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Android setup

JDK 8​

Android Studio depends on the javax library being present in the Java runtime, and the only reliable way to ensure this is to install an older version of Java. On Unix-like systems, you can use asdf or similar tools to manage your Java versions, and the template defines a known working version of Java in the .tool-versions file.

Android NDK​

An issue regarding building Rust's core library against the latest NDK means that when using Rust 1.67 and lower, only NDK versions 22 and older can be used. The issue has been patched in Rust 1.68, which is not yet stable at the time of writing.

Rust < 1.68:

Android Studio > SDK Manager > SDK Tools > uncheck Hide Obsolete Packages > NDK (version 22)

Rust >= 1.68:

Android Studio > SDK Manager > SDK Tools > NDK (side by side)

The Android NDK, or Native Development Kit, enables code written in other languages to be run on the JVM via the Java Native Interface, or JNI for short. In this case, we would like to pass the dynamic libraries created by Cargo to be included in the bundle when we run or build the project.

After following the instructions above, the NDK should be installed in your $ANDROID_HOME/ndk folder, where ANDROID_HOME usually is:

  • on Windows: %APPDATA%\Local\Android\sdk
  • on MacOS: ~/Library/Android/sdk
  • on Linux: set via the environment variable ANDROID_HOME, or ~/Android/sdk

ANDROID_NDK Gradle property​

echo "ANDROID_NDK=(path to NDK)" >> ~/.gradle/gradle.properties

Next, you need to make this NDK visible to Gradle. The way to do this depends on your current system and is unlikely to be portable, but generally you can add a gradle.properties in your ~/.gradle folder like this:

ANDROID_NDK=(path to NDK)

or edit one of the gradle.properties that resides within the android folder.

cargo-ndk​

cargo-ndk is a Cargo plugin for compiling code suitable for plugging into the JNI without additional configuration. Version 2.7.0 of cargo-ndk introduced changes that broke support for NDK version 22, so 2.6.0 must be used if you are on a Rust version below 1.68. If you still want to use cargo-ndk 2.7.0 or above on Rust versions below 1.68 with a workaround, see this article.

Rust < 1.68:

cargo install cargo-ndk --version 2.6.0

Rust >= 1.68:

cargo install cargo-ndk

Then run (all Rust versions)

cargo ndk -o ../android/app/src/main/jniLibs build

Then run the Flutter app normally with flutter run.

Remark: This tutorial will help you automatically execute cargo builds when building Flutter app.