android-kmp-shared

name	android-kmp-shared
description	Use when building Kotlin Multiplatform (KMP) shared modules, integrating with iOS, or sharing business logic across platforms.
category	architecture
risk	low
source	community
date_added	2026-03-31
metadata	{"triggers":["@kmp","kotlin-multiplatform","common-main","shared-module","expect-actual"]}

Android Kotlin Multiplatform (KMP) 🌍🤝

Professional patterns for sharing code between Android and iOS using the next-generation Kotlin Multiplatform technology.

⚡ When to Use

• Shared Business Logic: Centralizing ViewModels, Use Cases, and Domain Models.
• Data Layer Sharing: Using Ktor (Network) and SQLDelight (Database) across platforms.
• Modularization: Creating a cross-platform library module.
• Migration: Moving from 100% native to shared logic.
• Validation: Building one logic for both apps (e.g., Auth, Calculations).

🏗️ The Multiplatform Architecture

• commonMain: The heart of the app. Pure Kotlin code shared by all platforms.
• androidMain: Platform-specific implementation for Android.
• iosMain: Platform-specific implementation for iOS (via Kotlin/Native).

🛠️ Essential Shared Tools

1. Ktor (Networking)

• Benefit: Async, multiplatform HTTP client.
• Use ContentNegotiation and Serialization for shared DTOs.

2. SQLDelight (Local Persistence)

• Benefit: Type-safe SQL queries that generate Kotlin code.
• Shared schema, platform-specific drivers (SQLite for Android, Native for iOS).

3. Koin (Dependency Injection)

• Benefit: Simple and lightweight DI that works across commonMain.

4. kotlinx-datetime

• Use for consistent date/time logic without platform-specific issues (java.time vs NSDate).

🚀 The expect / actual Pattern

• Use for platform-specific APIs when no shared library exists.
• Rule: Avoid expect/actual if a shared library is available.
• Bad: expect fun getPlatformName(): String
• Good: Use interfaces and DI to provide platform-specific implementations.

🏁 Shared Logic Workflow

• ViewModel Sharing: Use multiplatform-viewmodel library for consistent lifecycle mapping.
• State Management: Use StateFlow in commonMain to expose UI state.
• iOS Interoperability: Be aware of Swift/Kotlin memory management and @ObjCName for clean iOS APIs.

📦 Gradle Configuration

kotlin {
    androidTarget()
    iosX64()
    iosArm64()
    iosSimulatorArm64()

    sourceSets {
        commonMain.dependencies {
            implementation("io.ktor:ktor-client-core:2.3.0")
        }
    }
}

🧪 Testing with KMP

• Tests in commonTest run on both Android and iOS targets.
• Use kotlin.test for standard assertions (assertTrue, assertEquals).
• Mocking: Use libraries like Mockative or KMock for multiplatform mocking.

🔗 Related Resources

• KMP Official Guide
• KMP Samples (By JetBrains)
• Clean Architecture Skill