UIKit scrolling, drawing, layers, animation, and haptics

UIKit rendering work belongs at different layers. Views own hierarchy and interaction. Layers own compositing properties. Custom drawing produces pixels. Haptics reinforce an action but never carry its only meaning.

Animate one source of truth

UIView.animate(withDuration: 0.25) {
    favoriteButton.configuration = self.favoriteConfiguration(isFavorite: true)
    self.view.layoutIfNeeded()
}

Update model state once, then animate the corresponding presentation. Do not animate a layer property and its owning constraint toward conflicting destinations.

Keep scrolling work bounded

Reuse cells, cancel obsolete image tasks, resize images near their display size, and move decoding away from the main actor. Measure hitching before adding caches. A cache has a key, size bound, eviction policy, privacy policy, and memory-warning response.

Draw the smallest region

Custom draw(_:) fits a badge or annotation whose pixels are cheaper than a hierarchy. Avoid invalidating the whole screen for a small change. Drawing does not add accessibility elements or interaction automatically.

Use transitions for ownership changes

Navigation and custom transitions coordinate source, destination, duration, interruption, and cancellation. An interactive transition must finish or restore a coherent state.

Haptics follow successful actions such as favorite or save. Respect user settings, device capability, and repetition. Visual and spoken feedback remain complete without vibration.

Validation boundary

Animation, scrolling performance, drawing, transition interruption, memory, energy, and physical-device haptics remain Not verified.

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References

Animation and haptics covers UIKit feedback APIs.
Core Animation provides layer-based animation.
UIScrollView defines scrolling behavior.