WWDC Notes

Practical Approaches to Great App Performance

Show Apple's description.
All apps benefit from a focus on performance and an increase in overall responsiveness. This information packed session gives you strategies for fixing performance problems using Instruments and other tools. Additionally, get practical advice based on experience in tuning Apple's own apps including Xcode and Photos on iOS.
  • All performance work should be based on measurement
  • Make sure to improve performance on features used by all users instead of edge cases
  • Two tests to do:
    • Unit tests:
      • Focused benchmarks
      • Isolate issues
      • Pinpoints regressions
    • Integration Tests
      • Measures user experience
      • Measures dependencies
      • Measures side effects
      • Use the Time Profile
    • On the bottom left, you have several filters, use them to best accommodate your necessities (to visualize just the things you care about)
    • How fast your application has to be to be considered instant? Apple considers an app instant when it is ready to be used as soon as the zoom animation from the home screen (when you tap the icon) is completed. This takes between 500ms to 600ms.
    • Be lazy, proactive, constant (regardless of the amount of data we need to load), and timely (no drop frames!)
    • Things to analyze/do:
    • On launch:
      • Load database early
      • Review the queries done during launch
      • Ensure required queries are efficient as possible
      • Evaluate if information is really needed during launch
    • Storyboards:
      • Ensure only the visible views are loaded (I’m sooo guilty on this one)
      • Do as little work as possible in the initializers
    • On the visible views
      • Load only the needed data synchronously
      • Schedule preheating of the remaining data asynchronously (on background threads)
      • Cache information

Missing anything? Corrections? Contributions are welcome 😃


Written by


Federico Zanetello

Federico Zanetello is an iOS Engineer with strong passion for Swift, minimalism, and design. When he’s not busy automating things, he can be found writing at fivestars.blog and/or playing with the latest shiny toys.