Fixes(SectionList) component preventing element unmounting, when sepe…

[Biki-das]

Summary:

Weirdly when using a Section List specifically when using the SectionSeperatorComponent, and adding additional Data on the renderItem List, there is a unmount occurring as the new Data is added, this only happens while using the SectionSeparatorComponent and limited to the same

Here is the Current Behaviour

Screen.Recording.2024-01-20.at.11.35.55.PM.mov

Here is the Expected Behaviour After Fixes

Screen.Recording.2024-01-20.at.11.32.43.PM.mov

The issues is happening because the Parent View gets removed, as we add Data, the separator moves causing the unmount, the solution that i proposed here is to conditionally render to make sure that our separator renders correctly which required to add an empty view as the itemSeparatorComponent.

Changelog:

[General] [Added] - Fixes SectionList Unmounting issue with separatorComponent on data addition and removal.

Test Plan:

i used the rn-tester App to test out the changes below is the code to test the same.
Update the snapshots to align with the changes.

import React, {useEffect, useState} from 'react';
import {
  StyleSheet,
  Text,
  View,
  SafeAreaView,
  StatusBar,
  SectionList,
  Image,
} from 'react-native';

interface Item {
  id: string;
  title: string;
  imgSrc: string;
}

interface Section {
  title: string;
  data: Item[];
}

const keyExtractor = (item: Item, index: number) => `${item.title}-${index}`;

const renderItem = ({item, index}: {item: Item; index: number}) => {
  return <ItemComponent item={item} index={index} />;
};

const additionalFruits = [
  {
    id: '7',
    title: 'Sandwich',
    imgSrc:
      'https://img.freepik.com/premium-vector/sanwich-vector-isolated-fast-food_484148-2.jpg',
  },
  {
    id: '8',
    title: 'Burger',
    imgSrc:
      'https://static.vecteezy.com/system/resources/thumbnails/033/494/666/original/animated-illustration-of-burger-cartoon-for-foods-menu-animation-free-video.jpg',
  },
  {
    id: '9',
    title: 'Juice',
    imgSrc:
      'https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcQHg9yLXE7Jlq4OM9ey64TW4D9qUFaeGU76rg&usqp=CAU',
  },
  {
    id: '10',
    title: 'Milkshake',
    imgSrc:
      'https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcROpBez3eZKvEVdxBce9XyG6j6caDFMjV_xUQ&usqp=CAU',
  },
];
const DATA: Section[] = [
  {
    title: 'Items',
    data: [
      {
        id: '1',
        title: 'Cake',
        imgSrc:
          'https://static.vecteezy.com/system/resources/previews/012/132/227/original/cute-cake-cartoon-icon-illustration-food-recreation-icon-concept-isolated-premium-flat-cartoon-style-vector.jpg',
      },
      {
        id: '2',
        title: 'Pizza',
        imgSrc:
          'https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcR2kYjlsayzKZx4hFo6fbH7S8pde2JRo2a0hfaeoz3O7bjqdJjhI0tFiSROM8G4UbdbwXU&usqp=CAU',
      },
      {
        id: '3',
        title: 'Coke',
        imgSrc:
          'https://png.pngtree.com/png-clipart/20220116/original/pngtree-cartoon-hand-painted-coke-bottle-png-image_7106844.png',
      },
      {
        id: '4',
        title: 'Noodles',
        imgSrc:
          'https://thumbs.dreamstime.com/z/cute-cartoon-vector-bowl-noodle-isolated-white-background-115120959.jpg',
      },
      {
        id: '5',
        title: 'Pasta',
        imgSrc:
          'https://t4.ftcdn.net/jpg/02/65/00/69/360_F_265006936_2dlz2VtcqZZUbco1VnDpU2diyd8OagFS.jpg',
      },
      {
        id: '6',
        title: 'Fries',
        imgSrc:
          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      },
    ],
  },
];

const ItemComponent = ({item, index}: {item: Item; index: number}) => {
  useEffect(() => {
    console.log('Mount of', index, item.title);
    return () => {
      console.log('Unmount of', index, item.title);
    };
  }, []);

  return (
    <View style={styles.card}>
      <Text style={styles.cardText}>{item.title}</Text>
      <Image source={{uri: item.imgSrc}} style={styles.imageStyles} />
    </View>
  );
};

const App = () => {
  const [data, setData] = useState(DATA);
  const fetchNextPage = () => {
    const newInnerData = [...data[0].data, ...additionalFruits];
    setData([{...data[0], data: newInnerData}]);
  };

  return (
    <SafeAreaView style={styles.container}>
      <View style={styles.scrollView}>
        <SectionList
          keyExtractor={keyExtractor}
          onEndReachedThreshold={0.5}
          onEndReached={fetchNextPage}
          sections={data}
          renderItem={renderItem}
          ItemSeparatorComponent={() => <View style={{height: 16}} />}
          renderSectionHeader={({section}) => (
            <Text style={styles.sectionHeaderText}>{section.title}</Text>
          )}
        />
      </View>
    </SafeAreaView>
  );
};

const styles = StyleSheet.create({
  container: {
    flex: 1,
    backgroundColor: '#F5F5F5',
    paddingTop: StatusBar.currentHeight,
  },
  scrollView: {
    paddingHorizontal: 16,
  },
  card: {
    backgroundColor: '#FFFFFF',
    flexDirection: 'row',
    alignItems: 'center',
    justifyContent: 'center',
    gap: 8,
    height: 200,
    padding: 16,
    borderRadius: 8,
    marginBottom: 16,
    borderWidth: 1,
  },
  cardText: {
    fontSize: 30,
  },
  headerText: {
    fontSize: 24,
    textAlign: 'center',
    marginBottom: 12,
  },
  footerText: {
    fontSize: 24,
    textAlign: 'center',
    marginTop: 12,
  },
  sectionHeaderText: {
    backgroundColor: '#FFFFFF',
    fontSize: 24,
    fontWeight: 'bold',
  },
  imageStyles: {
    height: '100%',
    width: 100,
  },
});

export default App;

[analysis-bot]

Platform	Engine	Arch	Size (bytes)	Diff
android	hermes	arm64-v8a	17,233,687	+38
android	hermes	armeabi-v7a	n/a	--
android	hermes	x86	n/a	--
android	hermes	x86_64	n/a	--
android	jsc	arm64-v8a	20,600,108	+3
android	jsc	armeabi-v7a	n/a	--
android	jsc	x86	n/a	--
android	jsc	x86_64	n/a	--

Base commit: fe7b9e5
Branch: main

[Biki-das]

@javache 😅 you were correct , it actually does not need a View and a Fragment works i have updated the snapshots and it passes, only thing is few iOS test are failing i am not sure they are failing due to my changes since the android counter part are passing and in the iOS ones , the restoring caches and hermes install are failing .

[Biki-das]

@huntie could you possibly check this out, has been on radio silence for a while now
😅

[huntie]

Don't think I'm the best owner for this — cc @NickGerleman perhaps?

[Biki-das]

@javache friendly ping 😃
will this need any more changes or this is good to land.
i have rebased it to main.

[Biki-das]

closing as reopen on #43223