Integration With Existing Apps #

This section will be updated shortly showing an integration into a more real world application such as the 2048 app that was used for Objective-C and Swift.

Key Concepts #

React Native is great when you are starting a new mobile app from scratch. However, it also works well for adding a single view or user flow to existing native applications. With a few steps, you can add new React Native based features, screens, views, etc.

The keys to integrating React Native components into your iOS application are to:

1. Understand what React Native components you want to integrate.
2. Create a Podfile with subspecs for all the React Native components you will need for your integration.
3. Create your actual React Native components in JavaScript.
4. Add a new event handler that creates a RCTRootView that points to your React Native component and its AppRegistry name that you defined in index.ios.js.
5. Start the React Native server and run your native application.
6. Optionally add more React Native components.
7. Debug.
8. Prepare for deployment (e.g., via the react-native-xcode.sh script).
9. Deploy and Profit!

The keys to integrating React Native components into your Android application are to:

1. Understand what React Native components you want to integrate.
2. Install react-native in your Android application root directory to create node_modules/ directory.
3. Create your actual React Native components in JavaScript.
4. Add com.facebook.react:react-native:+ and a maven pointing to the react-native binaries in node_modules/ to your build.gradle file.
5. Create a custom React Native specific Activity that creates a ReactRootView.
6. Start the React Native server and run your native application.
7. Optionally add more React Native components.
8. Debug.
9. Prepare for deployment.
10. Deploy and Profit!

Prerequisites #

The Android Getting Started guide will install the appropriate prerequisites (e.g., npm) for React Native on the Android target platform and your chosen development environment.

To ensure a smooth experience, make sure your android project is under $root/android.

General #

First, follow the Getting Started guide for your development environment and the iOS target platform to install the prerequisites for React Native.

To ensure a smooth experience, make sure your iOS project is under $root/ios.

CocoaPods #

CocoaPods is a package management tool for iOS and Mac development. We use it to add the actual React Native framework code locally into your current project.

It is technically possible not to use CocoaPods, but this requires manual library and linker additions that overly complicates this process.

Our Sample App #

Assume the app for integration is a 2048 game. Here is what the main menu of the native application looks like without React Native.

Assume the app for integration is a 2048 game. Here is what the main menu of the native application looks like without React Native.

Package Dependencies #

React Native integration requires both the React and React Native node modules. The React Native Framework will provide the code to allow your application integration to happen.

package.json #

We will add the package dependencies to a package.json file. Create this file in the root of your project if it does not exist.

Normally with React Native projects, you will put files like package.json, index.ios.js, etc. in the root directory of your project and then have your iOS specific native code in a subdirectory like ios/ where your Xcode project is located (e.g., .xcodeproj).

Below is an example of what your package.json file should minimally contain.

Version numbers will vary according to your needs. Normally the latest versions for both React and React Native will be sufficient.

Packages Installation #

Install the React and React Native modules via the Node package manager. The Node modules will be installed into a node_modules/ directory in the root of your project.

React Native Framework #

The React Native Framework was installed as Node module in your project above. We will now install a CocoaPods Podfile with the components you want to use from the framework itself.

Subspecs #

Before you integrate React Native into your application, you will want to decide what parts of the React Native Framework you would like to integrate. That is where subspecs come in. When you create your Podfile, you are going to specify React Native library dependencies that you will want installed so that your application can use those libraries. Each library will become a subspec in the Podfile.

The list of supported subspecs are in node_modules/react-native/React.podspec. They are generally named by functionality. For example, you will generally always want the Core subspec. That will get you the AppRegistry, StyleSheet, View and other core React Native libraries. If you want to add the React Native Text library (e.g., for <Text> elements), then you will need the RCTText subspec. If you want the Image library (e.g., for <Image> elements), then you will need the RCTImage subspec.

Podfile #

After you have used Node to install the React and React Native frameworks into the node_modules directory, and you have decided on what React Native elements you want to integrate, you are ready to create your Podfile so you can install those components for use in your application.

The easiest way to create a Podfile is by using the CocoaPods init command in the native iOS code directory of your project:

The Podfile will be created and saved in the iOS directory (e.g., ios/) of your current project and will contain a boilerplate setup that you will tweak for your integration purposes. In the end, Podfile should look something similar to this:

Pod Installation #

After you have created your Podfile, you are ready to install the React Native pod.

Your should see output such as:

If you get a warning such as "The swift-2048 [Debug] target overrides the FRAMEWORK_SEARCH_PATHS build setting defined in Pods/Target Support Files/Pods-swift-2048/Pods-swift-2048.debug.xcconfig. This can lead to problems with the CocoaPods installation", then make sure the Framework Search Paths in Build Settings for both Debug and Release only contain $(inherited).

Code Integration #

Now that we have a package foundation, we will actually modify the native application to integrate React Native into the application. For our 2048 app, we will add a "High Score" screen in React Native.

The React Native component #

The first bit of code we will write is the actual React Native code for the new "High Score" screen that will be integrated into our application.

Create a index.ios.js file #

First, create an empty index.ios.js file. For ease, I am doing this in the root of the project.

index.ios.js is the starting point for React Native applications on iOS. And it is always required. It can be a small file that requires other file that are part of your React Native component or application, or it can contain all the code that is needed for it. In our case, we will just put everything in index.ios.js

Add Your React Native Code #

In your index.ios.js, create your component. In our sample here, we will add simple <Text> component within a styled <View>

RNHighScores is the name of your module that will be used when you add a view to React Native from within your iOS application.

The Magic: RCTRootView #

Now that your React Native component is created via index.ios.js, you need to add that component to a new or existing ViewController. The easiest path to take is to optionally create an event path to your component and then add that component to an existing ViewController.

We will tie our React Native component with a new native view in the ViewController that will actually host it called RCTRootView .

Create an Event Path #

You can add a new link on the main game menu to go to the "High Score" React Native page.

Event Handler #

We will now add an event handler from the menu link. A method will be added to the main ViewController of your application. This is where RCTRootView comes into play.

When you build a React Native application, you use the React Native packager to create an index.ios.bundle that will be served by the React Native server. Inside index.ios.bundle will be our RNHighScore module. So, we need to point our RCTRootView to the location of the index.ios.bundle resource (via NSURL) and tie it to the module.

We will, for debugging purposes, log that the event handler was invoked. Then, we will create a string with the location of our React Native code that exists inside the index.ios.bundle. Finally, we will create the main RCTRootView. Notice how we provide RNHighScores as the moduleName that we created above when writing the code for our React Native component.

First import the RCTRootView library.

The initialProperties are here for illustration purposes so we have some data for our high score screen. In our React Native component, we will use this.props to get access to that data.

Note that RCTRootView initWithURL starts up a new JSC VM. To save resources and simplify the communication between RN views in different parts of your native app, you can have multiple views powered by React Native that are associated with a single JS runtime. To do that, instead of using [RCTRootView alloc] initWithURL, use RCTBridge initWithBundleURL to create a bridge and then use RCTRootView initWithBridge.

First import the React library.

The initialProperties are here for illustration purposes so we have some data for our high score screen. In our React Native component, we will use this.props to get access to that data.

Note that RCTRootView bundleURL starts up a new JSC VM. To save resources and simplify the communication between RN views in different parts of your native app, you can have multiple views powered by React Native that are associated with a single JS runtime. To do that, instead of using RCTRootView bundleURL, use RCTBridge initWithBundleURL to create a bridge and then use RCTRootView initWithBridge.

When moving your app to production, the NSURL can point to a pre-bundled file on disk via something like [[NSBundle mainBundle] URLForResource:@"main" withExtension:@"jsbundle"];. You can use the react-native-xcode.sh script in node_modules/react-native/packager/ to generate that pre-bundled file.

When moving your app to production, the NSURL can point to a pre-bundled file on disk via something like let mainBundle = NSBundle(URLForResource: "main" withExtension:"jsbundle"). You can use the react-native-xcode.sh script in node_modules/react-native/packager/ to generate that pre-bundled file.

Wire Up #

Wire up the new link in the main menu to the newly added event handler method.

One of the easier ways to do this is to open the view in the storyboard and right click on the new link. Select something such as the Touch Up Inside event, drag that to the storyboard and then select the created method from the list provided.

Test Your Integration #

You have now done all the basic steps to integrate React Native with your current application. Now we will start the React Native packager to build the index.ios.bundle packager and the server running on localhost to serve it.

App Transport Security #

Apple has blocked implicit cleartext HTTP resource loading. So we need to add the following our project's Info.plist (or equivalent) file.

Run the Packager #

Run the App #

If you are using Xcode or your favorite editor, build and run your native iOS application as normal. Alternatively, you can run the app from the command line using:

In our sample application, you should see the link to the "High Scores" and then when you click on that you will see the rendering of your React Native component.

Here is the native application home screen:

Here is the React Native high score screen:

If you are getting module resolution issues when running your application please see this GitHub issue for information and possible resolution. This comment seemed to be the latest possible resolution.

See the Code #

You can examine the code that added the React Native screen on GitHub.

You can examine the code that added the React Native screen on GitHub.

Add JS to your app #

In your app's root folder, run:

This creates a node module for your app and adds the react-native npm dependency. Now open the newly created package.json file and add this under scripts:

Copy & paste the following code to index.android.js in your root folder — it's a barebones React Native app:

Prepare your current app #

In your app's build.gradle file add the React Native dependency:

If you want to ensure that you are always using a specific React Native version in your native build, replace + with an actual React Native version you've downloaded from npm.

In your project's build.gradle file add an entry for the local React Native maven directory:

Make sure that the path is correct! You shouldn’t run into any “Failed to resolve: com.facebook.react:react-native:0.x.x" errors after running Gradle sync in Android Studio.

Next, make sure you have the Internet permission in your AndroidManifest.xml:

If you need to access to the DevSettingsActivity add to your AndroidManifest.xml:

This is only really used in dev mode when reloading JavaScript from the development server, so you can strip this in release builds if you need to.

Add native code #

You need to add some native code in order to start the React Native runtime and get it to render something. To do this, we're going to create an Activity that creates a ReactRootView, starts a React application inside it and sets it as the main content view.

If you are targetting Android version <5, use the AppCompatActivity class from the com.android.support:appcompat package instead of Activity.

If you are using a starter kit for React Native, replace the "HelloWorld" string with the one in your index.android.js file (it’s the first argument to the AppRegistry.registerComponent() method).

If you are using Android Studio, use Alt + Enter to add all missing imports in your MyReactActivity class. Be careful to use your package’s BuildConfig and not the one from the ...facebook... package.

We need set the theme of MyReactActivity to Theme.AppCompat.Light.NoActionBar because some components rely on this theme.

A ReactInstanceManager can be shared amongst multiple activities and/or fragments. You will want to make your own ReactFragment or ReactActivity and have a singleton holder that holds a ReactInstanceManager. When you need the ReactInstanceManager (e.g., to hook up the ReactInstanceManager to the lifecycle of those Activities or Fragments) use the one provided by the singleton.

Next, we need to pass some activity lifecycle callbacks down to the ReactInstanceManager:

We also need to pass back button events to React Native:

This allows JavaScript to control what happens when the user presses the hardware back button (e.g. to implement navigation). When JavaScript doesn't handle a back press, your invokeDefaultOnBackPressed method will be called. By default this simply finishes your Activity.

Finally, we need to hook up the dev menu. By default, this is activated by (rage) shaking the device, but this is not very useful in emulators. So we make it show when you press the hardware menu button (use Ctrl + M if you're using Android Studio emulator):

Now your activity is ready to run some JavaScript code.

Configure permissions for development error overlay #

If your app is targeting the Android API level 23 or greater, make sure you have the overlay permission enabled for the development build. You can check it with Settings.canDrawOverlays(this);. This is required in dev builds because react native development errors must be displayed above all the other windows. Due to the new permissions system introduced in the API level 23, the user needs to approve it. This can be acheived by adding the following code to the Activity file in the onCreate() method. OVERLAY_PERMISSION_REQ_CODE is a field of the class which would be responsible for passing the result back to the Activity.

Finally, the onActivityResult() method (as shown in the code below) has to be overridden to handle the permission Accepted or Denied cases for consistent UX.

Run your app #

To run your app, you need to first start the development server. To do this, simply run the following command in your root folder:

Now build and run your Android app as normal (./gradlew installDebug from command-line; in Android Studio just create debug build as usual).

If you are using Android Studio for your builds and not the Gradle Wrapper directly, make sure you install watchman before running npm start. It will prevent the packager from crashing due to conflicts between Android Studio and the React Native packager.

Once you reach your React-powered activity inside the app, it should load the JavaScript code from the development server and display:

Creating a release build in Android Studio #

You can use Android Studio to create your release builds too! It’s as easy as creating release builds of your previously-existing native Android app. There’s just one additional step, which you’ll have to do before every release build. You need to execute the following to create a React Native bundle, which’ll be included with your native Android app:

Don’t forget to replace the paths with correct ones and create the assets folder if it doesn’t exist!

Now just create a release build of your native app from within Android Studio as usual and you should be good to go!