swiftui-uikit-interop

Imported from thiennc-teso/ios-skills (skills/swiftui-uikit-interop/SKILL.md). Install upstream with npx skills add thiennc-teso/ios-skills --skill swiftui-uikit-interop. Copyright stays with the author.

SwiftUI-UIKit Interop

Bridge UIKit and SwiftUI in both directions: wrap UIKit views and controllers for use in SwiftUI, embed SwiftUI views into existing UIKit view hierarchies, and coordinate state updates safely. Targets Swift 6.3 / iOS 26+.

Contents

• Bridging Directions
• Representable Lifecycle and Coordinator
• State Synchronization and Feedback Loops
• Embedding SwiftUI in UIKit
• Route by Task
• Common Mistakes
• Review Checklist
• References

Bridging Directions

1. UIKit into SwiftUI:
   • UIViewRepresentable: Wraps a custom UIView (e.g., text views, maps, custom controls).
   • UIViewControllerRepresentable: Wraps a UIViewController (e.g., camera controllers, document pickers, share sheets).
2. SwiftUI into UIKit:
   • UIHostingController: Embeds SwiftUI views into UIKit view controller hierarchies.
   • UIHostingConfiguration: Embeds SwiftUI views directly into UICollectionView and UITableView cells (iOS 16+).

Representable Lifecycle and Coordinator

makeCoordinator() ──> makeUIView(context:) ──> updateUIView(uiView, context:) ──> dismantleUIView(uiView, coordinator:)

• makeCoordinator(): Called once to create the delegate/coordinator object.
• makeUIView(context:): Called once to instantiate the UIKit view and assign delegates.
• updateUIView(_:context:): Called on every SwiftUI state change affecting the view. Must be idempotent.
• dismantleUIView(_:coordinator:): Cleanup point when the view leaves the hierarchy. Invalidate timers, unregister observers.

State Synchronization and Feedback Loops

[!WARNING] Prevent infinite update cycles: When UIKit notifies the coordinator of a change (e.g., textViewDidChange), the coordinator updates SwiftUI state via @Binding. This triggers updateUIView. Always check for value equality before applying updates to the UIKit view:

if uiView.text != text { uiView.text = text }

Embedding SwiftUI in UIKit

When adding a UIHostingController as a child view controller:

1. addChild(hostingController)
2. view.addSubview(hostingController.view)
3. Set Auto Layout constraints
4. hostingController.didMove(toParent: self)

Use UIHostingConfiguration for modern cell layouts in UICollectionView/UITableView without manual controller management.

Route by Task

• For wrapping MKMapView, UITextView, and camera capture controllers, read Map, Text, and Camera Wrappers.
• For PHPickerViewController, MFMailComposeViewController, UIActivityViewController, and search controllers, read Picker, Mail, Share, and Search Wrappers.
• For PDFView, QLPreviewController, and MFMessageComposeViewController, read PDF and Message Wrappers.
• For embedding SwiftUI in UIKit table/collection cells, navigation transitions, and full hosting migration, read Hosting Migration.

Common Mistakes

• Re-creating heavy UIKit objects inside updateUIView instead of configuring the existing instance.
• Omitting equality checks in updateUIView, triggering continuous render feedback loops.
• Adding a UIHostingController's view without calling addChild and didMove(toParent:).
• Forgetting to clean up delegates, KVO, or NotificationCenter observers in dismantleUIView.
• Ignoring safe area insets and sizing calculations (sizeThatFits) in custom representables.

Review Checklist

• makeCoordinator used for delegates, target-actions, and data sources
• updateUIView guards against redundant assignments to avoid feedback loops
• Child view controller containment calls (addChild, didMove) properly paired
• Cell layouts in UIKit use UIHostingConfiguration where available
• Subscribed observers and display links invalidated in dismantleUIView
• Auto Layout constraints configured with translatesAutoresizingMaskIntoConstraints = false

References

• Map, text, and camera representable recipes
• Picker, mail, share, and search recipes
• PDF, QuickLook, and message composer recipes
• Hosting migration and UIHostingController guide
• UIViewRepresentable
• UIViewControllerRepresentable
• UIHostingController