Khanh Bui

The iPhone Duo goes on sale tomorrow. 6pm already knows how you're holding it. We built five layouts for one phone, all on the Xcode 27.1 simulator. What we learned designing a money app for a hinge 🧵

The difference between "animated" and "native" is what happens when your finger lets go. UIKit doesn't ask "how far did you drag?" It asks "where were you heading?" So in our Expo app, every swipe projects its release velocity with UIScrollView's own deceleration rate before deciding: project(v) = (v/1000 · 0.998) / (1 − 0.998) A short fast flick commits. A long slow drag springs home. And the spring that finishes the move inherits the finger's velocity, so there's no seam. That one function is 3 lines, runs as a worklet on the UI thread, and is unit-tested in Jest. We wrote up everything that makes 6pm's "close the day" swipe feel like iOS: Reanimated 4 worklets, rubber-banding, real UISheetPresentationController sheets instead of drawn ones, and a 4-word haptics vocabulary. All open source (Apache 2.0).

Sound on 🔊 Every motion in this video is the real app, screen-recorded: wheel detents, a sheet you can fling, swipe-to-confirm, a receipt that prints, a stamp at 60fps, a number that rolls. We added one click for every row the wheel passes, because that's how it feels in the hand with haptics. Built with Expo + Reanimated 4, all on the UI thread. Which one got you?