swift-java on Android

This repository contains a sample Android application that demonstrates how to call Swift code from a Android app. The example consists of an Android application (HashingApp) and a Swift library (hashing-lib) that performs a SHA256 hash on a given string. The Swift library uses swift-java and the new JNI mode to automatically generate Java wrappers for calling into the Swift library.

Overview

The project is structured into two main parts:

1. hashing-lib: A Swift package that uses swift-crypto to provide a hashing function. It is configured with a Gradle build script (build.gradle) that compiles the Swift code into an Android Archive (.aar) file. This module utilizes the swift-java project to create the necessary JNI bindings.

2. HashingApp: A standard Android application written in Kotlin using Jetpack Compose. It includes the .aar file generated by hashing-lib as a local dependency and calls the Swift hash function when the user presses a button.

Prerequisites

Before you can build and run this project, you need to have the following installed:

• Java Development Kit (JDK): Ensure the JAVA_HOME environment variable is set to your JDK installation path.
• Swift SDK for Android: You need to install the Swift Android SDK

Setup and Configuration

Publish swift-java packages locally

As the swift-java project does not yet publish the neccessary Java packages needed at runtime, we need to do it ourself, by performing the following steps:

1. Enter the hashing-lib directory

   cd hashing-lib

2. Resolve Swift Packages

   swift package resolve

3. Publish the swift-java packages to local Maven repo

   ./.build/checkouts/swift-java/gradlew --project-dir .build/checkouts/swift-java publishToMavenLocal

Building and Running the Project

The project must be built in two stages: first the Swift library, then the Android application.

Step 1: Build the Swift Library (hashing-lib)

1. Navigate to the hashing-lib directory:

   cd hashing-lib

2. Run the Gradle assemble command. This will compile the Swift code for all supported Android ABIs (arm64-v8a, armeabi-v7a, x86_64), run the jextract plugin, and package everything into an .aar file.

   ./gradlew assembleRelease

3. After a successful build, the Android library will be located at hashing-lib/build/outputs/aar/hashing-lib-release.aar.

Step 2: Build and Run the Android App (HashingApp)

1. Open the HashingApp project in Android Studio.

2. Android Studio will automatically sync the Gradle project. The app is already configured to include the .aar file from the hashing-lib build output directory.

3. Run the app on an Android emulator or a physical device.

4. Enter any text into the text field and press the "Hash" button. The app will call the Swift hash function, and the resulting SHA256 digest will be displayed on the screen.