Size Matters

Wrote an app in React Native platform that makes creating native apps a breeze. There is no native setup, you write javascript and Expo builds the binaries for you.

I love everything about Expo except the size of the binaries. Each binary weighs around 25 MB regardless of your app.

So the first thing I did was to migrate my existing Expo app to React Native.

Migrating to React Native

react-native init a new project with the same name
Copy the source files over from Expo project
Install all dependencies of the Expo project except Expo specific libraries.
Make neccesary adjustments to app.json file
Copy over your .git folder into the new project.
Download the signing key of your Android app from Expo using exp fetch:android:keystore and set it up
Build and test your app

This reduces the size to around 7.5 MB, thin but we can go thinner.

Reducing size of React Native App (Android)

This is what you have been waiting for, I know.

Open up android/app/build.gradle
Set def enableProguardInReleaseBuilds = true this would enable Progaurd to compress the Java Bytecode. This reduces the app size by a tad bit
Set def enableSeparateBuildPerCPUArchitecture = true . Android devices support two major device artitectures armebi and x86. By default RN builds the native librariers for both these artitectures into the same apk.

Setting the last function creates two distinct apk in the build folder. You have to upload both of this apk to Play Store and Google would take care of distributing the app to the correct architectures.

Using this split generates version numbers for both apks in the order of 104856 and such. This is auto-generated by the build to avoid version conflicts, so don’t freak out (I did).

This split reduced the apk size from around 7MB to 3.5MB for arm and 5MB for x86 respectively.