Introduction
In today’s fast-paced mobile and web development world, the need for a unified codebase is more important than ever. Developers want to share business logic across platforms without rewriting code for each target. Kotlin Multiplatform Mobile (KMM) offers a solution that allows you to write your core code once and run it on Android, iOS, and even the web. In this blog, we dive deep into the world of Kotlin Multiplatform, explore its benefits, compare it with traditional approaches, and provide practical coding examples that demonstrate how you can truly achieve “write once, run anywhere.”
The Evolution of Cross-Platform Development
Historically, developing for multiple platforms required separate codebases in languages like Java/Kotlin for Android, Swift/Objective-C for iOS, and JavaScript/TypeScript for the web. This fragmented approach led to increased development time, maintenance challenges, and inconsistent user experiences.
Kotlin Multiplatform addresses these challenges by allowing developers to write common code for business logic, networking, data management, and more, while still implementing platform-specific user interfaces. This results in a more maintainable and consistent codebase across all platforms.
What is Kotlin Multiplatform?
Kotlin Multiplatform is an extension of the Kotlin programming language that lets you share code between multiple platforms. While the UI is often implemented natively (using Jetpack Compose on Android, SwiftUI on iOS, or React for the web), the core logic – such as data models, business rules, and network layers – can be written once in Kotlin and reused across platforms.
Key Concepts
- Common Module: Contains platform-agnostic code (business logic, domain models, network operations) written in Kotlin.
- Platform-Specific Modules: Include code that deals with UI or platform-specific APIs.
- Expect/Actual Mechanism: Allows you to define an “expected” API in the common module, and then provide platform-specific “actual” implementations.
Benefits of Kotlin Multiplatform
Kotlin Multiplatform brings several benefits that make it an attractive choice for cross-platform development:
- Shared Business Logic: Write once and share critical business logic across Android, iOS, and web apps. This reduces code duplication and ensures consistency.
- Reduced Development Time: Fewer codebases mean faster development and easier maintenance.
- Native Performance: Each platform’s UI layer remains native, ensuring that performance and user experience aren’t compromised.
- Flexibility: KMM lets you share as much or as little code as needed. You can start by sharing a single layer (e.g., networking) and gradually increase the shared footprint.
- Modern Language Features: Benefit from Kotlin’s concise syntax, null safety, coroutines for asynchronous programming, and rich standard library.
Real-World Use Cases and Adoption
Leading companies are already experimenting with or fully adopting Kotlin Multiplatform for shared business logic and even entire apps. Some common scenarios include:
- Financial Applications: Sharing secure business logic for data encryption and network communication.
- E-commerce Platforms: Reusing data models and API clients to ensure consistency across mobile and web applications.
- Media and Entertainment Apps: Sharing complex algorithms for content recommendations or user personalization across platforms.
These real-world examples underscore how KMM can reduce time-to-market and improve code quality.
Getting Started with Kotlin Multiplatform
Below is a basic example demonstrating how to set up a Kotlin Multiplatform project that shares code between Android and iOS. We will focus on creating a simple shared function that returns a greeting message.
Project Structure
A typical Kotlin Multiplatform project includes:
- commonMain: Shared code.
- androidMain: Android-specific code.
- iosMain: iOS-specific code.
Step 1: Configure the Gradle Build
In your shared module’s build.gradle.kts file, configure the multiplatform settings:
plugins {
kotlin("multiplatform")
id("com.android.library")
}
kotlin {
android()
ios() // For iOS targets (iosX64, iosArm64, iosSimulatorArm64 can be configured as needed)
jvm("desktop") // Optional, if targeting desktop or web
sourceSets {
val commonMain by getting {
dependencies {
// Common dependencies can be declared here.
implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.4")
}
}
val androidMain by getting
val iosMain by getting
}
}
android {
compileSdk = 33
sourceSets["main"].manifest.srcFile("src/androidMain/AndroidManifest.xml")
}This configuration sets up the common module and the platform-specific source sets.
Step 2: Write Shared Code
Create a Kotlin file in commonMain (e.g., Greeting.kt):
package com.example.shared
fun getGreeting(): String = “Hello from Kotlin Multiplatform!”
This simple function is now accessible on every platform.
Step 3: Platform-Specific Implementation
While our getGreeting() function works across platforms, you can also use the expect/actual mechanism. For instance, if you need to access platform-specific functionality (like reading the device model), you can define an expected function:
In commonMain:
package com.example.shared
expect fun getPlatformName(): String
fun greetPlatform(): String {
return "Hello from ${getPlatformName()} using Kotlin Multiplatform!"
}
In androidMain:
package com.example.shared
actual fun getPlatformName(): String {
return "Android"
}
In iosMain (Swift interop):
package com.example.shared
import platform.UIKit.UIDevice
actual fun getPlatformName(): String {
return UIDevice.currentDevice.systemName() // Typically "iOS"
}Now, when you call greetPlatform(), it will return “Hello from Android using Kotlin Multiplatform!” on Android and “Hello from iOS using Kotlin Multiplatform!” on iOS.
Step 4: Integrating with Your Platform
- On Android:
Include your shared module as a dependency in your Android project, and call getGreeting() from an Activity or Fragment.
// In an Android Activity
import com.example.shared.getGreeting
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
val greeting = getGreeting()
findViewById<TextView>(R.id.greetingTextView).text = greeting
}
}- On iOS:
Use the Kotlin/Native framework generated from your shared module. With Xcode, import the generated framework and call getGreeting() in Swift.
import Shared
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
let greeting = Greeting().getGreeting()
greetingLabel.text = greeting
}
}- On the Web:
Kotlin Multiplatform also supports JavaScript targets. Although web support is evolving, you can compile shared logic to JavaScript and integrate with your web application using frameworks like React.
Challenges and Best Practices
While Kotlin Multiplatform offers many advantages, developers may face several challenges:
- Tooling and Debugging:
As a relatively new paradigm, IDE support and debugging tools are still evolving. Use IntelliJ IDEA and Android Studio with the latest Kotlin plugins for the best experience. - Platform-Specific Limitations:
Some APIs are inherently platform-specific, so not all code can be shared. Use the expect/actual pattern to clearly delineate shared vs. platform-specific code. - Gradual Adoption:
It’s best to start small by sharing a single module (such as network logic or data models) and gradually expand the shared codebase as you gain confidence. - Community and Resources:
Engage with the growing Kotlin Multiplatform community through forums, GitHub, and KotlinConf sessions. Microsoft, JetBrains, and early adopters are continuously sharing best practices and tools.
Best Practices:
- Modularize Your Code:
Keep your business logic, models, and utilities in the shared module to maximize reusability. - Isolate UI Code:
Keep UI code platform-specific to fully leverage native controls and design paradigms. - Test Thoroughly:
Use common tests in the shared module and platform-specific tests to ensure that your shared logic works as expected across platforms.
Future Trends in Kotlin Multiplatform
Kotlin Multiplatform is rapidly gaining traction. Future developments are expected to include:
- Enhanced IDE support and debugging tools for a smoother developer experience.
- Broader platform support (including more robust web targets and desktop applications).
- Deeper integration with popular frameworks (like Jetpack Compose for Android, SwiftUI for iOS, and modern JavaScript frameworks for web).
- Improved community libraries and tooling that further simplify cross-platform integration.
KMM is poised to become an essential part of any modern developer’s toolkit, enabling faster development cycles, consistent business logic, and a unified codebase across Android, iOS, and beyond.
Conclusion
Kotlin Multiplatform is a game-changer for cross-platform development. It allows developers to write shared business logic once and deploy it across Android, iOS, and web platforms while keeping the user interface native to each environment. This results in reduced development time, improved maintainability, and a consistent experience across devices.
Embracing Kotlin Multiplatform means joining a growing community and staying ahead of the curve in modern development practices. Whether you’re building a new app from scratch or looking to gradually share code in an existing project, KMM offers the flexibility and power to create robust, scalable, and high-performance applications.
As you explore KMM, remember that starting small, focusing on shared modules, and gradually expanding your code sharing will yield the best results. The future of cross-platform development is here—write once, run anywhere, and unlock the true potential of your applications with Kotlin Multiplatform.
Looking for an efficient way to develop mobile apps for Android, iOS, and Web? Kotlin Multiplatform (KMM) allows you to write code once and reuse it across platforms, reducing development time and costs while maintaining native performance. At 200OK Solutions, we specialize in KMM-based app development, helping businesses build scalable and high-performance apps.
