Building Cross-Platform Applications with Kotlin

1. Introduction

This tutorial aims to guide you on how to utilize Kotlin's multiplatform capabilities to build cross-platform applications.

By following this tutorial, you will learn:
- Setting up the development environment for Kotlin
- Understanding Kotlin Multiplatform Project (MPP)
- Building a simple cross-platform application with Kotlin

Prerequisites:
- Basic knowledge of Kotlin language
- Familiarity with IDEs, preferably IntelliJ IDEA

2. Step-by-Step Guide

2.1 Setting up the Kotlin Multiplatform Environment

Install the latest version of IntelliJ IDEA, which comes with Kotlin plugin.

2.2 Understanding Kotlin Multiplatform Project (MPP)

Kotlin MPP allows you to write the core code once and share it across multiple platforms. The shared code is compiled to platform-specific binaries.

2.3 Creating a Kotlin Multiplatform Project

In IntelliJ IDEA, start a new Kotlin Multiplatform Project. Choose the platforms you want to target.

3. Code Examples

3.1 Creating a Shared Module

Shared module is where the shared code resides.

expect class Sample() {
    fun checkMe(): Int
}

fun hello(): String = "Hello from ${Platform().platform}!"

This code represents a simple shared module. The expect keyword defines an expected platform-specific implementation. The hello() function will return a string including the platform name.

3.2 Creating Platform-Specific Implementations

In the platform-specific modules, you'll provide the actual implementation.

JVM Implementation

actual class Sample {
    actual fun checkMe() = 42
}

JS Implementation

actual class Sample {
    actual fun checkMe() = 7
}

Here, the actual keyword is used to provide the platform-specific implementation of the Sample class.

4. Summary

In this tutorial, we've covered:
- Setting up Kotlin Multiplatform environment
- Creating a Kotlin Multiplatform Project
- Writing shared code and platform-specific implementations

Next steps:
- Try creating more complex applications
- Explore more about Kotlin's standard library

Additional resources:
- Official Kotlin Website
- Kotlin Multiplatform Documentation

5. Practice Exercises

1. Create a simple calculator that performs basic operations (add, subtract, multiply, divide) as a Kotlin Multiplatform Project.

2. Create a "To-Do List" application using Kotlin Multiplatform, where the core logic is in the shared module and platform-specific UIs are in their respective modules.

Solutions:

1. Calculator - The core logic for calculations can reside in the shared module. Platform-specific modules will only contain UI and user input handling.

2. To-Do List - The shared module will hold the main logic for adding, removing, or modifying the tasks. The UI and user interaction will be handled in platform-specific modules.

Tips for further practice:

• Try adding more features to your applications.
• Experiment with different Kotlin libraries and frameworks.