On a phone screen the interviewer asks: "A user reports that scrolling stutters. Where would you start?" Walk through the diagnostic order and what you look at in each step.
Reproduce it first by narrowing the conditions (device, OS, screen, data volume), then find the regions where the main thread goes past 16ms (8ms at 120Hz) with Instruments Animation Hitches and Time Profiler. The usual causes are image decoding during cell setup, synchronous I/O, layout recalculation, and offscreen rendering.
Performance and debuggingMultiple choiceBasics
You inherit an app whose UICollectionView stutters while scrolling. Which of these can…
#scroll #main-thread
UIKitShort answerAdvanced
You get a report that scrolling stutters on a feed screen that mixes images and text…
#scroll #hitch
Performance and debuggingShort answerBasics
All you've got is vague feedback that "the app is slow." How do you approach that with…
#time-profiler
Performance and debuggingMultiple choiceIntro
Tapping a certain button freezes the screen for about a second. To see which function on…
#time-profiler