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Ingredients for a 
 healthy codebase Romain Piel

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@_rpiel Romain Piel at Songkick

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Songkick

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Architecture of an Android app?

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Let me tell you a story…

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John No knowledge in Android dev

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Let’s build an Android app ! John No knowledge in Android dev

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John MyActivity ApiManager

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John MyActivity ApiManager MyActivity

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John MyActivity ApiManager MyApplication MyActivity

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John MyActivity ApiManager MyApplication MyActivity DbManager

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Mary New hire !

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Mary This codebase looks so old! Let’s add change a few things… New hire !

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MyActivity ApiManager MyApplication MyActivity DbManager Mary John

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MyActivity ApiManager MyApplication MyActivity DbManager Retrofit Mary John

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MyActivity ApiManager MyApplication MyActivity DbManager Retrofit Mary NewFeature Activity NewFeature Fragment John

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MyActivity ApiManager MyApplication MyActivity DbManager Retrofit Mary NewFeature Activity NewFeature Fragment RxJava John

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App Mary John

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App Mary John

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App Mary John No idea where this crash is coming from

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Francis New hire !

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OMG ! Zero test ?! Francis New hire !

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Unit tests App Mary John Francis

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Unit tests App Mary John Francis Hard to catch up with the coverage & too many Android dependencies

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App Mary Francis UI tests John

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App Mary Francis UI tests Interactions with outside world = flaky tests John

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Mary John Francis App

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Mary John Francis App 1 year later…

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App

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App Dependant

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App Dependant • UI and business logic

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App Dependant • UI and business logic • Codebase and external libs

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App Dependant Hard to test

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App Dependant Hard to test Hard to maintain

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Another approach

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Systems should be • Independent of Frameworks • Testable • Independent of UI • Independent of Database • Independent of any external agency Clean architecture

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Let’s consider this problem

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No content

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No content

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Data layer

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Domain layer Data layer

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Presentation layer Domain layer Data layer

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Data layer Domain layer Data layer

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Data layer Domain layer Data layer

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Data layer : repository pattern ArtistRepository Retrofit client Db client

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Domain layer Presentation layer Domain layer Data layer

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Domain layer

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Domain layer • Orchestrates the flow of data with “use cases”

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Domain layer • Orchestrates the flow of data with “use cases” • Offers its services to the presentation layer

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Domain layer • Orchestrates the flow of data with “use cases” • Offers its services to the presentation layer • Pure Java module • No Android UI dependencies • No dependency to external source (db, content provider, shared preferences…)

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Presentation layer

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• Tied to the view lifecycle

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• Tied to the view lifecycle • Receives user inputs

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• Tied to the view lifecycle • Receives user inputs • Associated to specific view layouts (ListActivity)

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• Tied to the view lifecycle • Receives user inputs • Associated to specific view layouts (ListActivity) Your very first Android Activity will be likely to be huge and untestable

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View Presentation layer Domain layer Data Interaction

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View Presentation layer Domain layer Data Interaction

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[ ] View Presentation layer Domain layer Data Interaction

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Presentation layer View Presenter Model Data Interaction

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View Presenter Model Presentation layer interface SearchPresenter {
 void searchArtist(String searchTerm);
 void clickArtist(Artist artist);
 } interface SearchView {
 void showProgress();
 void hideProgress();
 void showArtists(List artists);
 }

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Model vs. View model class Artist {
 String displayName;
 String uri;
 String id;
 LocalDate onTourUntil;
 }

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class Artist {
 String displayName;
 String uri;
 String id;
 LocalDate onTourUntil;
 } Model vs. View model

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class ArtistViewModel {
 String name; boolean isOnTour; } Model vs. View model

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class ArtistViewModel {
 String name; boolean isOnTour; } public class ArtistViewHolder extends ViewHolder {
 
 @Bind(R.id.artist_name)
 TextView artistName; @Bind(R.id.on_tour)
 TextView onTour;
 
 public ArtistViewHolder(View itemView) {
 super(itemView);
 ButterKnife.bind(this, itemView);
 }
 
 @Override
 public void bind(ArtistViewModel viewModel) {
 artistName.setText(artistViewModel.name);
 onTour.setVisibility(artistViewModel.isOnTour ? View.VISIBLE : View.GONE );
 }
 }

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Presentation layer interface SearchPresenter {
 void searchArtist(String searchTerm);
 void clickArtist(ArtistViewModel artist);
 } interface SearchView {
 void showProgress();
 void hideProgress();
 void showArtists(List artists);
 } View Presenter View model

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Presentation layer class SearchFragment extends Fragment implements SearchView {
 
 SearchPresenter searchPresenter;
 
 @Override
 void showProgress() {
 // ...
 }
 
 @Override
 void hideProgress() {
 // ...
 }
 
 @Override
 void showArtists(List artists) {
 // ...
 } {...}
 }

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Presentation layer class SearchFragment extends Fragment implements SearchView {
 
 SearchPresenter searchPresenter;
 {...} 
 void onItemClick(ArtistViewModel artist) {
 searchPresenter.clickArtist(artist); }
 
 void search(String searchTerm) {
 searchPresenter.searchArtist(searchTerm); }
 }

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Presentation layer Domain layer Data layer

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Communication Presentation layer Domain layer Data layer Subscriber Observable Observable Rx all the things!

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interface ArtistRepository {
 Observable> search(String searchTerm);
 } Data layer Communication Rx all the things!

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interface ArtistRepository {
 Observable> search(String searchTerm);
 } Domain layer Data layer interface SearchArtistUseCase {
 void subscribe(Subscriber subscriber); void unsubscribe();
 } Communication Rx all the things!

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interface ArtistRepository {
 Observable> search(String searchTerm);
 } Presentation layer Domain layer Data layer interface SearchArtistUseCase {
 void subscribe(Subscriber subscriber); void unsubscribe();
 } interface SearchPresenter {
 void searchArtist(String searchTerm); void onDestroy();
 } Communication Rx all the things!

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Structure Dagger

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Structure Application
 component Dagger

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Structure Application
 component Application modules Repositories Dagger

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Structure Application
 component Activity component Application modules Repositories Dagger

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Structure Application
 component Activity component Application modules Repositories Activity modules Activity Dagger

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Structure Application
 component Activity component Application modules Repositories Fragment modules Presenter Use cases Activity modules Activity Dagger

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Structure

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Structure “Program to an interface, not an implementation” — Erich Gamma

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Structure “Program to an interface, not an implementation” — Erich Gamma • Decouple the client from the implementation

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Structure “Program to an interface, not an implementation” — Erich Gamma • Decouple the client from the implementation • Defines the vocabulary of the collaboration

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Structure “Program to an interface, not an implementation” — Erich Gamma • Decouple the client from the implementation • Defines the vocabulary of the collaboration • Easy to test

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Testing Presentation layer Domain layer Data layer Unit SearchUseCase ArtistRepository SearchPresenter SearchFragment

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Testing Presentation layer Domain layer Data layer Unit SearchUseCase ArtistRepository SearchPresenter SearchFragment Testable without Robolectric

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Testing Presentation layer Domain layer Data layer Unit SearchUseCase ArtistRepository SearchPresenter SearchFragment Testable without Robolectric Testable with Robolectric

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Testing Presentation layer Domain layer Data layer UI

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Testing Presentation layer Domain layer Data layer UI .json

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Testing Presentation layer Domain layer Data layer UI .json class ArtistRepositoryTestImpl {
 
 JsonLoader jsonLoader;
 
 Observable> search(String searchTerm) {
 return jsonLoader.load(“search/artist.json”);
 }
 }

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Conclusion

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Conclusion • Choose an architecture and stick with it

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Conclusion • Choose an architecture and stick with it • Test while you code

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Conclusion • Choose an architecture and stick with it • Test while you code • Always do what’s best for the codebase, not for the feature you’re implementing

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Songkick We’re hiring!

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Links • Uncle Bob’s clean architecture 
 http://blog.8thlight.com/uncle-bob/2012/08/13/the-clean-architecture.html
 • Fernando Cejas - Architecting Android…The clean way?
 http://fernandocejas.com/2014/09/03/architecting-android-the-clean-way
 https://github.com/android10/Android-CleanArchitecture
 • Martin Fowler - The repository pattern
 http://martinfowler.com/eaaCatalog/repository.html
 • Erich Gamma - Design Principles from Design Patterns
 http://www.artima.com/lejava/articles/designprinciples.html

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Thank you