README.md

Kotlin example for the Android Swift toolchain.

An example application for mixing Swift and Kotlin in an Android application. This allows you to reuse model layer code from your iOS application when porting to Android. The "binding" between the Kotlin or Java code and Swift is completely type safe with all JNI code automatically generated using a script. Building the Swift code is performed using the Swift Package manager and a small gradle plugin.

Requires a build of the latest Android toolchain downloadable here. Once you've extracted the toolchain, run swift-install/setup.sh to get started and install the gradle plugin. You then run ./gradlew installDebug or build the project in Android Studio. Make sure the that the ANDROID_HOME environment variable is set to the path to an Android SDK. The phone must be api 21 aka Android v5+ aka Lollipop or better (I used an LG K4.)

To create a new application, decide on a pair of interfaces to connect to and from your Swift code and place them in a Java Source. Use the command ./genswift.sh in the SwiftJava Project to generate Swift (& Java) sources to include in your application or adapt the genhello.sh script. Your app's only Package.swift dependency should be the core JNI interfacing code java_swift.

This example is coded to work with version 7 of the toolchain which has some additional requirements to work around requirements of the Swift port of Foundation. The cache directory used by web operations needs to be setup in the environment variable "TMPDIR". This would usually be the value of Context.getCacheDir().getPath() from the java side. In addition, to be able to use SSL you need to add a CARoot info file to the application's raw resources and copy it to this cache directory to be picked up by Foundation as follows:

setenv("URLSessionCertificateAuthorityInfoFile", cacheDir! + "/cacert.pem", 1)
setenv("TMPDIR", cacheDir!, 1)

If you don't want peer validation you have the following option (not recommended at all)

setenv("URLSessionCertificateAuthorityInfoFile", “INSECURE_SSL_NO_VERIFY”, 1)

Simple demo of Swift code accessed over JNI.

To build, setup the Gradle plugin, then run ./gradlew installDebug

This demo is licensed under the Creative Commons CC0 license: do whatever you want.