Data refresh does not reset current index

[ivanoikon]

Describe the bug After updating data to a shorter array scroll is not moving back to start position, instead it remains on a blank element.

To Reproduce Steps to reproduce the behavior:

1. Use Carousel with a data source like the following

const {width} = useWindowDimensions();
const ref = React.useRef<ICarouselInstance>(null);  
const baseOptions = {
    vertical: false,
    width: width - 2 * AppDimensions.margin.horizontalMargin,
    height: AppDimensions.height.poiListItem,
  };

<Carousel
              {...baseOptions}
              style={{width: width}}
              loop={false}
              ref={ref}
              data={items}
              defaultIndex={0}
              onSnapToItem={(index: number) => {
                //Stuff
              }}
              renderItem={_renderItem}
              onScrollBegin={() => setIsScrolling(true)}
              onScrollEnd={() => setIsScrolling(false)}
            />

2. Scroll to the end of the list
3. Refresh items using a rest request so the new size of items array is smaller than before
4. Carousel updates displayed items but doesn't scroll to the first one or to a valid/visible index

Expected behavior After a data refresh current index is updated to defaultIndex or to a valid position

Versions (please complete the following information):

• react: v18.2.0
• react-native: v0.74.0
• react-native-reanimated: v3.11.0
• react-native-reanimated-carousel: v3.5.1 or 4.0.0-alpha12
• react-native-gesture-handler: v2.16.2

Smartphone (please complete the following information):

• Device: iPhone *
• OS: iOS 17.5

[dosubot[bot]]

Hello @ivanoikon! I'm here to help you with any issues or questions you have regarding the repository. If you need assistance, feel free to ask.

To ensure that the react-native-reanimated-carousel scrolls back to the start position or a valid index after the data is refreshed with a smaller array, you can use the scrollTo method provided by the carouselController. This method allows you to programmatically scroll to a specific index.

Here is an example of how you can achieve this:

1. Ensure you have a reference to the carousel instance.
2. Use the scrollTo method to scroll to the desired index after the data is refreshed.

Here is a code snippet demonstrating this:

import React, { useRef, useEffect } from "react";
import Carousel from "./Carousel"; // Adjust the import path as necessary

const MyCarouselComponent = ({ data }) => {
  const carouselRef = useRef(null);

  useEffect(() => {
    if (carouselRef.current) {
      // Scroll to the start position (index 0) after data is refreshed
      carouselRef.current.scrollTo({ index: 0, animated: true });
    }
  }, [data]);

  return (
    <Carousel
      ref={carouselRef}
      data={data}
      renderItem={({ item }) => <MyItemComponent item={item} />}
      // other props
    />
  );
};

export default MyCarouselComponent;

In this example, the useEffect hook is used to detect changes in the data prop. When the data is refreshed, the scrollTo method is called to scroll the carousel back to the start position (index 0). Adjust the index as needed to scroll to a different valid index.

Additionally, the useCarouselController hook from react-native-reanimated-carousel can help manage the carousel's state when the data or size changes. This hook uses useAnimatedReaction to compute the new index for handlerOffset when the data or size changes, ensuring smooth transitions and valid indices.

import { useCarouselController } from "react-native-reanimated-carousel";

const { handlerOffset } = useCarouselController({
  vertical: false,
  size: 300,
  dataLength: data.length,
  defaultIndex: 0,
  loop: false,
});

By integrating these methods, you can ensure that the carousel scrolls to a valid index after the data is refreshed ^[1][2][3].

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[ivanoikon]

useEffect doesn't solve the problem, Carousel still scrolls to an invalid position. useCarouselController seems undocumented and throws an undefined error even when imported...

...but I found a workaround: I scroll to first position before updating data set of Carousel. Now it works properly but i think there's a problem in the component I hope it could be investigated and fixed in next releases. Thanks

[petros-g]

I have the same issue with react-native-reanimated-carousel. It seems like when data is changing and in the current index you have no data any more it can't do the scrolling.

the workaround @ivanoikon works for me

If it doesn't work for you another workaround is to set a key to the carousel based on data length. But It's not very performant to re-render the whole carousel when data changes