Buildling Android apps from Android itself, using Termux: a howto guide

[dfaure]

In order to build Android apps on my Android tablet directly, I found the very helpful comment #7227 (comment) but some things in there are a bit outdated, and the PR is closed for new comments.

So I don't know where else to write this information, but if anyone is looking for how to use termux to build Android apps, I wrote instructions (and provided a very basic test app) at https://github.com/dfaure/rust-android-hello-world

Input welcome, and feel free to mention this somewhere.

[robertkirkman]

Very good job and amazing project, thank you. It is a really perfect example showing how dramatic the amount of additional boilerplate is for running Rust hello world on Android without Termux runtime versus with Termux runtime, it can help people learn exactly what and how much Termux (a distribution of Bash for Android) is handling in the background, and it can also help people learn how to use Termux as their build environment for an app that doesn't need to bundle Termux as its runtime environment.

For a comparison, Rust hello world on Android with Termux runtime (Bash for Android):

pkg upgrade
pkg install rust
cargo new project1
cd project1
cargo run

[dfaure]

Thanks for that reply, I had no idea this worked. But I actually want to make a graphical application, I guess this doesn't allow doing that?

[robertkirkman]

That's a very good point because yes, it's slightly more difficult to build a graphical application without using an android_activity::AndroidApp android_main() NativeActivity as you have.

If you want your app to be entirely standalone and not depend on any other APK to launch, it's best to do it as you have.

However, there is also another way to build graphical Rust applications and run them on Android, that's different, it's the way that involves using the Termux:X11 app, and then using X11 GUI libraries originally intended for desktop Linux apps, but on Android, and also this way requires vendoring and patching Rust ecosystem windowing crates (libraries) to force them to allow the use of X11 on Android. One of the examples of the Rust ecosystem crates that must always be edited in order to use X11 on Android with Rust is winit:

termux-packages/x11-packages/alacritty/winit-treat-android-as-linux.diff

Line 1 in 4eb45af

diff --git a/Cargo.toml b/Cargo.toml

In this method, Termux:X11 abstracts the Android NativeActivity calls away from the app so that it can use X11 API calls and run exactly the same Rust codepaths that desktop Linux does.

This technique is what is used by all of the Rust software in the x11-packages folder of the termux-packages repository.