Dependency Injection on Android
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The document discusses dependency injection in Android, explaining its significance in software design by removing hard-coded dependencies and enhancing code reusability, modularity, and testability. It compares two popular frameworks, RoboGuice and Dagger, detailing their approaches and implementations using a kitkat machine example. The author concludes that dependency injection facilitates more modular applications and better testing, while noting the complexities and learning curve involved in using these frameworks.
![Example
-‐
KitKat
Machine:
Preparing
the
Graph
RoboGuice
public class KitKatMachineApplication extends
Application {
public void onCreate() {
super.onCreate();
RoboGuice.setBaseApplicationInjector
(this, Stage.PRODUCTION,
getModules());
}
protected Module[] getModules() {
List<Module> modules =
new ArrayList<Module>();
modules.add(
RoboGuice.newDefaultRoboModule(this));
modules.add(new IngredientsModule());
modules.add(new MachineModule());
return (Module[]) modules.toArray(new
Module[modules.size()]);
}
}
Dagger
public class KitKatMachineApplication extends
Application{
private ObjectGraph graph;
public void onCreate() {
super.onCreate();a
graph = ObjectGraph.create(
getModules().toArray());
}
protected List<Object> getModules() {
ArrayList<Object> modules =
new ArrayList<Object>();
modules.add(new AndroidModule(this));
modules.add(new IngredientsModule());
modules.add(new MachineModule());
return modules;
}
public void inject(Object object) {
graph.inject(object);
}
public ObjectGraph getApplicationGraph() {
return graph;
}
22](https://image.slidesharecdn.com/dependencyinjectionnormal-131126043636-phpapp02/85/Dependency-Injection-on-Android-23-320.jpg)
Dependency Injection on Android
- 1. Dependency Injec+on on Android By Joan Puig Sanz
- 2. About Joan Puig Sanz • Electrical Engineer • So<ware/hardware fan :) • Open Source Projects: – ServDroid: Simple web Server – BeyondAR Framework: Augmented Reality framework beyondar.com 1
- 3. //TODO: 1. What is Dependency Injec+on? 2. Simple Example: Factory PaPern 3. Android and Dependency Injec+on – KitKatMachine example with RoboGuice and Dagger – Compare RoboGuice and Dagger 4. Conclusions 2
- 4. What is Dependency Injec+on? “Dependency injec+on is a so<ware design paPern that allows the removal of hard-‐coded dependencies and makes it possible to change them, whether at run-‐+me or compile-‐+me” Dependency Injec+on is like ordering a hawaiian pizza but specifying the ingredients, for instance, instead of ham we want pepperoni. 3
- 5. What does Dependency Injec+on do? • It improves the code: reusable, modulable and testability • It allows the developer to focus on the code that adds a plus value to the app: – No need to worry about Singletons, Factories and others. 4
- 6. Factory paPern SIMPLE EXAMPLE 5
- 7. The Factory PaPern public interface Heater { public void on(); public void off(); public boolean isHot(); } public class ElectricHeater implements Heater { private boolean heating; public void on() { heating = true; } public void off() { heating = false; } public boolean isHot() { return heating; } }! Heater void on() void off() boolean isHot() ElectricHeater 6
- 8. The Factory PaPern – wri+ng it public class HeaterFactory { private HeaterFactory () {} private static Heater instance = new ElectricHeater(); public static Heater getInstance() { return instance; } public static void setInstance(Heater heater) { instance = heater; } } public class HotMachine{ public void start(){ heater = HeaterFactory.getInstance(); heater.on(); // Other stuff } }! 7
- 9. The Factory PaPern – Unit Test public void testHeater(){ Heater previous = HeaterFactory.getInstance(); try{ Heater mock = new mockHeater(); HeaterFactory.setInstance(mock); HotMachine machine = new HotMachine(); machine.start(); assertTrue(mock.isHot()); }finally{ HeaterFactory.setInstance(previous); } } 8
- 10. Implementa+on drawbacks • For every dependency we make we need to write the same code. • Our test had to pass the mock to the factory and then clean up a<erwards. • You cannot determine if HotMachine depends on Heater at first sight • It could be difficult to reuse HotMachine in a different context 9
- 11. Implementa+on drawbacks • For every dependency we make we need to write the same code. • Our test had to pass the mock to the factory and then clean up a<erwards. • You cannot determine if Machine depends on Heater at first sight • It could be difficult to reuse Machine in a different context 10
- 12. Factory PaPern with DI • We need to define a module specifying what are we going to inject. – Heater as ElectricHeater – We also can define how. public class HotMachine{ private final Heater heater; @Inject public HotMachine(Heater heater){ this.heater = heater; } public void start(){ heater.on(); //Other stuff } }! 11
- 13. Factory PaPern with DI – Unit Tes+ng ! public void testHeater(){ Heater mock= new mockHeater(); HotMachine machine = new HotMachine(mock); machine.start() assertTrue(mock.isHot()); }! 12
- 14. RoboGuice and Dagger ANDROID AND DEPENDENCY INJECTION 13
- 15. Android • We can create one ourselves… but it is not needed and it is a lot of work • The best ones are RoboGuice and Dagger – RoboGuice does injec+on during run+me • hPps://github.com/roboguice/roboguice – Dagger Generates code • hPps://github.com/square/dagger/ 14
- 16. Example -‐ KitKat Machine • Chocolate • Cookie • Machine Chocolate Heater Machine – Heater – Mold Cookie Mold The source code can be found here: hEp://beyondar.com/di.html 15
- 17. Example -‐ KitKat Machine: Steps 1. 2. 3. 4. Define dependencies Create modules Prepare the graph Inject dependencies 16
- 18. Example – KitKat Machine: Dependencies Chocolate Cookie Heater Mold ChocolateWithMilk TastyCookie ElectricHeater KitKatMold 17
- 19. Example – KitKat Machine: Dependencies Machine void makeKitKat(Chocolate, Cookie) Mold KitKatMachine Heater 18
- 20. Example – KitKat Machine: Dependencies ! public interface Cookie { public void doWhatCookiesDo(); } public class TastyCookie implements Cookie{ @Inject public TastyCookie(){ print("New cookie"); } public void doWhatCookiesDo(){ print("Yummie yummie”); } }! Cookie void doWhatCookiesDo() TastyCookie 19
- 21. Example – KitKat Machine: Dependencies public interface Machine { public void makeKitKat(Chocolate chocolate, Cookie cookie); }! RoboGuice @Singleton public class KitKatMachine implements Machine{ private Mold mold; private Heater heater; @Inject public KitKatMachine(Mold mold, Heater heater) { this.mold = mold; this.heater = heater; } public void makeKitKat(Chocolate chocolate, Cookie cookie){ heater.on(); Chocolate meltedChocolate = heater.melt(chocolate); mold.putToghether(cookie, chocolate); print (”Kitkat ready”); } Dagger public class KitKatMachine implements Machine{ private Mold mold; private Lazy<Heater> heater; @Inject public KitKatMachine(Mold mold, Lazy<Heater> heater) { this.mold = mold; this.heater = heater; } public void makeKitKat(Chocolate chocolate, Cookie cookie){ heater.get.on(); Chocolate meltedChocolate = heater.get().melt(chocolate); mold.putToghether(cookie, chocolate); print (”Kitkat ready”); } 20
- 22. Example -‐ KitKat Machine: Modules RoboGuice public class kitkatModule extends AbstractModule { protected void configure(){ bind(Cookie.class). toProvider(CookieProvider.class); bind(Chocolate.class). toProvider(ChocolateProvider.class); bind(Machine.class). to(KitkatMachine.class) } } public class ChocolateProvider implements Provider<Chocolate>{ @Override public Chocolate get() { return new ChocolateWithMilk(); } } Dagger @Module public class KitkatModule { @Provides public Chocolate provideChocolate() { return new ChocolateWithMilk(); } @Provides public Cookie provideCookie(){ return new TastyCookie(); } @Provides @Singleton public Machine } providesMachine(KitKatMachine machine){ return machine; } 21
- 23. Example -‐ KitKat Machine: Preparing the Graph RoboGuice public class KitKatMachineApplication extends Application { public void onCreate() { super.onCreate(); RoboGuice.setBaseApplicationInjector (this, Stage.PRODUCTION, getModules()); } protected Module[] getModules() { List<Module> modules = new ArrayList<Module>(); modules.add( RoboGuice.newDefaultRoboModule(this)); modules.add(new IngredientsModule()); modules.add(new MachineModule()); return (Module[]) modules.toArray(new Module[modules.size()]); } } Dagger public class KitKatMachineApplication extends Application{ private ObjectGraph graph; public void onCreate() { super.onCreate();a graph = ObjectGraph.create( getModules().toArray()); } protected List<Object> getModules() { ArrayList<Object> modules = new ArrayList<Object>(); modules.add(new AndroidModule(this)); modules.add(new IngredientsModule()); modules.add(new MachineModule()); return modules; } public void inject(Object object) { graph.inject(object); } public ObjectGraph getApplicationGraph() { return graph; } 22
- 24. Example -‐ KitKat Machine: Injec+ng dependencies public class HomeFragment extends #########{ @Inject Provider<Chocolate> chocolate; @Inject Provider<Cookie> cookie; @Inject Machine machine; // With Dagger we can use Lazy<Machine> to create a lazy singleton onResume(){ super.onResume() machine.makeKitKat(chocolate.get(), cookie.get()); } } ######### • RoboGuice: RoboFragment • Dagger: BaseFragment (your custom BaseFragment) 23
- 25. Example -‐ KitKat Machine: Injec+ng dependencies -‐ Dagger public class BaseFragment extends Fragment { public void onActivityCreated(Bundle savedInstanceState) { super.onActivityCreated(savedInstanceState); // Perform injection so that when this call returns all // dependencies will be available for use. ((KitKatMachineApplication) getApplication()).inject(this); } }! • The same goes for the Ac+vity. • It is highly customizable – For Instance: It is possible to personalize the modules that we want to inject into the Ac+vity (crea+ng a derivate graph) 24
- 26. Inject inject inject… OTHER STUFF TO INJECT 25
- 27. Injec+ng other stuff -‐ Qualifiers • It is also possible to inject Qualifiers: -‐ Module: @Provides @Named("app_version") public String getAppVersionCode(Context context) { return String.valueOf(getPackageInfo(context).versionCode); }! -‐ InjecSng: ! @Inject @Named("app_version") String version;! ! 26
- 28. Injec+ng other stuff -‐ RoboGuice • With RoboGuice we can inject views, preferences, fragments, extras and resources: @InjectView(R.id.myTextView) private TextView myTextView; @InjectResource(R.string.app_name) private String appName;! ! • We also can inject Context, Inflater, Services and some other Android Objects. – Check out DefaultRoboModule.java for more informa+on 27
- 29. Go! SIDE BY SIDE 28
- 30. Side by side RoboGuice • Can inject dependencies in private fields • Method Injec+on supported • Configure Proguard is hard (doable) • Ready to inject a lot of Android stuff • It uses Guice which is more server related • Very cool framework Dagger • Method Injec+on not supported… for now • Faster. In a big app it can reduce the startup +me in a few seconds • Configure Proguard is a pain in the ass • If you want to inject Android stuff you need to write the code to do it • It forces developers to write a bit more code • Remember that it generates code! • Very cool framework 29
- 31. Conclusions • Dependency injec+ons allows the developer to spend +me on the important parts • It makes the applica+on more modular • It helps tes+ng your applica+on • It makes your code less like spagheq, ravioli, lasagna and other Italian foods • The developer needs to understand the DI framework • Easier to implement at the beginning than at the end • Very cool frameworks :) 30