Understanding and Improving SwiftUI Performance
Article Summary
Airbnb's SwiftUI features were re-rendering way more than they should. The culprit? SwiftUI's hidden diffing algorithm was working against them.
Cal Stephens and Miguel Jimenez from Airbnb's iOS team discovered that common SwiftUI patterns were causing massive performance hits. Their investigation revealed how SwiftUI's reflection-based diffing works and why it often fails with real-world code.
Key Takeaways
- SwiftUI diffs views by reflection, but closures and reference types break the algorithm
- Custom @Equatable macro lets views control diffing without manual boilerplate
- Breaking large view bodies into smaller diffable pieces prevents unnecessary re-evaluation
- Custom SwiftLint rule alerts when view complexity exceeds threshold of 10
- Search screen scroll hitches reduced 15% after applying these techniques
Critical Insight
By understanding SwiftUI's diffing behavior and creating tooling to control it, Airbnb reduced scroll hitches by 15% on their most performance-critical screens.
