Kotlin Multiplatform Introduction for Android Engineers

Kotlin Multiplatform (KMP) is a toolkit developed by JetBrains that allows developers to create applications for multiple platforms with a single coding effort. It was first introduced in 2017 and has become a viable option for mobile app developers seeking to provide a unified user experience on both Android and iOS. By November 1, 2023, it reached its stable version, attracting even more attention.
This book primarily targets developers with experience in developing Android apps using Jetpack Compose. No prior knowledge of KMP is required. Through this book, Android engineers can leverage their existing knowledge of Kotlin and Jetpack Compose to expand their skill set into cross-platform development.
We will use the official tutorials provided by JetBrains and a learning-based TODO app to explain how to utilize KMP with a focus on code. Readers will acquire a foundation in KMP, learn how to implement its key features, and understand the benefits and limitations of sharing code across different platforms.Structure of This Book
The book is divided into two main parts: explanations of the official tutorials and a sample TODO app.Official Tutorials Explanation
The first part covers the basic concepts and implementation methods for using Kotlin Multiplatform (KMP) effectively, through two official tutorials.

• The business logic sharing version of the tutorial focuses on modular design in KMP, separating code by platform, and adapting behavior according to the platform. It also covers essential technologies for app development, such as HTTP communication and asynchronous processing.
• The UI sharing version teaches developing both business logic and UI in Kotlin. It focuses on the process of sharing business logic and UI using Compose Multiplatform, particularly applying Composable functions to iOS.

Sample TODO App Explanation
The second part explains content not covered in the tutorials using a TODO app created specifically for this book. The app comes in two versions: one aimed at sharing business logic and another for complete sharing, including the UI.

• The business logic sharing version explores accessing key-value stores and databases, architecture in more complex apps, and dependency injection on Android and iOS.
• The UI sharing version focuses on the technical challenges of UI sharing. It covers architecture and dependency injection with mostly Kotlin-shared code, navigation in common UIs, internationalization of strings, multi-resolution image support, and logging methods, crucial skills for successful UI sharing.