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.
Follow the instructions for building apps with native code from the [Getting Started guide](docs/getting-started.html) to configure your development environment for building React Native apps for iOS.
To ensure a smooth experience, create a new folder for your integrated React Native project, then copy your existing iOS project to a `/ios` subfolder.
Follow the instructions for building apps with native code from the [Getting Started guide](docs/getting-started.html) to configure your development environment for building React Native apps for Android.
To ensure a smooth experience, create a new folder for your integrated React Native project, then copy your existing Android project to a `/android` subfolder.
Next, you will install the `react` and `react-native` packages. Open a terminal or command prompt, then navigate to the root directory for your project and type the following commands:
This will create a new `/node_modules` folder in your project's root directory. This folder stores all the JavaScript dependencies required to build your project.
[CocoaPods](http://cocoapods.org) is a package management tool for iOS and macOS 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 that would require manual library and linker additions that would overly complicate this process.
Assume the [app for integration](https://github.com/JoelMarcey/iOS-2048) is a [2048](https://en.wikipedia.org/wiki/2048_%28video_game%29) 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 [2048](https://en.wikipedia.org/wiki/2048_%28video_game%29) game. Here is what the main menu of the native application looks like without React Native.
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. We will use CocoaPods to specify which of these "subspecs" your app will depend on.
The list of supported `subspec`s is available 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`.
You can specify which `subspec`s your app will depend on in a `Podfile` file. The easiest way to create a `Podfile` is by running the CocoaPods `init` command in the `/ios` subfolder of your project:
The `Podfile` will contain a boilerplate setup that you will tweak for your integration purposes. In the end, `Podfile` should look something similar to this:
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)`.
Now we will actually modify the native iOS application to integrate React Native. For our 2048 sample app, we will add a "High Score" screen in React Native.
`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`.
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.
> 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`.
> 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#L89) 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/scripts/` 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/scripts/` to generate that pre-bundled file.
> 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.
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` package and the server running on `localhost` to serve it.
> App Transport Security is good for your users. Make sure to re-enable it prior to releasing your app for production.
##### 2. Run the packager
To run your app, you need to first start the development server. To do this, simply run the following command in the root directory of your React Native project:
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.
> 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.
You can examine the code that added the React Native screen to our sample app on [GitHub](https://github.com/JoelMarcey/iOS-2048/commit/9ae70c7cdd53eb59f5f7c7daab382b0300ed3585).
You can examine the code that added the React Native screen to our sample app on [GitHub](https://github.com/JoelMarcey/swift-2048/commit/13272a31ee6dd46dc68b1dcf4eaf16c1a10f5229).
> 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`.
Add an entry for the local React Native maven directory to `build.gradle`. Be sure to add it to the "allprojects" block:
```
allprojects {
repositories {
...
maven {
// All of React Native (JS, Android binaries) is installed from npm
url "$rootDir/node_modules/react-native/android"
}
}
...
}
```
> 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.
### Configuring permissions
Next, make sure you have the Internet permission in 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.
### Code integration
Now we will actually modify the native Android application to integrate 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.
##### 1. Create a `index.android.js` file
First, create an empty `index.android.js` file in the root of your React Native project.
`index.android.js` is the starting point for React Native applications on Android, 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.android.js`.
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 achieved 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.
```java
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
if (!Settings.canDrawOverlays(this)) {
Intent intent = new Intent(Settings.ACTION_MANAGE_OVERLAY_PERMISSION,
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.
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):
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.android.bundle` package and the server running on localhost to serve it.
To run your app, you need to first start the development server. To do this, simply run the following command in the root directory of your React Native project:
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 will be included with your native Android app:
Now just create a release build of your native app from within Android Studio as usual and you should be good to go!
<blockclass="objc swift android"/>
### Now what?
At this point you can continue developing your app as usual. Refer to our [debugging](/docs/debugging.html) and [deployment](docs/running-on-device.html) docs to learn more about working with React Native.
