Android egui app

[devourers]

I would like to apologize in advance, because this is probably a very noob question, but I am fairly new to Rust and have little to no idea how android apps work.
My goal is to build a Rust app for android, but I would like to refrain from using android studio and just code in pure rust. I recently found out about cargo-apk, and using it wanted to build my app for phone. As a start I was trying to just run hello-world example from egui's repo, by adding #[cfg_attr(target_os = "android", ndk_glue::main(backtrace = "on"))] to main function, and running cargo apk run --lib with started emulator.
Here is the whole code:

use eframe::egui;

struct MyApp {
    name: String,
    age: u32,
}

impl Default for MyApp {
    fn default() -> Self {
        Self {
            name: "Arthur".to_owned(),
            age: 42,
        }
    }
}

impl eframe::App for MyApp {
    fn update(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
        egui::CentralPanel::default().show(ctx, |ui| {
            ui.heading("My egui Application");
            ui.horizontal(|ui| {
                ui.label("Your name: ");
                ui.text_edit_singleline(&mut self.name);
            });
            ui.add(egui::Slider::new(&mut self.age, 0..=120).text("age"));
            if ui.button("Click each year").clicked() {
                self.age += 1;
            }
            ui.label(format!("Hello '{}', age {}", self.name, self.age));
        });
    }
}

#[cfg_attr(target_os = "android", ndk_glue::main(backtrace = "on"))]
fn main() {
    let options = eframe::NativeOptions::default();
    eframe::run_native(
        "My egui App",
        options,
        Box::new(|_cc| Box::new(MyApp::default())),
    );
}

The programm starts, it also even outputs prinln!s to log, but then the log gives me thread '<unnamed>' panicked at 'Cannot get the native window, it's null and will always be null before Event::Resumed and after Event::Suspended. Make sure you only call this function between those events.', which I consider that my rust code died and that's it.
Can someone explain to me if it's

1. me doing something wrong.
2. Rust android develpoment with egui requiring something else
3. Rust egui not working on android as is.

Thanks in advance!

[Parth]

#1952 was merged about 1 month before your example ran, I believe these changes are still not released. Try to update your toml file to point to egui master and see if android works as expected. Let me know if it does, I'm personally curious.

@rib am I matching up the error above with your work correctly?

[rib]

from skimming that code in eframe it looks like it uses checked_add, so then maybe it's something else entirely unrelated - that's just what popped into my mind from seeing a similar error with egui in the past.

[rib]

the fact that the panic is in src/looper.rs:167 does generally make me think it's still likely to be an issue with how the repaint_after time is being mapped to Winit a control flow since that would potentially result in passing a timeout through to the Looper to poll with a timeout and it's liable to panic if it can't be converted into an int for the Looper API

[rib]

I think in some other app I have used an arbitrary threshold for this instead of relying on checked_add failing. checked_add might still accept ridiculously large durations that still won't be possible to convert into a valid timeout when polling later

[rib]

Yeah e.g. in this app I just have an arbitrary 1 second threshold:

https://github.com/rib/bluey/blob/5f351c50e6f396bc4fef9c050599f9668c63b339/bluey-ui/src/lib.rs#L144

[rib]

Maybe eframe should use a threshold along those lines instead of relying on checked_add

[Parth]

I'm approaching this from the iOS side of things but will ultimately need to answer these questions on android. Other things I would look into are:

• https://github.com/rib/android-activity/tree/main/examples/agdk-egui
• https://github.com/frgomes/egui-miniquad-demo

[expenses]

I've been working on writing an eframe app for android. It's pretty simple, things mostly just work as-is with eframe: expenses/android-eframe@a65a3f0.

[expenses]

Biggest problem so far is that the soft keyboard doesn't pop up when you focus on input text box. You also need to setup a TopBottomPanel or to pad out the screen at the top (where the camera notch and icons are).

[expenses]

rust-windowing/winit#2993 is a good start on the soft keyboard thing, but I'm blocked from trying it out because of #4709.

[DougAnderson444]

@expenses, I saw from https://github.com/rust-mobile/ndk/tree/master?tab=readme-ov-file that cargo-apk https://github.com/rust-mobile/cargo-apk is ⛔ deprecated in favour of xbuild. Does it matter which one we use?

[DougAnderson444]

For those following the soft keyboard issue, it's now tracking at rust-windowing/winit#3787 (superseding rust-windowing/winit#2993)

[DougAnderson444]

As a temporary workaround for the soft keyboard issue, there is also:
https://github.com/snail-with-tea/egui_virtual_keyboard