Building Your First Kotlin Multiplatform App: From Setup to iOS App Store with Compose Multiplatform (2025 Guide)

# Option 1: Using the KMP wizard (Recommended)
# Visit: https://kmp.jetbrains.com/
# Configure: Android + iOS + Compose Multiplatform

# Option 2: Android Studio
# New Project > Kotlin Multiplatform > Mobile Application

[versions]
kotlin = "2.1.21"
composeMultiplatform = "1.8.2"
sqlDelight = "2.0.2"
kotlinx-datetime = "0.6.0"
uuid = "0.8.4"

[libraries]
# SQLDelight for cross-platform database
sqlDelight-driver-android = { module = "app.cash.sqldelight:android-driver", version.ref = "sqlDelight" }
sqlDelight-driver-native = { module = "app.cash.sqldelight:native-driver", version.ref = "sqlDelight" }
sqlDelight-runtime = { module = "app.cash.sqldelight:runtime", version.ref = "sqlDelight" }
sqlDelight-coroutines = { module = "app.cash.sqldelight:coroutines-extensions", version.ref = "sqlDelight" }

# Cross-platform utilities
kotlinx-datetime = { module = "org.jetbrains.kotlinx:kotlinx-datetime", version.ref = "kotlinx-datetime" }
uuid = { module = "com.benasher44:uuid", version.ref = "uuid" }

[plugins]
sqlDelight = { id = "app.cash.sqldelight", version.ref = "sqlDelight" }

📱 Presentation Layer (UI)
├── 🎨 components/     # Reusable UI components
├── 📄 screens/        # Screen-level composables  
└── 🎭 theme/          # Material Design theme

💼 Domain Layer (Business Logic)
├── 📋 usecase/        # Business use cases
└── 📄 repository/     # Repository interfaces

💾 Data Layer (Data Management)  
├── 🗄️ local/          # SQLDelight database
├── 📊 repository/     # Repository implementations
└── 🔄 model/          # Data models

-- Subscription table with proper indexing for performance
CREATE TABLE subscription (
    id TEXT NOT NULL PRIMARY KEY,
    name TEXT NOT NULL,
    cost REAL NOT NULL,
    currency_code TEXT NOT NULL,
    billing_cycle TEXT NOT NULL,
    next_payment_date INTEGER NOT NULL,
    is_active INTEGER NOT NULL DEFAULT 1,
    created_at INTEGER NOT NULL,
    updated_at INTEGER NOT NULL,
    notes TEXT,
    FOREIGN KEY (currency_code) REFERENCES currency(code)
);

-- Performance indexes for common queries
CREATE INDEX idx_subscription_active ON subscription(is_active);
CREATE INDEX idx_subscription_next_payment ON subscription(next_payment_date);

-- Query: Get all subscriptions with currency info
selectAll:
SELECT
    s.*,
    c.symbol AS currency_symbol,
    c.name AS currency_name,
    c.exchange_rate_to_usd
FROM subscription s
JOIN currency c ON s.currency_code = c.code
ORDER BY s.next_payment_date ASC;

-- Query: Get only active subscriptions
selectActive:
SELECT
    s.*,
    c.symbol AS currency_symbol,
    c.name AS currency_name,
    c.exchange_rate_to_usd
FROM subscription s
JOIN currency c ON s.currency_code = c.code
WHERE s.is_active = 1
ORDER BY s.next_payment_date ASC;

-- Insert new subscription
insertSubscription:
INSERT INTO subscription (
    id, name, cost, currency_code, billing_cycle,
    next_payment_date, is_active, created_at, updated_at, notes
) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?);

-- Analytics query for monthly cost calculations
selectTotalMonthlyCostByActive:
SELECT
    s.currency_code,
    c.symbol AS currency_symbol,
    c.exchange_rate_to_usd,
    SUM(
        CASE
            WHEN s.billing_cycle = 'WEEKLY' THEN s.cost * 4.33
            WHEN s.billing_cycle = 'MONTHLY' THEN s.cost
            WHEN s.billing_cycle = 'QUARTERLY' THEN s.cost / 3.0
            WHEN s.billing_cycle = 'SEMI_ANNUALLY' THEN s.cost / 6.0
            WHEN s.billing_cycle = 'ANNUALLY' THEN s.cost / 12.0
            ELSE s.cost
        END
    ) AS monthly_cost
FROM subscription s
JOIN currency c ON s.currency_code = c.code
WHERE s.is_active = ?
GROUP BY s.currency_code, c.symbol, c.exchange_rate_to_usd;

# Android
./gradlew compileDebugKotlinAndroid    # Compile Android code
./gradlew installDebug                 # Install on device/emulator

# iOS (compilation check)
./gradlew compileKotlinIosX64         # Compile iOS code
./gradlew linkDebugFrameworkIosX64    # Link iOS framework

# All platforms
./gradlew build                       # Build all targets

# SQLDelight
./gradlew generateCommonMainKyklosDatabaseInterface

# Clean build
./gradlew clean build

# Build the iOS framework
./gradlew linkDebugFrameworkIosX64

# Navigate to iOS app directory
cd iosApp

# Open in Xcode
open iosApp.xcodeproj

# Clean and rebuild framework
./gradlew clean
./gradlew linkDebugFrameworkIosX64

# Reset simulator
xcrun simctl erase all
xcrun simctl boot "iPhone 15"