UIKit vs. SwiftUI: Key Differences for iOS Development

Both UIKit and SwiftUI are frameworks for building user interfaces on Apple platforms (iOS, macOS, watchOS, tvOS), but they have fundamental differences in design, syntax, and usage.

1. Declarative vs. Imperative Programming

✅ SwiftUI → Declarative

You describe what the UI should do (e.g., "Show a list of items").
The framework handles rendering and updates automatically.
Example:

List(items) { item in
    Text(item.name)
}

✅ UIKit → Imperative

You write how the UI should behave (e.g., manually managing UITableView cells, delegates, and data sources).
More control but requires boilerplate code.
Example:

func tableView(_ tableView: UITableView, cellForRowAt indexPath: IndexPath) -> UITableViewCell {
    let cell = tableView.dequeueReusableCell(withIdentifier: "Cell", for: indexPath)
    cell.textLabel?.text = items[indexPath.row].name
    return cell
}

2. Compatibility & Deployment

✅ SwiftUI

Requires iOS 13+ (some features need iOS 14/15+).
Best for new apps (not ideal for legacy support).
✅ UIKit

Works on iOS 2.0+ (fully stable for all versions).
Better for maintaining older apps.

3. Live Preview & Development Speed

✅ SwiftUI

Xcode Previews allow real-time UI updates without running the app.
Faster prototyping.
✅ UIKit

No built-in live preview (requires Storyboards/XIBs or running the app).
More time-consuming for UI adjustments.

4. State Management

✅ SwiftUI

Uses @State, @ObservedObject, @Binding for reactive updates.
Changes automatically trigger UI updates.
✅ UIKit

Manual state management (e.g., updating UILabel.text explicitly).
Requires delegation, notifications, or Combine for reactivity.

5. Cross-Platform Support

✅ SwiftUI

Works on iOS, macOS, watchOS, tvOS with the same codebase (with minor adjustments).
✅ UIKit

Primarily for iOS/tvOS (macOS requires AppKit adaptations).

6. Animation & Transitions

✅ SwiftUI

Easier animations with .animation() and withAnimation.
Example:

Button("Animate") {
    withAnimation {
        scale *= 1.5
    }
}
.scaleEffect(scale)

✅ UIKit

More powerful but requires UIView.animate(withDuration:).
Fine-grained control over animations.

7. Adoption & Ecosystem

✅ SwiftUI

Future of Apple development (Apple is pushing it hard).
Still missing some advanced controls (e.g., UICollectionView with complex layouts).
✅ UIKit

Mature & battle-tested (all major apps use it).
More third-party libraries and resources available.

Can You Mix Both?

Yes! You can use SwiftUI inside UIKit (UIHostingController) and UIKit inside SwiftUI (UIViewRepresentable).

SwiftUI:

Declarative Syntax:

SwiftUI uses a declarative approach, where you describe what the UI should look like, and the framework handles the underlying implementation details. This generally leads to less code and faster development.

Modern Framework:

SwiftUI is the newer framework, designed to be the future of UI development on Apple platforms.

Cross-Platform:

SwiftUI allows you to build UIs that can run on iOS, macOS, watchOS, and tvOS with minimal code changes.

Live Preview:
SwiftUI offers a live preview feature in Xcode, allowing you to see changes in real-time as you write code.

Final Verdict

SwiftUI → Best for new projects, rapid development, and Apple’s future ecosystem.
UIKit → Still essential for legacy apps, complex UIs, and full control.