floui-rs

Rust bindings for floui, pronounced "flowy", a proof-of-concept single header C++17 lib inspired by SwiftUI, which wraps native iOS and Android controls/widgets, and integrates into the de facto build environments of each platform (XCode and Android Studio).

Currently available controls:

Text
TextField
Button
VStack (Vertical UIStackView on iOS and LinearLayout on Android)
HStack (Horizontal UIStackView on iOS and LinearLayout on Android)
Spacer
Toggle/Check (tvOS doesn't support it)
Slider (tvOS doesn't support it)
ImageView
WebView
ScrollView

Usage

You can check out the floui-rs-template, which is structured to be able to build for both ios or android from the command-line.

If you would like to build purely for iOS and only using Rust (no Objective-C), check the example here.

Otherwise, if you would like to do it manually:

Build your library as a static-lib:

# Cargo.toml
[lib]
crate-type = ["static-lib"]

[dependencies]
floui = "0.1"

Build against the android and ios architectures you might need.

Rust

use floui::{enums::*, prelude::*, widgets::*};
use std::cell::RefCell;
use std::rc::Rc;

fn mygui(vc: &ViewController) -> MainView {
    let count = Rc::from(RefCell::from(0));
    MainView::new(
        &vc,
        &[
            &Button::new("Increment").foreground(Color::Blue).action({
                let count = count.clone();
                move |_| {
                    log("Increment clicked");
                    let mut c = count.borrow_mut();
                    *c += 1;
                    let t: Text = from_id("mytext").unwrap();
                    t.text(&format!("{}", c));
                }
            }),
            &Text::new("0").id("mytext").center().bold(),
            &Button::new("Decrement")
                .foreground(Color::Red)
                .action(move |_| {
                    log("Decrement clicked");
                    let mut c = count.borrow_mut();
                    *c -= 1;
                    let t: Text = from_id("mytext").unwrap();
                    t.text(&format!("{}", c));
                }),
        ],
    )
}

use std::os::raw::c_void;

#[no_mangle]
extern "C" fn floui_handle_events(arg1: *mut c_void) {
    unsafe { ViewController::handle_events(arg1); }
}

#[no_mangle]
extern "C" fn floui_main(arg1: *mut c_void, arg2: *mut c_void, arg3: *mut c_void) -> *mut c_void {
    let vc = unsafe { ViewController::new(arg1, arg2, arg3) };
    mygui(&vc).underlying() as _
}

Notes on certain usages

Sliders on Android take the full width of the LinearLayout, so this must be taken into consideration if code is shared also with iOS.
Adding images has to be in the project's resource file.
- In Android Studio: Resource Manager, Import Drawables. This will add the file to res/drawable. The file can be accessed directly ImageView::load("MyImage.jpg").
- In XCode: You can simply drag images into Assets.xcassets, then the image can be accessed directly ImageView::load("MyImage.jpg").
Using the WebView widget
- on iOS:
  - Requires adding WebKit.framework under General > Frameworks, Libraries and Embedded Content.
  - Requires enabling the ios-webview flag in your Cargo.toml.
  - Local files can be loaded using WebView::load_url() but need to be preceded by file:///, the files should be added to your xcode project.
- On Android:
  - To load local files, precede them with file:/// and the path of the file, which should be added to an assets folder (File > New > Folder > Assets folder). This then can be loaded using WebView::load_url().
  - To load http requests, you need to enable the internet permission in your AndroidManifest.xml: <uses-permission android:name="android.permission.INTERNET" />

Creating new widgets

Wrapping platform widgets doesn't require using C++, it requires that the widget implements WidgetExt, and the underlying (JNI jobject pointer for Android, UIView on iOS) can be retrieved. You can use the jni-rs crate and objc crates for such purposes.

Target-specific structure

iOS

Add the required ios rustup targets.
Install cargo-lipo.
Add the built library to your xcode project (under Build Phases > Link Binary with Libraries).
Modify the library search path to find the library (under Build Settings > Library Search Paths).
Modify your ViewController.m file:

#import "ViewController.h"

extern void *floui_main(void *, void *, void *);

@interface ViewController ()

@end

@implementation ViewController
- (void)viewDidLoad {
    [super viewDidLoad];
    floui_main((void *)CFBridgingRetain(self), nil, nil);
}

@end

Android

ANDROID_SDK_ROOT should be set to your android sdk directory.
ANDROID_NDK_ROOT should be set to your android ndk directory.
Add the required android rustup targets.
Create an Android Studio Native C++ project, choose toolchain C++ 17 in the last step.
Modify your CMakeLists.txt:

cmake_minimum_required(VERSION 3.4.1)
project(myapplication)

find_library(log-lib log)

add_library(myapplication SHARED native-lib.cpp)
add_library(rust-lib STATIC IMPORTED)

if (ANDROID_ABI STREQUAL x86)
    set(RUST_ARCH i686-linux-android)
elseif (ANDROID_ABI STREQUAL armeabi-v7a)
    set(RUST_ARCH armv7-linux-androideabi)
elseif (ANDROID_ABI STREQUAL arm64-v8a)
    set(RUST_ARCH aarch64-linux-android)
elseif (ANDROID_ABI STREQUAL x86_64)
    set(RUST_ARCH x86_64-linux-android)
else ()
    message(FATAL "Unknown architecture")
endif ()

set_property(TARGET rust-lib PROPERTY IMPORTED_LOCATION_DEBUG ${CMAKE_CURRENT_LIST_DIR}/app/target/${RUST_ARCH}/debug/libapp.a)
set_property(TARGET rust-lib PROPERTY IMPORTED_LOCATION_RELEASE ${CMAKE_CURRENT_LIST_DIR}/app/target/${RUST_ARCH}/release/libapp.a)

target_link_libraries(myapplication android rust-lib ${log-lib})

Modify your C++ file to just call the Rust lib.

#include <jni.h>
#include <string>

extern "C" void *floui_main(void *, void *, void *);

extern "C" void floui_handle_events(void *);

extern "C" JNIEXPORT jobject JNICALL
Java_com_example_myapplication_MainActivity_mainView(JNIEnv* env, jobject main_activity, jobject view) {
    return (jobject) floui_main(env, main_activity, view);
}

extern "C" JNIEXPORT void JNICALL
Java_com_example_myapplication_MainActivity_handleEvent(JNIEnv *env, jobject thiz, jobject view) {
    floui_handle_events(view);
}

Modify your MainActivity.java to look like:

package com.example.myapplication;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.constraintlayout.widget.ConstraintLayout;

import android.os.Bundle;
import android.view.View;

import com.google.android.material.slider.Slider;

public class MainActivity extends AppCompatActivity implements View.OnClickListener, Slider.OnChangeListener {
    static {
        System.loadLibrary("myapplication");
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ConstraintLayout layout = new ConstraintLayout(this);
        setContentView(layout);
        mainView(layout);
    }
    public native View mainView(View view);
    public native void handleEvent(View view);

    @Override
    public void onClick(View view) {
        handleEvent(view);
    }

    @Override
    public void onValueChange(@NonNull Slider slider, float value, boolean fromUser) {
        handleEvent(slider);
    }
}

floui 0.1.5