react / react/react-native

Nested Virtualized Lists in opposing directions firing all onViewableItemsChanged

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Component: FlatList Issue: Author Provided Repro Newer Patch Available
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Descrizione

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
Untitled-2022-08-26-1424 Untitled-2022-08-26-1424

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
  1. 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
  2. Create another FlatList (horizontal) to be rendered in the renderItem prop of the parent FlatList
  3. Add an onViewableItemsChanged to the nested (horizontal) FlatList
  4. 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

Guida per i contributori

Apri la guida per i contributori

Come iniziare

  1. Leggi tutta la issue e poi la guida ai contributi del progetto.
  2. Commenta sulla issue per dire che te ne occupi tu — evita che due persone facciano lo stesso lavoro.
  3. Fai un fork del repository e lavora su un branch.
  4. Apri una pull request che faccia riferimento al numero della issue.

Direzione di ricerca

Inizia da App.tsx nella riproduzione collegata ed esegui lo Snack oppure clona il repository per riprodurre le FlatLists verticali e orizzontali annidati. Poi traccia il comportamento di viewability di React Native FlatList/VirtualizedList coinvolto nelle liste annidate. Il lavoro è completato quando il callback interno segnala solo gli elementi visibili sia nella lista orizzontale sia nel viewport verticale del parent.

Scritto dal modello di indicizzazione a partire dal testo della issue.

Valutazione

Stack tecnologico
react-native
Ambito
mobile-dev
Tipo di issue
Bug
Difficoltà
4/5
Tempo stimato
3-5 giorni
Stato di attività
Ferma
Chiarezza
Abbastanza chiara
Idoneità per principianti
45/100

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