Demystifying dependency Injection: Dagger and Toothpick

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I come withknifes A story of Daggers and Toothpicks… Droidcon Krakow 2016 Danny Preussler @PreusslerBerlin

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@PreusslerBerlin Once upon atime

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@PreusslerBerlin A single activity

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@PreusslerBerlin public class LonelyActivityextends Activity { @Override protected void onCreate(Bundle state) { super.onCreate(state); setContentView(R.layout.activity_main); } }

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@PreusslerBerlin needs to

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@PreusslerBerlin needs to support

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@PreusslerBerlin needs to support Tracking

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@PreusslerBerlin The journey totestability starts

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@PreusslerBerlin Starring

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@PreusslerBerlin Tracker as component publicinterface Tracker { void trackStarted(); }

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@PreusslerBerlin GoogleAnalyticsTracker as Tracker publicclass GoogleAnalyticsTracker implements Tracker { @Override public void trackStarted() { } }

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@PreusslerBerlin Prolog The Untestable

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@PreusslerBerlin public class LonelyActivityextends Activity { private final Tracker tracker = new GoogleAnalyticsTracker(); @Override protected void onCreate(Bundle state) { super.onCreate(state); setContentView(R.layout.activity_main); tracker.trackStarted(); } }

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@PreusslerBerlin public class LonelyActivityextends Activity { private final Tracker tracker = new GoogleAnalyticsTracker(); @Override protected void onCreate(Bundle state) { super.onCreate(state); setContentView(R.layout.activity_main); tracker.trackStarted(); } } Not testable!

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@PreusslerBerlin A voice outof the dark: Inversion of Control!

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@PreusslerBerlin A voice outof the dark: Inversion of Control!

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@PreusslerBerlin Act I The Factory

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@PreusslerBerlin public class Dependencies{ static Dependencies instance = new Dependencies(); public static Dependencies getInstance() { return instance; } public Tracker getTracker() { return new GoogleAnalyticsTracker(); } …

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@PreusslerBerlin import static Dependencies.getInstance; classLonelyActivity extends Activity { Tracker tracker = getInstance().getTracker(); @Override protected void onCreate(Bundle state) { super.onCreate(state); ... tracker.trackStarted(); } }

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@PreusslerBerlin import static Dependencies.getInstance; classLonelyActivity extends Activity { Tracker tracker = getInstance().getTracker(); @Override protected void onCreate(Bundle state) { super.onCreate(state); ... tracker.trackStarted(); } }

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@PreusslerBerlin @Mock Tracker tracker; @Before publicvoid setup() { … Dependencies.instance = mock(Dependencies.class); when(Dependencies.instance.getTracker()) .thenReturn(tracker); } @Test public void should_track() { new SimpleActivity().onCreate(null); verify(tracker).trackStarted(); }

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@PreusslerBerlin +/- Somehow testable -Not very dynamic - Lots of code

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@PreusslerBerlin Act II The Map

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@PreusslerBerlin public class Dependencies{ static Map<Class, Class> modules = new HashMap<>(); static { modules.put( Tracker.class, new GoogleAnalyticsTracker()); } public static <T> T get(Class<T> clzz) { return (T) modules.get(clzz); } }

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@PreusslerBerlin public class Dependencies{ static Map<Class, Class> modules = new HashMap<>(); static { modules.put( Tracker.class, new GoogleAnalyticsTracker()); } public static <T> T get(Class<T> clzz) { return (T) modules.get(clzz); } }

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@PreusslerBerlin import static Dependencies.getInstance; classLonelyActivity extends Activity { Tracker tracker = getInstance().get(Tracker.class); @Override protected void onCreate(Bundle state) { super.onCreate(state); ... tracker.trackStarted(); } }

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@PreusslerBerlin + Testable + Dynamic -Instances created at startup

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@PreusslerBerlin Act III Reflection(s)

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@PreusslerBerlin public class Dependencies{ private final static Map<Class, Class> modules = new HashMap<>(); static { modules.put( Tracker.class, GoogleAnalyticsTracker.class); } static <T> T get(Class<T> clzz) { …

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@PreusslerBerlin public class GoogleAnalyticsTrackerimplements Tracker { GoogleAnalyticsTracker(Activity activity) { ...} GoogleAnalyticsTracker(Application application) { ...} GoogleAnalyticsTracker(Context context) { ...} ...

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@PreusslerBerlin public class GoogleAnalyticsTrackerimplements Tracker { GoogleAnalyticsTracker(Activity activity) { ...} GoogleAnalyticsTracker(Application application) { ...} @Inject GoogleAnalyticsTracker(Context context) { ...} ...

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@PreusslerBerlin package javax.inject; @Target({ METHOD,CONSTRUCTOR, FIELD }) @Retention(RUNTIME) public @interface Inject {}

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@PreusslerBerlin public class Dependencies{ private final static Map<Class, Class> modules = new HashMap<>(); static { modules.put( Tracker.class, GoogleAnalyticsTracker.class); } static <T> T get(Class<T> clzz) { …

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@PreusslerBerlin static <T> Tget(Class<T> clzz) { … Constructor<?>[] constructors = clzz.getDeclaredConstructors(); for(Constructor ctr: constructors) {

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@PreusslerBerlin static <T> Tget(Class<T> clzz) { … Constructor<?>[] constructors = clzz.getDeclaredConstructors(); for(Constructor ctr: constructors) {

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@PreusslerBerlin ... if(ctr.getDeclaredAnnotation(Inject.class) != null) { Class[]types = ctr.getParameterTypes(); Object[] params = new Object[types.length]; for (int i=1; i< params.length; i++) { params[i] = get(types[i]); }

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@PreusslerBerlin if(ctr.getDeclaredAnnotation(Inject.class) != null) { Class[]types = ctr.getParameterTypes(); Object[] params = new Object[types.length]; for (int i=1; i< params.length; i++) { params[i] = get(types[i]); }

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@PreusslerBerlin if(ctr.getDeclaredAnnotation(Inject.class) != null) { Class[]types = ctr.getParameterTypes(); Object[] params = new Object[types.length]; for (int i=1; i< params.length; i++) { params[i] = get(types[i]); }

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@PreusslerBerlin ... try { return (T)ctr.newInstance(params); } catch (Exception e) { ... }

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@PreusslerBerlin + Testable + Dynamic +Flexible

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@PreusslerBerlin Can we improvethat?

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@PreusslerBerlin import static Dependencies.getInstance; classLonelyActivity extends Activity { @Inject Tracker tracker; @Override protected void onCreate(Bundle state) { super.onCreate(state); ... tracker.trackStarted(); } }

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@PreusslerBerlin import static Dependencies.getInstance; classLonelyActivity extends Activity { @Inject Tracker tracker; @Override protected void onCreate(Bundle state) { super.onCreate(state); Dependencies.inject(this); ... tracker.trackStarted(); } }

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@PreusslerBerlin static void inject(Objectinstance) { Field[] fields = instance.getClass().getDeclaredFields(); for (Field f: fields) { if (f.getDeclaredAnnotation(Inject.class) != null){ try { field.set(instance, get(f.getType())); } catch (IllegalAccessException e) {...} ...

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@PreusslerBerlin OMG, We just built

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@PreusslerBerlin OMG, We just built Guice!

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@PreusslerBerlin OMG, We just built RoboGuice!

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@PreusslerBerlin OMG, We just built RoboGuice!

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@PreusslerBerlin import static Dependencies.getInstance; classLonelyActivity extends Activity { @Inject Tracker tracker; @Override protected void onCreate(Bundle state) { super.onCreate(state); Dependencies.inject(this); ... tracker.trackStarted(); } }

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@PreusslerBerlin - Reflection isslow

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@PreusslerBerlin "Avoid dependency injectionframeworks” - Google developer.android.com/training/articles/memory.html#DependencyInjection till early 2016

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@PreusslerBerlin Act IV Compiler Magic

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@PreusslerBerlin Annotation processing & Code generation

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@PreusslerBerlin Here comes Dagger asHero

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@PreusslerBerlin The end!?

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@PreusslerBerlin In its firstscreen appearance: Toothpick as unknown stranger

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@PreusslerBerlin “YOUR boilerplate sucks”

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@PreusslerBerlin “YOU don’t evenknow how to unit test!”

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@PreusslerBerlin Fight!

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@PreusslerBerlin The module

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@PreusslerBerlin @Module static class BaseModule{ ... BaseModule(Application application) { ... } @Provides public Tracker provideTracker() { return new GoogleAnalyticsTracker(); } }

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@PreusslerBerlin class BaseModule extendsModule { public BaseModule(Application application) { bind(Tracker.class) .to(GoogleAnalyticsTracker.class); ...

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@PreusslerBerlin The component

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@PreusslerBerlin @Component(modules = {BaseModule.class}) interfaceAppComponent { void inject(LonelyActivity activity); }

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@PreusslerBerlin “WHAT component???”

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@PreusslerBerlin Setup Dagger 0 :1 Toothpick

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@PreusslerBerlin Usage

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@PreusslerBerlin class LonelyActivity extendsActivity { @Inject Tracker tracker; @Override protected void onCreate(Bundle state) { super.onCreate(state); ... tracker.trackStarted(); } }

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@PreusslerBerlin class MainApplication extendsApplication { @Override public void onCreate() { super.onCreate(); DaggerDependencies_AppComponent .builder() .baseModule( new BaseModule(this)) .build()

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@PreusslerBerlin class LonelyActivity extendsActivity { @Inject Tracker tracker; @Override protected void onCreate(Bundle state) { super.onCreate(state); getApplication().getComponent().inject(this); tracker.trackStarted(); } }

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@PreusslerBerlin Scope scope = openScope("APPLICATION") scope.installModules( newBaseModule(application));

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@PreusslerBerlin import static Toothpick.openScope; classLonelyActivity extends Activity { @Inject Tracker tracker; @Override protected void onCreate(Bundle state) { super.onCreate(state); openScope("APPLICATION").inject(this); tracker.trackStarted(); } }

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@PreusslerBerlin Usage Dagger 1 :2 Toothpick

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@PreusslerBerlin Testing

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@PreusslerBerlin Testing

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@PreusslerBerlin @Mock Tracker tracker; classTestModule extends Dependencies.BaseModule { TestModule() { super(mock(Application.class)); } @Provides public Tracker provideTracker() { return tracker; } } }

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@PreusslerBerlin @Mock Tracker tracker; classTestModule extends Dependencies.BaseModule { TestModule() { super(mock(Application.class)); } @Provides public Tracker provideTracker() { return tracker; } } }

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@PreusslerBerlin @Test public void should_track(){ Application.set( DaggerDependencies_AppComponent .builder().baseModule( new TestModule()).build()); new LonelyActivity().onCreate(null); verify(tracker).trackStarted(); } ... }

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@PreusslerBerlin @Test public void should_track(){ Application.set( DaggerDependencies_AppComponent .builder().baseModule( new TestModule()).build()); new LonelyActivity().onCreate(null); verify(tracker).trackStarted(); } ... }

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@PreusslerBerlin @Mock Tracker tracker; @Rule publicToothPickRule toothPickRule = new ToothPickRule(this, "APPLICATION_SCOPE"); @Test public void should_track() { new LonelyActivity().onCreate(null); verify(tracker).trackStarted(); }

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@PreusslerBerlin @Mock Tracker tracker; @Rule publicToothPickRule toothPickRule = new ToothPickRule(this, "APPLICATION_SCOPE"); @Test public void should_track() { new LonelyActivity().onCreate(null); verify(tracker).trackStarted(); }

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@PreusslerBerlin Testing Dagger 1 :3 Toothpick

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@PreusslerBerlin Scopes

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@PreusslerBerlin @Singleton

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@PreusslerBerlin @Scope @Retention(RUNTIME) public @interface ActivityScope{} @ActivityScope @Subcomponent(modules = {ScopeModule.class}) interface ScopeComponent { void inject(ScopeActivity activity); }

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@PreusslerBerlin @Module static class ScopeModule{ private Activity activity; public ScopeModule(Activity activity) { this.activity = activity; } @Provides @ActivityScope public Activity provideActivity() { return activity; } }

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@PreusslerBerlin @Component(modules = {BaseModule.class}) interfaceAppComponent { void inject(LonelyActivity activity); ScopeComponent plus(ScopeModule module); }

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@PreusslerBerlin “That’s Annotation Porn!”

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@PreusslerBerlin public class ScopeActivityextends Activity { … private ScopeComponent scope; @Override protected void onCreate(Bundle state) { super.onCreate(state); setContentView(R.layout.activity_main); scope = createScope(this); scope.inject(this); … } // call from fragments... public ScopeComponent getScope() { return scope; } }

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@PreusslerBerlin public class ScopeActivityextends Activity { … private ScopeComponent scope; @Override protected void onCreate(Bundle state) { super.onCreate(state); setContentView(R.layout.activity_main); scope = createScope(this); scope.inject(this); … } // call from fragments... public ScopeComponent getScope() { return scope; } }

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@PreusslerBerlin “Stop this madness!”

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@PreusslerBerlin class ScopeModule extendsModule { public ScopeModule(Activity activity) { bind(Activity.class).toInstance(activity); }

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@PreusslerBerlin Scope scope = openScopes(”APPLICATION_SCOPE”, activity.getClass().getName()); scope.installModules( newScopeModule(activity));

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@PreusslerBerlin Scope scope = openScopes(”APPLICATION_SCOPE”, activity.getClass().getName()); scope.installModules( newScopeModule(activity));

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@PreusslerBerlin closeScope( activity.getClass().getName());

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@PreusslerBerlin Scopes Dagger 1 :4 Toothpick

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@PreusslerBerlin Performance

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1000 injections • Dagger1: 33 ms • Dagger 2: 31 ms • Toothpick: 35 ms 6400 injections • Dagger 1: 45 ms • Dagger 2: 42 ms • Toothpick: 66 ms

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@PreusslerBerlin Performance Dagger 2 :4 Toothpick

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@PreusslerBerlin And there ismore: SmoothieModule

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@PreusslerBerlin Ease of use Speed Roboguice Dagger Toothpick

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@PreusslerBerlin Dagger: + compile safe +feature rich + performant

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@PreusslerBerlin Dagger: -heavy weight - topdown - annotation porn - hard on unit tests

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@PreusslerBerlin Toothpick: + light weight +bottom up + less boilerplate + testing focus

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@PreusslerBerlin Toothpick: -not idiot proof -performance

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@PreusslerBerlin Choose the right tool foryour problem! ABetterToolbyTheMarmot,CCby2.0,flickr.com/photos/themarmot/6283203163

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@PreusslerBerlin github.com/ dpreussler/ understand_dependencies

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@PreusslerBerlin TP written by StephaneNicolas Daniel Molinero Reguera Presented by Danny Preussler Special thanks to Florina Muntenescu

Demystifying dependency Injection: Dagger and Toothpick

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