Dependency Injection on Android

Unit testing is a crucial tool for building quality software. In order to be able to write unit tests, your classes need to operate independently. Dependency injection is a technique that provides the decoupling your classes need to be easily unit tested. We’ll explore the concept of dependency injection, designing classes using the technique and apply it directly to Android development. The session will also cover the popular Android-focused dependency injection frameworks RoboGuice and Dagger, looking at how those tools make dependency injection easier and cleaner.

Transcript

1. Dependency Injection on Android David Truxall, Ph.D. https://github.com/davetrux/DevFest2014
2. About Me @davetrux blog.davidtruxall.com
3. Who are you?
4. Tools
5. What will we learn? Dependency Injection concepts Unit Testing Frameworks Code Structure
6. Definition Method for providing a class objects it depends upon instead of the class creating those objects
7. Why • Loose coupling • Unit Testing • Clean code
8. Why Not Always a cost…. Performance Memory App Start Up
9. Journey to Unit Testing You need to write tests Databases? Services? Web Services?
10. Journey to Unit Tests Dependency injection DI and Mocking Frameworks Code Structure Unit Tests
11. Unit Testing Android
12. Preliminary Concepts - Interfaces public interface DataProvider { void addTask(ToDo item); void deleteAll(); void deleteTask(final long id); List<ToDo> findAll(); }
13. Preliminary Concepts - Mock Objects Simulated objects that mimic the behavior of real objects in controlled a way
14. public class MockDataSource implements DataProvider { @Override public List<ToDo> findAll() { List<ToDo> data = new ArrayList<ToDo>(); ToDo item = new ToDo(); item.setId(11l); item.setTitle("Title 1"); data.add(item); // Add more objects... return data; } // Override More methods>.... }
15. Traditional Forms of DI • Constructor • Setter • Method • Framework
16. public interface Bird { public String call(); public void fly(); } public class Crow implements Bird { @Override public String call() { return "Caw Caw"; } @Override public void fly() { flapWings(); } //More code below... }
17. public String birdCall(String birdType){ Bird bird = null; if(birdType.equals("Owl")) { bird = new Owl(); } else if(birdType.equals("BlueJay")) { bird = new BlueJay(); } else if(birdType.equals("Crow")) { bird = new Crow(); } if(bird == null) {return "";} return bird.call().toUpperCase(); } BAD!
18. Constructor public class Example { private Bird mBird; public Example(Bird bird) { mBird = bird; } public String birdCall(){ return mBird.call().toUpperCase(); } }
19. Setter public class Example { private Bird mBird; public void setBird(Bird bird) { mBird = bird; } public String birdCall(){ return mBird.call().toUpperCase(); } }
20. Parameter public class Example { public String birdCall(Bird bird){ return bird.call().toUpperCase(); } }
21. What about Android?
22. ToDo - Look at the app
23. Your Fabulous App Application Activity Activity Service
24. Your Fabulous App Application Activity Activity Service Dependency Injection Container
25. Our ToDo App Dependency Injection by Hand Application Activity SQLite DataProvider
26. Our ToDo App Dependency Injection by Hand Application Activity DataProvider Interface SQLiteDataProvider
27. Test It ToDo App Unit Tests Mock Application Activity DataProvider Interface MockDataProvider
28. Go to the Code
29. Frameworks • Guice • RoboGuice • Dagger
30. Our ToDo App Framework Application Activity Module DataProvider Interface SQLiteDataProvider
31. Framework Unit Test Mock Application Activity Module DataProvider Interface MockDataProvider
32. Dagger http://square.github.io/dagger/ Fast - Speed over Features Compile-Time Validation Actively control scope for memory management
33. Go to the Code
34. @Override protected void onCreate(Bundle savedInstanceState) { // extend the application-scope object graph with // the modules for this activity mObjectGraph = ((Injector) getApplication()).getObjectGraph(); mObjectGraph.plus(getModules()); mObjectGraph.inject(this); super.onCreate(savedInstanceState); //Do your other Activity stuff now... }
35. Don’t • Make every class use the pattern • Store dependencies in static fields
36. Roboguice / Guice https://github.com/roboguice/roboguice Well known Lots of features Run-time validation Accused of being slow
37. Next Steps Mocking Frameworks BDD Design Patterns Butter Knife Android Annotations
38. Wrapping it Up Forms of DI Unit Testing Code Structure Frameworks
39. Shameless Plug #2 @davetrux blog.davidtruxall.com https://github.com/davetrux/DevFest2014
40. Resources Inversion of Control Containers and the Dependency Injection pattern A Beginner's Guide to Dependency Injection Clean Code in Android Applications When To Mock Create a new Android project with Robolectric unit test suppor fb-android-dagger Dependency Injection with Dagger on Android Android Apps with Dagger
41. You want this The Code https://github.com/davetrux/DevFest2014 The Presentation http://bit.ly/androidDI