Building from source

You will need to build React Native from source if you want to work on a new feature/bug fix, try out the latest features which are not released yet, or maintain your own fork with patches that cannot be merged to the core.

Android

Prerequisites

Assuming you have the Android SDK installed, run android to open the Android SDK Manager.

Make sure you have the following installed:

1. Android SDK version 28 (compileSdkVersion in build.gradle)
2. SDK build tools version 28.0.3 (buildToolsVersion in build.gradle)
3. Android Support Repository >= 28 (for Android Support Library)
4. Android NDK (download links and installation instructions below)

Point Gradle to your Android SDK:

Step 1: Set environment variables through your local shell.

Note: Files may vary based on shell flavor. See below for examples from common shells.

• bash: .bash_profile or .bashrc
• zsh: .zprofile or .zshrc
• ksh: .profile or $ENV

Example:

export ANDROID_SDK=/Users/your_unix_name/android-sdk-macosx
export ANDROID_NDK=/Users/your_unix_name/android-ndk/android-ndk-r17c

Step 2: Create a local.properties file in the android directory of your react-native app with the following contents:

Example:

sdk.dir=/Users/your_unix_name/android-sdk-macosx
ndk.dir=/Users/your_unix_name/android-ndk/android-ndk-r17c

Download links for Android NDK

1. Mac OS (64-bit) - http://dl.google.com/android/repository/android-ndk-r17c-darwin-x86_64.zip
2. Linux (64-bit) - http://dl.google.com/android/repository/android-ndk-r17c-linux-x86_64.zip
3. Windows (64-bit) - http://dl.google.com/android/repository/android-ndk-r17c-windows-x86_64.zip
4. Windows (32-bit) - http://dl.google.com/android/repository/android-ndk-r17c-windows-x86.zip

You can find further instructions on the official page.

Building the source

1. Installing the fork

First, you need to install react-native from your fork. For example, to install the master branch from the official repo, run the following:

npm install --save github:facebook/react-native#master

Alternatively, you can clone the repo to your node_modules directory and run npm install inside the cloned repo.

2. Adding gradle dependencies

Add gradle-download-task as dependency in android/build.gradle:

...
    dependencies {
        classpath 'com.android.tools.build:gradle:3.2.1'
        classpath 'de.undercouch:gradle-download-task:3.4.3'

        // NOTE: Do not place your application dependencies here; they belong
        // in the individual module build.gradle files
    }
...

3. Adding the :ReactAndroid project

Add the :ReactAndroid project in android/settings.gradle:

...
include ':ReactAndroid'

project(':ReactAndroid').projectDir = new File(
    rootProject.projectDir, '../node_modules/react-native/ReactAndroid')
...

Modify your android/app/build.gradle to use the :ReactAndroid project instead of the pre-compiled library, e.g. - replace implementation 'com.facebook.react:react-native:+' with implementation project(':ReactAndroid'):

...
dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:${rootProject.ext.supportLibVersion}'

    implementation project(':ReactAndroid')

    ...
}
...

4. Making 3rd-party modules use your fork

If you use 3rd-party React Native modules, you need to override their dependencies so that they don't bundle the pre-compiled library. Otherwise you'll get an error while compiling - Error: more than one library with package name 'com.facebook.react'.

Modify your android/app/build.gradle, and add:

configurations.all {
    exclude group: 'com.facebook.react', module: 'react-native'
}

Building from Android Studio

From the Welcome screen of Android Studio choose "Import project" and select the android folder of your app.

You should be able to use the Run button to run your app on a device. Android Studio won't start the packager automatically, you'll need to start it by running npm start on the command line.

Additional notes

Building from source can take a long time, especially for the first build, as it needs to download ~200 MB of artifacts and compile the native code. Every time you update the react-native version from your repo, the build directory may get deleted, and all the files are re-downloaded. To avoid this, you might want to change your build directory path by editing the ~/.gradle/init.gradle file:

gradle.projectsLoaded {
    rootProject.allprojects {
        buildDir = "/path/to/build/directory/${rootProject.name}/${project.name}"
    }
}

Troubleshooting

Gradle build fails in ndk-build. See the section about local.properties file above.