Integrating a C++ Library into Your React Native Project

Using native code, especially C++, can be an excellent way to enhance your React Native app by leveraging performance-critical logic or existing C++ libraries. This guide will walk you through setting up a C++ library in a React Native project using a development build.

Requirements

Before you start, make sure you have the following:

• React Native CLI installed (since the managed Expo Go app does not support custom native code).
• Development Build configuration for Expo, if you’re using Expo.
• A basic understanding of JNI (Java Native Interface) if you’re working with Android, or bridging concepts if you’re working with iOS.

Step 1: Set Up Your React Native Project

First, create a new React Native project (if you haven’t already):

npx react-native init MyApp
cd MyApp        

For Expo projects, you would need to create a development build. Check Expo’s Development Build Documentation for details.

Step 2: Add Your C++ Library

1. Create a New Folder for Native Code: Inside your project, add a folder for the C++ files, e.g., cpp/.
2. Add Your C++ Code: Inside the cpp/ folder, create a C++ file (e.g., MyLibrary.cpp). This file will contain the native code you want to use in React Native.

Step 3: Configure Android to Use the C++ Library

1. Update build.gradle: Add NDK support in your Android project if not enabled. Open android/app/build.gradle and add the following under defaultConfig:
2. Configure CMake: Create a CMakeLists.txt file in your project’s root directory or the cpp/ directory.
3. Update Android Native Code Bridge: To expose this method to JavaScript, create a native module. Add a new file, MyModule.java, in android/app/src/main/java/com/myapp/:

Step 4: Write the JavaScript Bridge

1. In your React Native code, create a JavaScript file to wrap the native module:
2. Now, you can use addNumbers in your React Native code:

Step 5: Build and Run Your App

Finally, you need to rebuild the Android project to link the native code:

cd android
./gradlew clean
cd ..
npx react-native run-android        

If using Expo with development builds, make sure your build reflects these changes. For more details, refer to Expo’s Development Builds documentation.

With this setup, you’ve successfully integrated a C++ library in your React Native project, enabling you to call native C++ functions directly from JavaScript. This opens up possibilities for using optimized C++ code, accessing hardware-accelerated libraries, or reusing existing C++ code in your React Native app.