Android and Kotlin

WalletKit’s Kotlin bindings are generated with UniFFI and built by the workspace xtask. This page describes how to build, test, and publish them locally.

Before you begin

• Use the android Nix shell, which provides the Rust toolchain, the Android NDK, and the linkers. The xtask doesn’t enter the shell for you, so run it through nix develop .#android, or provide the same dependencies yourself.
• For Gradle’s Android tasks, install the Android SDK and NDK from Android Studio, in Settings > Android SDK. Then set sdk.dir, and ndk.dir if needed, in kotlin/local.properties.

The Kotlin project in kotlin/ has two modules:

• walletkit: the Android library with the generated bindings
• walletkit-tests: JUnit tests of the bindings

Build the bindings

To cross-compile WalletKit and generate the Kotlin bindings, run the following command:

nix develop .#android --command cargo xtask kotlin build

Run the Kotlin tests

To build a host library for macOS or Linux, generate bindings, and run the JUnit suite on the JVM, run the following command. The android shell provides the JDK 17 and nargo that the tests need:

nix develop .#android --command cargo xtask kotlin test

Test with an app before release

To try local changes in an Android app, publish them to Maven Local:

1. Build and publish a version, for example 0.3.1:

   nix develop .#android --command cargo xtask kotlin local 0.3.1
   

   The command builds the Rust library for arm64-v8a, armeabi-v7a, x86_64, and x86, generates the Kotlin bindings, and publishes them to ~/.m2/repository/org/world/walletkit/.

2. In the app, add mavenLocal() to the Gradle repositories and set the WalletKit dependency to the version that you published.

To use Rust from a non-default location, set RUSTUP_HOME and CARGO_HOME when you run the command.