okHttpClientProvider) { assert module != null; this.module = module; assert okHttpClientProvider != null; this.okHttpClientProvider = okHttpClientProvider; } @Override public Retrofit get() { return Preconditions.checkNotNull( module.providesRetrofit(okHttpClientProvider.get()), "Cannot return null from a non-@Nullable @Provides method"); } public static Factory<Retrofit> create( NetworkModule module, Provider<OkHttpClient> okHttpClientProvider) { return new NetworkModule_ProvidesRetrofitFactory(module, okHttpClientProvider); } }
114. Generated Code Under The Hood public final class NetworkModule_ProvidesRetrofitFactory implements Factory<Retrofit> { private final NetworkModule module; private final Provider<OkHttpClient> okHttpClientProvider; public NetworkModule_ProvidesRetrofitFactory( NetworkModule module, Provider<OkHttpClient> okHttpClientProvider) { assert module != null; this.module = module; assert okHttpClientProvider != null; this.okHttpClientProvider = okHttpClientProvider; } @Override public Retrofit get() { return Preconditions.checkNotNull( module.providesRetrofit(okHttpClientProvider.get()), "Cannot return null from a non-@Nullable @Provides method"); } public static Factory<Retrofit> create( NetworkModule module, Provider<OkHttpClient> okHttpClientProvider) { return new NetworkModule_ProvidesRetrofitFactory(module, okHttpClientProvider); } }
115. Generated Code Under The Hood public final class DaggerNetworkComponent implements NetworkComponent { private Provider<OkHttpClient> providesOkHttpClientProvider; private Provider<Retrofit> providesRetrofitProvider; private Provider<FacebookService> providesFaceookServiceProvider; private DaggerNetworkComponent(Builder builder) { assert builder != null; initialize(builder); } public static Builder builder() { return new Builder(); } public static NetworkComponent create() { return new Builder().build(); } @SuppressWarnings("unchecked") private void initialize(final Builder builder) { this.providesOkHttpClientProvider = DoubleCheck.provider( NetworkModule_ProvidesOkHttpClientFactory.create(builder.networkModule)); this.providesRetrofitProvider = DoubleCheck.provider( NetworkModule_ProvidesRetrofitFactory.create( builder.networkModule, providesOkHttpClientProvider)); this.providesFaceookServiceProvider = DoubleCheck.provider( NetworkModule_ProvidesFaceookServiceFactory.create( builder.networkModule, providesRetrofitProvider)); } @Override public FacebookService facebookService() { return providesFaceookServiceProvider.get(); } }
116. Generated Code Under The Hood private void initialize(final Builder builder) { this.providesOkHttpClientProvider = NetworkModule_ProvidesOkHttpClientFactory.create(builder.networkModule); this.providesRetrofitProvider = NetworkModule_ProvidesRetrofitFactory.create( builder.networkModule, providesOkHttpClientProvider); this.providesFacebookServiceProvider = NetworkModule_ProvidesFacebookServiceFactory.create( builder.networkModule, providesRetrofitProvider); }
117. Generated Code Under The Hood private void initialize(final Builder builder) { this.providesOkHttpClientProvider = NetworkModule_ProvidesOkHttpClientFactory.create(builder.networkModule); this.providesRetrofitProvider = NetworkModule_ProvidesRetrofitFactory.create( builder.networkModule, providesOkHttpClientProvider); this.providesFacebookServiceProvider = NetworkModule_ProvidesFacebookServiceFactory.create( builder.networkModule, providesRetrofitProvider); } @Override public FacebookService facebookService() { return providesFacebookServiceProvider(); }
118. Generated Code Under The Hood class StatusUpdateActivity extends AppCompatActivity { @Inject PostStatus postStatus; @Inject PostImage postImage; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); NetworkComponent daggerNetworkComponent = DaggerNetworkComponent.create(); DaggerStatusUpdateComponent.builder() .networkComponent(daggerNetworkComponent) .facebookModule(new FacebookModule()) .build() .inject(this); } }
119. Generated Code Under The Hood public final class StatusUpdateActivity_MembersInjector implements MembersInjector<StatusUpdateActivity> { private final Provider<PostStatus> postStatusProvider; private final Provider<PostImage> postImageProvider; public StatusUpdateActivity_MembersInjector( Provider<PostStatus> postStatusProvider, Provider<PostImage> postImageProvider) { assert postStatusProvider != null; this.postStatusProvider = postStatusProvider; assert postImageProvider != null; this.postImageProvider = postImageProvider; } public static MembersInjector<StatusUpdateActivity> create( Provider<PostStatus> postStatusProvider, Provider<PostImage> postImageProvider) { return new StatusUpdateActivity_MembersInjector(postStatusProvider, postImageProvider); } @Override public void injectMembers(StatusUpdateActivity instance) { if (instance == null) { throw new NullPointerException("Cannot inject members into a null reference"); } instance.postStatus = postStatusProvider.get(); instance.postImage = postImageProvider.get(); } public static void injectPostStatus( StatusUpdateActivity instance, Provider<PostStatus> postStatusProvider) { instance.postStatus = postStatusProvider.get(); } public static void injectPostImage( StatusUpdateActivity instance, Provider<PostImage> postImageProvider) { instance.postImage = postImageProvider.get(); } }
120. Generated Code Under The Hood public void injectMembers(StatusUpdateActivity instance) { if (instance == null) { throw new NullPointerException("Cannot inject members into a null reference"); } instance.postStatus = postStatusProvider.get(); instance.postImage = postImageProvider.get(); }
121. General Rules of Thumbs
122. Favour Constructor Injection
123. Favour Constructor Injection public class FacebookService { @Inject private InterfaceFacebookApi apiInterface; public FacebookService() { //Inject here } public void postStatus(String status) { apiInterface.postStatus(status); } }
124. Favour Constructor Injection public class FacebookService { @Inject private InterfaceFacebookApi apiInterface; private DbFacebook dbFacbook; public FacebookService() { //Inject here } public void postStatus(String status) { apiInterface.postStatus(status); //Save on fail } public void saveStatus(String status) { dbFacbook.saveStatus(status); } }
125. Favour Constructor Injection public class FacebookService { @Inject private InterfaceFacebookApi apiInterface; private DbFacebook dbFacbook; public FacebookService() { //Inject here } public void postStatus(String status) { apiInterface.postStatus(status); //Save on fail } public void saveStatus(String status) { //NULL POINTER EXECPTION dbFacbook.saveStatus(status); } }
126. Favour Constructor Injection public class FacebookService { @Inject private InterfaceFacebookApi apiInterface; @Inject private DbFacebook dbFacbook; public FacebookService() { //Inject here } public void postStatus(String status) { apiInterface.postStatus(status); //Save on fail } public void saveStatus(String status) { dbFacbook.saveStatus(status); } public void postImage(String imageLink) { apiInterface.postImage(imageLink); } }
127. Favour Constructor Injection public class FacebookService { private final InterfaceFacebookApi apiInterface; private final DbFacebook dbFacbook; public FacebookService() { //Inject here } public void postStatus(String status) { apiInterface.postStatus(status); //Save on fail } public void saveStatus(String status) { dbFacbook.saveStatus(status); } public void postImage(String imageLink) { apiInterface.postImage(imageLink); } }
128. Favour Constructor Injection
129. Favour Constructor Injection
130. Favour Constructor Injection public class FacebookService { private final InterfaceFacebookApi apiInterface; private final DbFacebook dbFacbook; @Inject public FacebookService(InterfaceFacebookApi apiInterface, DbFacebook dbFacbook) { this.apiInterface = apiInterface; this.dbFacbook = dbFacbook; } public void postStatus(String status) { apiInterface.postStatus(status); //Save on fail } public void saveStatus(String status) { dbFacbook.saveStatus(status); } public void postImage(String imageLink) { apiInterface.postImage(imageLink); } }
131. Favour Constructor Injection class StatusUpdateActivity extends AppCompatActivity { @Inject PostStatus postStatus; @Inject PostImage postImage; @Override protected void onCreate(@Nullable Bundle savedInstanceState) { super.onCreate(savedInstanceState); NetworkComponent daggerNetworkComponent = DaggerNetworkComponent.create(); DaggerStatusUpdateComponent.builder() .networkComponent(daggerNetworkComponent) .facebookModule(new FacebookModule()) .build() .inject(this); } }
132. Don’t use Singleton everywhere -Use Singleton only when the state is mutable -Don’t use if there’s no mutable object -Use if expensive
133. Don’t use Singleton everywhere -Use Singleton only when the state is mutable @Singleton public class DbConnectionCounter { public Integer connectionCount = 0; @Inject public DbConnectionCounter(Context context) { //Implementation } void increment() { connectionCount = connectionCount++; } void decerement() { if (connectionCount > 0) { connectionCount = connectionCount--; } } }
134. Don’t use Singleton everywhere -Immutable, don’t use public class PostStatus { private final FacebookService service; @Inject public PostStatus(FacebookService service) { this.service = service; } public void execute(String status) { service.postStatus(status); } }
135. Don’t use Singleton everywhere -Use if the object is expensive to create @Module public class NetworkModule { @Provides @Singleton OkHttpClient providesOkHttpClient() { return new OkHttpClient.Builder().build(); } @Provides @Singleton Retrofit providesRetrofit(OkHttpClient okHttpClient) { return new Retrofit.Builder().client(okHttpClient).build(); } }
136. Use @Inject when you can @Module public class NetworkModule { @Provides @Singleton OkHttpClient providesOkHttpClient() { return new OkHttpClient.Builder().build(); } @Provides @Singleton Retrofit providesRetrofit(OkHttpClient okHttpClient) { return new Retrofit.Builder().client(okHttpClient).build(); } @Provides @Singleton FacebookService providesFacebookService(Retrofit retrofit) { return new FacebookService(retrofit); } }
137. Use @Inject when you can @Module public class NetworkModule { @Provides @Singleton OkHttpClient providesOkHttpClient() { return new OkHttpClient.Builder().build(); } @Provides @Singleton Retrofit providesRetrofit(OkHttpClient okHttpClient) { return new Retrofit.Builder().client(okHttpClient).build(); } @Provides @Singleton FacebookService providesFacebookService(Retrofit retrofit) { return new FacebookService(retrofit); } }
138. Use @Inject when you can public class FacebookService { private final InterfaceFacebookApi apiInterface; @Inject public FacebookService(Retrofit retrofit) { this.apiInterface = retrofit.create(InterfaceFacebookApi.class); } public void postStatus(String status) { apiInterface.postStatus(status); } public void postImage(String imageLink) { apiInterface.postImage(imageLink); } }
139. Use static @Provides Methods @Module public class AppModule { @Provides ErrorMessageFactory errorMessageFactory() { return new ErrorMessageFactory(); } } @Component(modules = AppModule.class) public interface AppComponent { ErrorMessageFactory errorMessageFactory(); }
140. Use static @Provides Methods public final class DaggerAppComponent implements AppComponent { private Provider<ErrorMessageFactory> errorMessageFactoryProvider; //... @Override public ErrorMessageFactory errorMessageFactory() { return errorMessageFactoryProvider.get(); } //... }
141. Use static @Provides Methods @Module public class AppModule { @Provides ErrorMessageFactory errorMessageFactory() { return new ErrorMessageFactory(); } } @Component(modules = AppModule.class) public interface AppComponent { ErrorMessageFactory errorMessageFactory(); }
142. Use static @Provides Methods @Module public class AppModule { @Provides static ErrorMessageFactory errorMessageFactory() { return new ErrorMessageFactory(); } } @Component(modules = AppModule.class) public interface AppComponent { ErrorMessageFactory errorMessageFactory(); }
143. Use static @Provides Methods public final class DaggerAppComponent implements AppComponent { //... @Override public ErrorMessageFactory errorMessageFactory() { return AppModule.errorMessageFactory(); } //... }
144. Use static @Provides Methods @Module public class AppModule { @Provides static ErrorMessageFactory errorMessageFactory() { return new ErrorMessageFactory(); } }
145. Use static @Provides Methods @Module public abstract class AppModule { @Provides static ErrorMessageFactory errorMessageFactory() { return new ErrorMessageFactory(); } }
146. Avoid @Singleton on providing abstractions @Provides @Singleton NetworkManager provideNetworkManager(NetworkManagerImpl networkManagerImpl) { return networkManagerImpl; }
147. Avoid @Singleton on providing abstractions @Provides NetworkManager provideNetworkManager(NetworkManagerImpl networkManagerImpl) { return networkManagerImpl; } @Singleton public class NetworkManagerImpl implements NetworkManager { }
148. Don’t Stress on scoping
149. Q & A