Rust on Android

Libraries and tools for Rust programming on Android targets:

Name	Description	Badges
ndk-sys	Raw FFI bindings to the NDK
ndk	Safe abstraction of the bindings
ndk-context	Android handles
ndk-glue	Startup code
ndk-build	Everything for building apk's
cargo-apk	Build tool

See ndk-examples for examples using the NDK and the README files of the crates for more details.

Supported NDK versions

android-ndk-rs aims to support at least the LTS and Rolling Release branches of the NDK, as described on their wiki. Additionally the Beta Release might be supported to prepare for an upcoming release.

As of writing (2021-07-24) the following NDKs are tested:

Branch	Version	Status	Working
r18	18.1.5063045	Deprecated	❌
r19	19.2.5345600	Deprecated	✔️
r20	20.1.5948944	Deprecated	✔️
r21	21.4.7075529	Deprecated	✔️
r22	22.1.7171670	Deprecated	✔️
r23	beta 1/2	Deprecated	✔️
r23	23.0.7272597-beta3	Deprecated	✔️ Workaround in #189
r23	23.1.7779620	LTS	✔️ Workaround in #189
r24	24.0.7856742-beta1	Rolling Release	✔️ Workaround in #189

Hello world

Quick start for setting up a new project with support for Android. For communication with the Android framework in our native Rust application we require a NativeActivity. ndk-glue will do the necessary initialization when calling main but requires a few adjustments:

Cargo.toml

[lib]
crate-type = ["lib", "cdylib"]

Wraps main function using attribute macro ndk::glue::main:

src/lib.rs

#[cfg_attr(target_os = "android", ndk_glue::main(backtrace = "on"))]
pub fn main() {
    println!("hello world");
}

src/main.rs

fn main() {
    $crate::main();
}

Install cargo apk for building, running and debugging your application:

$ cargo install cargo-apk

We can now directly execute our Hello World application on a real connected device or an emulator:

$ cargo apk run

Logging and stdout

Stdout is redirected to the android log api when using ndk-glue. Any logger that logs to stdout, like println!, should therefore work.

Use can filter the output in logcat

$ adb logcat RustStdoutStderr:D *:S

Android logger

Android logger can be setup using feature "logger" and attribute macro like so:

src/lib.rs

#[cfg_attr(target_os = "android", ndk_glue::main(logger(level = "debug", tag = "my-tag")))]
pub fn main() {
    log!("hello world");
}

App/APK configuration

Android APKs contain a file called AndroidManifest.xml, which has things like permission requests and feature declarations, plus configuration of activities, intents, resource folders and more. This file is autogenerated by cargo-apk. To control what goes in it through Cargo.toml, refer to cargo-apk's README.

Overriding crate paths

The macro ndk_glue::main tries to determine crate names from current Cargo.toml. In cases when it is not possible the default crate names will be used. You can override this names with specific paths like so:

#[ndk_glue::main(
  ndk_glue = "path::to::ndk_glue",
)]
fn main() {}

JNI

Java Native Interface (JNI) allows executing Java code in a VM from native applications. To access the JNI use the AndroidContext from the ndk-context crate. ndk-examples contains a jni_audio example which will print out all output audio devices in the log.

• jni, JNI bindings for Rust