GoReactPoc

The repository is about to run go code on mobile.

More detailed plan

• compile Golang package with gomobile
• embed this output into an Android / iOS app mainly with React Native
  • first go is with Android because it is simpler

Part I. Implementation Java for Android

1. Install golang. Recommended to use goenv.

2. Install JDK (required by gomobile as well) - version 17 will do it for not. Recommend to use some tool - I have used SDKMAN for it.

3. Install Android Studio for easy SDK/NDK management. Android 16 - Api 36 installed with NDK 29.0.14206865

4. Here are some of my configured env vars maybe it helps you

   GOROOT=/Users/YOUR_USERNAME/.goenv/versions/1.24.2
   GOPATH=/Users/YOUR_USERNAME/go/1.24.2
   ANDROID_HOME=/Users/YOUR_USERNAME/Library/Android/sdk
   ANDROID_NDK_HOME=/Users/YOUR_USERNAME/Library/Android/sdk/ndk/29.0.14206865
   SDKMAN_DIR=/Users/YOUR_USERNAME/.sdkman
   SDKMAN_CANDIDATES_API=https://api.sdkman.io/2
   SDKMAN_BROKER_API=https://broker.sdkman.io
   SDKMAN_PLATFORM=darwinarm64
   SDKMAN_CANDIDATES_DIR=/Users/YOUR_USERNAME/.sdkman/candidates
   binary_input=/Users/YOUR_USERNAME/.sdkman/tmp/java-17.0.12-tem.bin

5. You maybe need to run go install golang.org/x/mobile/cmd/gomobile@latest check it by execute gomoblie command in the terminal

6. Run make install in project root

7. Run make pre-build-java in project root - or check the Makefile if you want to do things manually - what this does is:

   1. use gomobile to compile go code
   2. copy the binary where the GoInJava app expects it to be (/app/libs)
   3. Add the following to the build.gradle file

   dependencies {
           implementation fileTree(dir: 'libs', include: ['*.aar'])
      }

8. GoInJava project is in Android Studio

   1. To build the project run make build-java-android or ./gradlew in the GoInJava folder
   2. It uses Gradle and every time you update the *.aar file you have to run a build otherwise it does not detect the changes

9. Start an emulator in Android Studio and load the app there and you can try

Part II. Implementation with React Native

1. Create new Expo app for react native - select Blank (TypeScript). npx create-expo-app --template I named it GoInReact.
2. Now a Kotlin/Java wrapper required. cd GoInReact and create expo module npx create-expo-module@latest --local. I used the following namings. ✔ What is the name of the local module? … calculator ✔ What is the native module name? … Calculator ✔ What is the Android package name? … expo.module.gocalculator
3. That command created a structure under module and the CalculatorModule class. This class should be implemented for each platform and in this layer the golang lib call can be achieved.
4. For testing run npm start which will open App.tsx. This React Component calls out for the module created above and the underlying implementation will be called depending on the platform:
   1. Web = CalculatorModule.web.ts
   2. Android = CalculatorModule.kt
   3. iOS = CalculatorModule.swift
5. After the module created have to build the whole together with Gradle otherwise it will not work. Use the following command to cleanup the sample generated code: npx expo prebuild --clean --platform android
6. Execute npm run android in GoInReact folder and it should result like this:

Part II.A Implementing to Android emulator - with Kotlin wrapper

1. Build Go module and copy the poc.aar file under ./modules/calculator/android/src/libs (run make pre-build-react-android in the root directory)

2. Add the source above to the Gradle build file at ./modules/calculator/android/build.gradle

      dependencies {
            implementation(name: 'poc', ext: 'aar')
      }

3. WARNING this is a tricky part because this folder is not in repo! It is created by the command at section II/5 . So now need to change the the prebuild Gradle config and rerun it to make things work

   1. Go to android/build.gradle and add this to repositories section like this

      allprojects {
         repositories {
            ... // Leave everything you jave as-is, but add the following:
            flatDir { dirs "$rootDir/../modules/golang-calculator/android/src/libs" }
         }
      }

   2. now run make build-react-android in root folder

4. Now check that things are still fine rerun npm run android in GoInReact folder and things still should work.

5. Now to do some useful things open CalculatorModule.kt and add some code.

   It is important to reference your go package name (what you used in main.go) - this is some kind of convention. In our case it will be 'calculator'.

      import calculator.Calculator as goCalculator // check your go files package name
   
     Function("hello") {
      var sum = goCalculator.add(3.0, 5.0)
   
      "3+5 is $sum (calculated by go calculator)!"
    }

6.Now run npm run android and the result should look like this:

TODO try to parametrize the calls for calculator

Part II.B Implementing for iOS emulator

TODO

References: Using Golang + Gomobile To Build Android Application How to run GoLang code in your React-Native Android application using Expo Go React Native + Go Backend