Integrating SwiftUI with UIKit and back again

The introduction of SwiftUI brought a whole new paradigm to developing apps on all of Apple's platforms. Certainly now that iOS 14 is here, it's never been a better way to learnQ However in most day-to-day codebases, getting SwiftUI to integrate nicely in existing UIKit code will be of critical importance. This presentation covers integrating SwiftUI into UIKit, and vice versa, in order to use the best of both worlds to build better products faster.

Transcript

1. Integrating SwiftUI with UIKit and back again Tim Oliver iOS Software Engineer, Drivemode @TimOliverAU
2. Who? •From Perth, Australia, currently living in Japan. •Been a fan of iOS development since iPhone 3G. •Full-time iOS developer since 2013, at Realm and Mercari, and Drivemode. •Loves publishing open source libraries. •Enjoys karaoke and video games in free time.
3. Side-Projects iComics TOCropViewController
4. The Good ‘ol Days •400 Mhz single core CPU •128MB of system memory. •320x480 screen size. •Extremely slow GPU. •No Grand Central Dispatch. •Manual memory management. •Some language called “Objective-C”
5. There’s never
 been a better 
 time to start! 
 Apple, 2019
6. That being said…
7. Crusty Pragmatic…
8. Our recommended best practice is to support the latest shipping OS version (currently iOS 13), plus one prior version (iOS 12). The vast majority of devices support this mix of iOS versions. Apple Staff Member, June 2020
 https://developer.apple.com/forums/thread/650223
15. https://github.com/jordansinger/SwiftUI-Kit
20. •It’s absolutely amazing. •Saves so much time and effort. ☺ •Potentially quite limiting. •MANY edge cases. •Potential show-stopping bugs. Thinking About It
21. By default, aim to build in SwiftUI. If the quality dips too much, or the implementation gets too hacky, defer back to UIKit. New Modus Operandi
22. Best of Both Worlds SwiftUI SwiftUI SwiftUI SwiftUI
23. An Example •Exploring building entirely in SwiftUI. •Big requirement that app allows dynamic routing/UI state restoration. •“Possible”, but quite hacky in SwiftUI. •Quite trivial to combine SwiftUI with UINavigationController.
24. Wrapping in a classic view controller •It’s completely possible to make the external interface look like a regular UIKit view controller.
25. Modify look of parent navigation controller
26. What about pushing new view controllers? •Not accessible to View by default. •“Could” manually inject from UIHostingController •Actually helps promote decoupling between views. •Check out the “coordinator” or “router” code patterns.
27. Delegates / Event Callbacks • You can expose regular closures from a SwiftUI view. •Can access directly via rootView property. •Can be used to route interactions to any of the regular Cocoa methods
28. Wrapping UIKit in SwiftUI •EXTREMELY simple interface. •Optional Coordinator for delegates.
29. One big gotcha. •SwiftUI is value type (Structs), UIKit is reference type (objects) PageView
 (UIView Container) Receives Array of
 SwiftUI views UIPageViewController Generated Hosting Controllers UIPageViewController Delegate Updated state, which refreshed hosted SwiftUI views •SwiftUI elements will be refreshed, but UIKit ones do not. •Compare UIKit state to SwiftUI to avoid infinite loops.
30. Getting Position of Elements •Use gesture recognisers to capture the location. •Can also potentially use GeometryReader feature. •Somewhat brittle if layout changes after the fact.
31. In Conclusion •Take advantage of SwiftUI’s speed and flexibility. •Be aware of limitations, so you can mitigate if necessary. •Best of both worlds can create some amazing experiences quickly. •Have fun!
32. Thanks for Listening! TimOliver @TimOliverAU