Nested Virtualized Lists in opposing directions firing all onViewableItemsChanged
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Description
Description
Nested Bidirectional FlatList onViewableItemsChanged Issue
| App Image | Layout Image |
|---|---|
![]() |
![]() |
The above images describe the layout where this problem has arisen. Essentially it's a 2D FlatList.
When the Vertical FlatList mounts and the onViewableItemsChanged prop callbacks fire for only the elements on the screen, the expected behavior is working.
However, once the nested FlatLists mount, instead of firing the onViewableItemsChanged callback for only the nested Horizontal FlatList items that are within the visible viewport, it fires for all rendered list items (including those that are out of the viewport). It seems that the correct viewability is determined on horizontal lists, however, the VirtualizedList doesn't check if those horizontal lists are vertically visible.
Below, I've illustrated the expected vs actual behavior with images/emojis
🎇 - Vertical FlatList onViewableItemsChanged callback fires
🔥 - Horizontal FlatList onViewableItemsChanged callback fires
| Expected | Actual |
|---|---|
![]() |
![]() |
I provided a minimum setup repo below you can clone. Only changed the App.tsx file to recreate the above steps.
React Native Version
0.71.0
Output of npx react-native info
System:
OS: macOS 12.6
CPU: (10) arm64 Apple M1 Max
Memory: 204.02 MB / 32.00 GB
Shell: 5.8.1 - /bin/zsh
Binaries:
Node: 16.18.0 - ~/.nvm/versions/node/v16.18.0/bin/node
Yarn: 1.22.19 - ~/.nvm/versions/node/v16.18.0/bin/yarn
npm: 8.19.2 - ~/.nvm/versions/node/v16.18.0/bin/npm
Watchman: Not Found
Managers:
CocoaPods: Not Found
SDKs:
iOS SDK:
Platforms: DriverKit 21.4, iOS 16.0, macOS 12.3, tvOS 16.0, watchOS 9.0
Android SDK:
API Levels: 29, 30, 31, 32, 33
Build Tools: 29.0.3, 30.0.2, 30.0.3, 31.0.0, 32.0.0, 33.0.0, 33.0.0
System Images: android-29 | Intel x86 Atom_64, android-29 | Google APIs Intel x86 Atom_64, android-29 | Google Play ARM 64 v8a, android-29 | Google Play Intel x86 Atom_64, android-31 | Google Play ARM 64 v8a, android-32 | Google APIs ARM 64 v8a, android-32 | Google Play ARM 64 v8a, android-33 | Google Play ARM 64 v8a
Android NDK: Not Found
IDEs:
Android Studio: 2021.3 AI-213.7172.25.2113.9014738
Xcode: 14.0.1/14A400 - /usr/bin/xcodebuild
Languages:
Java: 11.0.11 - /Users/vvella/.jenv/shims/javac
npmPackages:
@react-native-community/cli: Not Found
react: 18.1.0 => 18.1.0
react-native: 0.70.4 => 0.71.0
react-native-macos: Not Found
npmGlobalPackages:
*react-native*: Not Found
Steps to reproduce
- Create a vertical FlatList that contains a 2D data array with a length long enough to make the list run off of your screen and require scrolling
- Create another FlatList (horizontal) to be rendered in the renderItem prop of the parent FlatList
- Add an onViewableItemsChanged to the nested (horizontal) FlatList
- Observe that all items rendered (regardless of vertical viewability) fire their onViewableItemsChanged callback
Snack, code example, screenshot, or link to a repository
Taken from the tester app
See that InnerViewable shows "56,57,58"
All of which are horizontally viewable but not vertically shown in the viewport
Snack: https://snack.expo.dev/@vincentvella/great-almond
Repo: https://github.com/vincentvella/bidirectional-virtualized-list-issue
Guide de contribution
Ouvrir le guide de contribution
Par où commencer
- Lisez l'issue en entier, puis le guide de contribution du projet.
- Signalez en commentaire que vous la prenez — cela évite que deux personnes fassent le même travail.
- Forkez le dépôt et travaillez sur une branche.
- Ouvrez une pull request qui référence le numéro de l'issue.
Piste de recherche
Commencez par App.tsx dans la reproduction liée et exécutez le Snack ou clonez le dépôt pour reproduire les FlatLists verticales et horizontales imbriquées. Suivez ensuite le comportement de viewability de React Native FlatList/VirtualizedList impliqué dans les listes imbriquées. La tâche est terminée lorsque le callback interne ne signale que les éléments visibles à la fois dans la liste horizontale et dans le viewport vertical du parent.
Rédigé par le modèle d'indexation à partir du texte de l'issue.
Évaluation
- Stack technique
- react-native
- Domaine
- mobile-dev
- Type d'issue
- Bug
- Difficulté
- 4/5
- Temps estimé
- 3-5 jours
- Activité
- À l'abandon
- Clarté
- Plutôt claire
- Accessibilité débutants
- 45/100



