Integrating with Existing Apps

Since React makes no assumptions about the rest of your technology stack – it’s commonly noted as simply the V in MVC – it’s easily embeddable within an existing non-React Native app. In fact, it integrates with other best practice community tools like CocoaPods.

Requirements

• CocoaPods – gem install cocoapods
• Node.js
  • Install nvm with its setup instructions here. Then run nvm install node && nvm alias default node, which installs the latest version of Node.js and sets up your terminal so you can run it by typing node. With nvm you can install multiple versions of Node.js and easily switch between them.
• Install the react-native package from npm by running the following command in the root directory of your project:
  • npm install react-native

At this point you should have the React Native package installed under a directory named node_modules as a sibling to your .xcodeproj file.

Install React Native Using CocoaPods

CocoaPods is a package management tool for iOS/Mac development. We need to use it to download React Native. If you haven't installed CocoaPods yet, check out this tutorial.

When you are ready to work with CocoaPods, add the following lines to Podfile. If you don't have one, then create it under the root directory of your project.

# Depending on how your project is organized, your node_modules directory may be
# somewhere else; tell CocoaPods where you've installed react-native from npm
pod 'React', :path => './node_modules/react-native', :subspecs => [
  'Core',
  'RCTImage',
  'RCTNetwork',
  'RCTText',
  'RCTWebSocket',
  # Add any other subspecs you want to use in your project
]

Remember to install all subspecs you need. The <Text> element cannot be used without the RCTText subspec, for example.

Then install your pods:

$ pod install

Create Your React Native App

There are two pieces you’ll need to set up:

1. The root JavaScript file that will contain your actual React Native app and other components
2. Wrapper Objective-C code that will load up your script and create a RCTRootView to display and manage your React Native components

First, create a directory for your app’s React code and create a simple index.ios.js file:

$ mkdir ReactComponent
$ touch ReactComponent/index.ios.js

Copy & paste following starter code for index.ios.js – it’s a barebones React Native app:

'use strict';

import React from 'react';
import {
  AppRegistry,
  StyleSheet,
  Text,
  View
} from 'react-native';

var styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: 'red'
  }
});

class SimpleApp extends React.Component {
  render() {
    return (
      <View style={styles.container}>
        <Text>This is a simple application.</Text>
      </View>
    )
  }
}

AppRegistry.registerComponent('SimpleApp', () => SimpleApp);

SimpleApp will be your module name, which will be used later on.

Add Container View To Your App

You should now add a container view for the React Native component. It can be any UIView in your app.

However, let's subclass UIView for the sake of clean code. Let's name it ReactView. Open up Yourproject.xcworkspace and create a new class ReactView (You can name it whatever you like :)).

// ReactView.h

#import <UIKit/UIKit.h>
@interface ReactView : UIView
@end

In a view controller that wants to manage this view, go ahead and add an outlet and wire it up:

// ViewController.m

@interface ViewController ()
@property (weak, nonatomic) IBOutlet ReactView *reactView;
@end

NOTE For Swift apps there is no need for that.

Here I disabled AutoLayout for simplicity. In real production world, you should turn on AutoLayout and setup constraints by yourself.

Add RCTRootView To Container View

Ready for the most interesting part? Now we shall create the RCTRootView, where your React Native app lives.

In ReactView.m, we need to first initiate RCTRootView with the URI of your index.ios.bundle. index.ios.bundle will be created by packager and served by React Native server, which will be discussed later on.

NSURL *jsCodeLocation = [NSURL URLWithString:@"http://localhost:8081/index.ios.bundle?platform=ios"];
// For production use, this `NSURL` could instead point to a pre-bundled file on disk:
//
//   NSURL *jsCodeLocation = [[NSBundle mainBundle] URLForResource:@"main" withExtension:@"jsbundle"];
//
// To generate that file, run the curl command and add the output to your main Xcode build target:
//
//   curl http://localhost:8081/index.ios.bundle -o main.jsbundle
RCTRootView *rootView = [[RCTRootView alloc] initWithBundleURL:jsCodeLocation
                                                    moduleName: @"SimpleApp"
                                             initialProperties:nil
                                                 launchOptions:nil];

Then add it as a subview of the ReactView.

[self addSubview:rootView];
rootView.frame = self.bounds;

Swift apps

Add the following to ReactView.swift file:

import UIKit
import React

class ReactView: UIView {

  let rootView: RCTRootView = RCTRootView(bundleURL: NSURL(string: "http://localhost:8081/index.ios.bundle?platform=ios"),
    moduleName: "SimpleApp", initialProperties: nil, launchOptions: nil)

  override func layoutSubviews() {
    super.layoutSubviews()

    loadReact()
  }

  func loadReact () {
        addSubview(rootView)
        rootView.frame = self.bounds
  }
}

And then make sure your view is added in a ViewContainer or story board file.

Start Development Server

In root directory, we need to start React Native development server.

(JS_DIR=`pwd`/ReactComponent; cd node_modules/react-native; npm run start -- --root $JS_DIR)

This command will start up a React Native development server within our CocoaPods dependency to build our bundled script. The --root option indicates the root of your React Native apps – this will be our ReactComponent directory containing the single index.ios.js file. This running server will package up the index.ios.bundle file accessible via http://localhost:8081/index.ios.bundle.

Update App Transport Security

On iOS 9 and above the app won't be a able to connect over http to localhost unless specifically told so. See this thread for alternatives and instructions: http://stackoverflow.com/questions/31254725/transport-security-has-blocked-a-cleartext-http.

It is recommended that you add an App Transport Security exception for localhost in your app's Info.plist file:

<key>NSAppTransportSecurity</key>
<dict>
    <key>NSExceptionDomains</key>
    <dict>
        <key>localhost</key>
        <dict>
            <key>NSTemporaryExceptionAllowsInsecureHTTPLoads</key>
            <true/>
        </dict>
    </dict>
</dict>

If you don't do this, you will see the error - Could not connect to development server. when connecting to your server over http.

Compile And Run

Now compile and run your app. You shall now see your React Native app running inside of the ReactView.

Live reload and all of the debugging tools will work from the simulator. Just make sure that DEBUG=1 is set under Build Settings -> Preprocessor Macros. If you're using Cocoapods and a custom configuration (that is, not "Debug"), make sure you've specified it to be a debug configuration using the xcodeproj setting in your Podfile. Also make sure you've got a simple React component totally encapsulated behind an Objective-C UIView subclass.

Conclusion

So under the hood, when RCTRootView is initialized, it will try to download, parse and run the bundle file from React Native development server. This means all you need to do is to implement your own container view or view controller for the RCTRootView – the RCTRootView ingests your bundled JS and renders your React components. Bravo!

You can checkout full source code of a sample application here.