iOS 26 - UIKit Gets SwiftUI Superpowers: Observable and updateProperties

The line between UIKit and SwiftUI continues to blur in the most delightful way. With iOS 26, Apple has brought one of SwiftUI's most beloved features—automatic observation tracking—directly into UIKit. Combined with the new updateProperties() lifecycle method, UIKit developers can now enjoy the reactive programming benefits that SwiftUI developers have been raving about since long.

The End of Manual UI Updates

Remember this familiar UIKit code?

class ProfileViewController: UIViewController {
    var user: User? {
        didSet { updateUI() }
    }

    func updateUI() {
        nameLabel.text = user?.name
        avatarImageView.image = user?.avatar

        setNeedsLayout()
    }
}

Forget to call updateUI()? Your UI stays stale. Call it too often? Performance takes a hit. This tedious pattern has been the bane of UIKit developers for years.

Those days are officially over.

Introducing Automatic Observation Tracking

iOS 26 brings Swift's @Observable macro to UIKit with full automatic tracking capabilities. When you access observable properties in specific UIKit methods, the framework automatically establishes dependencies and invalidates views when those properties change.

Basic Observable Integration

Here's how simple it becomes:

@Observable class UnreadMessagesModel {
    var showStatus: Bool
    var statusText: String
}

class MessageListViewController: UIViewController {
    var unreadMessagesModel: UnreadMessagesModel
    var statusLabel: UILabel

    override func viewWillLayoutSubviews() {
        super.viewWillLayoutSubviews()
        // UIKit automatically tracks these dependencies
        statusLabel.alpha = unreadMessagesModel.showStatus ? 1.0 : 0.0
        statusLabel.text = unreadMessagesModel.statusText
    }
}

That's it! No manual setNeedsLayout() calls, no property observers, no update methods. UIKit automatically:

1. Tracks dependencies on showStatus and statusText during the first layout
2. Invalidates the view whenever these properties change
3. Reruns viewWillLayoutSubviews() to keep your UI in sync

Collection Views Made Effortless

The real magic happens with collection views. Configure cells once, and they automatically update when their models change:

@Observable class ListItemModel {
    var icon: UIImage
    var title: String
    var subtitle: String
}

func collectionView(
    _ collectionView: UICollectionView, 
    cellForItemAt indexPath: IndexPath
) -> UICollectionViewCell {
    let cell = collectionView.dequeueReusableCell(withReuseIdentifier: "Cell", for: indexPath)
    let listItemModel = listItemModel(for: indexPath)

    cell.configurationUpdateHandler = { cell, state in
        var content = UIListContentConfiguration.subtitleCell()
        content.image = listItemModel.icon    // Automatically tracked
        content.text = listItemModel.title     // Automatically tracked
        content.secondaryText = listItemModel.subtitle  // Automatically tracked
        cell.contentConfiguration = content
    }
    return cell
}

Any change to your ListItemModel properties while the cell is visible will automatically trigger the configuration handler. No more manual cell reloading!

Meet updateProperties(): The New Lifecycle Method

iOS 26 introduces a game-changing addition to the UIKit lifecycle: updateProperties(). This method runs just before layoutSubviews() but operates independently, giving you finer-grained control over your updates.

Why updateProperties() Matters

Traditional UIKit forces you to handle both property updates and layout in layoutSubviews(). This leads to:

• Unnecessary work when only properties change
• Performance bottlenecks from over-invalidation
• Coupling between property logic and layout logic

The new updateProperties() method solves this by creating a dedicated phase for property updates:

@Observable class BadgeModel {
    var badgeCount: Int?
}

class MyViewController: UIViewController {
    var model: BadgeModel
    let folderButton: UIBarButtonItem

    override func updateProperties() {
        super.updateProperties()
        if let badgeCount = model.badgeCount {
            folderButton.badge = .count(badgeCount)
        } else {
            folderButton.badge = nil
        }
    }
}

Understanding the Update Cycle

Here's how the enhanced UIKit update cycle works:

1. Trait Updates - UIKit updates the trait collection
2. updateProperties() - Your property configuration runs (NEW!)
3. layoutSubviews() - Layout calculations and positioning
4. Display Pass - Drawing and rendering

This separation means:

• Property changes don't force unnecessary layout passes
• Layout changes don't trigger redundant property updates
• Better performance through targeted invalidation

You can manually trigger property updates using:

• setNeedsUpdateProperties() - Schedule an update for the next cycle
• updatePropertiesIfNeeded() - Force an immediate update if pending

Seamless Animations with flushUpdates

iOS 26 also introduces the flushUpdates animation option, which automatically handles observable updates within animation blocks:

// Before iOS 26 - Manual approach
UIView.animate(withDuration: 0.3) {
    model.badgeColor = .red
    view.layoutIfNeeded()  // Required manual call
}

// iOS 26 - Automatic approach
UIView.animate(withDuration: 0.3, options: [.flushUpdates]) {
    model.badgeColor = .red
    // UIKit automatically handles the rest!
}

The flushUpdates option works with any invalidating changes, including Auto Layout constraints:

UIView.animate(options: [.flushUpdates]) {
    topSpacingConstraint.constant = 20
    leadingEdgeConstraint.isActive = false
    trailingEdgeConstraint.isActive = true
}

Backwards Compatibility

The best part? You can start using automatic observation tracking today, even on iOS 18! Simply add this key to your Info.plist:

<key>UIObservationTrackingEnabled</key>
<true/>

In iOS 26, this feature is enabled by default, so the plist key becomes unnecessary.

Best Practices and Considerations

Where Observation Works

Automatic tracking is supported in specific UIKit methods:

• viewWillLayoutSubviews() in view controllers
• layoutSubviews() in views
• updateProperties() in both (iOS 26+)
• Cell configuration handlers
• Various update-related callbacks

Performance Tips

• Cache expensive computations since update methods may run frequently
• Keep mutations on the main thread to avoid UI inconsistencies
• Be mindful of retain cycles - Observable objects are retained while observed

The Bigger Picture

This integration represents more than just a convenience feature—it's a fundamental shift in how UIKit and SwiftUI interoperate. Apple is clearly committed to bringing the best ideas from both frameworks together, creating a unified development experience.

With automatic observation tracking and updateProperties(), UIKit developers can now:

• Write less boilerplate code for UI updates
• Achieve better performance through intelligent invalidation
• Create more maintainable apps with clearer data flow
• Gradually adopt SwiftUI patterns without full migration

Ready to modernize your UIKit apps?

1. Update to iOS 26 SDK and compile your existing apps
2. Identify manual update patterns in your codebase
3. Convert appropriate models to use @Observable
4. Implement updateProperties() for property-specific logic
5. Leverage flushUpdates for smoother animations

The future of UIKit is here, and it's more reactive, more performant, and more delightful than ever. Welcome to the new era of iOS development!