How to Create a React Native SDK: A Comprehensive Guide

React Native is a popular framework for building mobile applications, combining the best parts of native development with the flexibility of React. As React Native grows in popularity, the need for reusable libraries or SDKs (Software Development Kits) becomes important for developers looking to share functionality across multiple applications. In this blog, we'll explore the steps involved in creating a React Native SDK, from setting up the project to distributing it for others to use.

Why Create an SDK for React Native?
An SDK allows developers to encapsulate functionality into reusable packages that can be shared across multiple applications. This reduces redundancy and ensures that updates or changes to core logic can be implemented across all applications seamlessly. Use cases for React Native SDKs include:

Handling payments
Implementing analytics and tracking
Managing authentication
Abstracting complex business logic or UI components

Steps to Create a React Native SDK

1. Set Up the Project

Before you can create an SDK, you need to set up a React Native project that will serve as the foundation for your SDK.

1.1. Install React Native CLI
First, ensure that you have React Native CLI installed:

npm install -g react-native-cli

1.2. Create a New React Native Project
Create a new project where you’ll develop your SDK:

npx react-native init MySDK

Navigate to your project directory:

cd MySDK

2. Setup TypeScript (Optional but Recommended)
TypeScript helps with type safety and improves the development experience. To add TypeScript to your React Native SDK:

npm install --save-dev typescript @types/react @types/react-native

Then rename your .js files to .ts or .tsx and create a tsconfig.json file:

{
  "compilerOptions": {
    "target": "es5",
    "module": "commonjs",
    "strict": true,
    "jsx": "react-native",
    "esModuleInterop": true,
    "skipLibCheck": true,
    "forceConsistentCasingInFileNames": true
  },
  "exclude": ["node_modules"]
}

3. Create Reusable Modules
The core of your SDK will be reusable components or modules. Depending on what functionality your SDK provides, you may need to create native modules (for Android/iOS) or JavaScript components.
3.1. Create a Native Module
React Native allows you to write native code for Android and iOS that interacts with JavaScript. Let’s create a simple native module.

iOS
Create a new Objective-C or Swift file in the ios/ directory (for this example, we’ll use Objective-C):

1. Go to ios/MySDK and add a new file called MyModule.m:

#import "React/RCTBridgeModule.h"

@interface RCT_EXTERN_MODULE(MyModule, NSObject)
RCT_EXTERN_METHOD(sayHello:(RCTPromiseResolveBlock)resolve rejecter:(RCTPromiseRejectBlock)reject)
@end

2.In MyModule.swift, implement the native functionality:

@objc(MyModule)
class MyModule: NSObject {
  @objc
  func sayHello(_ resolve: @escaping RCTPromiseResolveBlock, rejecter reject: @escaping RCTPromiseRejectBlock) {
    resolve("Hello from iOS Native Module!")
  }
}

For Android, you will create a new Java/Kotlin module:

1.Create a new file under android/app/src/main/java/com/mysdk/ called MyModule.java:

package com.mysdk;

import com.facebook.react.bridge.ReactApplicationContext;
import com.facebook.react.bridge.ReactContextBaseJavaModule;
import com.facebook.react.bridge.ReactMethod;
import com.facebook.react.bridge.Promise;

public class MyModule extends ReactContextBaseJavaModule {

    public MyModule(ReactApplicationContext reactContext) {
        super(reactContext);
    }

    @Override
    public String getName() {
        return "MyModule";
    }

    @ReactMethod
    public void sayHello(Promise promise) {
        promise.resolve("Hello from Android Native Module!");
    }
}

3.2. Export Native Modules to JavaScript
You’ll need to bridge your native code to JavaScript.

In index.js, export the native module like this:

import { NativeModules } from 'react-native';

const { MyModule } = NativeModules;

export const sayHello = async () => {
  try {
    const message = await MyModule.sayHello();
    return message;
  } catch (error) {
    console.error(error);
  }
};

4. Create JavaScript Components
Not all functionality in your SDK needs to be written in native code. You can also create pure JavaScript components or hooks.

Here’s an example of a simple reusable button component:

import React from 'react';
import { TouchableOpacity, Text, StyleSheet } from 'react-native';

const MyButton = ({ title, onPress }) => {
  return (
    <TouchableOpacity style={styles.button} onPress={onPress}>
      <Text style={styles.text}>{title}</Text>
    </TouchableOpacity>
  );
};

const styles = StyleSheet.create({
  button: {
    backgroundColor: '#007BFF',
    padding: 10,
    borderRadius: 5,
  },
  text: {
    color: '#fff',
    textAlign: 'center',
  },
});

export default MyButton;

5. Publish Your SDK
Once your SDK is ready, it’s time to package and distribute it. You can publish it to npm so other developers can install and use it.

5.1. Prepare for Publishing
Update your package.json to include the necessary information:

{
  "name": "my-react-native-sdk",
  "version": "1.0.0",
  "main": "index.js",
  "react-native": "index.js",
  "author": "Your Name",
  "license": "MIT"
}

Make sure your .npmignore file excludes unnecessary files like build artifacts and node_modules.

5.2. Publish to npm
To publish your SDK, first login to npm:

npm login

Then publish your package:

npm publish

5.3. Install in Another Project
Once published, your SDK can be installed in any React Native project:

npm install my-react-native-sdk

Developers can then use it in their applications:

import { sayHello } from 'my-react-native-sdk';

const App = () => {
  useEffect(() => {
    sayHello().then(message => console.log(message));
  }, []);

  return <Text>Check the console for the message!</Text>;
};

6. Testing and Documentation
Testing your SDK across different environments (iOS, Android) is crucial. Use a combination of manual testing and automated tests (e.g., Jest, Detox) to ensure it works as expected.

In addition, providing comprehensive documentation is key to making your SDK easy for others to use. Document your SDK features, APIs, and provide examples.

Conclusion
Creating a React Native SDK involves setting up reusable components or modules that can be shared across multiple applications. By combining native code with JavaScript components, you can create a flexible and powerful SDK that serves different needs.

Whether you're creating a payment gateway SDK, analytics tool, or authentication system, following the steps outlined in this blog will help you build and distribute a React Native SDK effectively.