Modularization & Build Variants

As an app grows, splitting it into Gradle modules improves build times (parallel + incremental), enforces boundaries, and enables reuse.

A typical module graph

flowchart TB
    APP[":app"] --> FEATURE_LIST[":feature:articles"]
    APP --> FEATURE_SETTINGS[":feature:settings"]
    FEATURE_LIST --> CORE_DATA[":core:data"]
    FEATURE_SETTINGS --> CORE_DATA
    CORE_DATA --> CORE_MODEL[":core:model"]
    FEATURE_LIST --> CORE_UI[":core:ui"]

:app — wires everything together (DI, navigation host).
:feature:* — one feature each (screens + ViewModels).
:core:* — shared building blocks (model, data, ui, network).

Dependencies point inward: features depend on core, never the reverse, and features do not depend on each other.

Declaring modules

// settings.gradle.kts
include(":app", ":core:model", ":core:data", ":feature:articles")

A feature module’s build.gradle.kts depends on the core modules it needs:

dependencies {
    implementation(project(":core:data"))
    implementation(project(":core:ui"))
}

Version catalogs across modules

A single gradle/libs.versions.toml keeps every module on the same dependency versions — exactly the pattern the guide’s examples/ use:

dependencies {
    implementation(libs.androidx.activity.compose)
    implementation(platform(libs.compose.bom))
}

Build types and flavors

Build types (debug, release) differ in signing, shrinking, and logging. Product flavors create variants like free/paid or dev/prod:

android {
    buildTypes {
        release {
            isMinifyEnabled = true
            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"))
        }
    }
    flavorDimensions += "tier"
    productFlavors {
        create("free") { dimension = "tier" }
        create("paid") { dimension = "tier" }
    }
}

This yields variants like freeDebug, paidRelease.

Exercises

Sketch the module graph for an app with two features that share a data layer.
Add a release build type that enables minification.

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