MixedApp

This Repository contains a step-by-step guide on how to integrate React Native into an iOS application.

The repository starts with a simple app, with two tabs:

• The home tab is a native view where the team is going to work using native technologies
• The settings tab will be a React Native view.

Every commit represents a step toward integrating the React Native into the app.

You can checkout every commit to see if the current state of the project.

Initial Commit

This commit is the initial state. We have the iOS app in the MixedApp folder and currently both tabs are native views.

The goal is to replace the Settings view with a React Native view.

Add the ios folder

First step to integrate React Native is to move your ios project into a dedicated ios folder.

1. create a new ios folder
2. move the MixedApp folder inside the ios folder

Create the package.json and install js dependencies

We now need to add the React and React Native dependencies to our project.

1. Create a package.json file inside the MixedApp folder. It must be a sibling of the previous ios folder

2. Paste the following content inside the package.json

{
  "name": "MixedApp",
  "version": "0.0.1",
  "private": true,
  "scripts": {
    "start": "yarn react-native start"
  }
}

3. Navigate to the MixedApp folder and run the following command:

yarn add react-native@latest

4. One of the warning line would be something like:

warning " > react-native@0.75.3" has unmet peer dependency "react@^18.2.0".

so make sure to run also

yarn add react@^18.2.0

5. Add a .gitignore file to ignore the node_modules folder

Create the index.js file

The index.js file is the entry point for the JS module we want to load in our app. At the same level of the package.json

1. Create and index.js file
2. Add the following content to the index.js file

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

const Settings = ({data}) => {
  return (
    <View style={styles.container}>
      <Text>Settings</Text>
      <Text>{data}</Text>
    </View>
  );
};

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#EEEEEE',
  },
});

// Module name
AppRegistry.registerComponent('Settings', () => Settings);

Configure iOS dependencies

Now, it's time to link the React Native dependencies to the iOS project.

The tool we use to do that is Cocoapods and Ruby Gems.

Follow the install instructions in the Cocoapods website

We use Ruby Bundler to manage the ruby dependencies.

1. Create a Gemfile at the same level of the package.json file with this content

source 'https://rubygems.org'

# You may use http://rbenv.org/ or https://rvm.io/ to install and use this version
ruby ">= 2.6.10"

# Exclude problematic versions of cocoapods and activesupport that causes build failures.
gem 'cocoapods', '>= 1.13', '!= 1.15.0', '!= 1.15.1'
gem 'activesupport', '>= 6.1.7.5', '!= 7.1.0'

2. Inside the iOS folder, create a Podfile file, with this content

# Resolve react_native_pods.rb with node to allow for hoisting
require Pod::Executable.execute_command('node', ['-p',
  'require.resolve(
    "react-native/scripts/react_native_pods.rb",
    {paths: [process.argv[1]]},
  )', __dir__]).strip

platform :ios, min_ios_version_supported
prepare_react_native_project!

linkage = ENV['USE_FRAMEWORKS']
if linkage != nil
  Pod::UI.puts "Configuring Pod with #{linkage}ally linked Frameworks".green
  use_frameworks! :linkage => linkage.to_sym
end

target 'MixedApp' do
  config = use_native_modules!

  use_react_native!(
    :path => config[:reactNativePath],
    # An absolute path to your application root.
    :app_path => "#{Pod::Config.instance.installation_root}/.."
  )

  post_install do |installer|
    # https://github.com/facebook/react-native/blob/main/packages/react-native/scripts/react_native_pods.rb#L197-L202
    react_native_post_install(
      installer,
      config[:reactNativePath],
      :mac_catalyst_enabled => false,
      # :ccache_enabled => true
    )
  end
end

3. Navigate inside the ios folder
4. run the bundle install command
5. run the bundle exec pod install command
6. update the .gitignore file to ignore the **/ios/Pods, the **/ios/generated folder, and the .xcode.env.local file

Modify the iOS code

Now it's time to modify the iOS code to connect with React Native.

React Native is kickstarted by a class called RCTAppDelegate. As the name implies, React Native works with the AppDelegate hierarchy chain, and not with the SceneDelegate hierarchy.

1. Open the project with the command open ios/MixedApp.xcworkspace
2. Delete the SceneDelegate.swift file
3. In Xcode, select your app icon and the Info tab.
4. Delete the Application Scene Manifest line
5. Open the AppDelegate.swift file and apply the following changes

import UIKit
+ import React
+ import React_RCTAppDelegate

@main
-class AppDelegate: UIResponder, UIApplicationDelegate {
+class AppDelegate: RCTAppDelegate {


-  func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
-    // Override point for customization after application launch.
-    return true
-  }
+ override func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
+    super.moduleName = "Settings"
+    self.initialProps = [:];

+    super.application(application, didFinishLaunchingWithOptions: launchOptions)

+    let rootViewController = TabViewController()
+    self.window.rootViewController = rootViewController
+    self.window.makeKeyAndVisible()

+    return true
+}

+  override func sourceURL(for bridge: RCTBridge) -> URL? {
+    return bundleURL()
+  }

+  override func bundleURL() -> URL?
+  {
+  #if DEBUG
+    return RCTBundleURLProvider.sharedSettings().jsBundleURL(forBundleRoot: "index")
+  #else
+    return NSBundle.main .url(forResource: "main", withExtension: "jsbundle")
+  #endif
+  }

-  // MARK: UISceneSession Lifecycle

-  func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
-    // Called when a new scene session is being created.
-    // Use this method to select a configuration to create the new scene with.
-    return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
-  }
-
-  func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
-    // Called when the user discards a scene session.
-    // If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
-    // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
-  }
}

6. Open the SettingsViewController.swift file and modify it as it follows

import Foundation
+import React
+import React_RCTAppDelegate

class SettingsViewController: UIViewController {

  override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view.
-    self.view.backgroundColor = .red
+    self.view = (RCTSharedApplication()?.delegate as? RCTAppDelegate)?.rootViewFactory .view(withModuleName: "Settings", initialProperties: [:])
  }
}

7. Select your app in Xcode.
8. Select Build Settings
9. in the top right corner, filter for User Script Sandboxing
10. Set the value to NO.

Now you can build and run your app, but you'll see an error like this one.

The problem is that Metro is not running. The next step will fix this.

Configure Metro

Metro is the JS bundler that provides JS files to your app while you develop it.

To configure it properly, follow these steps:

1. From the same folder where the package.json is, run yarn add --dev @react-native/metro-config
2. Create a new file metro.config.js with this content

const {getDefaultConfig, mergeConfig} = require('@react-native/metro-config');

/**
 * Metro configuration
 * https://reactnative.dev/docs/metro
 *
 * @type {import('metro-config').MetroConfig}
 */
const config = {};

module.exports = mergeConfig(getDefaultConfig(__dirname), config);

3. create a new file .watchmanconfig with this content:

{}

4. Run yarn start to start metro.
5. In another terminal, navigate to the ios folder
6. Run bundle exec pod install. This is needed because the yarn add @react-native/metro-config changed the node_modules folder and native dependencies are out of sync.
7. From Xcode, build and run your app.

If you now navigate to the Settings tab, you should see your JS being loaded.

If you now modify the index.js file, you can update how it looks in your app, in real time!

Pass data between Native and JS

To pass data between the native side and the JS side, you can use the initialProperties dictionary of the SettingsViewController.

1. Modify the SettingsViewController.swift as it follows:

  override func viewDidLoad() {
    super.viewDidLoad()

-    self.view = (RCTSharedApplication()?.delegate as? RCTAppDelegate)?.rootViewFactory .view(withModuleName: "Settings", initialProperties: [:])
+    self.view = (RCTSharedApplication()?.delegate as? RCTAppDelegate)?.rootViewFactory .view(withModuleName: "Settings", initialProperties: ["data":"Hello from React Native"])
  }

2. Rebuild and rerun the app