playbook/antigravity-awesome-skills/skills/expo-brownfield/references/brownfield-isolated.md

Brownfield: Isolated Approach

Build the React Native + Expo code as a prebuilt native library, AAR on Android and XCFramework on iOS, and consume it from the existing native app like any other dependency.

When to use

• Native and React Native are owned by different teams or release on different cadences.
• The native team must not be required to install Node.js, Yarn, or React Native tooling.
• React Native code lives in a separate repo or monorepo from the native app.
• You want the smallest possible footprint on the existing native build pipeline.

If a single team owns both layers, is comfortable with React Native tooling and needs deep integration, see ./brownfield-integrated.md.

What you produce

Platform	Artifact	Default location
Android	{group}:{libraryName}:{version} AAR	Local Maven (~/.m2) by default; remote Maven also supported
iOS	Set of .xcframeworks — see the iOS section below for how ios.buildReactNativeFromSource (default false on SDK 56+) controls whether you get 5 frameworks or 2 — or a single Swift Package via --package	./artifacts

The JavaScript bundle is embedded inside the artifact in release builds, so the native app does not need Metro at runtime in production.

Prerequisites

• Expo SDK 55 or later — brownfield support, expo-brownfield, and the required runtime classes are only available on SDK 55+. Earlier SDKs will not work.
• Node.js (LTS) — runs JavaScript and the Expo CLI.
• Yarn — manages JavaScript dependencies.

Node and Yarn are only needed in the environment that builds the artifact. The consuming native app does not need them.

---

1) Set up the Expo project

Create a new Expo project

npx create-expo-app@latest my-project --template default@sdk-55

Pin to SDK 55 or later — earlier SDKs do not support brownfield. The project can live in a separate repo or alongside the native app in a monorepo; it does not need to be inside the native project.

Install expo-brownfield

cd my-project
npx expo install expo-brownfield

The plugin self-registers in app.json with defaults derived from your app config.

Configure the plugin (optional)

To override the auto-generated names, expand the plugin entry in app.json:

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

iOS options — targetName (XCFramework target name), bundleIdentifier (framework bundle ID).

Android options — libraryName (AAR name), group (Maven group ID), package (Android package), version (library version), publishing (Maven publication targets — see Publishing the Android AAR).

Speed up iOS builds with prebuilt Expo modules

Enable expo-build-properties's ios.usePrecompiledModules so pod install downloads each Expo module as a prebuilt .xcframework instead of compiling it from source. build:ios detects those xcframeworks under ios/Pods/ and bundles them into the Swift Package output alongside the brownfield framework, React, Hermes, and ReactNativeDependencies.

{
  "expo": {
    "plugins": [
      ["expo-build-properties", { "ios": { "usePrecompiledModules": true } }],
      "expo-brownfield"
    ]
  }
}

When precompiled modules are detected, build:ios is pinned to a single flavor (--debug or --release) per package — Swift Package Manager has no per-configuration overload for .binaryTarget(path:). Build once per flavor and distribute the two packages side by side.

---

2) Build the native libraries

Android

npx expo-brownfield build:android

Produces an AAR and publishes it to the local Maven repository at ~/.m2. The Maven coordinates come from the plugin config — e.g. com.example:mybrownfield:1.0.0.

Publishing the Android AAR

The plugin's publishing option controls where the AAR is published. When unset, it defaults to local Maven. To push to other targets (e.g. a shared CI Maven, an internal Artifactory/Nexus, or a folder pulled into another build), declare the publications explicitly:

{
  "expo": {
    "plugins": [
      [
        "expo-brownfield",
        {
          "android": {
            "libraryName": "mybrownfield",
            "group": "com.example",
            "version": "1.0.0",
            "publishing": [
              { "type": "localMaven" },
              {
                "type": "localDirectory",
                "name": "build",
                "path": "./out/maven"
              },
              {
                "type": "remotePublic",
                "name": "company",
                "url": "https://maven.example.com/releases"
              },
              {
                "type": "remotePrivate",
                "name": "artifactory",
                "url": { "variable": "ARTIFACTORY_URL" },
                "username": { "variable": "ARTIFACTORY_USER" },
                "password": { "variable": "ARTIFACTORY_TOKEN" }
              }
            ]
          }
        }
      ]
    ]
  }
}

Supported type values: localMaven, localDirectory, remotePublic, remotePrivate. For private repos, credentials and URL accept either inline strings or { "variable": "ENV_VAR_NAME" } to read from the environment at publish time.

By default, build:android runs every declared publication. To pick specific publications or repositories from the command line, use the CLI flags:

npx expo-brownfield build:android --task publishReleasePublicationToCompanyRepository
npx expo-brownfield tasks:android   # list available publish tasks and repositories

iOS

npx expo-brownfield build:ios

Outputs to ./artifacts. The set depends on the ios.buildReactNativeFromSource flag (set via expo-build-properties):

• buildReactNativeFromSource: false (default on SDK 56+) — React Native is consumed as a prebuilt binary, so build:ios emits five xcframeworks side-by-side: {TargetName}.xcframework, React.xcframework, ReactNativeDependencies.xcframework, ExpoModulesJSI.xcframework, and hermesvm.xcframework.
• buildReactNativeFromSource: true (default on SDK 55, opt-in on SDK 56+) — React Native is compiled from source and statically linked into the brownfield framework, leaving two xcframeworks: {TargetName}.xcframework and hermesvm.xcframework.

To force source builds on SDK 56+, add expo-build-properties to app.json:

{
  "expo": {
    "plugins": [
      ["expo-build-properties", { "ios": { "buildReactNativeFromSource": true } }],
      "expo-brownfield"
    ]
  }
}

Every xcframework in the produced set must be embedded in the consuming app (Embed & Sign). The Swift Package output below (--package) wires this for you automatically.

iOS deployment target: the brownfield artifact inherits the Expo project's iOS deployment target (16.4 on SDK 56+). The consuming app's deployment target must be set to 16.4 or higher; otherwise Xcode will refuse to link the embedded frameworks. If the host app is on an older floor (e.g. iOS 14.0), bump its IPHONEOS_DEPLOYMENT_TARGET before adding the artifact.

Ship as a Swift Package (recommended)

Pass --package [name] to bundle the output as a self-contained Swift Package instead of separate .xcframework directories. The host iOS app then consumes it via Add Package Dependencies → Add Local in Xcode and links every bundled framework automatically — no manual drag-and-drop, no per-framework "Embed & Sign" toggles.

npx expo-brownfield build:ios --release --package MyAppPackage

The flag accepts an optional name. If omitted, the package is named {TargetName}Artifacts. The resulting directory is a complete Swift Package:

artifacts/MyAppPackage/
├── Package.swift
└── xcframeworks/
    ├── MyAppPackage.xcframework
    ├── hermesvm.xcframework
    ├── React.xcframework
    └── ReactNativeDependencies.xcframework

When usePrecompiledModules is enabled, the package directory is suffixed with the build flavor (e.g. MyAppPackage-release/) and includes every prebuilt Expo module xcframework. Run build:ios --debug --package … and build:ios --release --package … separately, and point your host app at the matching package for each build configuration.

Generate native projects for debugging

To inspect or debug the generated native code, run prebuild:

npx expo prebuild

This creates android/ and ios/ directories containing the brownfield wrappers:

Android (Kotlin): ReactNativeHostManager, BrownfieldActivity, ReactNativeFragment, ReactNativeViewFactory, BrownfieldMessaging.

iOS (Swift): ReactNativeHostManager, ReactNativeViewController, ReactNativeView (SwiftUI), BrownfieldMessaging, ReactNativeDelegate.

---

3) Consume from the native app

Android

Add the Maven dependency

In app/build.gradle.kts:

dependencies {
  implementation("com.example:mybrownfield:1.0.0")
}

If consuming from the local Maven repo, register mavenLocal() in settings.gradle.kts:

dependencyResolutionManagement {
  repositories {
    google()
    mavenCentral()
    mavenLocal()
  }
}

Note: mavenLocal() must be added under dependencyResolutionManagement, not the deprecated top-level allprojects { repositories { ... } } block.

If the artifact is published to a remote Maven, declare that repository in the same dependencyResolutionManagement block instead — credentials follow Gradle's standard maven { url = uri(...); credentials { username = ...; password = ... } } form.

Show a React Native screen

Extend BrownfieldActivity and call showReactNativeFragment():

import android.os.Bundle
import com.example.mybrownfield.BrownfieldActivity
import com.example.mybrownfield.showReactNativeFragment

class ExpoActivity : BrownfieldActivity() {
  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    showReactNativeFragment()
  }
}

BrownfieldActivity extends AppCompatActivity and forwards configuration changes. showReactNativeFragment() registers the React Native root fragment and wires native back-button handling automatically.

Register the activity in AndroidManifest.xml:

<activity
  android:name=".ExpoActivity"
  android:theme="@style/Theme.AppCompat.Light.NoActionBar"
  android:configChanges="keyboard|keyboardHidden|orientation|screenLayout|screenSize|smallestScreenSize|uiMode"
/>

Launch it from native code:

startActivity(Intent(this, ExpoActivity::class.java))

iOS

Add the artifacts to the Xcode project

If you built a Swift Package (build:ios --package …):

• In Xcode, File → Add Package Dependencies… → Add Local…, then select the generated package directory (e.g. artifacts/MyAppPackage/).
• Add the package's product to your app target. Xcode links every bundled XCFramework through the aggregate library product — no manual "Embed & Sign" step.
• If you produced both debug and release packages (because usePrecompiledModules is enabled), point the host app at the matching package per build configuration.

If you built standalone XCFrameworks (default output):

• Drag every .xcframework produced under ./artifacts into the Xcode project navigator.
• In the import dialog, check Copy items if needed and add them to your app target.
• Under the app target's General tab → Frameworks, Libraries, and Embedded Content, set every framework to Embed & Sign. Forgetting one (commonly hermesvm.xcframework) is a leading cause of runtime "Library not loaded" crashes — see ./troubleshooting.md.

Initialize React Native at app launch

Call ReactNativeHostManager.shared.initialize() from AppDelegate before any React Native view is created. Initialization is asynchronous-friendly but must precede the first ReactNativeViewController/ReactNativeView instantiation.

import UIKit
import MyAppBrownfield // Replace with your target name

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
  func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
  ) -> Bool {
    ReactNativeHostManager.shared.initialize()
    return true
  }
}

Present a React Native view (UIKit)

import UIKit
import MyAppBrownfield

class ViewController: UIViewController {
  @IBAction func openReactNative(_ sender: Any) {
    let rnViewController = ReactNativeViewController(moduleName: "main")
    navigationController?.pushViewController(rnViewController, animated: true)
  }
}

Pass props and launch options if needed:

let rnViewController = ReactNativeViewController(
  moduleName: "main",
  initialProps: ["userId": "123"],
  launchOptions: [:]
)

Note: moduleName must match the name registered via AppRegistry.registerComponent(...) in the Expo project's JS entry point. The default Expo template registers "main".

Present a React Native view (SwiftUI)

import SwiftUI
import MyAppBrownfield

struct ContentView: View {
  @State private var showReactNative = false

  var body: some View {
    Button("Open React Native") {
      showReactNative = true
    }
    .fullScreenCover(isPresented: $showReactNative) {
      ReactNativeView(moduleName: "main")
    }
  }
}

---

Development vs. production

Development (debug builds)

Start Metro in the Expo project:

npx expo start

Build and run the native app in debug. React Native screens load JS from the Metro dev server over HTTP with full hot reloading. The device or emulator must be able to reach the dev machine — see ./troubleshooting.md if Metro connections fail.

Production (release builds)

The JS bundle is embedded inside the AAR/XCFramework. Metro is not used. Build the native app in Release configuration and confirm the React Native screen loads.

---

Related references

• ./brownfield-integrated.md — Alternative: add RN directly to the native build.
• ./comparison.md — Decide between isolated and integrated.
• ./troubleshooting.md — Common Metro, build, and integration issues.