OpenSwiftUI

OpenSwiftUI is an OpenSource implementation of Apple's SwiftUI DSL (Domain-specific language).

The project's goal is to stay close to the original API as possible.

Currently, this project is in early development.

Background

Apple introduced SwiftUI at WWDC 19. Since then, developing applications with graphical user interfaces became more comfortable to read, write, and maintain. Unfortunately, the principle "Learn once, apply anywhere" works on Apple platforms, only.

Swift runs on Apple platforms, the web, Linux, Windows, and even on embedded devices. Wouldn't it be great if you could write GUI based applications with SwiftUI on platforms that run Swift?

SwiftUI on your platform

OpenSwiftUI provides the API — other projects can implement the actual rendering of UI elements for different platforms like Linux, Windows, Embedded, and many more.

SwiftUIEmbedded is one of the first projects that make use of OpenSwiftUI (Demo).

Contributing

Over time and collective guesswork, it should be possible to re-create the complete SwiftUI API from Apple. Check the Status overview to see what's missing or needs to be completed.

A good starting point is to get familiar with the SwiftUI interface, focus on certain functionality, and try to re-implement it. A helpful tool is to use reflection (Mirror(reflecting: …)) to peek into SwiftUI types and instances. This reveals the internal structure of instances (properties, types, names and inheritance).

Once you implemented a missing piece, please feel free to contribute a pull request.

Please note:

Private methods and properties of SwiftUI should be prefixed by an _ (underscore) and marked as public in OpenSwiftUI. Doing this is necessary because the frontend might need access.

Xcode 11.2 or higher is required.

Status

Views and Controls

Essentials

Status	Name	Notes
✅	protocol View

Text

Status	Name	Notes
✅	struct Text
❌	struct TextField
❌	struct SecureField
✅	struct Font

Images

Status	Name	Notes
⚠️	struct Image	CGImage not supported

Buttons

Status	Name	Notes
✅	struct Button
❌	struct NavigationLink
❌	struct MenuButton
❌	struct EditButton
❌	struct PasteButton

Value Selectors

Status	Name	Notes
❌	struct Toggle
⚠️	struct Picker
❌	struct DatePicker
❌	struct Slider
⚠️	struct Stepper

Supporting Types

Status	Name	Notes
✅	struct ViewBuilder
✅	protocol ViewModifier

View Layout and Presentation

Stacks

Status	Name	Notes
✅	struct HStack
✅	struct VStack
✅	struct ZStack

Lists and Scroll Views

Status	Name	Notes
❌	struct List
❌	protocol DynamicViewContent
✅	protocol Identifiable	Provided by Swift.
✅	struct ForEach
❌	struct ScrollView
⚠️	enum Axis

Container Views

Status	Name	Notes
❌	struct Form
⚠️	struct Group
❌	struct GroupBox
❌	struct Section

Spacer and Dividers

Status	Name	Notes
✅	struct Spacer
✅	struct Divider

Architectural Views

Status	Name	Notes
❌	struct NavigationView
❌	struct TabView
❌	struct HSplitView
❌	struct VSplitView

Presentations

Status	Name	Notes
❌	struct Alert
❌	struct ActionSheet

Conditionally Visible Items

Status	Name	Notes
✅	struct EmptyView
❌	struct EquatableView

Infrequently Used Views

Status	Name	Notes
⚠️	struct AnyView	init?(_fromValue value: Any) missing.
✅	struct TupleView

Drawing and Animation

Essentials

Status	Name	Notes
⚠️	protocol Shape

Animation

Status	Name	Notes
❌	struct Animation
❌	protocol Animatable
❌	protocol AnimatableModifier
❌	func withAnimation<Result>(Animation?, () -> Result) -> Result
❌	struct AnimationPair
❌	struct EmptyAnimationData
❌	struct AnyTransition

Shapes

Status	Name	Notes
⚠️	struct Rectangle
✅	enum Edge
❌	struct RoundedRectangle
⚠️	struct Circle
❌	struct Ellipse
❌	struct Capsule
❌	struct Path

Transformed Shapes

Status	Name	Notes
❌	protocol InsettableShape
❌	struct ScaledShape
❌	struct RotatedShape
❌	struct OffsetShape
❌	struct TransformedShape

Paints, Styles, and Gradients

Status	Name	Notes
✅	struct Color
❌	struct ImagePaint
❌	struct Gradient
❌	struct LinearGradient
❌	struct AngularGradient
❌	struct RadialGradient
❌	struct ForegroundStyle
❌	struct FillStyle
❌	protocol ShapeStyle
❌	enum RoundedCornerStyle
❌	struct SelectionShapeStyle
❌	struct SeparatorShapeStyle
❌	struct StrokeStyle

Geometry

Status	Name	Notes
❌	struct GeometryProxy
❌	struct GeometryReader
❌	protocol GeometryEffect
❌	struct Angle
❌	struct Anchor
❌	struct UnitPoint
❌	enum CoordinateSpace
❌	struct ProjectionTransform
❌	protocol VectorArithmetic

State and Data Flow

Bindings

Status	Name	Notes
⚠️	struct Binding

Data-Dependent Views

Status	Name	Notes
✅	struct State
❌	struct ObservedObject
❌	struct EnvironmentObject
❌	struct FetchRequest
❌	struct FetchedResults
⚠️	protocol DynamicProperty	func update() missing.

Environment Values

Status	Name	Notes
✅	struct Environment
✅	struct EnvironmentValues

Preferences

Status	Name	Notes
❌	protocol PreferenceKey
❌	struct LocalizedStringKey

Transactions

Status	Name	Notes
❌	struct Transaction

Gestures

Basic Gestures

Status	Name	Notes
❌	struct TapGesture
❌	struct LongPressGesture
❌	struct DragGesture
❌	struct MagnificationGesture
❌	struct RotationGesture

Combined Gestures

Status	Name	Notes
❌	struct SequenceGesture
❌	struct SimultaneousGesture
❌	struct ExclusiveGesture

Custom Gesture

Status	Name	Notes
❌	protocol Gesture
❌	struct AnyGesture

Dynamic View Properties

Status	Name	Notes
❌	struct GestureState
❌	struct GestureStateGesture

Gesture Support

Status	Name	Notes
❌	struct GestureMask
❌	struct EventModifiers

Legend

Symbol	Description
✅	Done
❌	Open
⚠️	Incomplete

Resources

SwiftUI Interface

Compared to what you can see in Xcode, this gist shows you more than just the public interfaces. It shows private properties, and the body of @inlinable marked properties, functions, and initializers.

/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks/SwiftUI.framework/Versions/A/Modules/SwiftUI.swiftmodule/x86_64.swiftinterface

SwiftWebUI

SwiftWebUI is an implementation of SwiftUI for the web by Helge Heß. This project's goal is focused exclusively on the web. It deviates a little bit from SwiftUI by taking some shortcuts here and there -- but looks quite complete in functionality and is great for inspiration.

SwiftUI symbols

This command prints the symbol table of SwiftUI via the llvm-mn utility.

nm -gUj /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Library/Developer/CoreSimulator/Profiles/Runtimes/iOS.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/SwiftUI.framework/SwiftUI | swift-demangle | sed 's/SwiftUI.//g' | sed 's/Swift.//g'

You can also have a look at this gist instead.

Links

• SwiftUI @ViewBuilder Result is a TupleView, How is Apple Using It And Able to Avoid Turning Things Into AnyVIew?
• https://stackoverflow.com/questions/56434549/what-enables-swiftuis-dsl
• Building Custom Views with SwiftUI
• SwiftUI Essentials
• Data Flow Through SwiftUI
• Introducing SwiftUI: Building Your First App
• SwiftUI On All Devices

Special thanks

I want to give special thanks to Helge Heß. He created SwiftWebUI, contributed many suggestions to OpenSwiftUI, and helped with insights of his findings.

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Contact

• Devran "Cosmo" Uenal
• Twitter: @maccosmo
• LinkedIn: devranuenal

License

OpenSwiftUI is released under the MIT License.