How Airbnb Revolutionized iOS UI Development with Epoxy

How Airbnb's Epoxy Framework Solved Our Biggest iOS UI Headaches (And How You Can Use It Too)

If you've ever built a complex iOS interface with UIKit, you know the pain. Massive view controllers. Endless delegate methods. State management spaghetti code. By 2018, Airbnb's iOS codebase was drowning in these problems - until they built Epoxy, a declarative UI framework that completely changed their approach to iOS development.

The difference between traditional UIKit and Epoxy - less code, fewer bugs

Why UIKit Was Failing Airbnb

Airbnb's app had grown into one of the most complex iOS codebases in the world:

• 300+ unique screen types
• 5,000+ UI components
• 40+ engineers committing daily

The traditional UIKit approach was crumbling under this scale:

The 5 Worst UIKit Pain Points

1. View controllers with 3,000+ lines of UI code
2. Crash-prone manual diffing in tables/collections
3. State spread across 10+ properties per screen
4. Brittle inheritance hierarchies for custom cells
5. 50% of bugs were UI-related

One engineer confessed: "I spent more time debugging UICollectionView quirks than building actual features."

The Epoxy Solution: Declarative UI Done Right

Epoxy's core philosophy was simple: Describe what you want, not how to do it. Instead of:

// Traditional UIKit (Imperative)
func updateUI() {
    if isLoading {
        spinner.startAnimating()
        tableView.isHidden = true
    } else {
        spinner.stopAnimating()
        tableView.isHidden = false
        tableView.reloadData()
    }
}

Epoxy let developers write:

// Epoxy (Declarative)
List {
    if isLoading {
        LoadingSpinner()
    } else {
        items.map { item in
            ItemRow(item)
        }
    }
}

Key Technical Innovations

What made Epoxy special under the hood:

Feature	Benefit
Diffing Algorithm	Only updates changed views
Batching System	Prevents UI flickering
State Management	Single source of truth
Style Propagation	Consistent theming

Real Impact on Airbnb's Codebase

The numbers spoke for themselves after adoption:

Code Reduction

• 72% fewer lines for list UIs
• 58% smaller view controllers
• 90% less state management code

Quality Improvements

• 66% fewer UI-related crashes
• 40% faster onboarding
• 3x quicker iteration

Adopting Epoxy: Challenges and Solutions

Migration wasn't without hurdles:

1. Learning Curve

Developers used to UIKit needed to rethink UI development. Solution:

• Interactive workshops
• Gradual adoption path
• Dedicated "Epoxy mentors"

2. Performance Optimization

Early versions had issues with ultra-large lists. Fixes included:

• Smart cell recycling
• Background diffing
• Priority-based rendering

3. Legacy Integration

They created adapters for:

EpoxyAdapter(legacyViewController)
    .insert(into: self)

Epoxy vs. SwiftUI: How They Compare

When SwiftUI launched, many asked: "Why not just use that?" Key differences:

	Epoxy	SwiftUI
Minimum iOS	iOS 12+	iOS 13+
UIKit Integration	Seamless	Clunky
Diffing Control	Customizable	Opaque

Getting Started with Epoxy

Basic setup for Blogger developers:

// 1. Add to Podfile
pod 'Epoxy'

// 2. Basic list example
import Epoxy

final class MyViewController: CollectionViewController {
  override func viewDidLoad() {
    super.viewDidLoad()
    setSections([
      Section(items: [
        TextRow("Hello Epoxy!")
          .style(.body)
      ])
    ])
  }
}

Future of Epoxy

Airbnb continues investing in:

• SwiftUI interoperability
• Animation APIs
• Form builders
• Accessibility enhancements

The framework remains fully open-source on GitHub.

Key Takeaways

1. Declarative wins for complex UIs
2. Incremental adoption beats rewrites
3. Open-source pays off long-term

As one Airbnb engineer summarized: "Epoxy didn't just change our code - it changed how we think about iOS development."