react / react/react-native

Flatlist onMomentumScrollEnd called inconsistently between Android and iOS

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#48,423 8 comments 4 reactions 0 assignees View on GitHub

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Needs: Triage :mag: Platform: Android Platform: iOS
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Description

Description

it seems the behavior isn't consistent between android and ios.

on android it works when you flick and release, it also works when you scroll and hold thereby controlling the scrolling.

on IOS it only works when you flick and let the scroll momentum end by itself.

https://reactnative.dev/docs/scrollview#onmomentumscrollend
Called when the momentum scroll ends (scroll which occurs as the ScrollView glides to a stop).
in this case, i believe it means the behavior is incorrect on Android because it's called when it glides to a stop and when the user controls the stop.
or since there's no specific event for when both the scroll and glide are ended by the user controlling it, we should fix the behavior on iOS to behave the same on Android and update the docs to Called when the momentum scroll ends (scroll which occurs as the ScrollView stops).

Steps to reproduce
  1. android: flick and release -> momentum end event called
  2. android: scroll and hold at one position then release -> momentum end event called
  3. ios: flick and release -> momentum end event called
  4. ios: scroll via scrollbar, hold then release -> momentum end event is called
  5. ios: flick and release via scrollbar -> momentum end event is called
  6. ios: scroll, hold at one position then release -> momentum end event is not called
React Native Version

0.76.5

Same behavior on both the new and old architecture

Affected Platforms

Runtime - Android, Runtime - iOS

Output of npx react-native info
expo-env-info 1.2.1 environment info:
    System:
      OS: macOS 14.3.1
      Shell: 5.9 - /bin/zsh
    Binaries:
      Node: 20.18.0 - ~/.nvm/versions/node/v20.18.0/bin/node
      Yarn: 1.22.22 - ~/.nvm/versions/node/v20.18.0/bin/yarn
      npm: 10.8.2 - ~/.nvm/versions/node/v20.18.0/bin/npm
    Managers:
      CocoaPods: 1.16.2 - /opt/homebrew/bin/pod
    SDKs:
      iOS SDK:
        Platforms: DriverKit 23.2, iOS 17.2, macOS 14.2, tvOS 17.2, visionOS 1.0, watchOS 10.2
    IDEs:
      Android Studio: 2022.3 AI-223.8836.35.2231.11090377
      Xcode: 15.2/15C500b - /usr/bin/xcodebuild
    npmPackages:
      expo: ~52.0.23 => 52.0.23 
      expo-router: ~4.0.15 => 4.0.15 
      react: 18.3.1 => 18.3.1 
      react-dom: 18.3.1 => 18.3.1 
      react-native: 0.76.5 => 0.76.5 
      react-native-web: ~0.19.13 => 0.19.13 
    npmGlobalPackages:
      eas-cli: 13.4.2
    Expo Workflow: managed
Stacktrace or Logs
no errors, just inconsistent behavior
Reproducer

https://snack.expo.dev/@hichemfa/onmomentumscrollend-example

Screenshots and Videos

Android:

https://github.com/user-attachments/assets/706f34b0-c19c-49c2-887c-d035d2119fee

iOS:

https://github.com/user-attachments/assets/9a0cafe0-7370-4359-bd63-4dcc16cb9a51

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the linked Snack reproducer and the ScrollView onMomentumScrollEnd documentation, then compare the six Android and iOS reproduction steps. Determine which platform behavior is intended and verify the result against both the new and old architectures. Done means the event behavior is consistent with the agreed semantics and the documentation accurately describes it.

Written by the indexing model from the issue text.

Assessment

Tech stack
android, ios, react-native
Domain
mobile
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
48/100

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