Managing Multi-module Android Project with Gradle Plugin and Kotlin

©2020 Wantedly, Inc.
Managing Multi-module Project
with Gradle Plugin and Kotlin
.droidcon APAC 2020
15 Dec 2020 - Malvin Sutanto
Photo by Jan Antonin Kolar on Unsplash

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Introduction
Malvin Sutanto
Software Engineer - Android
Twitter/ Medium: @malvinsutanto

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Multi module setup
in Android projects

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Multi module setup in Android

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• Faster build time

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• Easier to manage and work with

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• Easier to manage and work with
• New features
• Instant apps
• Dynamic feature modules

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However

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• Each module need a build.gradle file

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• Duplicate build script across modules

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• Duplicate build script across modules
• Build files became hard to maintain

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build.gradle file
for a library module
plugins {
id 'com.android.library'
id 'kotlin-android'
}
android {
compileSdkVersion 30
buildToolsVersion "30.0.2"
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
testInstrumentationRunner "androidx.test.runner.AndroidJUnitRunner"
consumerProguardFiles "consumer-rules.pro"
}
buildTypes {
release {
minifyEnabled false
proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'),
'proguard-rules.pro'
}
}
compileOptions {
sourceCompatibility JavaVersion.VERSION_1_8
targetCompatibility JavaVersion.VERSION_1_8
}
kotlinOptions {
jvmTarget = '1.8'
}
}
dependencies {
implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version"
implementation 'androidx.core:core-ktx:1.2.0'
implementation 'androidx.appcompat:appcompat:1.1.0'
implementation 'com.google.android.material:material:1.1.0'
testImplementation 'junit:junit:4.+'
androidTestImplementation 'androidx.test.ext:junit:1.1.1'
androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'
}

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build.gradle file
for a library module
plugins {
id 'kotlin-android'
}
android {
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
}
}
compileOptions {
}
kotlinOptions {
jvmTarget = '1.8'
}
}
dependencies {
}
• Declares Gradle plugins
• Sets build parameters
• Declares dependencies

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Gradle plugin
Simpliﬁes build scripts

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What is Gradle?

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What is Gradle?
• “Generic” build automation tool

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What is Gradle?
• Declares input and output files

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What is Gradle?
• Declares input and output files
• Tasks as its core

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Gradle Build phases
Gradle build phases

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Gradle Build phases
Gradle build phases
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Gradle Build phases
Gradle build phases
*OJUJBMJ[BUJPO $POpHVSBUJPO

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Gradle Build phases
Gradle build phases
*OJUJBMJ[BUJPO $POpHVSBUJPO &YFDVUJPO

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build.gradle file
Domain Specific Language (DSL)
plugins {
id 'kotlin-android'
}
android {
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
}
}
compileOptions {
}
kotlinOptions {
jvmTarget = '1.8'
}
}
dependencies {
}
• Conﬁguration ﬁle
• Describes build steps
• Available in Groovy and Kotlin
Gradle Build.gradle file

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build.gradle file
plugins {
id 'kotlin-android'
}
android {
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
}
}
compileOptions {
}
kotlinOptions {
jvmTarget = '1.8'
}
}
dependencies {
}
Extension block

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build.gradle file
plugins {
id 'kotlin-android'
}
android {
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
}
}
compileOptions {
}
kotlinOptions {
jvmTarget = '1.8'
}
}
dependencies {
}
Gradle plugins
Extension block

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Gradle plugin

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Gradle Plugin

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Gradle Plugin
• Extends the Gradle model
• Adds new configuration block and options

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Gradle Plugin
• Configures project according conventions
• Adds new tasks
• Configures sensible defaults

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Gradle Plugin
• Configures project according conventions
• Adds new tasks
• Configures sensible defaults
• Applies specific configuration
• Enforces standards

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Types of Gradle Plugin
Gradle Plugin

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Script plugin
• Additional build script that is located separately.
• Can exist in local ﬁlesystem or remote location.
• Multiple script plugins can be applied.
• apply from: 'other.gradle'
Gradle Plugin

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Script plugin
• Additional build script that is located separately.
• Can exist in local ﬁlesystem or remote location.
• Multiple script plugins can be applied.
• apply from: 'other.gradle'
Binary plugin
• Written programmatically by implementing
Plugin interface,
• Applied using unique plugin id
• plugins {
id 'kotlin-android'
}
Gradle Plugin

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Creating a Gradle Plugin

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Gradle Plugin

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What will the plugin do?
Gradle Plugin

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For each module, it will:
Gradle Plugin

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Gradle Plugin

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• Apply other Gradle plugins
Gradle Plugin

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• Set common build parameters
Gradle Plugin

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• Specify default proguard files
Gradle Plugin

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• Enable Java 8 features
Gradle Plugin

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• Declare dependencies
Gradle Plugin

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• Configure Jacoco and custom extensions
Gradle Plugin

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my-lib/build.gradle.kts
Gradle Plugin

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plugins {
id("com.android.library") // or .application
id("my-custom-plugin-id")
}
android {
buildTypes {
getByName("debug") {
isTestCoverageEnabled = true
}
}
}
myPluginOptions {
jacoco {
isEnabled = true
}
}
dependencies { … }
Gradle Plugin

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plugins {
}
android {
buildTypes {
getByName(“debug") {
}
}
}
myPluginOptions {
jacoco {
isEnabled = true
}
}
Gradle Plugin

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plugins {
id("com.android.library")
}
android {
buildTypes {
}
}
}
myPluginOptions {
jacoco {
isEnabled = true
}
}
Gradle Plugin

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plugins {
}
android {
buildTypes {
}
}
}
myPluginOptions {
jacoco {
isEnabled = true
}
}
plugins {
id 'kotlin-android'
}
android {
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
}
}
compileOptions {
}
kotlinOptions {
jvmTarget = '1.8'
}
}
dependencies {
}
Gradle Plugin

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Gradle plugin
Setup

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my-project/
- buildSrc/
- build.gradle.kts
- src/main/kotlin/com/mypackage/
- MyCustomPlugin.kt
- app/
- my-lib/
Project Structure
Gradle Plugin

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my-project/
- buildSrc/
- build.gradle.kts
- src/main/kotlin/com/mypackage
- MyCustomPlugin.kt
- app/
- my-lib/
Project Structure
Gradle Plugin

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buildSrc/src/build.gradle.kts
plugins {
`java-gradle-plugin`
`kotlin-dsl`
}
repositories {
google()
mavenCentral()
}
dependencies {
implementation("com.android.tools.build:gradle:$agpVersion")
implementation(kotlin("gradle-plugin"))
}
Gradle Plugin

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plugins {
`kotlin-dsl`
}
repositories {
google()
mavenCentral()
}
dependencies {
}
Gradle Plugin

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plugins {
`kotlin-dsl`
}
repositories {
google()
mavenCentral()
}
dependencies {
}
https://android-developers.googleblog.com/2020/12/announcing-android-studio-arctic-fox.html
Gradle Plugin

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my-project/
- buildSrc/
- build.gradle.kts
- src/main/kotlin/com/mypackage/
- MyCustomPlugin.kt
- app/
- my-lib/
Project Structure
Gradle Plugin

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Gradle Plugin buildSrc/src/main/kotlin/com/mypackage/MyCustomPlugin.kt

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Gradle Plugin
class MyCustomPlugin : Plugin {
buildSrc/src/main/kotlin/com/mypackage/MyCustomPlugin.kt

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Gradle Plugin
Module

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Gradle Plugin
override fun apply(project: Project) {
// TODO: Write build configurations here.
}
}
Module

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Gradle plugin
Implementation

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Gradle Plugin

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project.plugins.apply("kotlin-android")
}

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project.plugins.apply("kotlin-android")
}
Plugin id
// build.gradle
plugins {
id 'kotlin-android'
}

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Gradle Plugin

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…
val androidExtension = project.extensions.getByName("android")
if (androidExtension is BaseExtension) {
androidExtension.applyAndroidSettings()
}
}
private fun BaseExtension.applyAndroidSettings() {
compileSdkVersion(30)
defaultConfig {
targetSdkVersion(30)
minSdkVersion(23)
// etc.
}
}

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…
}
}
defaultConfig {
minSdkVersion(23)
// etc.
}
}
// build.gradle
android {
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
}
}

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…
}
}
defaultConfig {
minSdkVersion(23)
// etc.
}
}
// build.gradle
android {
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
}
}
Base class for all Android plugin extension classes

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…
}
}
defaultConfig {
minSdkVersion(23)
// etc.
}
}
// build.gradle
android {
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
}
}

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Gradle Plugin

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Types of plugin
Gradle Plugin

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Application module Library module
id("com.android.application") id("com.android.library")
Types of plugin
Gradle Plugin

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Application module
• Set isMinifyEnabled only on release
Library module
Types of plugin
Gradle Plugin

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Application module
• Specify proguard ﬁles using proguardFiles()
Library module
Types of plugin
Gradle Plugin

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Application module
• Specify proguard ﬁles using proguardFiles()
Library module
• Specify proguard ﬁles using
consumerProguardFiles()
Types of plugin
Gradle Plugin

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…
val androidExtension = project.extensions.getByName(“android")
androidExtension.applyProguardSettings()
}
}

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private fun BaseExtension.applyProguardSettings() {
val proguardFile = "proguard-rules.pro"
when (this) {
is LibraryExtension -> defaultConfig {
consumerProguardFiles(proguardFile)
}
is AppExtension -> buildTypes {
getByName("release") {
isMinifyEnabled = true
isShrinkResources = true
proguardFiles(
getDefaultProguardFile("proguard-android-optimize.txt"),
proguardFile
)
}
}
}
}

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when (this) {
}
proguardFiles(
proguardFile
)
}
}
}
}
proguard-rules.pro files in each module’s root

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when (this) {
}
proguardFiles(
proguardFile
)
}
}
}
}

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when (this) {
}
proguardFiles(
proguardFile
)
}
}
}
}
// build.gradle
plugins {
id 'my-custom-plugin-id'
}

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when (this) {
}
proguardFiles(
proguardFile
)
}
}
}
}
// build.gradle
plugins {
}
// build.gradle
android {
defaultConfig {
...
consumerProguardFiles "proguard-rules.pro"
}
}

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when (this) {
}
proguardFiles(
proguardFile
)
}
}
}
}

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when (this) {
}
proguardFiles(
proguardFile
)
}
}
}
}
// build.gradle
plugins {
id 'com.android.application'
}

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when (this) {
}
proguardFiles(
proguardFile
)
}
}
}
}
Enable obfuscation only on "release" build
// build.gradle
plugins {
id 'com.android.application'
}

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Gradle Plugin

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…
...
androidExtension.enableJava8(project)
}
}

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private fun BaseExtension.enableJava8(project: Project) {
compileOptions {
isCoreLibraryDesugaringEnabled = true
sourceCompatibility = JavaVersion.VERSION_1_8
targetCompatibility = JavaVersion.VERSION_1_8
}
project.tasks.withType().configureEach {
kotlinOptions {
jvmTarget = "1.8"
}
}
}

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compileOptions {
}
project.tasks.withType().configureEach {
kotlinOptions {
jvmTarget = "1.8"
}
}
}
Java 8 core library desugaring

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Gradle Plugin

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compileOptions {
}
project.dependencies {
add("coreLibraryDesugaring", "com.android.tools:desugar_jdk_libs:1.0.9")
}
...
}

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compileOptions {
}
add("coreLibraryDesugaring", "com.android.tools:desugar_jdk_libs:1.0.9")
}
...
} Configuration name

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add("implementation", "androidx.core:core-ktx:1.2.0")
add("testImplementation", "junit:junit:4.12")
add("androidTestImplementation", "androidx.test.ext:junit:1.1.1")
}

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Gradle Plugin

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plugins {
}
android {
buildTypes {
getByName("debug") {
}
}
}
myPluginOptions {
jacoco {
isEnabled = true
}
}
Gradle Plugin

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project.extensions.create("myPluginOptions")
…
…
androidExtension.configureJacoco(project)
}
}

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…
…
}
}
Extension class

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…
…
}
}
Extension class
// build.gradle.kts
myPluginOptions {
jacoco {
isEnabled = true
}
}

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open class MyPluginOptionExtension {
val jacoco: JacocoOptions = JacocoOptions()
fun jacoco(action: Action) {
action.execute(jacoco)
}
}
class JacocoOptions {
var isEnabled: Boolean = true
}
Gradle Plugin buildSrc/src/main/kotlin/com/mypackage/MyPluginOptionExtension.kt

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// build.gradle.kts
myPluginOptions {
jacoco {
isEnabled = true
}
}
}
}
} // build.gradle
myPluginOptions {
jacoco {
enabled true
}
}

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}
}
}
// build.gradle.kts
myPluginOptions {
jacoco {
isEnabled = true
}
}

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}
}
}
// build.gradle.kts
myPluginOptions {
jacoco {
isEnabled = true
}
}
https://docs.gradle.org/current/userguide/custom_gradle_types.html
https://docs.gradle.org/current/userguide/lazy_conﬁguration.html#lazy_conﬁguration

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…
…
}
}

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private fun BaseExtension.configureJacoco(project: Project) {
project.afterEvaluate {
val jacocoOptions = project.extensions.getByType()
.jacoco
if (jacocoOptions.isEnabled) {
project.plugins.apply("jacoco")
when (this@configureJacoco) {
is LibraryExtension -> configureJacocoTasks(project, libraryVariants)
is AppExtension -> configureJacocoTasks(project, applicationVariants)
}
}
}
}
private fun configureJacocoTasks(
project: Project,
variants: DomainObjectSet
) { ... }

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.jacoco
}
}
}
}
project: Project,
) { ... }
// build.gradle.kts
myPluginOptions {
jacoco {
isEnabled = true
}
}

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.jacoco
}
}
}
}
project: Project,
) { ... }

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.jacoco
}
}
}
}
project: Project,
) { ... }
"debug"
"release"

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.jacoco
}
}
}
}
project: Project,
) { ... }
"debug"
"release"
"debug"
"release"
"flavorDebug"
"flavorRelease"

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project: Project,
) {
variants.all {
val variantName = name
val isDebuggable = buildType.isDebuggable
if (!isDebuggable) return@all
project.tasks.register("jacoco${variantName.capitalize()}Report") {
// Set up the rest of the Jacoco tasks dependency, exec files, etc.
}
}
}

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project: Project,
) {
variants.all {
}
}
}
Skip non-debuggable builds

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project: Project,
) {
variants.all {
}
}
}

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project: Project,
) {
variants.all {
}
}
}
"debug"
"release"
"flavorDebug"
"flavorRelease"

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project: Project,
) {
variants.all {
}
}
}
./gradlew :lib:jacocoDebugReport
./gradlew :app:jacocoFlavorDebugReport
"debug"
"release"
"flavorDebug"
"flavorRelease"

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project: Project,
) {
variants.all {
}
}
}

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Apply Gradle plugin
on other modules

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plugins { ... }
gradlePlugin {
plugins {
register("my-custom-plugin") {
id = "my-custom-plugin-id"
implementationClass = "com.mypackage.MyCustomPlugin"
}
}
}
repositories { ... }
dependencies { ... }
Gradle Plugin

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plugins { ... }
gradlePlugin {
plugins {
}
}
}
// lib/build.gradle.kts
plugins {
}
Gradle Plugin

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plugins { ... }
gradlePlugin {
plugins {
}
}
}
// lib/build.gradle.kts
plugins {
}
class MyCustomPlugin : Plugin { ... }
Gradle Plugin

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Gradle plugin
Beneﬁts

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Benefits
Gradle Plugin

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Benefits
• Share build logic across modules
• Reduce maintenance cost when updating build scripts
Gradle Plugin

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Benefits
• Higher degree of modularization
• Better organization and comprehensibility
Gradle Plugin

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Benefits
• Higher degree of modularization
• Better organization and comprehensibility
• Encapsulates logic
• Declarative build scripts
• Automatically configures tasks and its dependencies
Gradle Plugin

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Our experience
Gradle Plugin

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• Helped migration to build.gradle.kts
Our experience
Gradle Plugin

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• Make use of Gradle API
• Apply Gradle plugin to build.gradle files written in Groovy
Our experience
Gradle Plugin

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• Make use of Gradle API
• Apply Gradle plugin to build.gradle files written in Groovy
• Gradually migrate to Kotlin build.gradle.kts files
Our experience
Gradle Plugin

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plugins {
id 'kotlin-android'
}
android {
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
}
}
compileOptions {
}
kotlinOptions {
jvmTarget = '1.8'
}
}
dependencies {
}
Our experience
Gradle Plugin

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plugins {
id 'kotlin-android'
}
android {
defaultConfig {
minSdkVersion 23
targetSdkVersion 30
versionCode 1
versionName "1.0"
}
buildTypes {
release {
minifyEnabled false
}
}
compileOptions {
}
kotlinOptions {
jvmTarget = '1.8'
}
}
dependencies {
}
// build.gradle
plugin {
}
myPluginOptions {
jacoco {
enabled true
}
}
Our experience
Gradle Plugin

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// build.gradle
plugin {
}
myPluginOptions {
jacoco {
enabled true
}
}
Our experience
Gradle Plugin

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// build.gradle
plugin {
}
myPluginOptions {
jacoco {
enabled true
}
}
// build.gradle.kts
plugin {
}
myPluginOptions {
jacoco {
isEnabled = true
}
}
Our experience
Gradle Plugin

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Our experience
Gradle Plugin

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• buildSrc vs standalone plugin
Our experience
Gradle Plugin

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• Plugin is very specific to each project
Our experience
Gradle Plugin

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• Plugin is very specific to each project
• But, split the plugins when necessary depending on its purpose
• e.g., Jacoco as its own plugin
Our experience
Gradle Plugin

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Summary

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Summary
Gradle Plugin

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Summary
• Maintaining build.gradle files can be tedious
Gradle Plugin

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Summary
• Gradle plugin can simplify the maintenance
process
Gradle Plugin

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Summary
• Gradle plugin can simplify the maintenance
process
• Make Gradle plugin configurable using
extension
Gradle Plugin

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Thank you
@MalvinSutanto

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Managing Multi-module Android Project with Gradle Plugin and Kotlin

Managing Multi-module Android Project with Gradle Plugin and Kotlin

Malvin Sutanto

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