[iOS][Fabric] Pinch-zoomed ScrollView breaks (position jumps, cannot zoom back out) after its size changes
Nadie ha tomado este issue todavía.
- Lenguaje dominante
- C++
- Estrellas
- 127k
- Forks
- 25.3k
- Merge medio
- 1 d 23 h
- PR fusionados (30 d)
- 4
Descripción
Description
On iOS with the new architecture, a ScrollView with maximumZoomScale > 1 gets into a broken state whenever its size changes while the user is zoomed in (device rotation, or the layout around it changing):
- The scrolled position jumps to a different spot.
- The content can no longer be zoomed all the way back out; it stays stuck against one side or corner.
The only way to recover is to zoom all the way out in the broken state and then resize again (rotate back and forth). After that it works again until the next resize while zoomed.
Cause. RCTScrollViewComponentView returns _containerView from viewForZoomingInScrollView:, so while zoomed in that view carries UIScrollView's scale transform. In updateState:oldState: a content size change does
_containerView.frame = CGRect{RCTCGPointFromPoint(data.contentBoundingRect.origin), contentSize};
...
self->_scrollView.contentSize = contentSize;
- Setting
frameon a view whosetransformis not the identity is undefined behavior per the UIView docs ("If the transform property is not the identity transform, the value of this property is undefined and therefore should be ignored"). In practice UIKit shrinks the container'sboundsby the zoom scale, so when the user zooms back out to scale 1 the content is smaller than the scroll view and sits in a corner. contentSizeis set to the unzoomed size whilezoomScale != 1. UIScrollView itself keepscontentSizeat the zoomed size, so the offset is clamped to the wrong range and the position jumps.
The same code is on main today. prepareForRecycle already hints at it: "Invalidate cached content size so that updateState: recalculates the container frame after zoomScale reset (which may have mutated it in RTL)".
Fix: lay the container out through bounds/center and give the scroll view the zoomed content size. PR: https://github.com/react/react-native/pull/58498
Steps to reproduce
- Run the reproducer on an iOS device or simulator (new architecture is on by default).
- Pinch to zoom in (2x or more) and pan somewhere away from the top-left.
- Tap "Resize" (changes the ScrollView's height) or rotate the device.
- The position jumps. Pinch back out: the content stays stuck in a corner and does not fill the ScrollView.
- Zoom out fully, resize again: it recovers.
React Native Version
0.87.1
Affected Platforms
Runtime - iOS
Output of npx @react-native-community/cli info
Not run: the reproducer repository is a fresh `reproducer-react-native` template pinned to react-native 0.87.1, run on iOS 18 simulator/device.
Stacktrace or Logs
No crash or log output; the bug is visual.
MANDATORY Reproducer
https://github.com/mifi/reproducer-react-native
Screenshots and Videos
None yet.
Guía de contribución
Primeros pasos
- Lee el issue completo y luego la guía de contribución del proyecto.
- Comenta en el issue que vas a ocuparte — evita que dos personas hagan lo mismo.
- Haz un fork del repositorio y trabaja en una rama.
- Abre un pull request que haga referencia al número del issue.
Línea de trabajo
Comienza con updateState:oldState: y prepareForRecycle de RCTScrollViewComponentView y luego ejecuta el ejemplo reproducer-react-native en iOS. Verifica el comportamiento mientras haces zoom y cambias el tamaño o giras; se considera terminado cuando la posición de desplazamiento permanece estable y el contenido puede volver a alejarse completamente después de los cambios de tamaño.
Escrito por el modelo de indexación a partir del texto del issue.
Evaluación
- Stack tecnológico
- ios, objective-c, react-native
- Área
- mobile
- Tipo de issue
- Error
- Dificultad
- 3/5
- Tiempo estimado
- 1-2 días
- Estado de actividad
- Estancado
- Claridad
- Bien especificado
- Aptitud para principiantes
- 25/100