DI @ Android

Experience of Dependency Injection with Robots

Transcript

1. DI @ Android Experience of Dependency Injection with Robots Alex Korovyansky Thumbtack Expertise Day Jul 19, 2014
2. Dependency Injection 2
3. Dependency Injection • Software design pattern that implements inversion of control and allows a program design to follow the dependency inversion principle. The term was coined by Martin Fowler. 2
4. Dependency Injection • Software design pattern that implements inversion of control and allows a program design to follow the dependency inversion principle. The term was coined by Martin Fowler. • Separates behaviour of something from its required classes 2
5. Dependency Injection • Software design pattern that implements inversion of control and allows a program design to follow the dependency inversion principle. The term was coined by Martin Fowler. • Separates behaviour of something from its required classes 2 Component Service
6. ! ! public class Component { private final Service service; public Component() { this.service = new ServiceImpl(); } public void doStuff() { return service.doStuff(); } } 3 ? ! ! ! public interface Service { public void doStuff(); }
7. 4 ! ! ! public class CatsService implements Service { @Override public void doStuff() { System.out.println("Cats are better than dogs!") } } ! public class DogsService implements Service { @Override public void doStuff() { System.out.println("Dogs are better than cats!") } }
8. ! ! public class Component { private final Service service; public Component() { this.service = new CatsService(); } public void doStuff() { return service.doStuff(); } } 5 ? ! ! ! public interface Service { public void doStuff(); }
9. Basic Idea 6 Component <<interface>> Service ServiceImpl Assembler <<create>>
10. Styles 7 • Constructor Injection • Setter Injection • Interface Injection
11. 8 ! ! ! public class Component { private final Service service; public Component(Service service) { this.service = service; } public void doStuff() { return service.doStuff(); } } ^^ Constructor Injection ^^
12. Frameworks 9
13. Frameworks • PicoContainer 9
14. Frameworks • PicoContainer • Spring 9
15. Frameworks • PicoContainer • Spring • Guice 9
16. Frameworks • PicoContainer • Spring • Guice • Avalon 9
17. Frameworks • PicoContainer • Spring • Guice • Avalon • … 9
18. JSR-330 10
19. JSR-330 • @Inject 10
20. JSR-330 • @Inject • @Named 10
21. JSR-330 • @Inject • @Named • @Qualifier 10
22. JSR-330 • @Inject • @Named • @Qualifier • @Scope 10
23. JSR-330 • @Inject • @Named • @Qualifier • @Scope • @Singelton 10
24. Advantages of DI 11
25. Advantages of DI • Loosely coupled programs 11
26. Advantages of DI • Loosely coupled programs • Following single responsibility principle 11
27. Advantages of DI • Loosely coupled programs • Following single responsibility principle • Easy to write tests / extend / maintain 11
28. Advantages of DI • Loosely coupled programs • Following single responsibility principle • Easy to write tests / extend / maintain • Reduction of boilerplate code 11
29. Advantages of DI • Loosely coupled programs • Following single responsibility principle • Easy to write tests / extend / maintain • Reduction of boilerplate code • Parallel development 11
30. Advantages of DI • Loosely coupled programs • Following single responsibility principle • Easy to write tests / extend / maintain • Reduction of boilerplate code • Parallel development • … 11
31. What about Android? 12
32. Frameworks • PicoContainer • Spring • Guice • Avalon • … 13
33. Guice 14
34. Guice • Powerful, dynamic, well-tested, wide-spread, etc… 14
35. Guice • Powerful, dynamic, well-tested, wide-spread, etc… • Canonical standard for dependency injection 14
36. Guice • Powerful, dynamic, well-tested, wide-spread, etc… • Canonical standard for dependency injection • Configuration problems fail at runtime 14
37. Guice • Powerful, dynamic, well-tested, wide-spread, etc… • Canonical standard for dependency injection • Configuration problems fail at runtime • Slow initialization, slow injection, memory problems 14
39. Frameworks • PicoContainer • Spring • Guice • Avalon • … 16
41. “ObjectGraph” goals 18
42. “ObjectGraph” goals • Static analysis of all dependencies and injections 18
43. “ObjectGraph” goals • Static analysis of all dependencies and injections • Fail as early as possible (compile-time, not runtime) 18
44. “ObjectGraph” goals • Static analysis of all dependencies and injections • Fail as early as possible (compile-time, not runtime) • Eliminate reflection on methods and annotations at runtime 18
45. “ObjectGraph” goals • Static analysis of all dependencies and injections • Fail as early as possible (compile-time, not runtime) • Eliminate reflection on methods and annotations at runtime • Have negligible memory impact 18
46. “ObjectGraph” Development 19
47. “ObjectGraph” Development • ~5 weeks of heads-down work by Jesse Wilson 19
48. “ObjectGraph” Development • ~5 weeks of heads-down work by Jesse Wilson • Bob Lee served as technical advisor 19
49. “ObjectGraph” Development • ~5 weeks of heads-down work by Jesse Wilson • Bob Lee served as technical advisor • “Giant” boolean switch in Square’s applications 19
50. “ObjectGraph” Development • ~5 weeks of heads-down work by Jesse Wilson • Bob Lee served as technical advisor • “Giant” boolean switch in Square’s applications • 2 weeks after, they dropped Guice completely 19
51. “ObjectGraph” Development • ~5 weeks of heads-down work by Jesse Wilson • Bob Lee served as technical advisor • “Giant” boolean switch in Square’s applications • 2 weeks after, they dropped Guice completely • Renamed to Dagger before first release 19
52. “ObjectGraph” Development • ~5 weeks of heads-down work by Jesse Wilson • Bob Lee served as technical advisor • “Giant” boolean switch in Square’s applications • 2 weeks after, they dropped Guice completely • Renamed to Dagger before first release • Open sourced — http://github.com/square/dagger 19
53. Dagger 20 Tweeter Twitter API HTTP Client User Manager Shared Preferences Account Manager
54. DAG-er 21 Tweeter Twitter API HTTP Client User Manager Shared Preferences Account Manager
55. Dagger 22
56. Dagger • ObjectGraph: central dependency manager and injector 22
57. Dagger • ObjectGraph: central dependency manager and injector • @Module + @Provides: mechanism for providing dependencies 22
58. Dagger • ObjectGraph: central dependency manager and injector • @Module + @Provides: mechanism for providing dependencies • @Inject: mechanism for requesting dependencies 22
59. Dagger • ObjectGraph: central dependency manager and injector • @Module + @Provides: mechanism for providing dependencies • @Inject: mechanism for requesting dependencies • Plus some other sugar, magic and conventions 22
60. Providing Dependencies 23
61. Providing Dependencies • Modules are classes that provide dependencies 23
62. Providing Dependencies • Modules are classes that provide dependencies • @Module annotation on the class 23
63. Providing Dependencies • Modules are classes that provide dependencies • @Module annotation on the class • @Provider annotation on a method indicates that its return type is a dependency 23
64. 24 public class NetworkModule { public OkHttpClient provideOkHttpClient() { return new OkHttpClient(); } public TwitterApi provideTwitterApi(OkHttpClient client) { return new TwitterApi(client); } }
65. 25 @Module public class NetworkModule { public OkHttpClient provideOkHttpClient() { return new OkHttpClient(); } public TwitterApi provideTwitterApi(OkHttpClient client) { return new TwitterApi(client); } }
66. 26 @Module public class NetworkModule { @Provides public OkHttpClient provideOkHttpClient() { return new OkHttpClient(); } @Provides public TwitterApi provideTwitterApi(OkHttpClient client) { return new TwitterApi(client); } }
67. 27 @Module public class NetworkModule { @Provides @Singleton public OkHttpClient provideOkHttpClient() { return new OkHttpClient(); } @Provides @Singleton public TwitterApi provideTwitterApi(OkHttpClient client) { return new TwitterApi(client); } }
68. Providing Dependencies 28 TwitterApi NetworkModule#provideOkHttpClient NetworkModule#provideTwitterApi OkHttpClient
69. Providing Dependencies 28 TwitterApi NetworkModule#provideOkHttpClient NetworkModule#provideTwitterApi OkHttpClient
70. Providing Dependencies 28 TwitterApi NetworkModule#provideOkHttpClient NetworkModule#provideTwitterApi OkHttpClient
71. Providing Dependencies 28 TwitterApi NetworkModule#provideOkHttpClient NetworkModule#provideTwitterApi OkHttpClient
72. Providing Dependencies 29
73. Providing Dependencies • Modules are classes that provide dependencies 29
74. Providing Dependencies • Modules are classes that provide dependencies • @Module annotation on the class 29
75. Providing Dependencies • Modules are classes that provide dependencies • @Module annotation on the class • @Provider annotation on a method indicates that its return type is a dependency 29
76. Providing Dependencies • Modules are classes that provide dependencies • @Module annotation on the class • @Provider annotation on a method indicates that its return type is a dependency • Designed to be composed together 29
77. 30 @Module public class TwitterModule { private final String user; public TwitterModule(String user) { this.user = user; } @Provides @Singleton public Tweeter provideTweeter(TwitterApi api) { return new Tweeter(api, user); } ! @Provides @Singleton public Timeline provideTimeline(TwitterApi api) { return new Timeline(api, user); } }
78. Providing Dependencies 31 TwitterApi NetworkModule#provideOkHttpClient NetworkModule#provideTwitterApi OkHttpClient Tweeter TweeterModule#provideTweeter Timeline TweeterModule#provideTimeline
79. Providing Dependencies 31 TwitterApi NetworkModule#provideOkHttpClient NetworkModule#provideTwitterApi OkHttpClient Tweeter TweeterModule#provideTweeter Timeline TweeterModule#provideTimeline
80. Providing Dependencies 31 TwitterApi NetworkModule#provideOkHttpClient NetworkModule#provideTwitterApi OkHttpClient Tweeter TweeterModule#provideTweeter Timeline TweeterModule#provideTimeline
81. Providing Dependencies 31 TwitterApi NetworkModule#provideOkHttpClient NetworkModule#provideTwitterApi OkHttpClient Tweeter TweeterModule#provideTweeter Timeline TweeterModule#provideTimeline
82. Providing Dependencies 31 TwitterApi NetworkModule#provideOkHttpClient NetworkModule#provideTwitterApi OkHttpClient Tweeter TweeterModule#provideTweeter Timeline TweeterModule#provideTimeline
83. Listing Injection Points 32
84. Listing Injection Points • All injection points must be listed on a module 32
85. Listing Injection Points • All injection points must be listed on a module • Used for aggressive static analysis 32
86. Listing Injection Points • All injection points must be listed on a module • Used for aggressive static analysis • Potentially not needed for full compilation... 32
87. Listing Injection Points • All injection points must be listed on a module • Used for aggressive static analysis • Potentially not needed for full compilation... • ...but absolutely required for incremental compilation 32
88. 33 @Module public class ExampleModule { @Provides @Singleton Foo provideFoo() { return new Foo(); } @Provides @Singleton Bar provideBar() { return new Bar(); } }
89. 34 @Module( injects = { Component1.class, ComponentN.class } ) @Module public class ExampleModule { @Provides @Singleton Foo provideFoo() { return new Foo(); } @Provides @Singleton Bar provideBar() { return new Bar(); } }
90. Requesting Dependencies 35
91. Requesting Dependencies • @Inject annotation required 35
92. Requesting Dependencies • @Inject annotation required • Field injection and constructor injection only 35
93. Constructor Injection 36
94. Constructor Injection • @Inject on a single constructor 36
95. Constructor Injection • @Inject on a single constructor • All constructor arguments are dependencies 36
96. Constructor Injection • @Inject on a single constructor • All constructor arguments are dependencies • Dependencies can be stored in private and final fields 36
97. 37 public class TweeterApp { private final Tweeter tweeter; private final Timeline timeline; @Inject public TweeterApp(Tweeter tweeter, Timeline timeline){ this.tweeter = tweeter; this.timeline = timeline; } // ... }
98. Constructor Injection • @Inject on a single constructor • All constructor arguments are dependencies • Dependencies can be stored in private and final fields 38
99. Constructor Injection • @Inject on a single constructor • All constructor arguments are dependencies • Dependencies can be stored in private and final fields • Dagger must create the object 38
100. Constructor Injection • @Inject on a single constructor • All constructor arguments are dependencies • Dependencies can be stored in private and final fields • Dagger must create the object • @Provides not required for downstream injection 38
101. Field Injection 39
102. Field Injection • @Inject on fields which are dependencies 39
103. Field Injection • @Inject on fields which are dependencies • Field may not be private or final 39
104. 40 public class TweeterApp { @Inject Tweeter tweeter; @Inject Timeline Timeline; // ... }
105. 41 public class TweeterActivity extends Activity { @Inject Tweeter tweeter; @Inject Timeline Timeline; // ... }
106. Field Injection • @Inject on fields which are dependencies • Field may not be private or final 42
107. Field Injection • @Inject on fields which are dependencies • Field may not be private or final • Injection happens after the object is “alive” 42
108. Field Injection • @Inject on fields which are dependencies • Field may not be private or final • Injection happens after the object is “alive” • Object often must be responsible for injecting itself 42
109. The ObjectGraph 43
110. The ObjectGraph • Central module (dependency) manager 43
111. The ObjectGraph • Central module (dependency) manager • Injector 43
112. The ObjectGraph • Central module (dependency) manager • Injector • Can be extended to create “scopes” 43
113. 44 ObjectGraph og = ObjectGraph.create( new NetworkModule(), new TwitterModule("korovyansk") );
114. 44 ObjectGraph og = ObjectGraph.create( new NetworkModule(), new TwitterModule("korovyansk") ); // Using constructor injection: TweeterApp app = og.get(TweeterApp.class);
115. 44 ObjectGraph og = ObjectGraph.create( new NetworkModule(), new TwitterModule("korovyansk") ); // Using constructor injection: TweeterApp app = og.get(TweeterApp.class); // Using field injection: TweeterApp app = new TweeterApp(); og.inject(app);
116. How to start usage in Android? 45
117. Android 46
118. Android • Entry objects are managed objects constructed by OS
 (impossible to use Constructor injection for OS components) 46
119. Android • Entry objects are managed objects constructed by OS
 (impossible to use Constructor injection for OS components) • Field injection is Android style
 (including Activities, Fragments, Services, Views) 46
120. Android • Entry objects are managed objects constructed by OS
 (impossible to use Constructor injection for OS components) • Field injection is Android style
 (including Activities, Fragments, Services, Views) • Application is the best place to keep ObjectGraph 46
121. Android • Entry objects are managed objects constructed by OS
 (impossible to use Constructor injection for OS components) • Field injection is Android style
 (including Activities, Fragments, Services, Views) • Application is the best place to keep ObjectGraph • Modules and their “injects” segment parts of your app
 using .plus() method 46
122. 47 ! // build.gradle ! dependencies { compile 'com.squareup.dagger:dagger:1.2.1' provided 'com.squareup.dagger:dagger-compiler:1.2.1' ! // ... }
123. 48 public class ExampleApp extends Application { private ObjectGraph objectGraph; ! @Override public void onCreate() { super.onCreate(); objectGraph = ObjectGraph.create( new ExampleModule() ); } ! public ObjectGraph getObjectGraph() { return objectGraph; } }
124. 49 public class ExampleActivity1 extends Activity { @Inject Foo foo; @Inject Bar bar; ! @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ! ExampleApp app = (ExampleApp) getApplication(); app.getObjectGraph().inject(this); ! // ... } }
125. 50 public class ExampleActivityN extends Activity { @Inject Foo foo; @Inject Bar bar; ! @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); ! ExampleApp app = (ExampleApp) getApplication(); app.getObjectGraph().inject(this); ! // ... } }
126. 51 @Module( injects = { ExampleActivity1.class, ExampleActivityN.class } ) public class ExampleModule { @Provides @Singleton Foo provideFoo() { return new Foo(); } @Provides @Singleton Bar provideBar() { return new Bar(); } }
127. Android* 52
128. Android* • Mock mode for parallel and robust development
 (based on flavours and overriding of Modules) 52
129. Android* • Mock mode for parallel and robust development
 (based on flavours and overriding of Modules) • Test mode for unit and functional testing
 (based on overriding Modules to follow test scenarios) 52
130. Android* • Mock mode for parallel and robust development
 (based on flavours and overriding of Modules) • Test mode for unit and functional testing
 (based on overriding Modules to follow test scenarios) • Mortar and Flow
 (work with UI with DI in mind) 52
131. Android Barcamp 53
132. Android Barcamp • August 2, 2014 @ IT-Loft Omsk, starting from 14-00 53
133. Android Barcamp • August 2, 2014 @ IT-Loft Omsk, starting from 14-00 • Fluid program and advanced topics of Android Dev 53
134. Android Barcamp • August 2, 2014 @ IT-Loft Omsk, starting from 14-00 • Fluid program and advanced topics of Android Dev • Take part for FREE! 53
135. Android Barcamp • August 2, 2014 @ IT-Loft Omsk, starting from 14-00 • Fluid program and advanced topics of Android Dev • Take part for FREE! • More details in +Android Developers Omsk 53
136. Demos 54
137. Demos • U2020
 (https://github.com/JakeWharton/u2020) 54
138. Demos • U2020
 (https://github.com/JakeWharton/u2020) • OmskQuest
 (https://github.com/Apps4Omsk/OmskOmsk) 54
139. Demos • U2020
 (https://github.com/JakeWharton/u2020) • OmskQuest
 (https://github.com/Apps4Omsk/OmskOmsk) • More @ GitHub
 Search: “provided com.squareup.dagger:dagger-compiler" 54
140. Personal Experience 55
141. Q&A 
 Alex Korovyansky korovyansk@gmail.com http://about.me/korovyansk 56