firstItem doesn't work reliably

Is this a bug report, a feature request, or a question?

Bug report

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• I have read the guidelines regarding bug report.
• I have reviewed the documentation in its entirety, including the dedicated documentations 📚.
• I have searched for existing issues and made sure that the problem hasn’t already been reported.
• I am using the latest plugin version.
• I am following the issue template closely in order to produce a useful bug report.

Have you made sure that it wasn’t a React Native bug?

Yes

Is the bug specific to iOS or Android? Or can it be reproduced on both platforms?

It’s reproducible on both platforms but has slightly different behaviour on each. On iOS index 14 is shown, on Android, index 6 is shown, when firstItem is 30.

Is the bug reproducible in a production environment (not a debug one)?

Yes

Environment

Here’s a snack which reproduces the behaviour: https://snack.expo.io/@thekevinbrown/snap-carousel-first-item-bug

That environment’s details: react-native-snap-carousel: 3.8.0 Expo v33.0.0

Expected Behavior

Expected carousel to load with a green screen focused (slide index 30)

Actual Behavior

Carousel loads with slide index 14 focused or 6 focused depending on platform.

Reproducible Demo

https://snack.expo.io/@thekevinbrown/snap-carousel-first-item-bug

Steps to Reproduce

1. Load more than a few pages of any type of slide into snap-carousel
2. Set firstItem to a number > 14
3. Carousel starts on various indexes which are not the one you passed in as a prop.

Other Notes

I commented with this snack on #496, but I don’t think it was noticed, and is likely to be a different issue now that I read that issue more closely, so I figured I’d open a new one. Thanks for your help!

[GH974]

@thekevinbrown Hi, I have the same issue, i resolve this in use initialNumToRender={data.length}, but i slow performance

[rontalx]

@thekevinbrown Did you pass to the Carousel component the relevant getItemLayout & initialScrollIndex properties for your use-case? for example:

          firstItem={this.props.firstSlideIndex}
          initialScrollIndex={this.props.firstSlideIndex}
          getItemLayout={(_: ListItemData, index: number) => ({
            length: CARD_WIDTH,
            offset: CARD_WIDTH * index,
            index,
          })}

The branch just enables usage of them, so using the branch without implementing the props wouldn’t make any change. I haven’t tested your snack specifically but I’ve reproduced exactly the same issue and now it’s resolved also in my production environment on bigger lists. LMK how it goes