> 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.
<blockclass="objc swift android"/>
## 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.
<blockclass="objc swift"/>
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 `subspec`s 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.
8. [Prepare](/react-native/releases/next/docs/signed-apk-android.html) for [deployment](/react-native/docs/running-on-device-android.html).
9. Deploy and Profit!
<blockclass="objc swift android"/>
## Prerequisites
<blockclass="android"/>
The [Android Getting Started guide](/react-native/docs/getting-started.html) will install the appropriate prerequisites (e.g., `npm`) for React Native on the Android target platform and your chosen development environment.
First, follow the [Getting Started guide](/react-native/docs/getting-started.html) for your development environment and the iOS target platform to install the prerequisites for React Native.
[CocoaPods](http://cocoapods.org) 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.
```bash
$ sudo gem install cocoapods
```
> It is technically possible not to use CocoaPods, but this requires manual library and linker additions that overly complicates this process.
Assume the [app for integration](https://github.com/JoelMarcey/iOS-2048) is a <ahref="https://en.wikipedia.org/wiki/2048_(video_game)">2048</a> game. Here is what the main menu of the native application looks like without React Native.
Assume the [app for integration](https://github.com/JoelMarcey/swift-2048) is a <ahref="https://en.wikipedia.org/wiki/2048_(video_game)">2048</a> game. Here is what the main menu of the native application looks like without React Native.
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](https://github.com/facebook/react/releases) and [React Native](https://github.com/facebook/react-native/releases) will be sufficient.
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.
```bash
# From the directory containing package.json project, install the modules
# The modules will be installed in node_modules/
$ npm install
```
## React Native Framework
The React Native Framework was installed as Node module in your project [above](#package-dependencies). 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 `subspec`s 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 `subspec`s are in [`node_modules/react-native/React.podspec`](https://github.com/facebook/react-native/blob/master/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:
```bash
## In the directory where your native iOS code is located (e.g., where your `.xcodeproj` file is located)
$ pod init
```
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:
<blockclass="objc"/>
```
# The target name is most likely the name of your project.
target 'NumberTileGame' do
# Your 'node_modules' directory is probably in the root of your project,
# but if not, adjust the `:path` accordingly
pod 'React', :path => '../node_modules/react-native', :subspecs => [
# Add any other subspecs you want to use in your project
]
end
```
<blockclass="objc swift"/>
#### Pod Installation
After you have created your `Podfile`, you are ready to install the React Native pod.
```bash
$ pod install
```
Your should see output such as:
```bash
Analyzing dependencies
Fetching podspec for `React` from `../node_modules/react-native`
Downloading dependencies
Installing React (0.26.0)
Generating Pods project
Integrating client project
Sending stats
Pod installation complete! There are 3 dependencies from the Podfile and 1 total pod installed.
```
<blockclass="swift"/>
> 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)`.
<blockclass="objc swift"/>
## 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 `require`s 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`
```bash
# In root of your project
$ touch 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>`
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 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](#the-react-native-component) when writing the code for our React Native component.
<blockclass="objc"/>
First `import` the `RCTRootView` library.
```
#import "RCTRootView.h"
```
> 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`](https://github.com/facebook/react-native/blob/master/React/Base/RCTBridge.h#L93) to create a bridge and then use `RCTRootView initWithBridge`.
<blockclass="swift"/>
First `import` the `React` library.
```
import React
```
> 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`](https://github.com/facebook/react-native/blob/master/React/Base/RCTBridge.h#L93) to create a bridge and then use `RCTRootView initWithBridge`.
<blockclass="objc"/>
> 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.
<blockclass="swift"/>
> 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.
<blockclass="objc swift"/>
#### 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.
# From the root of your project, where the `node_modules` directory is located.
$ npm start
```
### 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:
```bash
# From the root of your project
$ react-native run-ios
```
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.
> If you are getting module resolution issues when running your application please see [this GitHub issue](https://github.com/facebook/react-native/issues/4968) for information and possible resolution. [This comment](https://github.com/facebook/react-native/issues/4968#issuecomment-220941717) seemed to be the latest possible resolution.
### See the Code
<blockclass="objc"/>
You can examine the code that added the React Native screen on [GitHub](https://github.com/JoelMarcey/iOS-2048/commit/9ae70c7cdd53eb59f5f7c7daab382b0300ed3585).
<blockclass="swift"/>
You can examine the code that added the React Native screen on [GitHub](https://github.com/JoelMarcey/swift-2048/commit/13272a31ee6dd46dc68b1dcf4eaf16c1a10f5229).
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`:
> 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`.
> 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.
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 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:
```java
@Override
public void onBackPressed() {
if (mReactInstanceManager != null) {
mReactInstanceManager.onBackPressed();
} else {
super.onBackPressed();
}
}
```
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 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](https://facebook.github.io/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:
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:
