16. Custom Native Module Development: Writing Swift/Kotlin Native Code for React Native • React Native: Cross-Platform Mobile Engineering • Rishabh Ki Kaksha

React Native: Cross-Platform Mobile Engineering › 16. Custom Native Module Development: Writing Swift/Kotlin Native Code for React Native

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Course Syllabus

Module 1: React Native Internals, Bridge vs JSI Architecture

01. React Native Evolution: The Legacy Bridge Architecture vs The New Architecture (TurboModules & Fabric) 02. JavaScript Interface (JSI), Hermes JS Engine & C++ Shared Memory Integration 03. Expo Bare Workflow vs React Native CLI: When to Use What in Big Tech

Module 2: Core Components, Flexbox & Responsive Mobile Layouts

04. Core Primitives: View, Text, Image, ScrollView & High-Performance FlatList/FlashList Optimization 05. Mobile Flexbox Mastery: SafeAreaView, Dimensions, PixelRatio & Multi-Screen Scaling 06. Keyboard Handling Architecture: KeyboardAvoidingView & Input Accessories

Module 3: React Navigation 6/7 & Native Stack Architecture

07. React Navigation: Native Stack Navigator vs Stack Navigator Performance Differences 08. Bottom Tabs, Material Top Tabs & Drawer Navigation Nested Routing 09. Deep Linking & Universal Links (iOS Associated Domains & Android App Links)

Module 4: 60FPS Native Animations: Reanimated 3 & Gesture Handler

10. The Native Animation Thread: Animated API vs React Native Reanimated 3 Worklets 11. Complex Gesture Interactions with React Native Gesture Handler (Pan, Pinch, Fling) 12. Shared Element Transitions & Interactive Drag-to-Dismiss Bottom Sheets

Module 5: Offline Storage, SQLite, MMKV & Native Modules Bridging

13. High-Speed Local Storage: AsyncStorage vs MMKV (100x Faster Sync KV Store) 14. Offline-First Architecture: WatermelonDB / SQLite with Background Cloud Synchronization 15. Native Device Hardware Access: Camera, Geolocation, Biometrics (FaceID/Fingerprint) & Push Notifications 16. Custom Native Module Development: Writing Swift/Kotlin Native Code for React Native

Module 6: Mobile DevOps: EAS Build, OTA Updates & App Store/Play Store Release

17. Mobile App Performance Profiling: Flipper, React Native DevTools & Memory Leak Detection 18. Over-The-Air (OTA) Live Updates with EAS Update / CodePush Architecture 19. Mobile App Security: SSL Pinning, Secure Keystore Storage & Code Obfuscation (ProGuard) 20. Cloud CI/CD & App Store Deployment: Automated Builds with EAS Build & Fastlane Automation

Interactive Lesson Studio

# 16. Custom Native Module Development: Writing Swift/Kotlin Native Code for React Native

> React Native Notes by Rishabh - Topic 16

---

### 1. The Modern TurboModule Architecture (C++ Codegen ⚙️)

Naye React Native architecture me TypeScript interface se C++ bindings auto-generate hoti hain (`Codegen`):

```typescript
// Spec file: NativeBatterySpec.ts
import type { TurboModule } from 'react-native';
import { TurboModuleRegistry } from 'react-native';

export interface Spec extends TurboModule {
    getBatteryLevel(): Promise<number>;
    multiply(a: number, b: number): number; // Synchronous Native C++ call!
}

export default TurboModuleRegistry.getEnforcing<Spec>('NativeBattery');
```

---

### 2. Native Kotlin Implementation (Android)

```kotlin
package com.rishabhkaksha

import com.facebook.react.bridge.ReactApplicationContext
import com.facebook.react.bridge.Promise
import android.os.BatteryManager
import android.content.Context

class NativeBatteryModule(reactContext: ReactApplicationContext) : NativeBatterySpec(reactContext) {
    override fun getName() = "NativeBattery"

override fun getBatteryLevel(promise: Promise) {
        val bm = reactApplicationContext.getSystemService(Context.BATTERY_SERVICE) as BatteryManager
        val level = bm.getIntProperty(BatteryManager.BATTERY_PROPERTY_CAPACITY)
        promise.resolve(level)
    }

override fun multiply(a: Double, b: Double): Double {
        return a * b
    }
}
```

---

### 3. Master Comparison Matrix

---

### 4. Interview Ke 3 Sawal Is Topic Se

1. **JSI (JavaScript Interface) TurboModules ko fast kaise banata hai?** -> JavaScript engine C++ Host Objects ke pointers ko directly invoke karta hai bina JSON stringify/parse kiye.
2. **Swift Native Module ko Objective-C / React Native runtime ke sath expose karne ke liye kya zaroori hota hai?** -> `@objc` attribute aur Objective-C bridging header (`RCT_EXTERN_MODULE`).
3. **Native UI Component (Fabric) aur Native Module (TurboModule) me kya difference hai?** -> TurboModule functional APIs provide karta hai (like battery level, encryption); Fabric component native visual views render karta hai (like custom video player).

---
**Next Topic:** 17. Mobile App Performance Profiling: Flipper, React Native DevTools & Memory Leak Detection

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Rishabh Gehlot

PHP 8+ & Laravel 11 Master Track