I\'m using react-native, and everything was working well while I was developing, but, when I built the APK (using this tutorial: https://facebook.github.io/react-native/docs/sig
I guess you are looking for how to generate signed apk.
it seem you did not have a react.gradle file under android/app: you can bundle the JavaScript package and drawable resources manually by doing the following in a terminal:
$ mkdir -p android/app/src/main/assets
$ react-native bundle --platform android --dev false --entry-file index.android.js \
--bundle-output android/app/src/main/assets/index.android.bundle \
--assets-dest android/app/src/main/res/
$ cd android && ./gradlew assembleRelease
after following this process app.release.apk will be under android\app\build\outputs\apk directory.