Posted by rekireki 1 day ago
First things, I want to thank all the people who work on the foundational crates and tools such as: - https://github.com/rust-mobile/android-activity - https://github.com/jni-rs/jni-rs - https://github.com/gfx-rs/wgpu - https://github.com/rust-windowing/winit - and many others
When I started I had to learn what tools and examples already exist. Luckily, there's a good set of examples using both NativeActivity and GameActivity: https://github.com/rust-mobile/rust-android-examples
The basic approach is that we take android-activity, winit and wgpu and that's it. On top of that you can find a few egui examples in the rust-android-examples repo.
Alright, so after I've got the basic examples running, I wanted to combine them with iced. Iced is a crossplatform gui library focusing on desktop and web. The mobile support is explicitly a non-goal, as far as I can tell at the moment of writing. Yet, there's an issue where some people posted their experiments. That's how I knew it was possible: https://github.com/iced-rs/iced/issues/302
There's a way to integrate iced in wgpu applications, so called integration example: https://github.com/iced-rs/iced/tree/0.14.0/examples/integra...
Above I mentioned that using winit and wgpu in combination with android-activity is enough to build the app. Putting together 1 + 1 I got 2: let's use iced integration example with android-activity. It was quite easy to compile with almost no errors. First issue I encountered is that there was no text rendered. I solved this by loading fonts the way it was shown here: https://github.com/pop-os/cosmic-text/issues/243#issue-21899...
Then I patched a few widgets to add touch support. And that's it. My role here was to take all the prior work and combine it together in a way that there's a working example.
Some other ways of building Android apps using Rust: - xilem has an explicit goal to support mobile https://github.com/linebender/xilem - egui supports mobile https://github.com/emilk/egui - game engines such as Fyrox and Bevy support mobile: - https://github.com/FyroxEngine/Fyrox - https://github.com/bevyengine/bevy - pretty much anything built on top of winit and wgpu
All of the above is related to building native apps using either NativeActivity or GameActivity. I'm leaving webview out of scope of current post.
What about iOS? As far as I know it should be similar or maybe simpler compared to Android. I haven't built it yet, but the next time I have a sizeable amount of free time, I'll try to make it work. The plan is the same: pick winit, wgpu, iced integration example, mix it together until it works. It'll require the same trick to load fonts, and maybe something else, but no visible blockers as of now.
Once again, thanks to all the people who made it possible and I wish you have a great time building mobile apps with Rust!
I'm hoping this can be a reality sooner rather than later. But we're definitely lacking in manpower willing or able to work on the more foundational pieces. Winit in particular is sadly undermaintained. 1 or 2 people working full time on Winit and/or other platform integration pieces would do wonders for the ecosystem.
* I don't trust Swift on Android to be well supported, either now, or in the future. I would never want to rely on something Appley on a non Apple platform
* I dislike Swift and find it to be an unpleasant language. This is personal pref of coures, just like preferred flavors of ice cream
* Dart looks interesting and like a good option, though I don't want to learn a new language and Dart doesn't appeal to me because it feels like they took javascript and made it more like Java, and Java is in about the middle of my list of preferred langs (see above comment about preferred flavors of ice cream). Flutter is a killer app though and might be enough to sway me.
* Kotlin is a nice language, though not nice enough to where I'd want to use it outside of Android. The ties to the JVM-world tooling/dependency management is very offputting to me.
Overall I have a strong desire to use my preferred language(s) for everything if possible, so things like this are quite attractive to me for that reason. Now that said, when I write Android apps right now, what I typically use is Kotlin or Java because I've found I always end up having to write at least part of the app in those, so might as well keep it simple and consistent in one lang. But I'm always on the lookout!
> I dislike Swift and find it to be an unpleasant language.
On Android this appears to be less of an issue, but on iOS there's documentation floating around that you really want to use e.g NSURLSession for battery/radio reasons. Spotify even went so far as to write a cross-platform lib for this kind of thing some years back.
Once you start using JNI or Objective-C++ to hand off “computationally expensive” work to common C++ (now Rust) libraries, you end up needing to become an expert across a lot of areas.
If 95% of your competitive advantage lies in doing things everywhere with low memory, then taking on an additional 2-3 stacks (SwiftUI + React + Compose) as well as all the bindings and build system and etc overhead can be pretty gnarly.
If 95% of your value add is in your web-based UI, consolidating to a single JS stack of React + React Native + Node can greatly reduce your idea-to-market time, I’d imagine a full Rust stack could do the same if your value add requires maximum performance and only a little UI iteration.
many company literally just give up use web wrapper instead because its just so much work
https://docs.slint.dev/latest/docs/slint/guide/backends-and-...
But, I have only used it with Romanian and English.
Try here: https://slintpad.com/. (just replace the Text with TextInput) and see if it works.
Slint does support decent text input and IME. Including text selection with the native handle. As a demo for android you can try the demo from https://material.slint.dev/ ("Download APK")
The DSL was pleasant but still had some rough edges. I think they made some nice QoL improvements in the latest releases, but I've not kept up with it. The compile times were quite something, though you can use the previewer tool to prototype faster.
Definitely worth giving Slint a shot, they learnt a lot from QML imo
The compelling use case would be sharing business logic between iOS/Android/desktop/web. If you can write core logic in Rust once and have thin UI layers per platform, that's valuable. But Iced's UI abstraction needs to be good enough that you're not fighting platform-specific behaviors constantly. Flutter tried this approach and succeeded commercially but still gets criticized for "not feeling native" on either platform.
Performance is where this could shine. Rust + Iced should theoretically have lower memory overhead and faster startup than the Kotlin runtime + Compose. For apps that manipulate large datasets locally (photo editors, video editors, CAD tools), avoiding GC pauses matters. But for typical CRUD apps that are 90% API calls and list scrolling, I doubt users would notice the difference.
The real barrier is developer experience. Kotlin has incredible IDE support via IntelliJ/Android Studio, instant hot reload, comprehensive documentation, and thousands of libraries. Rust's mobile tooling is immature by comparison. Unless you're already a Rust shop building a performance-critical app, the learning curve probably isn't justified. I'd love to be proven wrong though - more competition in the mobile development space would be healthy.
There were no good examples for how to do this but once it was set up it worked extremely well.
It uses tokio for Android/iOS/desktop and even embeds a web server for fake API for end to end testing (even on mobile)
Most of times it's just a personal preference, but sometimes it's due to using Rust libraries or already having code written in Rust that can be reused. There is Rust <-> Kotlin FFI (also Rust <-> Dart) but sometimes people don't like it
Not at the level of JVM/ART, or even C++ on VS and Live++.
Many of the UI frameworks have domain-specific hot-reloading on top of that (e.g. Dioxus can hot-reload CSS assets and RSX without resorting to binary patching) which covers the common case of wanting to quickly iterate on design details.
I've found the domain-specific stuff to be completely instant (even faster than a typical browser hot-reload). The hotpatching is typically around 0.5-2 seconds for me, but that does partially depend on project size (and of course hardware - I'm running an Apple M1 Pro).
Still, I can see that they could eventually improve those issues.
There is a really long way to go though, and accessibility on mobile comes with its own challenges as well. It will take a long time.
The native renderer should be available in 2026! (technically it's available now as a preview, but I wouldn't recommend using it until after the next release)
Slint uses the NativeActivity by default, but it supports IME by implementing the IME support in Java in the Slint's android backend.
The "lingua franca" for language bindings is the C ABI which every other OS's platform libraries (Win32/Cocoa/GTK) support.
Although, the username they picked in this case does seem a bit specific to the topic of the single comment they wrote. So it remains to be seen if this particular case was a throwaway account only used once, or if they will keep it.
See, both of us can make comments in that same condescending style, pretending to be polite.