Andrew Kurniadi (Google Developer Expert Android, CEO-Lumio.ID) - Introduction to Depedency Injection in Android

1. Andrew Kurniadi
Google Developer Expert
CEO lumio.id
Dependency Injection in Android

2. “Ideally Java classes should
be as independent as
possible from other Java
classes.”

3. Why?

4. Dependency Injection
• Easier to test
• Mock objects
• Class Reusability

5. Hard Dependency
public class Tweeter{
private HttpClient client;
public Tweeter() {
client = new HttpClient();
}
}

6. No Hard Dependency
public class Tweeter{
private HttpClient client;
public Tweeter(HttpClient client) {
this.client = client;
}
}

8. Introducing Dagger 2

9. History of Dagger 2
• Guice by Google
• Dagger by Square
• Dagger 2

10. Benefit of Dagger 2
• Simpler generated code
• Injection occur at compile time
• Faster Performance
• Easier to Debug

11. Dagger 2 API
• @Module for the classes whose methods provide
dependencies
• @Provides for the methods
within @Module classes
• @Inject to request a dependency (a constructor, a
field, or a method)
• @Component is a bridge interface between
modules and injection

12. Independent Class
public class Engine {
private int rpm;
public Engine(){
this.rpm = 0;
}
public void accelerate(int value){
rpm = rpm + value;
}
...
}

13. Dependent Class
public class Vehicle {
private Engine engine;
public Engine engine){
this.engine = engine;
}
public void increaseSpeed(int value){
engine.accelerate(value);
}
...
}

14. @Module Class
@Module
public class VehicleModule {
@Provides @Singleton
Engine provideEngine(){
return new engine();
}
@Provides @Singleton
Vehicle provideVehicle(){
return new Vehicle(new Engine());
}
}

15. @Inject
@Inject
public Vehicle(Engine engine){
this.engine = engine;
}

16. Bridging @Module and @Inject
@Singleton
@Component(modules = {VehicleModule.class})
public interface VehicleComponent {
Vehicle provideVehicle();
}

17. Dependency Injection
public class MainActivity extends ActionBarActivity {
Vehicle vehicle;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
VehicleComponent component =
DaggerVehicleComponent.builder().vehicleModule(new
VehicleModule()).build();
vehicle = component.provideVehicle();
Toast.makeText(this, String.valueOf(vehicle.getSpeed()),
Toast.LENGTH_SHORT).show();
}
}
MAGIC

18. There’s More….
• Scopes
• Subcomponents
• Testing with Mockito

19. Andrew Kurniadi
Thank You
Google Developer Expert
CEO lumio.id