Generating Signed APK

Android requires that all apps be digitally signed with a certificate before they can be installed, so to distribute your Android application via Google Play store, you'll need to generate a signed release APK. The Signing Your Applications page on Android Developers documentation describes the topic in detail. This guide covers the process in brief, as well as lists the steps required to package the JavaScript bundle.

Generating a signing key

You can generate a private signing key using keytool. On Windows keytool must be run from C:\Program Files\Java\jdkx.x.x_x\bin.

$ keytool -genkey -v -keystore my-release-key.keystore -alias my-key-alias -keyalg RSA -keysize 2048 -validity 10000

This command prompts you for passwords for the keystore and key, and to provide the Distinguished Name fields for your key. It then generates the keystore as a file called my-release-key.keystore.

The keystore contains a single key, valid for 10000 days. The alias is a name that you will use later when signing your app, so remember to take note of the alias.

On Mac if you not sure where is your jdk bin folder is then perform the following command to find it, $ /usr/libexec/java_home it will output the directroy of jdk which looks like this, /Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home then navigate to that directory by the following command, $ cd /Library/Java/JavaVirtualMachines/jdk1.8.0_161.jdk/Contents/Home/ Now you can perform the keytool command with sudo permission as shown below, $ sudo keytool -genkey -v -keystore my-release-key.keystore -alias my-key-alias -keyalg RSA -keysize 2048 -validity 10000 Note: Remember to keep your keystore file private and never commit it to version control.

Setting up gradle variables

1. Place the my-release-key.keystore file under the android/app directory in your project folder.
2. Edit the file ~/.gradle/gradle.properties or android/gradle.properties and add the following (replace ***** with the correct keystore password, alias and key password),

MYAPP_RELEASE_STORE_FILE=my-release-key.keystore
MYAPP_RELEASE_KEY_ALIAS=my-key-alias
MYAPP_RELEASE_STORE_PASSWORD=*****
MYAPP_RELEASE_KEY_PASSWORD=*****

These are going to be global gradle variables, which we can later use in our gradle config to sign our app.

Note about saving the keystore:

Once you publish the app on the Play Store, you will need to republish your app under a different package name (losing all downloads and ratings) if you want to change the signing key at any point. So backup your keystore and don't forget the passwords.

Note about security: If you are not keen on storing your passwords in plaintext and you are running OSX, you can also store your credentials in the Keychain Access app. Then you can skip the two last rows in ~/.gradle/gradle.properties.

Adding signing config to your app's gradle config

Edit the file android/app/build.gradle in your project folder and add the signing config,

...
android {
    ...
    defaultConfig { ... }
    signingConfigs {
        release {
            if (project.hasProperty('MYAPP_RELEASE_STORE_FILE')) {
                storeFile file(MYAPP_RELEASE_STORE_FILE)
                storePassword MYAPP_RELEASE_STORE_PASSWORD
                keyAlias MYAPP_RELEASE_KEY_ALIAS
                keyPassword MYAPP_RELEASE_KEY_PASSWORD
            }
        }
    }
    buildTypes {
        release {
            ...
            signingConfig signingConfigs.release
        }
    }
}
...

Generating the release APK

Simply run the following in a terminal:

$ cd android
$ ./gradlew assembleRelease

Gradle's assembleRelease will bundle all the JavaScript needed to run your app into the APK. If you need to change the way the JavaScript bundle and/or drawable resources are bundled (e.g. if you changed the default file/folder names or the general structure of the project), have a look at android/app/build.gradle to see how you can update it to reflect these changes.

Note: Make sure gradle.properties does not include org.gradle.configureondemand=true as that will make release build skip bundling JS and assets into the APK.

The generated APK can be found under android/app/build/outputs/apk/app-release.apk, and is ready to be distributed.

Testing the release build of your app

Before uploading the release build to the Play Store, make sure you test it thoroughly. First uninstall any previous version of the app you already have installed. Install it on the device using:

$ react-native run-android --variant=release

Note that --variant=release is only available if you've set up signing as described above.

You can kill any running packager instances, all your framework and JavaScript code is bundled in the APK's assets.

Split APKs by ABI to reduce file size

By default, the generated APK has the native code for both x86 and ARMv7a CPU architectures. This makes it easier to share APKs that run on almost all Android devices. However, this has the downside that there will be some unused native code on any device, leading to unnecessarily bigger APKs.

You can create an APK for each CPU by changing the following line in android/app/build.gradle:

- def enableSeparateBuildPerCPUArchitecture = false
+ def enableSeparateBuildPerCPUArchitecture = true

Upload both these files to markets which support device targetting, such as Google Play and Amazon AppStore and the users will automatically get the appropriate APK. If you want to upload to other markets such as APKFiles, which do not support multiple APKs for a single app, change the following line as well to create the default universal APK with binaries for both CPUs.

- universalApk false  // If true, also generate a universal APK
+ universalApk true  // If true, also generate a universal APK

Enabling Proguard to reduce the size of the APK (optional)

Proguard is a tool that can slightly reduce the size of the APK. It does this by stripping parts of the React Native Java bytecode (and its dependencies) that your app is not using.

IMPORTANT: Make sure to thoroughly test your app if you've enabled Proguard. Proguard often requires configuration specific to each native library you're using. See app/proguard-rules.pro.

To enable Proguard, edit android/app/build.gradle:

/**
 * Run Proguard to shrink the Java bytecode in release builds.
 */
def enableProguardInReleaseBuilds = true