An example React Native project using a jsi-rs module

How to reproduce (Android)

1. Create a blank React Native project: npx react-native@latest init example

2. Create a blank Cargo project inside: cd example && cargo init --lib example-jsi-module

3. Add jsi, jni, and cxx as dependencies of example-jsi-module

   • jsi will allow us to create a React Native module
   • jni is needed for interop with Java code on Android
   • cxx is needed to initialize jsi because JSI is implemented in C++ with smart pointers

4. Write the code in example-jsi-module/src

5. Update android/build.gradle to add the following plugin under buildscript.dependencies:

   buildscript {
       repositories {
         // don't remove the existing repositories, just add maven b/c the Rust plugin is hosted there
         maven {
           url "https://plugins.gradle.org/m2/"
         }
       }
       dependencies {
         // don't remove the existing dependencies, just add this one
         classpath("io.github.MatrixDev.android-rust:plugin:0.3.2")
       }
   }

   This plugin will compile example-jsi-module using the Android NDK as part of building our application for Android

6. Make sure the Android NDK is installed. Version 23 should work

7. Update android/app/build.gradle to add the following lines:

   apply plugin: "io.github.MatrixDev.android-rust"
   androidRust {
       module("example-jsi-module") {
           it.path = file("../example-jsi-module")
   
           // default abi targets are arm and arm64; if you want to run on Android
           // Emulator then you may need to add x86_64
           
           // targets = ["arm", "arm64", "x86", "x86_64"]
       }
   }

   Note: when you compile the program, this Gradle plugin will install all of the Rust Android targets if they are not already installed

8. Write the code in android/app/src/main/java/com/example/ExampleJsiModule.java. This will be called when the application starts, and it gives us a pointer to the React Native runtime so we can initialize our Rust code

9. Write the code in android/app/src/main/java/com/example/ExampleJsiPackage.java. This lets React Native discover our module

10. In android/app/src/main/java/com/example/MainApplication.java, add the following line to getPackages():

    packages.add(new ExampleJsiPackage());

11. Add a couple of lines to App.tsx to call our native module (I added them near the top):

    // call our Rust module
    const {ExampleJsiModule} = NativeModules;
    ExampleJsiModule.install();

12. Connect your Android device or start an emulator

13. Run npm run start and press A to deploy to Android

14. You should see hello from Rust in the terminal after the app loads