swift-cross-ui: A Swift repository from stackotter

A SwiftUI-like framework for creating cross-platform apps in Swift.

This package is still quite a work-in-progress so don't expect it to be very useful or stable yet.

NOTE: SwiftCrossUI does not attempt to replicate SwiftUI's API perfectly because SwiftCrossUI is intended to be simpler than SwiftUI. However, many concepts from SwiftUI should still be transferrable.

Community

Discussion about SwiftCrossUI now happens in the SwiftCrossUI Discord server (it used to happen in a channel of the SwiftGtk Discord server). Feel free to join if you want to get involved, discuss the library, or just be kept up-to-date on progress!

Supporting SwiftCrossUI

If you find SwiftCrossUI useful, please consider supporting me by becoming a sponsor. I spend most of my spare time working on open-source projects, and each sponsorship helps me focus more time on making high quality libraries and tools for the community.

Backends

Work has been started to support multiple different backends. Switching backends only requires changing a single line of code! Currently there's the Gtk 4 backend, as well as an experimental AppKit backend (AppKitBackend, macOS-only). All examples use GtkBackend for maximum compatibility, but you can update them manually to try out the various available backends. Work is being done to allow the backend used by the examples to be changed from the command line.

GtkBackend: Requires gtk 4 to be installed, has maximum compatibility, and supports all SwiftCrossUI features.
AppKitBackend: Experimental, only supports macOS, and currently supports a very limited subset of SwiftCrossUI features.
QtBackend: Experimental, requires qt5 to be installed, and currently supports a very limited subset of SwiftCrossUI features.

Example

Here's a simple example app demonstrate how easy it is to get started with SwiftCrossUI:

import SwiftCrossUI
// Import whichever backend you need
import GtkBackend

class CounterState: Observable {
    @Observed var count = 0
}

@main
struct CounterApp: App {
    // Optionally, you can explicitly select which imported backend to use (this is done for
    // you if only one backend is imported).
    //  typealias Backend = GtkBackend

    let identifier = "dev.stackotter.CounterApp"

    let state = CounterState()

    var body: some Scene {
        WindowGroup("CounterApp") {
            HStack {
                Button("-") { state.count -= 1 }
                Text("Count: \(state.count)")
                Button("+") { state.count += 1 }
            }
            .padding(10)
        }
    }
}

To run this example, run these commands:

git clone https://github.com/stackotter/swift-cross-ui
cd swift-cross-ui/Examples
swift run CounterExample

Other examples

A few examples are included with SwiftCrossUI to demonstrate some of its basic features;

CounterExample, a simple app with buttons to increase and decrease a count.
RandomNumberGeneratorExample, a simple app to generate random numbers between a minimum and maximum.
WindowingExample, a simple app showcasing how WindowGroup is used to make multi-window apps and control the properties of each window.
GreetingGeneratorExample, a simple app demonstrating dynamic state and the ForEach view.
FileViewerExample, an app showcasing integration with the system's file chooser.
NavigationExample, an app showcasing NavigationStack and related concepts.
SplitExample, an app showcasing sidebar-based navigation with multiple levels.
StressTestExample, an app used to test view update performance.
SpreadsheetExample, an app showcasing tables.
ControlsExample, an app showcasing the various types of controls available.

Running examples on other backends

All examples use GtkBackend by default but you can override this using the SCUI_BACKEND environment variable like so;

SCUI_BACKEND=QtBackend swift run CounterExample

Documentation

Here's the documentation site. Keep in mind that the project is still very much a work-in-progress, proper documentation and tutorials will be created once the project has matured a bit, because otherwise I have to spend too much time keeping the documentation up-to-date.

Dependencies

Swift 5.5 or higher
Gtk 4 (only required for GtkBackend)
clang (only required on Linux for GtkBackend)
Qt5 (only required for QtBackend)

macOS: Installing Gtk 4

Install Gtk 4 using HomeBrew or the package manager of your choice.

brew install pkg-config gtk4

If you run into errors related to libffi or FFI when trying to build a swift-cross-ui project (likely caused by having Xcode CLTs installed), try running the following command to patch libffi:

sed -i '' 's/-I..includedir.//g' $(brew --prefix)/Library/Homebrew/os/mac/pkgconfig/*/libffi.pc

Linux: Installing Gtk 4 and Clang

Install Gtk 4 and Clang using apt or the package manager of your choice. On most GNOME-based systems, Gtk should already be installed (although you should verify that it's Gtk 4).

sudo apt install libgtk-4-dev clang

If you run into errors related to not finding gtk/gtk.h when trying to build a swift-cross-ui project, try restarting your computer. This has worked in some cases (although there may be a more elegant solution).

Windows (experimental): Installing Gtk 4 through vcpkg

Installing Gtk 4 using vcpkg is the supported method for setting up SwiftCrossUI on Windows.

Install vcpkg

git clone https://github.com/microsoft/vcpkg C:\vcpkg
C:\vcpkg\bootstrap-vcpkg.bat

NOTE: It's important to install vcpkg to the root of C: or any other drive due to limitations of the Gtk build system.

Install Gtk 4 globally (recommended)

Run the following command to install Gtk 4 globally. This can take 45 minutes or longer depending on your machine. Running this command in the root of your drive will ensure that vcpkg doesn't run in manifest mode.

C:\vcpkg\vcpkg.exe install gtk --triplet x64-windows

After installation, you must make the following changes to your environment variables:

Set the PKG_CONFIG_PATH environment variable to C:\vcpkg\installed\x64-windows\lib\pkgconfig. This is only required for building.
Add C:\vcpkg\installed\x64-windows\bin to your Path environment variable. This is only required for running.

If installing globally fails, try deleting C:\vcpkg and starting over, otherwise file an issue to the vcpkg repository and let me know at stackotter@stackotter.dev.

Install Gtk 4 with project manifest (more unreliable)

NOTE: If the absolute path to your project contains spaces, it is possible that vcpkg will break, and installing globally will be a more reliable strategy.

You can install Gtk 4 inside your package workspace, to have a package-specific dependency store. First, create a vcpkg.json at your package root. You can download the vcpkg.json file from this repo, or create it yourself;

{
    "name": "swift-cross-ui",
    "version-string": "main",
    "dependencies": ["gtk"]
}

Change directory to your package root, then run the following command to build and install dependencies.

C:\vcpkg\vcpkg.exe install --triplet x64-windows

After installation, you must make the following changes to your environment variables:

Set the PKG_CONFIG_PATH environment variable to PACKAGE_ROOT\vcpkg_installed\x64-windows\lib\pkgconfig to allow SwiftPM to consume the installed packages.
Add C:\path\to\your\project\vcpkg_installed\x64-windows\bin to your PATH environment variable.

If you run into issues (potentially related to libsass), try installing globally instead (see above).

Distribute SwiftCrossUI Apps

vcpkg_installed\<triplet>\bin contains all required DLLs for running a SwiftCrossUI application on Windows, but not all of them are necessary.

To identify which of them are required, you can use the Dependencies tool to inspect the compiled executable, and copy all vcpkg-installed DLLs along with the executable for distribution.

Installing Qt5

# On macOS
brew install qt@5
brew link qt@5

# Linux with apt
sudo apt install qtcreator qtbase5-dev qt5-qmake cmake

Usage

Just add SwiftCrossUI as a dependency in your Package.swift. See below for an example package manifest:

import PackageDescription

let package = Package(
  name: "Example",
  dependencies: [
    .package(url: "https://github.com/stackotter/swift-cross-ui", branch: "main")
  ],
  targets: [
    .executableTarget(
      name: "Example",
      dependencies: [
        .product(name: "SwiftCrossUI", package: "swift-cross-ui")
      ]
    )
  ]
)