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expo-brownfield is a toolkit for adding React Native views to existing native Android and iOS applications. It provides:

• Built-in APIs for bi-directional communication and navigation between native and React Native apps
• Config plugin for automatic setup of brownfield targets in your Expo project
• CLI for building and publishing artifacts to Maven repositories (Android) and XCFrameworks (iOS)

Installation

If you are installing this in an existing React Native app, make sure to install expo in your project.

Usage

Communication API

The Communication API enables bi-directional, message-based communication between the native (host) app and React Native.

Sending messages from React Native to native

import * as Brownfield from 'expo-brownfield';

Brownfield.sendMessage({
  type: 'MyMessage',
  data: {
    language: 'TypeScript',
    expo: true,
    platforms: ['android', 'ios'],
  },
});

Receiving messages from native in React Native

import * as Brownfield, { type MessageEvent } from 'expo-brownfield';
import { useEffect } from 'react';

function MyComponent() {
  useEffect(() => {
    const handleMessage = (event: MessageEvent) => {
      console.log('Received message:', event);
    };

    Brownfield.addMessageListener(handleMessage);

    return () => {
      Brownfield.removeMessageListener(handleMessage);
    };
  }, []);

  // ...
}

Sending messages from native to React Native

import expo.modules.brownfield.BrownfieldMessaging

BrownfieldMessaging.sendMessage(mapOf(
    "type" to "MyAndroidMessage",
    "timestamp" to System.currentTimeMillis(),
    "data" to mapOf(
        "platform" to "android"
    )
))

import ExpoBrownfield

BrownfieldMessaging.sendMessage([
    "type": "MyIOSMessage",
    "timestamp": Date().timeIntervalSince1970,
    "data": [
        "platform": "ios"
    ]
])

Receiving messages from React Native in native

import expo.modules.brownfield.BrownfieldMessaging

val listenerId = BrownfieldMessaging.addListener { event ->
    println("Message from React Native: $event")
}

// Later, to remove the listener:
BrownfieldMessaging.removeListener(listenerId)

import ExpoBrownfield

let listenerId = BrownfieldMessaging.addListener { message in
    print("Message from React Native: \(message)")
}

// Later, to remove the listener:
BrownfieldMessaging.removeListener(id: listenerId)

Configuration in app config

The expo-brownfield package provides a config plugin that can be used to configure the brownfield integration when using Continuous Native Generation (CNG). This plugin allows you to customize how your Expo project is packaged and integrated into your existing native app.

Example app.json with config plugin

{
  "expo": {
    "plugins": [
      [
        "expo-brownfield",
        {
          "ios": {
            "targetName": "MyBrownfieldTarget",
            "bundleIdentifier": "com.example.brownfield"
          },
          "android": {
            "group": "com.example",
            "libraryName": "brownfield",
            "package": "com.example.brownfield",
            "version": "1.0.0"
          }
        }
      ]
    ]
  }
}

Configurable properties

CLI

The expo-brownfield library includes a CLI for building and publishing to Maven repositories (Android) and XCFrameworks (iOS).

Commands

build:android

Builds and publishes the brownfield library and its dependencies to Maven repositories.

build:ios

Builds the brownfield XCFramework and copies the Hermes XCFramework to the artifacts directory.

tasks:android

Lists all available publish tasks and Maven repositories.

API

import * as Brownfield from 'expo-brownfield';

Hooks

Methods

Event subscriptions

const subscription = addMessageListener((event) => {
  console.log('Received message from native:', event);
});

// Later, to remove the listener:
subscription.remove();

Interfaces

Types