SwiftUI Generations

Apple brought many improvements to SwiftUI year over year since iOS 13 was introduced in 2019. But sometimes it is frustrating that we cannot use certain functionality because it is meant to be used with a more recent iOS version. AsyncImage, for example, is not a view doing magic tricks. Everything it does can already be done on iOS 13. It simply is packaged in an "Apple approved" API and therefore will be available for the next few years.

So if you are limited to use a non-current SwiftUI version (e.g. iOS 13 and iOS 14 as of September 2021), you can build workarounds for the missing features or use third party libraries which implement the feature with their custom API.

With this project I'm proposing an alternate solution: we backport the new Apple APIs to iOS 13 in the best/most compatible way. I'm trying to bring the most important SwiftUI features of iOS 14 and 15 back to iOS 13.

So far I have the following implemented:

• AsyncImage
• Label (including LabelStyle protocol and LabelStyleConfiguration)
• ProgressView (including ProgressViewStyle protocol and ProgressViewStyleConfiguration), but without tint color initializer.
• iOS 15 Colors like mint, teal, cyan, indigo and brown
• iOS 14 Fonts like title2, title3 and caption2
• onChange(of: V, perform: @escaping (V) -> Void) value tracker for iOS 13.
• navigationTitle(...) for iOS 13
• renamed accessibilityXYZ(...) modifiers for iOS 13
• StateObject object wrapper for iOS 13.
• AppStorage object wrapper for iOS 13 (including defaultAppStorage() View modifier).
• SceneStorage object wrapper for iOS 13. (Needs integration into SceneDelegate to manage the persistence of the values.)
• ScenePhase for iOS 13 (requires the custom SceneManager to hook into the UIScene)

The sources can be found in the SwiftUIShim directory. All structs and protocols have been amended with @available to make clear, as of which iOS target the shim would not be necessary as SwiftUI contains native functionality.

The project consists of 2 main targets:

• SwiftUIShim: library implementing all necessary shims/polyfills to make a feature available on iOS 13/14
• DemoApp: implementing the basic demo screens using various SwiftUI features

The SwiftUIShim library and the DemoApp target are respecting the iOS deployment target set on the Xcode project level in the build settings. You can set it to any value between 13.0 and 15.x, clean the build folder and rebuild the DemoApp. A specific version of the library and demo app is created, which can be tested on a respective simulator instance or iOS device.
You can build different DemoApp instances for each major iOS release and compare them side by side, as they all have different product names and bundle identifiers.

Use Xcode 13.2 to build and test.