U+2019: Modern Android Architecture

There's plenty of ways to design an Android application, most of them are correct and some of them scale well. The Cash Android app is growing in size and complexity, which constantly prompts us to re-evaluate our design decisions. This talk will provide a thorough overview of the state of our app's architecture, the challenges we're facing and how we're planning to address them. The topics will include:

* Modularization
* Build tooling
* Navigation
* RxJava
* Testing
* and more

Square is widely known for building great open source software, and this talk will go over our open source stack and ways in which your project can benefit from the tools we built!

Transcript

1. U+2019 @egorand Modern Android Architecture
2. U+2020
5. Stored Balance
6. Stored Balance P2P Payments
7. Stored Balance P2P Payments Cash Card
8. Stored Balance P2P Payments Cash Card In-App Receipts
9. Stored Balance P2P Payments Cash Card In-App Receipts Cash-Ins
10. Stored Balance P2P Payments Cash Card In-App Receipts Instant Cash-Outs* Cash-Ins
11. Stored Balance P2P Payments Cash Card In-App Receipts Instant Cash-Outs* Boosts Cash-Ins
12. Stored Balance P2P Payments Cash Card In-App Receipts Instant Cash-Outs* Boosts Bitcoin Cash-Ins
13. Challenges
14. Release Model • Release trains • Go-live every 2 weeks • Only hot-fixes allowed in between • Daily server deploys
15. Backwards Compat • ~24% of customers on older versions • Mission-critical • Frequent server deploys • Moving fast
16. Workstreams • Features developed in parallel • Shared codebase • Merges into master • Android/iOS parity
17. Migration to Kotlin • Better developer experience • Faster builds • Large codebase • Complex code
18. Architectural debt • Multiple presenter implementations • Navigation framework • Testability • Large modules
19. Architecture Overview
20. app presenters backend viewmodels api db protos
21. protos Protocol Buffer messages Generated code Gradle configs for pulling and compiling protos
22. Protocol Buffers Schema Compilers for many platforms Binary on the wire Backwards compatible
23. Workflow .proto files uploaded to Artifactory .zip with protos gets pulled down Protos compiled into .java/.kt Generated code checked into git
24. Wire .proto compiler built at Square Android-aware Java + Kotlin CLI + Gradle
25. message Person { // The customer's full name. required string name = 1; // The customer's ID number. required int32 id = 2; // Email address for the customer. optional string email = 3; enum PhoneType { MOBILE = 0; HOME = 1; /** Could be phone or fax. */ WORK = 2; } message PhoneNumber { // The customer's phone number. required string number = 1; // The type of phone stored here. optional PhoneType type = 2 [default = HOME]; } // A list of the customer's phone numbers. repeated PhoneNumber phone = 4; } .proto public final class Person extends Message { public final String name; public final Integer id; public final String email; public final List<PhoneNumber> phone; // constructors, equals, hashCode, toString public static final class Builder {} public enum PhoneType implements WireEnum { MOBILE(0), HOME(1), WORK(2); } public static final class PhoneNumber extends Message<PhoneNumber, PhoneNumber.Builder> { public final String number; public final PhoneType type; // constructors, equals, hashCode, toString public static final class Builder {} } .java (458 lines in original) Wire 2
26. message Person { // The customer's full name. required string name = 1; // The customer's ID number. required int32 id = 2; // Email address for the customer. optional string email = 3; enum PhoneType { MOBILE = 0; HOME = 1; /** Could be phone or fax. */ WORK = 2; } message PhoneNumber { // The customer's phone number. required string number = 1; // The type of phone stored here. optional PhoneType type = 2 [default = HOME]; } // A list of the customer's phone numbers. repeated PhoneNumber phone = 4; } .proto data class Person( val name: String, val id: Int, val email: String? = null, val phone: List<PhoneNumber> = emptyList(), val unknownFields: ByteString = ByteString.EMPTY ) : Message { enum class PhoneType(private val value: Int) : WireEnum { MOBILE(0), HOME(1), WORK(2); } data class PhoneNumber( val number: String, val type: PhoneType? = PhoneType.HOME, val unknownFields: ByteString = ByteString.EMPTY ) : Message } .kt (206 lines in original) Wire 3
27. Wire 2 task generateProtos(type: JavaExec) { classpath = configurations.wire main = 'com.squareup.wire.WireCompiler' args = [ '--proto_path=protos/src/test/proto', '--java_out=protos/src/test/proto-java', '--android', 'squareup.cash.Person' ] } apply plugin: 'com.squareup.wire' wire { sourcePath 'com.squareup.cash:protos:+' roots 'squareup.cash.Person' kotlin { out "${buildDir}/generated/custom" } } Wire 3
28. b viewmodels api p Retrofit interface OkHttp interceptors Networking helpers
29. interface AppService { @POST("/2.0/cash/initiate-payment") fun initiatePayment( @Body request: InitiatePaymentRequest ): Observable<InitiatePaymentResponse> @POST("/2.0/cash/get-profile") fun getProfile( @Body request: GetProfileRequest ): Observable<GetProfileResponse> // other methods } AppService RxJava Observables Request/response are protos
30. Blockers InitiatePaymentResponse responseContext: ResponseContext ResponseContext blockers: List<Blocker> SetNameBlocker PasscodeBlocker SetAddressBlocker
31. Client 1. InitiatePaymentRequest Server 1. Passcode verification required 2. Send a passcode verification blocker
32. Client 3. Display PasscodeVerification screen 4. Prompt for passcode 5. Send passcode hash to server
33. Client Server 6. IDV required 7. Send IDV blocker etc.
34. ackend protos db DB schema in .sq files Generated SQLDelight code Migrations in .sqm files
35. ORM Room SQLDelight Annotate entities Use custom DSL Annotate entities Write SQL Bring your own DSL Write SQL Use generated code
36. Why?
37. Everyone understands SQL SQL is standardized SQL has tooling
38. import com.example.sqldelight.hockey.data.PlayerVals; import com.example.sqldelight.hockey.data.Date; CREATE TABLE player ( id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, first_name TEXT NOT NULL, last_name TEXT NOT NULL, number INTEGER AS Integer NOT NULL, team INTEGER, age INTEGER AS Integer NOT NULL, birth_date INTEGER AS Date NOT NULL, weight REAL AS Float NOT NULL, shoots TEXT AS PlayerVals.Shoots NOT NULL, position TEXT AS PlayerVals.Position NOT NULL, FOREIGN KEY (team) REFERENCES team(id) ); insertPlayer: INSERT INTO player (first_name, last_name, number, team) VALUES (?, ?, ?, (SELECT id FROM team WHERE name = ?)); selectAll: SELECT * FROM player JOIN team ON player.team = team.id; forTeam: SELECT first_name, last_name, number, team.name AS teamName FROM player JOIN team ON player.team = team.id WHERE team.id = :team_id OR :team_id = -1; SQLDelight IDE plugin Gradle plugin Migrations verifier Multiplatform!
39. Workflow Add SQL to .sq files Run ./gradlew :db:assemble Use generated code
40. Workflow: Migrations Add SQL to a new .sqm file Run ./gradlew :db:verifyMigration
41. app enters backend Facades for :db and :api Models for upper layers based on protos Mostly interfaces
42. class AppMessagePresenter( cashDatabase: CashDatabase ) { private val appMessageQueries = cashDatabase.appMessageQueries }
43. class AppMessagePresenter( cashDatabase: CashDatabase ) { private val appMessageQueries = cashDatabase.appMessageQueries override fun subscribe() { val activityInlineAppMessage = appMessageQueries .foregroundVideo(ACTIVITY_INLINE) .asObservable(ioScheduler) .mapToKOptional() } }
44. class AppMessagePresenter( cashDatabase: CashDatabase, profileManager: ProfileManager ) { private val appMessageQueries = cashDatabase.appMessageQueries override fun subscribe() { val activityInlineAppMessage = appMessageQueries .foregroundVideo(ACTIVITY_INLINE) .asObservable(ioScheduler) .mapToKOptional() } }
45. class AppMessagePresenter( cashDatabase: CashDatabase, profileManager: ProfileManager ) { private val appMessageQueries = cashDatabase.appMessageQueries override fun subscribe() { val activityInlineAppMessage = combineLatest( appMessageQueries .foregroundVideo(ACTIVITY_INLINE) .asObservable(ioScheduler) .mapToKOptional(), profileManager.profile() ) { appMessage, profile -> // a lot of code } } }
46. AppMessageManager activityInlineAppMessage(): Observable<AppMessage> RealAppMessageManager FakeAppMessageManager
47. class RealAppMessageManager( cashDatabase: CashDatabase, profileManager: ProfileManager ) { private val appMessageQueries = cashDatabase.appMessageQueries override fun activityInlineAppMessage(): Observable<AppMessage> { return combineLatest( appMessageQueries .foregroundVideo(ACTIVITY_INLINE) .asObservable(ioScheduler) .mapToKOptional(), profileManager.profile() ) { appMessage, profile -> // a lot of code } } }
48. class AppMessagePresenter( appMessageManager: AppMessageManager ) { override fun subscribe() { val activityInlineAppMessage = appMessageManager .activityInlineAppMessage .subscribe() } }
49. class FakeAppMessageManager : AppMessageManager { val activityInlineAppMessages = BehaviorRelay.create<AppMessage>() override fun activityInlineAppMessage() = activityInlineAppMessages.hide() }
50. class AppMessagePresenterTest { private val appMessageManager = FakeAppMessageManager() }
51. class AppMessagePresenterTest { private val appMessageManager = FakeAppMessageManager() private fun makePresenter() { return AppMessagePresenter(appMessageManager) } }
52. class AppMessagePresenterTest { private val appMessageManager = FakeAppMessageManager() private fun makePresenter() { return AppMessagePresenter(appMessageManager) } @Test fun `appMessage is included in viewmodel`() { val viewModel = Observable.wrap(makePresenter()).test() val expectedAppMessage = AppMessage() appMessageManager.activityInlineAppMessages.accept(appMessage) } }
53. class AppMessagePresenterTest { private val appMessageManager = FakeAppMessageManager() private fun makePresenter() { return AppMessagePresenter(appMessageManager) } @Test fun `appMessage is included in viewmodel`() { val viewModel = Observable.wrap(makePresenter()).test() val expectedAppMessage = AppMessage() appMessageManager.activityInlineAppMessages.accept(appMessage) with(viewModel.latest()) { assertThat(appMessage).isEqualTo(expectedAppMessage) } } }
54. a pres viewmodels ViewModels: presenter → view ViewEvents: view → presenter Data classes
55. ViewModel ViewEvent View Presenter
56. ViewModel ViewEvent data class SendPaymentViewModel( val toolbarActionText: String, val toolbarAmount: String, val selectedInstrument: String? = null ) sealed class SendPaymentViewEvent { object SendPayment : SendPaymentViewEvent() class UpdateNote( val note: String = "" ) : SendPaymentViewEvent() }
57. app presenters Subscribe to ViewEvents Emit ViewModels Handle navigation
58. Stateless
59. class FileBlockerPresenter : ObservableTransformer<FileBlockerViewEvent, FileBlockerViewModel>
60. class FileBlockerPresenter : ObservableTransformer<FileBlockerViewEvent, FileBlockerViewModel> { override fun apply( viewEvents: Observable<FileBlockerViewEvent> ): ObservableSource<FileBlockerViewModel> { return viewEvents.publish { events -> Observable.merge( listOf( events.filterIsInstance<NavigationAction>().compose(navigationLogic), events.filterIsInstance<SupportClick>().compose(goToSupport), events.filterIsInstance<CaptureCompleted>().compose(uploadBitmaps) ) ) } } }
61. class FileBlockerPresenter : ObservableTransformer<FileBlockerViewEvent, FileBlockerViewModel> { override fun apply( viewEvents: Observable<FileBlockerViewEvent> ): ObservableSource<FileBlockerViewModel> { return viewEvents.publish { events -> Observable.merge( listOf( events.filterIsInstance<NavigationAction>().compose(navigationLogic), events.filterIsInstance<SupportClick>().compose(goToSupport), events.filterIsInstance<CaptureCompleted>().compose(uploadBitmaps) ) ) } } private val navigationLogic = ObservableTransformer<NavigationAction, FileBlockerViewModel> { events -> events.doOnNext { event -> navigator.goTo( when (event) { // convert an event into a navigation target } } } }
62. class FileBlockerPresenterTest
63. class FileBlockerPresenterTest { private lateinit var events: PublishSubject<FileBlockerViewEvent> private lateinit var viewModels: TestObserver<FileBlockerViewModel> private val navigator = FakeNavigator() }
64. class FileBlockerPresenterTest { private lateinit var events: PublishSubject<FileBlockerViewEvent> private lateinit var viewModels: TestObserver<FileBlockerViewModel> private val navigator = FakeNavigator() private fun setupPresenter() { events = PublishSubject.create<FileBlockerViewEvent>() val presenter = FileBlockerPresenter(navigator) viewModels = events .compose(presenter) .test() } }
65. class FileBlockerPresenterTest { private lateinit var events: PublishSubject<FileBlockerViewEvent> private lateinit var viewModels: TestObserver<FileBlockerViewModel> private val navigator = FakeNavigator() private fun setupPresenter() { events = PublishSubject.create<FileBlockerViewEvent>() val presenter = FileBlockerPresenter(navigator) viewModels = events .compose(presenter) .test() } @Test fun captureCompleted_noDialogMessage() { } }
66. class FileBlockerPresenterTest { private lateinit var events: PublishSubject<FileBlockerViewEvent> private lateinit var viewModels: TestObserver<FileBlockerViewModel> private val navigator = FakeNavigator() private fun setupPresenter() { events = PublishSubject.create<FileBlockerViewEvent>() val presenter = FileBlockerPresenter(navigator) viewModels = events .compose(presenter) .test() } @Test fun captureCompleted_noDialogMessage() { navigator.nextScreen = Profile } }
67. class FileBlockerPresenterTest { private lateinit var events: PublishSubject<FileBlockerViewEvent> private lateinit var viewModels: TestObserver<FileBlockerViewModel> private val navigator = FakeNavigator() private fun setupPresenter() { events = PublishSubject.create<FileBlockerViewEvent>() val presenter = FileBlockerPresenter(navigator) viewModels = events .compose(presenter) .test() } @Test fun captureCompleted_noDialogMessage() { navigator.nextScreen = Profile events.onNext(CaptureCompleted()) } }
68. class FileBlockerPresenterTest { private lateinit var events: PublishSubject<FileBlockerViewEvent> private lateinit var viewModels: TestObserver<FileBlockerViewModel> private val navigator = FakeNavigator() private fun setupPresenter() { events = PublishSubject.create<FileBlockerViewEvent>() val presenter = FileBlockerPresenter(navigator) viewModels = events .compose(presenter) .test() } @Test fun captureCompleted_noDialogMessage() { navigator.nextScreen = Profile events.onNext(CaptureCompleted()) viewModels.assertValueAt(0, Uploading) viewModels.assertValueCount(1) } }
69. class FileBlockerPresenterTest { private lateinit var events: PublishSubject<FileBlockerViewEvent> private lateinit var viewModels: TestObserver<FileBlockerViewModel> private val navigator = FakeNavigator() private fun setupPresenter() { events = PublishSubject.create<FileBlockerViewEvent>() val presenter = FileBlockerPresenter(navigator) viewModels = events .compose(presenter) .test() } @Test fun captureCompleted_noDialogMessage() { navigator.nextScreen = Profile events.onNext(CaptureCompleted()) viewModels.assertValueAt(0, Uploading) viewModels.assertValueCount(1) assertThat(navigator.takeNextScreen()).isEqualTo(Profile) } }
70. app Emit ViewEvents Render ViewModels Only talk to presenters
71. class FileBlockerView( context: Context, attrs: AttributeSet? ) : RelativeLayout(context, attrs)
72. class FileBlockerView( context: Context, attrs: AttributeSet? ) : RelativeLayout(context, attrs) { private lateinit var presenter: FileBlockerPresenter }
73. class FileBlockerView( context: Context, attrs: AttributeSet? ) : RelativeLayout(context, attrs) { private lateinit var presenter: FileBlockerPresenter private val viewEvents = PublishSubject.create<FileBlockerViewEvent>() }
74. class FileBlockerView( context: Context, attrs: AttributeSet? ) : RelativeLayout(context, attrs) { private lateinit var presenter: FileBlockerPresenter private val viewEvents = PublishSubject.create<FileBlockerViewEvent>() private lateinit var disposables: CompositeDisposable }
75. class FileBlockerView( context: Context, attrs: AttributeSet? ) : RelativeLayout(context, attrs) { private lateinit var presenter: FileBlockerPresenter private val viewEvents = PublishSubject.create<FileBlockerViewEvent>() private lateinit var disposables: CompositeDisposable override fun onAttachedToWindow() { super.onAttachedToWindow() disposables = CompositeDisposable() } }
76. class FileBlockerView( context: Context, attrs: AttributeSet? ) : RelativeLayout(context, attrs) { private lateinit var presenter: FileBlockerPresenter private val viewEvents = PublishSubject.create<FileBlockerViewEvent>() private lateinit var disposables: CompositeDisposable override fun onAttachedToWindow() { super.onAttachedToWindow() disposables = CompositeDisposable() disposables += viewEvents .compose(presenter) .observeOn(AndroidSchedulers.mainThread()) .errorHandlingSubscribe(::renderViewModel) } }
77. class FileBlockerView( context: Context, attrs: AttributeSet? ) : RelativeLayout(context, attrs) { private lateinit var presenter: FileBlockerPresenter private val viewEvents = PublishSubject.create<FileBlockerViewEvent>() private lateinit var disposables: CompositeDisposable override fun onAttachedToWindow() { super.onAttachedToWindow() disposables = CompositeDisposable() disposables += viewEvents .compose(presenter) .observeOn(AndroidSchedulers.mainThread()) .errorHandlingSubscribe(::renderViewModel) } override fun onDetachedFromWindow() { super.onDetachedFromWindow() disposables.dispose() } }
78. What’s next?
79. Better modularization • Key to faster builds • Shard by feature • Rely on common modules • Move Android dependencies up
80. presenters backend viewmodels api db protos app
81. app P2P Support Card
82. More Kotlin • Finish migration to Kotlin • Remove javac build step • More libraries converted to Kotlin • Multiplatform!
83. Sharing code with iOS • Kotlin, yes, kudos • SQLDelight • Retrofit + OkHttp + Wire + Okio • Entire stack except for UI
84. Thanks! @egorand