Demo app for React Europe lightning talk (Paris, May 2017), showing how to create reusable react-native components that can be consumed by existing Android applications that don't want to take a dependency on npm and associated infrastructure.

The Java code includes one sample native Android module. Here are some other such samples, for both Android and iOS.

While this sample is primarily Android-oriented, Tommy Nguyen has been kind enough to make the basic demo app run on macOS as well.

• Install Git
• Install Node.js
• Install Yarn
• Install Android Studio, following instructions on the React Native Getting Started page.
• From a shell with Node and Git in the path:
  • git clone https://github.com/petterh/react-europe-demo.git in the folder where you want the repository
  • cd react-europe-demo\DemoApp\reactnativedemolibrary
  • yarn (creates a node_modules folder)
• Open react-europe-demo\DemoApp in Android Studio
• Build and run the app module (debug, for now – emulator or device doesn't matter). You should see something like this:
  
• From a shell with Node and Git in the path, start the development server:
  • cd react-europe-demo\DemoApp\reactnativedemolibrary
  • yarn start
• Click the Open React Native Activity button. You should see something like this:
  

• Install Homebrew
• Install Node: brew install node watchman
• Install Yarn: brew install yarn
• Clone the repo: git clone https://github.com/petterh/react-europe-demo.git
• Install npm packages:

cd react-europe-demo\DemoApp\reactnativedemolibrary
yarn

• Open the Xcode project iOSHostApp/iOSHostApp.xcodeproj
• Make sure iOSHostApp scheme is selected, then click on build and run

The React Native watcher should automatically start before the app does. The app should look something like this:

Note: The host app currently can only be run in the simulator because it is hard-coded to load JavaScript from localhost.

This repository is structured as follows:

react-europe-demo
  |
  +-- DemoApp
  |     |
  |     +-- app
  |     |
  |     +-- reactnativedemolibrary
  |
  +-- Artifacts
  |
  +-- HostApp1
  |
  +-- HostApp2
  :
  |
  +-- HostApp_n
  |
  +-- iOSHostApp
        |
        +-- ReactFramework
        |
        +-- iOSHostApp
        |
        +-- iOSHostApp.xcodeproj

DemoApp is an Android Studio project with two modules:

• app: A test-bed application that depends on the reactnativedemolibrary module. This module isn't strictly necessary, but a great convenience.
• reactnativedemolibrary: A react-native library with some JavaScript and a Java native module. (TODO: Add a resource as well, such as an image.)
  • The JavaScript bundle;
  • any other assets, such as images;
  • a Maven POM holding the reactnativedemolibrary code;
  • a Maven POM holding the react-native code.

Artifacts contains reactnativedemolibrary artifacts to be consumed by the various host apps. (In real life this might be published as a maven artifact to Azure DevOps or similar.)

HostApp1 shows the HelloWorld JavaScript component in its own activity, just like DemoApp.

HostApp2 shows the HelloWorld JavaScript component hosted within a normal Android layout.

iOSHostApp is where the iOS app lives:

• ReactFramework: React Native library with a demo native module.
• iOSHostApp: Host app that embeds ReactFramework.
• iOSHostApp.xcodeproj: Xcode project for building both the framework and the host app.

Note that iOSHostApp contains two projects -- one provider and one consumer.

The demo app links in react-native via reactnativedemolibrary. In Getting started above, the JavaScript isn't bundled with the apk, but loaded from the dev server.

• For production, the JavaScript must be bundled into the apk, done via the react-native bundle command.
• We also need to pack up our code into something a host app can consume. For this we utilize a Gradle plugin called maven-publish to create a POM. Source
• Finally, we need to package react-native for host app consumption. Look for copyReactNativeTask in reactnativedemolibrary/build.gradle.

All three steps are invoked by the script create-artifacts.cmd (create-artifacts.sh on Mac). Run it from react-europe-demo\DemoAppto generate something like this:

react-europe-demo/Artifacts
  |
  +-- assets
  |     |
  |     +-- index.android.bundle
  |     +-- (additional non-essential files -- haven't gotten map to work (TODO))
  |
  +-- maven
  |     |
  |     +-- com
  |           +-- contoso
  |           |     |
  |           |     +-- react
  |           |           +-- reactnativedemolibrary
  |           |                 +-- 0.1
  |           |                 |     +-- reactnativedemolibrary-0.1.aar
  |           |                 |     +-- reactnativedemolibrary-0.1.pom
  |           |                 |     +-- (additional files)
  |           |                 +-- maven-metadata.xml
  |           |                 +-- (additional files)
  |           +-- facebook
  |           |     |
  |                 +-- react
  |                       +-- reactnativedemolibrary
  |                             +-- 0.44.0
  |                             |     +-- react-native-0.44.0.aar
  |                             |     +-- react-native-0.44.0.pom
  |                             |     +-- react-native-0.44.0-javadoc.jar
  |                             |     +-- react-native-0.44.0-sources.jar
  |                             |     +-- (additional files)
  |                             +-- maven-metadata.xml
  |                             +-- (additional files)
  +-- res (not yet used; intended for images)

Why do we package the react-native we got from npm into Artifacts/maven? After all, react-native is available from maven jcenter. The version is, however, quite old. There's an ongoing discussion whether to update it whenever a new version is released, or to remove it altogether. Either one is fine by me, but the current situation is just asking for trouble:

• React-Native Maven is no longer actively updated with releases
• Remove react-native package from maven central and jcenter

In other words, we really can't use the one currently available from jcenter. Bundling it ourselves has the added benefit of ensuring version consistency between react-native and our JavaScript code.

You need to

• reference reactnativedemolibrary;
• tweak build.gradle to include the JS assets;
• add a new Activity;
• potentially ensure you don't generate an .apk referencing 64-bit libraries.

Once that's done, you can just run the host app, and everything should work.

Add a maven url build.gradle, pointing it to wherever your artifacts reside:

allprojects {
    repositories {
        jcenter()
        ...
        maven {
            // Get reactnativedemolibrary and react-native from here
            url "$rootDir/../Artifacts/maven"
        }
    }
}

While copying the JS bundle manually is always an option, getting Gradle to do it for you is better:

task copyAssets(type: Copy) {
    from "$rootDir/../Artifacts/assets"
    into "src/main/assets"
}

afterEvaluate {
    android.applicationVariants.all { variant ->
        variant.javaCompiler.dependsOn(copyAssets)
    }
}

Sources:

• Gradle Copy class
• Run task before compilation using Android Gradle plugin

Create an Activity to host the react-native view:

public class ReactActivity1 extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        View view = ReactNativeDemoLibrary.start(this, false);
        setContentView(view);
    }
}

Host app #2 displays the HelloWorld component alongside other Android Views.

React Native introduced 64-bits support for Android in release 0.59.

In earlier versions, any host app may need to add something like this to build.gradle:

android {
    ...
    defaultConfig {
        ...
        ndk {
            abiFilters "armeabi-v7a", "x86"
        }
    }
}

The various Android apps explicitly call SoLoader.init because of this issue. I have a PR to fix it. Once this is in (assuming Facebook accepts it) I'll remove them.