Using contentOffset causes invalid scroll events to fire when ScrollView is first mounted

[mozzius]

Description

When using the contentOffset prop on ScrollView, we've observed that this causes extra scroll events to fire when the component is mounted. Specifically, it sends an event with the contentOffset equal to the value passed to the prop, then sends a second one - if the contentOffset is positive, it's the same value again, and if it's negative, it's 0.

We're trying to use a negative contentOffset.y value in conjunction with a paddingTop style so that the scrollview content can be offset from the top a certain distance.

Expected behaviour: no scroll events are fired until the scrollview is actually scrolled

It appears to be iOS only, but I have only tried android on the emulator so I can't be completely certain

Steps to reproduce

1. Create a ScrollView that has an onScroll handler that logs contentOffset
2. Add a contentOffset of { x: 0, y: -100 }
3. Observe the logs look like this:

-100
0

React Native Version

0.74.5

Affected Platforms

Runtime - iOS

Output of npx react-native info

System:
  OS: macOS 15.0
  CPU: (8) arm64 Apple M1
  Memory: 169.59 MB / 16.00 GB
  Shell:
    version: 3.7.1
    path: /opt/homebrew/bin/fish
Binaries:
  Node:
    version: 22.5.1
    path: /opt/homebrew/bin/node
  Yarn:
    version: 1.22.22
    path: ~/.yarn/bin/yarn
  npm:
    version: 10.2.5
    path: /opt/homebrew/bin/npm
  Watchman:
    version: 2024.07.29.00
    path: /opt/homebrew/bin/watchman
Managers:
  CocoaPods:
    version: 1.15.2
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.0
      - iOS 18.0
      - macOS 15.0
      - tvOS 18.0
      - visionOS 2.0
      - watchOS 11.0
  Android SDK:
    API Levels:
      - "33"
      - "34"
    Build Tools:
      - 30.0.3
      - 33.0.0
      - 33.0.1
      - 34.0.0
    System Images:
      - android-34 | Google APIs ARM 64 v8a
      - android-35 | Google Play ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2023.1 AI-231.9392.1.2311.11330709
  Xcode:
    version: 16.0/16A242d
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 11.0.24
    path: /opt/homebrew/opt/openjdk@11/bin/javac
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 18.2.0
    wanted: 18.2.0
  react-native:
    installed: 0.74.5
    wanted: 0.74.5
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

n/a

Reproducer

https://snack.expo.dev/@mozzius/contentoffset-causing-incorrect-scroll-events-repro

Screenshots and Videos