Kotlin Functions


Building Kotlin Android Libraries: Share Your Code with the Community

Creating Android apps often involves reusing code across projects or sharing functionalities with other developers. Building libraries is an excellent way to encapsulate and distribute reusable code, empowering others to leverage your work and contribute to the Android development community. In this blog, we’ll explore the process of building Kotlin Android libraries, along with best practices and tips to foster effective collaboration.

Building Kotlin Android Libraries: Share Your Code with the Community

Android development thrives on collaboration and sharing knowledge within the community. When you build a library in Kotlin, you open the doors to contribution and encourage others to build upon your work. In this guide, we’ll walk you through the process of building a Kotlin Android library, covering essential aspects such as defining the library’s goals, writing clean Kotlin code, testing, documentation, versioning, and more.

1. Setting Up the Project

Before diving into writing code, setting up the project correctly is crucial. You have a few options to get started:

Android Studio Template: Android Studio provides a library template that streamlines the process. Go to File > New > New Module and select Android Library.

Manual Setup: If you prefer more control, create a new Android module and set its plugin to com.android.library.

2. Defining the Library

2.1. Library Goals and Features

Clearly define the goals and scope of your library. Identify the specific functionalities it will provide and the problems it aims to solve. Maintaining a clear vision will help you focus on essential features and avoid feature creep.

2.2. Designing a Clean API

A well-designed API is crucial for a successful library. Strive for simplicity, consistency, and ease of use. Hide implementation details and expose only the necessary functions. Use clear and meaningful names for classes and methods.

3. Writing the Kotlin Code

3.1. Kotlin Language Overview

Kotlin is a powerful and expressive language that brings numerous features to Android development. Familiarize yourself with Kotlin’s key features such as null safety, extension functions, data classes, and coroutines.

3.2. Common Kotlin Features for Libraries

  • Data Classes: Use data classes to model data structures effectively.
  • Extensions: Leverage extension functions to add functionality to existing classes without subclassing.
  • Coroutines: Consider using coroutines to write asynchronous and concurrent code more elegantly.
  • Companion Objects: Use companion objects to define static methods and constants.
// Example of a data class and an extension function
data class User(val name: String, val age: Int)

fun User.isAdult() = age >= 18

4. Unit Testing and Test Coverage

4.1. Importance of Testing in Libraries

Unit testing is essential to ensure the reliability of your library. Write unit tests for each function and edge case to catch bugs early and provide a seamless experience to the users.

4.2. Writing Unit Tests with Kotlin and JUnit

Kotlin works seamlessly with JUnit for unit testing. Ensure you use dependency injection to facilitate mocking and keep tests isolated.

class MathUtils {
    fun add(a: Int, b: Int): Int = a + b

class MathUtilsTest {
    fun testAddition() {
        val mathUtils = MathUtils()
        assertEquals(5, mathUtils.add(2, 3))

4.3. Measuring Test Coverage with Jacoco

Use Jacoco to measure your test coverage and identify areas that lack test cases. Aim for high test coverage to ensure robustness.

5. Documentation

Writing Clear and Comprehensive Docs

Proper documentation is crucial for your library’s adoption. Include usage examples, explanations, and any potential gotchas. Keep the documentation up-to-date with the codebase.

5.1. Generating API Documentation with Dokka

Dokka is a documentation engine for Kotlin that generates API documentation from code comments. Integrating Dokka into your build process ensures that your documentation stays in sync with your code.

6. Versioning and Dependency Management

6.1. Semantic Versioning

Follow semantic versioning to ensure compatibility and provide users with a clear understanding of the changes between releases.

6.2. Publishing to Maven Central

Make your library accessible to others by publishing it to Maven Central or other package repositories. This allows developers to easily include your library as a dependency in their projects.

7. Proguard and Code Obfuscation

Protecting Library Code with Proguard

If your library contains sensitive code or assets, consider using Proguard to obfuscate and shrink your code, making it harder to reverse engineer.

8. Sample App for Demonstration

Creating a Sample App for the Library

Include a sample app in your library to demonstrate its capabilities and provide users with a hands-on experience.

9. Collaboration and Contribution

Hosting the Project on GitHub

GitHub is the go-to platform for hosting open-source projects. Share your library’s code and invite others to collaborate.

Code Review and Pull Requests

Encourage contributions from the community and conduct code reviews to maintain code quality. Be responsive to pull requests and foster a welcoming environment for contributors.


Building Kotlin Android libraries is a rewarding way to share your expertise and contribute to the vibrant Android development community. By following best practices, writing clean code, and fostering collaboration, you can create powerful and widely adopted libraries that make a positive impact on Android app development. So go ahead, start building, and let your code shine in the hands of developers worldwide!

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Experienced Android Engineer specializing in Kotlin with over 5 years of hands-on expertise. Proven record of delivering impactful solutions and driving app innovation.