[FlatList] always mount and unmount some top items even if initialScrollIndex was set

[irrigator]

Description

Set initialScrollIndex to " immediately renders the items starting at this initial index". However, some tops items are mount and unmount after the initial items are mount and unmount.

Reproduction Steps

Run the sample code below on React Native 0.45.1. The expected behavior is:

item 101 was mount => item 98 ~ 100 and item 102 ~ 104 was mount (because windowSize is 7).

The actual behavior is:

item 101 was mount => item 101 was unmount => item 1 ~ 4 was mount => item 1 ~ 4 was unmount => item 97 ~ item 104 was mount.

Sample Code

import React from 'react';
import { View, Text, FlatList, Dimensions, Button } from 'react-native';
import _ from 'lodash';
const { width, height } = Dimensions.get('window');

class Item extends React.PureComponent {
  componentDidMount() {
    console.info('mount', this.props.item);
  }

  componentWillUnmount() {
    console.info('unmount', this.props.item);
  }

  render() {
    return (
      <View
        style={{
          width,
          height,
          justifyContent: 'center',
          alignItems: 'center',
        }}
      >
        <Text>{this.props.item}</Text>
      </View>
    );
  }
}

export default class PlayWithFlatList extends React.PureComponent {
  render() {
    const data = _.range(1, 200);
    return (
      <View style={{ flex: 1 }}>
        <FlatList
          ref={node => (this.list = node)}
          data={data}
          keyExtractor={(item, index) => item}
          renderItem={({ item }) =>
            <Item item={item} />}
          horizontal={true}
          pagingEnabled={true}
          initialScrollIndex={100}
          initialNumToRender={1}
          windowSize={7}
          getItemLayout={(data, index) => ({
            length: width,
            offset: width * index,
            index,
          })}
        />
      </View>
    );
  }
}

Additional Information

• React Native version: 0.45.1
• Platform: both
• Development Operating System: macOS
• Build tools: Xcode 8.3.3

[hramos]

Hi there! This issue is being closed because it has been inactive for a while. Maybe the issue has been fixed in a recent release, or perhaps it is not affecting a lot of people. Either way, we're automatically closing issues after a period of inactivity. Please do not take it personally!

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