---
name: swiftui-uikit-interop
description: "Bridge UIKit and SwiftUI — wrap UIKit views/view controllers in SwiftUI using UIViewRepresentable/UIViewControllerRepresentable, embed SwiftUI in UIKit with UIHostingController, and handle the Coordinator delegate pattern. Use when integrating camera previews, map views, web views, mail compose, document scanners, PDF renderers, text views with attributed text, or any third-party UIKit SDK into a SwiftUI app. Also use when migrating a UIKit app to SwiftUI incrementally, or when needing UIKit features not yet available in native SwiftUI."
---

# SwiftUI-UIKit Interop

Bridge UIKit and SwiftUI in both directions. Wrap UIKit views and view controllers for use in SwiftUI, embed SwiftUI views inside UIKit screens, and synchronize state across the boundary. Targets iOS 26+ with Swift 6.2 patterns; notes backward-compatible to iOS 16 unless stated otherwise.

See `references/representable-recipes.md` for complete wrapping recipes and `references/hosting-migration.md` for UIKit-to-SwiftUI migration patterns.

## Contents

- [UIViewRepresentable Protocol](#uiviewrepresentable-protocol)
- [UIViewControllerRepresentable Protocol](#uiviewcontrollerrepresentable-protocol)
- [The Coordinator Pattern](#the-coordinator-pattern)
- [UIHostingController](#uihostingcontroller)
- [Sizing and Layout](#sizing-and-layout)
- [State Synchronization Patterns](#state-synchronization-patterns)
- [Swift 6.2 Sendable Considerations](#swift-62-sendable-considerations)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## UIViewRepresentable Protocol

Use `UIViewRepresentable` to wrap any `UIView` subclass for use in SwiftUI.

### Required Methods

```swift
struct WrappedTextView: UIViewRepresentable {
    @Binding var text: String

    func makeUIView(context: Context) -> UITextView {
        // Called ONCE when SwiftUI inserts this view into the hierarchy.
        // Create and return the UIKit view. One-time setup goes here.
        let textView = UITextView()
        textView.delegate = context.coordinator
        textView.font = .preferredFont(forTextStyle: .body)
        return textView
    }

    func updateUIView(_ uiView: UITextView, context: Context) {
        // Called on EVERY SwiftUI state change that affects this view.
        // Synchronize SwiftUI state into the UIKit view.
        // Guard against redundant updates to avoid loops.
        if uiView.text != text {
            uiView.text = text
        }
    }
}
```

### Lifecycle Timing

| Method | When Called | Purpose |
|--------|-----------|---------|
| `makeCoordinator()` | Before `makeUIView`. Once per representable lifetime. | Create the delegate/datasource reference type. |
| `makeUIView(context:)` | Once, when the representable enters the view tree. | Allocate and configure the UIKit view. |
| `updateUIView(_:context:)` | Immediately after `makeUIView`, then on every relevant state change. | Push SwiftUI state into the UIKit view. |
| `dismantleUIView(_:coordinator:)` | When the representable is removed from the view tree. | Clean up observers, timers, subscriptions. |
| `sizeThatFits(_:uiView:context:)` | During layout, when SwiftUI needs the view's ideal size. iOS 16+. | Return a custom size proposal. |

**Why `updateUIView` is the most important method:** SwiftUI calls it every time any `@Binding`, `@State`, `@Environment`, or `@Observable` property read by the representable changes. All state synchronization from SwiftUI to UIKit happens here. If you skip a property, the UIKit view will fall out of sync.

### Optional: dismantleUIView

```swift
static func dismantleUIView(_ uiView: UITextView, coordinator: Coordinator) {
    // Remove observers, invalidate timers, cancel subscriptions.
    // The coordinator is passed in so you can access state stored on it.
    coordinator.cancellables.removeAll()
}
```

### Optional: sizeThatFits (iOS 16+)

```swift
@available(iOS 16.0, *)
func sizeThatFits(
    _ proposal: ProposedViewSize,
    uiView: UITextView,
    context: Context
) -> CGSize? {
    // Return nil to fall back to UIKit's intrinsicContentSize.
    // Return a CGSize to override SwiftUI's sizing for this view.
    let width = proposal.width ?? UIView.layoutFittingExpandedSize.width
    let size = uiView.sizeThatFits(CGSize(width: width, height: .greatestFiniteMagnitude))
    return size
}
```

## UIViewControllerRepresentable Protocol

Use `UIViewControllerRepresentable` to wrap a `UIViewController` subclass -- typically for system pickers, document scanners, mail compose, or any controller that presents modally.

```swift
struct DocumentScannerView: UIViewControllerRepresentable {
    @Binding var scannedImages: [UIImage]
    @Environment(\.dismiss) private var dismiss

    func makeUIViewController(context: Context) -> VNDocumentCameraViewController {
        let scanner = VNDocumentCameraViewController()
        scanner.delegate = context.coordinator
        return scanner
    }

    func updateUIViewController(_ uiViewController: VNDocumentCameraViewController, context: Context) {
        // Usually empty for modal controllers -- nothing to push from SwiftUI.
    }

    func makeCoordinator() -> Coordinator { Coordinator(self) }
}
```

### Handling Results from Presented Controllers

The coordinator captures delegate callbacks and routes results back to SwiftUI through the parent's `@Binding` or closures:

```swift
extension DocumentScannerView {
    final class Coordinator: NSObject, VNDocumentCameraViewControllerDelegate {
        let parent: DocumentScannerView

        init(_ parent: DocumentScannerView) { self.parent = parent }

        func documentCameraViewController(
            _ controller: VNDocumentCameraViewController,
            didFinishWith scan: VNDocumentCameraScan
        ) {
            parent.scannedImages = (0..<scan.pageCount).map { scan.imageOfPage(at: $0) }
            parent.dismiss()
        }

        func documentCameraViewControllerDidCancel(_ controller: VNDocumentCameraViewController) {
            parent.dismiss()
        }

        func documentCameraViewController(
            _ controller: VNDocumentCameraViewController,
            didFailWithError error: Error
        ) {
            parent.dismiss()
        }
    }
}
```

## The Coordinator Pattern

### Why Coordinators Exist

UIKit delegates, data sources, and target-action patterns require a reference type (`class`). SwiftUI representable structs are value types and cannot serve as delegates. The Coordinator is a `class` instance that SwiftUI creates and manages for you -- it lives as long as the representable view.

### Structure

Always nest the Coordinator inside the representable or in an extension. Store a reference to `parent` (the representable struct) so the coordinator can write back to `@Binding` properties.

```swift
struct SearchBarView: UIViewRepresentable {
    @Binding var text: String
    var onSearch: (String) -> Void

    func makeCoordinator() -> Coordinator { Coordinator(self) }

    func makeUIView(context: Context) -> UISearchBar {
        let bar = UISearchBar()
        bar.delegate = context.coordinator  // Set delegate HERE, not in updateUIView
        return bar
    }

    func updateUIView(_ uiView: UISearchBar, context: Context) {
        if uiView.text != text {
            uiView.text = text
        }
    }

    final class Coordinator: NSObject, UISearchBarDelegate {
        var parent: SearchBarView

        init(_ parent: SearchBarView) { self.parent = parent }

        func searchBar(_ searchBar: UISearchBar, textDidChange searchText: String) {
            parent.text = searchText
        }

        func searchBarSearchButtonClicked(_ searchBar: UISearchBar) {
            parent.onSearch(parent.text)
            searchBar.resignFirstResponder()
        }
    }
}
```

### Key Rules

1. **Set the delegate in `makeUIView`/`makeUIViewController`, never in `updateUIView`.** The update method runs on every state change -- setting the delegate there causes redundant assignment and can trigger unexpected side effects.

2. **The coordinator's `parent` property is updated automatically.** SwiftUI updates the coordinator's reference to the latest representable struct value before each call to `updateUIView`. This means the coordinator always sees current `@Binding` values through `parent`.

3. **Use `[weak coordinator]` in closures** to avoid retain cycles between the coordinator and UIKit objects that capture it.

## UIHostingController

Embed SwiftUI views inside UIKit view controllers using `UIHostingController`.

### Basic Embedding

```swift
final class ProfileViewController: UIViewController {
    private let hostingController = UIHostingController(rootView: ProfileView())

    override func viewDidLoad() {
        super.viewDidLoad()

        // 1. Add as child
        addChild(hostingController)

        // 2. Add and constrain the view
        hostingController.view.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(hostingController.view)
        NSLayoutConstraint.activate([
            hostingController.view.topAnchor.constraint(equalTo: view.topAnchor),
            hostingController.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            hostingController.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            hostingController.view.bottomAnchor.constraint(equalTo: view.bottomAnchor),
        ])

        // 3. Notify the child
        hostingController.didMove(toParent: self)
    }
}
```

The three-step sequence (addChild, add view, didMove) is mandatory. Skipping any step causes containment callbacks to misfire, which breaks appearance transitions and trait propagation.

### Sizing Options (iOS 16+)

```swift
@available(iOS 16.0, *)
hostingController.sizingOptions = [.intrinsicContentSize]
```

| Option | Effect |
|--------|--------|
| `.intrinsicContentSize` | The hosting controller's view reports its SwiftUI content size as `intrinsicContentSize`. Use in Auto Layout when the hosted view should size itself. |
| `.preferredContentSize` | Updates `preferredContentSize` to match SwiftUI content. Use when presenting as a popover or form sheet. |

### Updating the Root View

When data changes in UIKit, push new state into the hosted SwiftUI view:

```swift
func updateProfile(_ profile: Profile) {
    hostingController.rootView = ProfileView(profile: profile)
}
```

For observable models, pass an `@Observable` object and SwiftUI tracks changes automatically -- no need to reassign `rootView`.

### UIHostingConfiguration (iOS 16+)

Render SwiftUI content directly inside `UICollectionViewCell` or `UITableViewCell` without managing a child hosting controller:

```swift
@available(iOS 16.0, *)
func collectionView(
    _ collectionView: UICollectionView,
    cellForItemAt indexPath: IndexPath
) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "cell", for: indexPath)
    cell.contentConfiguration = UIHostingConfiguration {
        ItemRow(item: items[indexPath.item])
    }
    return cell
}
```

## Sizing and Layout

### intrinsicContentSize Bridging

UIKit views wrapped in `UIViewRepresentable` communicate their natural size to SwiftUI through `intrinsicContentSize`. SwiftUI respects this during layout unless overridden by `frame()` or `fixedSize()`.

### fixedSize() and frame() Interactions

| SwiftUI Modifier | Effect on Representable |
|-----------------|------------------------|
| No modifier | SwiftUI uses `intrinsicContentSize` as ideal size; the view is flexible. |
| `.fixedSize()` | Forces the representable to its ideal (intrinsic) size in both axes. |
| `.fixedSize(horizontal: true, vertical: false)` | Fixes width to intrinsic; height remains flexible. |
| `.frame(width:height:)` | Overrides the proposed size; UIKit view receives this size. |

### Auto Layout with UIHostingController

When embedding `UIHostingController` as a child, pin its view with constraints. Use `.sizingOptions = [.intrinsicContentSize]` so Auto Layout can query the SwiftUI content's natural size for self-sizing cells or variable-height sections.

## State Synchronization Patterns

### @Binding: Two-Way Sync (SwiftUI <-> UIKit)

Use `@Binding` when both sides read and write the same value. The coordinator writes to `parent.bindingProperty` in delegate callbacks; `updateUIView` reads the binding and pushes it into the UIKit view.

```swift
// SwiftUI -> UIKit: in updateUIView
if uiView.text != text { uiView.text = text }

// UIKit -> SwiftUI: in Coordinator delegate method
func textViewDidChange(_ textView: UITextView) {
    parent.text = textView.text
}
```

### Closures: One-Way Events (UIKit -> SwiftUI)

For fire-and-forget events (button tapped, search submitted, scan completed), pass a closure instead of a binding:

```swift
struct WebViewWrapper: UIViewRepresentable {
    let url: URL
    var onNavigationFinished: ((URL) -> Void)?
}
```

### Environment Values

Access SwiftUI environment values inside representable methods via `context.environment`:

```swift
func updateUIView(_ uiView: UITextView, context: Context) {
    let isEnabled = context.environment.isEnabled
    uiView.isEditable = isEnabled

    // Respond to color scheme changes
    let colorScheme = context.environment.colorScheme
    uiView.backgroundColor = colorScheme == .dark ? .systemGray6 : .white
}
```

### Avoiding Update Loops

`updateUIView` is called whenever SwiftUI state changes -- including changes triggered by the coordinator writing to a `@Binding`. Guard against redundant updates to prevent infinite loops:

```swift
func updateUIView(_ uiView: UITextView, context: Context) {
    // GUARD: Only update if values actually differ
    if uiView.text != text {
        uiView.text = text
    }
}
```

Without the guard, setting `uiView.text` may trigger the delegate's `textViewDidChange`, which writes to `parent.text`, which triggers `updateUIView` again.

## Swift 6.2 Sendable Considerations

UIKit delegate protocols are not `Sendable`. When the coordinator conforms to a UIKit delegate, it inherits main-actor isolation from UIKit. Mark coordinators `@MainActor` or use `nonisolated` only for methods that truly do not touch UIKit state. In Swift 6.2 with strict concurrency:

```swift
@MainActor
final class Coordinator: NSObject, UISearchBarDelegate {
    var parent: SearchBarView
    init(_ parent: SearchBarView) { self.parent = parent }
    // Delegate methods are main-actor-isolated -- safe to access UIKit and @Binding.
}
```

If passing closures across isolation boundaries, ensure they are `@Sendable` or captured on the correct actor.

## Common Mistakes

### DO / DON'T

**DON'T:** Create the UIKit view in `updateUIView`.
**DO:** Create the view once in `makeUIView`; only configure/update it in `updateUIView`.
*Why:* `updateUIView` runs on every state change. Creating a new view each time destroys all UIKit state (selection, scroll position, first responder) and leaks memory.

**DON'T:** Set delegates in `updateUIView`.
**DO:** Set delegates in `makeUIView`/`makeUIViewController` only.
*Why:* Redundant delegate assignment on every update can reset internal delegate state in UIKit views like `WKWebView` or `MKMapView`.

**DON'T:** Hold strong references to the Coordinator from closures.
**DO:** Use `[weak coordinator]` in closures.
*Why:* UIKit objects often store closures (completion handlers, action blocks). A strong reference to the coordinator that holds a reference to the UIKit view creates a retain cycle.

**DON'T:** Forget to call `parent.dismiss()` or completion handlers.
**DO:** Use the coordinator to track dismissal and invoke `parent.dismiss()` in all delegate exit paths.
*Why:* Modal controllers presented by SwiftUI (via `.sheet`) need their dismiss binding toggled, or the sheet state becomes inconsistent.

**DON'T:** Ignore `dismantleUIView` for views that hold observers or timers.
**DO:** Clean up `NotificationCenter` observers, `Combine` subscriptions, and `Timer` instances in `dismantleUIView`.
*Why:* Without cleanup, observers and timers continue firing after the view is removed, causing crashes or stale state updates.

**DON'T:** Force `UIHostingController`'s view to fill the parent without proper constraints.
**DO:** Use Auto Layout constraints or `sizingOptions` for proper embedding.
*Why:* Setting `frame` manually breaks adaptive layout, trait propagation, and safe area handling.

**DON'T:** Try to use `@State` in the Coordinator -- it is not a `View`.
**DO:** Use regular stored properties on the Coordinator and communicate to SwiftUI via `parent`'s `@Binding` properties.
*Why:* `@State` only works inside `View` conformances. Using it on a class has no effect.

**DON'T:** Skip the `addChild`/`didMove(toParent:)` dance when embedding `UIHostingController`.
**DO:** Always call `addChild(_:)`, add the view to the hierarchy, then call `didMove(toParent:)`.
*Why:* Skipping containment causes viewWillAppear/viewDidAppear to never fire, breaks trait collection propagation, and causes visual glitches.

## Review Checklist

- [ ] View/controller created in `make*`, not `update*`
- [ ] Coordinator set as delegate in `make*`, not `update*`
- [ ] `@Binding` used for two-way state sync
- [ ] `updateUIView` handles all SwiftUI state changes with redundancy guards
- [ ] `dismantleUIView` cleans up observers/timers if needed
- [ ] No retain cycles between coordinator and closures (`[weak coordinator]`)
- [ ] `UIHostingController` properly added as child (`addChild` + `didMove(toParent:)`)
- [ ] Sizing strategy chosen (`intrinsicContentSize` vs fixed `frame` vs `sizeThatFits`)
- [ ] Environment values read in `updateUIView` via `context.environment` where needed
- [ ] Coordinator marked `@MainActor` for Swift 6.2 strict concurrency
- [ ] Modal controllers dismiss in all delegate exit paths (success, cancel, error)
- [ ] `UIHostingConfiguration` used for collection/table view cells instead of manual hosting (iOS 16+)

## References

- Wrapping recipes: `references/representable-recipes.md`
- Migration patterns: `references/hosting-migration.md`
- Apple docs: [UIViewRepresentable](https://sosumi.ai/documentation/SwiftUI/UIViewRepresentable)
- Apple docs: [UIViewControllerRepresentable](https://sosumi.ai/documentation/SwiftUI/UIViewControllerRepresentable)
- Apple docs: [UIHostingController](https://sosumi.ai/documentation/SwiftUI/UIHostingController)
