À l'automne dernier, nous avons eu la chance de développer une nouvelle app pour un de nos clients en partant de zéro. L'objectif ? Créer une application minimale à mettre entre les mains de dizaines de beta testeurs, en 8 semaines et avec 2 développeurs. Partant d'une feuille blanche, nous avons pu mettre en œuvre les dernières avancées de la stack Android sans être contraints par l'existant. Développeurs débutants comme expérimentés, vous repartirez de ce talk avec nos apprentissages clés sur l'architecture ainsi que sur les bibliothèques et astuces pour faciliter la maintenance et la stabilité de l'application. En bonus, nous répondrons à la question : "Une app full-compose, est-ce que c'est cool ?"

1. Nicolas HAAN - 24/01/2023
Comment développer une
application Android en 8 semaines ?

2. BAM en quelques mots
• 120 experts du développement mobile
• 3 domaines d’expertise (Développement,
Produit et design)
• + 150 projets (UEFA, TF1, URGO, Pass
Culture)
• 2 bureaux en France (Paris et Nantes)

3. M33

4. La tribe native de BAM

5. The project

6. The project
• 2 developers, 8 weeks
• A finished MVP, not a POC
• State of the art technical stack,
architecture and testing strategy
• A code base ready to taken over
• A new app from scratch

7. Architecture
Gradle
Modularisation
Dependency
management
Unit Testing
UI layer

8. Architecture?
Let's go clean!

9. Clean Architecture

10. Google Architecture guidelines

11. Google Architecture guidelines

12. Google Architecture guidelines
• Separation of concerns
• Drive UI from data models
• Single source of truth
• Unidirectional Data Flow

13. Modular architecture

14. FeatureScreen
FeatureViewModel
FeatureUseCase FeatureRepository
FeatureDataSource
ApiService
DATA
DOMAIN
UI

15. FeatureScreen
FeatureViewModel
FeatureUseCase FeatureRepository
FeatureDataSource
ApiService
Transformer le state
exposé par le VM en
vues affichables,
récupérer les actions
utilisateur
aggrégation des données des
UseCase pour construire le state
de l'écran,
récupérer les évènements de la
Vue et les dispatcher vers les
UseCases
Implémentation des règles
métiers, agrégations des
sources de données,
abstraction des repositories
Single Source of Truth de
la donnée, règles métiers
du cache et de la
persistence
abstraction de
l'implémentation de la
datasource, préparation
des paramètres des WS,
mapping Dto <-> Domain
appel réseau, parsing
des JSON, remontée
des erreurs

16. Architecture
• Strict separation of concern
• Heavy modularisation (~22 modules for 5 screens)
• Confident that it will scale well and can be taken over

17. Gradle:
Beyond Android Studio Template

18. Groovy or KTS?
KTS promises
• Available since Android Gradle Plugin 4.1.0 (August 2020)
• The Kotlin syntax we all know and love available for Gradle!
• Autocompletion and type safety in Gradle
• The future of Gradle configuration files

19. Groovy or KTS?
• In 2022, templates are still using Groovy, even in Flamingo
• Manual migration
• Autocompletion not really useful in day to day use
• Not all libraries and open source projects have adopted it

20. 🤷

21. Modularisation:
Convention plugins

22. Sharing build logic
"Historical method"
subprojects {
tasks.withType(Test::class.java) {
// ...
}
}
allprojects {
repositories {
// ..
}
apply(plugin = "jacoco")
jacoco {
toolVersion = "0.8.7"
}
}
• Using subprojects
and allprojects
closures
• Not very flexible
• Not explicit from a
module point of view

23. Sharing build logic
modular gradle files
apply from: "$rootDir/dependencies.gradle"
apply from: "$rootDir/gradle/baseFeature.gradle"
apply from: "$rootDir/gradle/flavors.gradle"
• doesn't scale well
• Doesn't work well with
KTS (see here and here)

24. Sharing build logic
Convention plugin
• create convention
plugins to be applied to
relevant modules
• There can be several
modular and
composable plugins
• Plugins are explicitly
applied to each module
buildSrc
androidBase.kts
flavors.kts
core/moduleX
...
domain/moduleY

25. Sharing build logic
Convention plugin
plugins {
id("com.android.library")
id("kotlin-android")
id("kotlin-kapt")
id("org.jlleitschuh.gradle.ktlint")
}
android {
compileSdk = findIntProperty("compileSdkVersion")
defaultConfig {
minSdk = findIntProperty("minSdkVersion")
targetSdk = findIntProperty("targetSdkVersion")
testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
vectorDrawables {
useSupportLibrary = true
}
}
compileOptions {
sourceCompatibility = JavaVersion.VERSION_11
targetCompatibility = JavaVersion.VERSION_11
}

26. Sharing build logic
Convention plugin
plugins {
id("com.android.library")
id("kotlin-android")
id("kotlin-kapt")
id("org.jlleitschuh.gradle.ktlint")
}
android {
compileSdk = findIntProperty("compileSdkVersion")
defaultConfig {
minSdk = findIntProperty("minSdkVersion")
targetSdk = findIntProperty("targetSdkVersion")
testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
vectorDrawables {
useSupportLibrary = true
}
}
compileOptions {
sourceCompatibility = JavaVersion.VERSION_11
targetCompatibility = JavaVersion.VERSION_11
}
kotlinOptions {
jvmTarget = JavaVersion.VERSION_11.toString()
}
buildTypes {
release {
isMinifyEnabled = true
proguardFiles(
getDefaultProguardFile("proguard-android-optimize.txt"),
"proguard-rules.pro"
)
}
}
testOptions {
unitTests.isReturnDefaultValues = true
unitTests.all {
it.testLogging {
events = setOf(
TestLogEvent.STARTED,
TestLogEvent.PASSED,
TestLogEvent.SKIPPED,
TestLogEvent.FAILED
)
showStandardStreams = true
}
}
}
flavorDimensions.add("environment")
productFlavors {
register("dev") {
dimension = "environment"
}
register("staging") {
dimension = "environment"
}
register("prod") {
dimension = "environment"
}
}
}
dependencies {
implementation(Koin.android)
implementation(Koin.compose)
}
fun findStringProperty(propertyName: String): String {
return findProperty(propertyName) as String
}
fun findIntProperty(propertyName: String): Int {
return (findProperty(propertyName) as String).toInt()
}
plugins {
id("com.client.app.convention.androidBase")
id("com.client.app.convention.flavors")
}
android {
namespace = "com.client.app.logging"
}
dependencies {
implementation(libs.appcenter.crashes)
}
moduleX/build.gradle.kts

27. Sharing build logic
Convention plugin
plugins {
id("com.android.library")
id("kotlin-android")
id("kotlin-kapt")
id("org.jlleitschuh.gradle.ktlint")
}
android {
compileSdk = findIntProperty("compileSdkVersion")
defaultConfig {
minSdk = findIntProperty("minSdkVersion")
targetSdk = findIntProperty("targetSdkVersion")
testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
vectorDrawables {
useSupportLibrary = true
}
}
compileOptions {
sourceCompatibility = JavaVersion.VERSION_11
targetCompatibility = JavaVersion.VERSION_11
}
kotlinOptions {
jvmTarget = JavaVersion.VERSION_11.toString()
}
buildTypes {
release {
isMinifyEnabled = true
proguardFiles(
getDefaultProguardFile("proguard-android-optimize.txt"),
"proguard-rules.pro"
)
}
}
testOptions {
unitTests.isReturnDefaultValues = true
unitTests.all {
it.testLogging {
events = setOf(
TestLogEvent.STARTED,
TestLogEvent.PASSED,
TestLogEvent.SKIPPED,
TestLogEvent.FAILED
)
showStandardStreams = true
}
}
}
flavorDimensions.add("environment")
productFlavors {
register("dev") {
dimension = "environment"
}
register("staging") {
dimension = "environment"
}
register("prod") {
dimension = "environment"
}
}
}
dependencies {
implementation(Koin.android)
implementation(Koin.compose)
}
fun findStringProperty(propertyName: String): String {
return findProperty(propertyName) as String
}
fun findIntProperty(propertyName: String): Int {
return (findProperty(propertyName) as String).toInt()
}
plugins {
id("com.client.app.convention.androidBase")
id("com.client.app.convention.flavors")
}
android {
namespace = "com.client.app.logging"
}
dependencies {
implementation(libs.appcenter.crashes)
}
moduleX/build.gradle.kts

28. Sharing build logic
Convention plugin
plugins {
id("com.android.library")
id("kotlin-android")
id("kotlin-kapt")
id("org.jlleitschuh.gradle.ktlint")
}
android {
compileSdk = findIntProperty("compileSdkVersion")
defaultConfig {
minSdk = findIntProperty("minSdkVersion")
targetSdk = findIntProperty("targetSdkVersion")
testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
vectorDrawables {
useSupportLibrary = true
}
}
compileOptions {
sourceCompatibility = JavaVersion.VERSION_11
targetCompatibility = JavaVersion.VERSION_11
}
kotlinOptions {
jvmTarget = JavaVersion.VERSION_11.toString()
}
buildTypes {
release {
isMinifyEnabled = true
proguardFiles(
getDefaultProguardFile("proguard-android-optimize.txt"),
"proguard-rules.pro"
)
}
}
testOptions {
unitTests.isReturnDefaultValues = true
unitTests.all {
it.testLogging {
events = setOf(
TestLogEvent.STARTED,
TestLogEvent.PASSED,
TestLogEvent.SKIPPED,
TestLogEvent.FAILED
)
showStandardStreams = true
}
}
}
flavorDimensions.add("environment")
productFlavors {
register("dev") {
dimension = "environment"
}
register("staging") {
dimension = "environment"
}
register("prod") {
dimension = "environment"
}
}
}
dependencies {
implementation(Koin.android)
implementation(Koin.compose)
}
fun findStringProperty(propertyName: String): String {
return findProperty(propertyName) as String
}
fun findIntProperty(propertyName: String): Int {
return (findProperty(propertyName) as String).toInt()
}
plugins {
id("com.client.app.convention.androidBase")
id("com.client.app.convention.flavors")
}
android {
namespace = "com.client.app.logging"
}
dependencies {
implementation(libs.appcenter.crashes)
}
moduleX/build.gradle.kts

29. Sharing build logic
Convention plugin
plugins {
id("com.android.library")
id("kotlin-android")
id("kotlin-kapt")
id("org.jlleitschuh.gradle.ktlint")
}
android {
compileSdk = findIntProperty("compileSdkVersion")
defaultConfig {
minSdk = findIntProperty("minSdkVersion")
targetSdk = findIntProperty("targetSdkVersion")
testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
vectorDrawables {
useSupportLibrary = true
}
}
compileOptions {
sourceCompatibility = JavaVersion.VERSION_11
targetCompatibility = JavaVersion.VERSION_11
}
kotlinOptions {
jvmTarget = JavaVersion.VERSION_11.toString()
}
buildTypes {
release {
isMinifyEnabled = true
proguardFiles(
getDefaultProguardFile("proguard-android-optimize.txt"),
"proguard-rules.pro"
)
}
}
testOptions {
unitTests.isReturnDefaultValues = true
unitTests.all {
it.testLogging {
events = setOf(
TestLogEvent.STARTED,
TestLogEvent.PASSED,
TestLogEvent.SKIPPED,
TestLogEvent.FAILED
)
showStandardStreams = true
}
}
}
flavorDimensions.add("environment")
productFlavors {
register("dev") {
dimension = "environment"
}
register("staging") {
dimension = "environment"
}
register("prod") {
dimension = "environment"
}
}
}
dependencies {
implementation(Koin.android)
implementation(Koin.compose)
}
fun findStringProperty(propertyName: String): String {
return findProperty(propertyName) as String
}
fun findIntProperty(propertyName: String): Int {
return (findProperty(propertyName) as String).toInt()
}
moduleX/build.gradle.kts
plugins {
id("com.client.app.convention.androidBase")
id("com.client.app.convention.flavors")
}
android {
namespace = "com.client.app.logging"
}
dependencies {
implementation(libs.appcenter.crashes)
}

30. Sharing build logic
Next step: explicit convention plugin
class AndroidLibraryJacocoConventionPlugin : Plugin<Project> {
override fun apply(target: Project) {
with(target) {
with(pluginManager) {
apply("org.gradle.jacoco")
apply("com.android.library")
}
val extension =
extensions.getByType<LibraryAndroidComponentsExtension>()
configureJacoco(extension)
}
}
}

31. Dependencies:
refreshVersions library

32. Dependencies
dependencies {
implementation 'androidx.core:core-ktx:1.9.0'
implementation "androidx.compose.ui:ui:$compose_version"
implementation "androidx.compose.material3:material3:1.0.1"
implementation "androidx.compose.ui:ui-tooling-preview:$compose_version"
implementation 'androidx.lifecycle:lifecycle-runtime-ktx:2.5.1'
implementation 'androidx.activity:activity-compose:1.6.1'
implementation "com.google.accompanist:accompanist-webview:0.28.0"
testImplementation 'junit:junit:4.13.2'
androidTestImplementation 'androidx.test.ext:junit:1.1.3'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.4.0'
androidTestImplementation "androidx.compose.ui:ui-test-junit4:$compose_version"
debugImplementation "androidx.compose.ui:ui-tooling:$compose_version"
debugImplementation "androidx.compose.ui:ui-test-manifest:$compose_version"
}

33. Dependencies

34. Dependencies
Custom dependency management
• No built-in mechanism to
centralise dependencies*
• Custom dependencies
management breaks Android
Studio dependencies update

35. Dependencies
refreshVersions library
• Centralize dependencies
declarations and versions in
versions.properties
• Helpful gradle task for
version updates and even
migration!

36. Dependencies
refreshVersions library
./gradlew refreshVersions

37. Dependencies
refreshVersions library: migration
dependencies {
val composeVersion: String = project.properties["composeVersion"] as String
implementation("androidx.core:core-ktx:1.7.0")
implementation("androidx.lifecycle:lifecycle-runtime-ktx:2.3.1")
implementation("androidx.activity:activity-compose:1.3.1")
implementation("androidx.compose.ui:ui:$composeVersion")
implementation("androidx.compose.ui:ui-tooling-preview:$composeVersion")
implementation("androidx.compose.material3:material3:1.0.0-alpha02")
implementation("net.openid:appauth:0.11.1")
testImplementation("junit:junit:4.13.2")
androidTestImplementation("androidx.test.ext:junit:1.1.3")
androidTestImplementation("androidx.test.espresso:espresso-core:3.4.0")
androidTestImplementation("androidx.compose.ui:ui-test-junit4:$composeVersion")
debugImplementation("androidx.compose.ui:ui-tooling:$composeVersion")
debugImplementation("androidx.compose.ui:ui-test-manifest:$composeVersion")
}
./gradlew refreshVersionsMigrate

38. Dependencies
refreshVersions library: migration
dependencies {
implementation(AndroidX.core.ktx)
implementation(AndroidX.lifecycle.runtime.ktx)
implementation(AndroidX.activity.compose)
implementation(AndroidX.compose.ui)
implementation(AndroidX.compose.ui.toolingPreview)
implementation(AndroidX.compose.material3)
implementation("net.openid:appauth:_")
testImplementation(Testing.junit4)
androidTestImplementation(AndroidX.test.ext.junit)
androidTestImplementation(AndroidX.test.espresso.core)
androidTestImplementation(AndroidX.compose.ui.testJunit4)
debugImplementation(AndroidX.compose.ui.tooling)
debugImplementation(AndroidX.compose.ui.testManifest)
}

39. RefreshVersions
Other features
• Support gradle plugins versions as well
• RefreshVersionsBot (~Dependabot)
• Support for Gradle VersionCatalog
• Migration still works after initial migration!
dependencies {
implementation(AndroidX.compose.ui)
implementation(AndroidX.compose.ui.toolingPreview)
implementation(AndroidX.compose.material3)
implementation("com.google.accompanist:accompanist-webview:0.28.0")
}

40. RefreshVersions
Other features
• Support gradle plugins versions as well
• RefreshVersionsBot (~Dependabot)
• Support for Gradle VersionCatalog
• Migration still works after initial migration!
dependencies {
implementation(AndroidX.compose.ui)
implementation(AndroidX.compose.ui.toolingPreview)
implementation(AndroidX.compose.material3)
implementation(libs.accompanist.webview)
}

41. New Gradle features and trends since 3~4 years
• Kotlin script (KTS)
• Convention plugins
• Convention plugins (explicit)
• pluginManagement { } block
• dependencyResolutionManagement { } block
• Version catalog
+ modularisation
+ third party libraries 🤯

42. Unit Testing:
the Outside-In strategy

43. Unit testing
Common issues
• fragile tests
• many test doubles ("mocks") to implement
• testing private methods
• testing behaviours (implementations)
• Unit tests different from acceptance tests
• Should I test pass-through classes?

44. Unit testing
Common issues
FeatureScreen
FeatureViewModel
FeatureUseCase FeatureRepository
FeatureDataSource
ApiService
Backend

45. Outside-In Strategy
Testing each class in isolation
FeatureScreen
FeatureViewModel
FeatureUseCase FeatureRepository
FeatureDataSource
ApiService
MockWebServer
Unit tests

46. mocked JSON files

47. @Test
fun `Application ToBeCompleted has a correct UI header`() = runTest {
val contractReference = "CFR20221025MHP37ZZ"
val validJson =
readMockFile("mocked-responses/api/v1/Applications/$contractReference/details")
restartKoinWithMockedWebServer(
responses = listOf(validJson),
featureModule = featureModule,
testKoinModule = testKoinModule,
)
val viewModel: ApplicationDetailViewModel =
get(parameters = { parametersOf(contractReference) })
viewModel.onAction(ApplicationDetailScreenAction.OnResume)
viewModel.uiState.test {
val details =
awaitForItemIs(ApplicationDetailScreenState.Details::class)
assertEquals(ToBeCompleted, details.finalState)
}
}
// GIVEN
// WHEN
// THEN
// THEN
mockWebServer
Koin
Turbine

48. Generate the network model:
Using OpenAPI generator

49. OpenAPI
• The specification used by Swagger tools
• Describes the API (endpoints, objects...)
• Can be used as a contract between the
backend and the frontend
• Can be used to generate the code of the
client and/or the server

50. spec.json
OpenAPI Generator
*Api.kt
*Dto.kt

51. OpenAPI Generator
spec.json
OpenAPI Generator
/**
* Tweet delete by Tweet ID
* Delete specified Tweet (in the path) by ID.
* @param id The ID of the Tweet to be deleted.
* @return TweetDeleteResponse
* ...
*/
fun deleteTweetById(id: kotlin.String) : TweetDeleteResponse
data class Tweet (
/* Unique identifier of this Tweet. This is returned
as a string in order to avoid complications with
languages and tools that cannot handle large integers.
*/
@Json(name = "id")
val id: kotlin.String,
/* The content of the Tweet. */
@Json(name = "text")
val text: kotlin.String,
/* Unique identifier of this User.*/
@Json(name = "author_id")
val authorId: kotlin.String? = null,
// ...

52. OpenAPI Generator
• Allows to integrate BFF updates in a blink of an eye
• Quite flexible to integrate
• see more: https://www.bam.tech/article/customize-openapi-generator-output-for-
your-android-app

53. UI layer:
full Compose!

54. Jetpack Compose
• Really easy to implement the client Design System
• Works really well with MVI approach
• Webviews are buggy
• Jetpack Compose navigation s*cks!

55. Thank you!