Setting Up a Jetpack Compose Multi-Module Gradle Project

Jetpack Compose, Google's modern UI toolkit for Android, has revolutionized mobile app development with its declarative approach. As your Android projects grow in complexity, embracing a multi-module Gradle architecture becomes essential. This blog post delves into setting up a Jetpack Compose multi-module Gradle project, exploring advanced concepts, best practices, and practical examples to enhance your app's scalability and maintainability.

Why Use a Multi-Module Architecture?

Advantages of a Multi-Module Project

Improved Scalability: Dividing your codebase into multiple modules enables independent development and scaling of features.
Enhanced Code Maintainability: Smaller, focused modules reduce complexity and make debugging easier.
Faster Build Times: Gradle can rebuild only the affected modules, saving time during development.
Encapsulation of Dependencies: Modules can have their specific dependencies, minimizing dependency conflicts.

Multi-Module Structure in Compose Projects

A Compose project often contains modules like:

app: Hosts the application entry point.
core: Includes common utilities, themes, and Compose extensions.
feature modules: Encapsulate independent app features, e.g., feature-login or feature-dashboard.
data: Manages data sources and repositories.

Setting Up the Multi-Module Gradle Project

1. Creating the Modules

Begin by creating the necessary modules:

Create the core module:
```
./gradlew :core:create
```
Create feature modules: Repeat for each feature, e.g., feature-login and feature-dashboard.
```
./gradlew :feature-login:create
./gradlew :feature-dashboard:create
```
Create the data module:
```
./gradlew :data:create
```

2. Configuring Gradle Files

Each module will have its build.gradle or build.gradle.kts file. Here's how to configure them:

app Module

plugins {
    id("com.android.application")
    kotlin("android")
}

android {
    namespace = "com.example.app"
    compileSdk = 34

    defaultConfig {
        applicationId = "com.example.app"
        minSdk = 21
        targetSdk = 34
        versionCode = 1
        versionName = "1.0"
    }

    buildFeatures {
        compose = true
    }

    composeOptions {
        kotlinCompilerExtensionVersion = "1.5.2"
    }
}

dependencies {
    implementation(project(":core"))
    implementation(project(":feature-login"))
    implementation(project(":feature-dashboard"))
    implementation(project(":data"))
    implementation("androidx.compose.ui:ui:1.5.2")
    implementation("androidx.compose.material:material:1.5.2")
}

core Module

plugins {
    id("com.android.library")
    kotlin("android")
}

android {
    namespace = "com.example.core"
    compileSdk = 34
    defaultConfig {
        minSdk = 21
    }
    buildFeatures {
        compose = true
    }
    composeOptions {
        kotlinCompilerExtensionVersion = "1.5.2"
    }
}

dependencies {
    implementation("androidx.compose.ui:ui:1.5.2")
    implementation("androidx.compose.material:material:1.5.2")
}

Feature Modules (e.g., feature-login)

Each feature module should depend on core and other required modules:

plugins {
    id("com.android.library")
    kotlin("android")
}

android {
    namespace = "com.example.feature_login"
    compileSdk = 34
    defaultConfig {
        minSdk = 21
    }
    buildFeatures {
        compose = true
    }
    composeOptions {
        kotlinCompilerExtensionVersion = "1.5.2"
    }
}

dependencies {
    implementation(project(":core"))
    implementation("androidx.compose.ui:ui:1.5.2")
    implementation("androidx.compose.material:material:1.5.2")
}

Best Practices for Jetpack Compose Multi-Module Projects

1. Design for Reusability

Core Module: Centralize reusable components such as themes, utility functions, and common UI elements.
Feature Modules: Make feature-specific modules self-contained and expose only the necessary interfaces.

2. Dependency Management

Use Gradle's Version Catalogs to maintain consistent dependencies:

[versions]
compose = "1.5.2"

[libraries]
compose-ui = { group = "androidx.compose.ui", name = "ui", version.ref = "compose" }
compose-material = { group = "androidx.compose.material", name = "material", version.ref = "compose" }

3. Testing in Multi-Module Projects

Test UI elements in isolation using Compose's testing framework.
Write integration tests for cross-module interactions.

4. Keep Modules Decoupled

Define contracts (interfaces) for communication between modules.
Use dependency injection tools like Hilt to manage dependencies efficiently.

5. Modular Navigation

Jetpack Compose's navigation component supports modular architecture:

Define navigation routes:

object Routes {
    const val Login = "login"
    const val Dashboard = "dashboard"
}

Set up NavHost in the app module:

NavHost(navController = navController, startDestination = Routes.Login) {
    composable(Routes.Login) { LoginScreen(navController) }
    composable(Routes.Dashboard) { DashboardScreen(navController) }
}

Advanced Use Cases

Dynamic Feature Modules

Leverage Dynamic Delivery for large apps to download specific feature modules on demand.

Gradle Build Optimization

Use Gradle's Configuration Cache and parallel builds to reduce build times.

Custom Annotations and Code Generation

Integrate KSP (Kotlin Symbol Processing) for custom annotation-based code generation to automate repetitive tasks.

Conclusion

A multi-module Gradle project structure is a powerful way to manage complex Jetpack Compose applications. By following the steps and best practices outlined here, you can create scalable, maintainable, and efficient Android apps. Start small and refactor your existing projects incrementally to reap the benefits of modularity.