Kotlin Multiplatform a quick introduction

In the changing world of software development it has become essential to write code that can be deployed across platforms without having to rewrite it. This is where Kotlin, a programming language developed by JetBrains comes into play, with its multiplatform capabilities. Kotlin Multiplatform, a feature of Kotlin enables developers to share code between platforms such as iOS, Android, Web and Desktop. This significantly reduces the time and effort required for development. In this blog post we will delve into the realm of Kotlin Multiplatform. Explore its features, setup process and how to create cross platform applications. Whether you are a Kotlin developer or new, to the language this guide aims to provide you with the knowledge to excel in using Kotlin Multiplatform.

Understanding Kotlin Multiplatform

Kotlin Multiplatform expands upon the capabilities of the Kotlin language by offering a shared codebase that can be utilized across platforms while still allowing for platform implementations when necessary. Here are some notable advantages that set it apart in the field of platform development:

1. Code Reusability: Write your business logic once in Kotlin. Share it seamlessly across platforms.

2. Flexibility: With Kotlin Multiplatform you have the freedom to adopt UI approaches based on platforms while maintaining a common logical layer.

3. Native Performance: Applications created using Kotlin Multiplatform can take advantage of the performance that comes from compiling the code into platform binaries. One of the aspects of Kotlin Multiplatform is its interoperability, with existing platform specific code making it an attractive choice for projects that want to transition to a multiplatform approach gradually. Unlike platform frameworks like React Native or Flutter Kotlin Multiplatform doesn't attempt to unify the UI layer. Instead it focuses on sharing UI logic such as network operations, data storage and business logic while ensuring native UI and optimal performance, on each platform.

Setting Up Your Environment

To start with Kotlin Multiplatform, you need to set up your environment. The following steps will guide you through this process:

Install IntelliJ IDEA: Download and install IntelliJ IDEA, a popular IDE for Kotlin development.

Create a New Project: Open IntelliJ IDEA and create a new project. Select "Kotlin" from the left panel and then choose "Multiplatform Library" or "Multiplatform Application".

Configure Your Build Script: Kotlin Multiplatform projects use Gradle to manage dependencies and project configurations. Here is a basic setup in your build.gradle.kts file:

{
    kotlin("multiplatform") version "1.4.0"
}
kotlin {
    // Specify targets here (e.g., JVM, iOS, Android)
    jvm()
    iosX64()
    iosArm64()
}

This configuration sets up a project targeting JVM and iOS platforms. You can add or remove targets as per your requirement.

Building Your First Multiplatform Application

Creating a multiplatform application with Kotlin involves writing common code that can be used across all platforms and platform-specific code for each target. Let's start by building a simple application that shares business logic across Android and iOS.

1. Creating the Common Module: In your multiplatform project, you'll have a common module where you can write code that's shared across platforms. For example, a simple function to return a greeting message:

// Common code in src/commonMain/kotlin

fun greet(): String {

    return "Hello from Kotlin Multiplatform!"

}

2. Adding Platform-Specific Code: You may need different implementations for certain functions on different platforms. Kotlin Multiplatform uses the expect and actual keywords for this. In the common module, declare an expect function:

// Common code

expect fun platformName(): String

// Android-specific code in src/androidMain/kotlin

actual fun platformName(): String {

    return "Android"

}



// iOS-specific code in src/iosMain/kotlin

actual fun platformName(): String {

    return "iOS"

}

3. Building the UI: For Android, you can create a UI using XML or Jetpack Compose. For iOS, use SwiftUI or Interface Builder. Each platform will call the common code to display the greeting message.

4. Running the Application: Build and run the application on both Android and iOS. You will see the same greeting message, "Hello from Kotlin Multiplatform!" displayed, with the platform name appended accordingly.

Advanced Topics in Kotlin Multiplatform

As you get comfortable with the basics, you can explore more advanced features of Kotlin Multiplatform. Here are a few:

1. Networking with Ktor: Ktor is a multiplatform library for making HTTP requests. You can use it to handle network operations in your shared code.

// Common code

expect class HttpClientEngineFactory {

    fun create(): HttpClientEngine

}

// Usage in shared code

val httpClient = HttpClient(HttpClientEngineFactory().create())

This allows you to write networking logic once and use it across platforms.

2. Serialization with kotlinx.serialization: This library allows for serializing and deserializing data structures in a platform-agnostic way.

3. Coroutines for Asynchronous Programming: Kotlin's coroutines are a powerful feature for managing asynchronous tasks. They work seamlessly in a multiplatform project, allowing you to write asynchronous code in the common module.

Best Practices and Common Mistakes

When working with Kotlin Multiplatform it's important to consider the following practices:

1. Prioritize Shared Code: Strive to maximize the use of shared code, in the module. This helps reduce duplication and simplifies maintenance.

2. Be Mindful of Platform Specific Differences: While sharing logic is advantageous remember that each platform has its characteristics. Take these differences into account when writing platform code.

3. Perform Regular Testing on All Platforms: Make sure to test your application on all target platforms to identify any platform issues early on.

4. Stay Updated with Kotlin Changes: Kotlin Multiplatform is evolving rapidly so its essential to stay updated on language and library updates and changes.

There are also some mistakes you should avoid;

1. Neglecting Memory Management in Native Platforms: Pay attention to how memory's managed, particularly on platforms like iOS that use reference counting.

2. Disregarding Platform Specific Conventions: Each platform has its set of conventions and best practices especially when it comes to UI design. Ignoring these can result in an application that feels out of sync with the platforms standards.

Conclusion

Kotlin Multiplatform provides a solution, for sharing code across platforms while maintaining an experience. To efficiently develop platform applications it is important to have a solid understanding of the underlying principles ensure the environment is properly configured and adhere to recommended approaches. Although Kotlin Multiplatform may initially appear intimidating the benefits, in terms of code reuse and ease of maintenance are significant.

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