Multiple call to render item

It’s a questiob but may turn out to be a bug.

Problem: _renderItems gets called thrice How to replicate:

Following is the code to display a carousel in a very simple example:

import React, {PureComponent} from 'react'
import { ScrollView, Text, View, SafeAreaView,Platform, Dimensions, StyleSheet  } from 'react-native';
import Carousel from 'react-native-snap-carousel';

export default class SnapDemo extends PureComponent {

    constructor(props){
        super(props)
         this.state = {data: [{'num':1},{'num':2},{'num':3}]}
    }

    _renderItem (item) {
        console.log(item)
        return(<View key={item.item.num} style={{backgroundColor:'orange', height:100}}><Text>{item.item.num}</Text></View>)
    }

    render(){
       return(
            <SafeAreaView style={{height: 600}}>
           <Carousel
                  data={this.state.data}
                  renderItem={this._renderItem}
                  itemWidth={Dimensions.get('window').width * 0.85}
                  sliderWidth={Dimensions.get('window').width}
                  containerCustomStyle={{flex:1}}
                  removeClippedSubviews={true}
                  keyExtractor={(item, index) => index.toString()}
                  slideStyle={{ flex: 1 }}/>

        </SafeAreaView>
        )
    }
}

There are 2 problems:

1. RenderItems is getting called thrice Image

2. I see a virtualized key warning message despite official docs mentioning that explicit key isn’t required to be specified Image

[baeteja]

I have a similar problem. The renderItem gets triggered multiple times for the same index. It also triggers the renderItem with index 0 up to four times - no idea why this is happening

<Carousel lockScrollWhileSnapping ref={(c) => { this.carousel = c; }} windowSize={1} initialNumToRender={1} maxToRenderPerBatch={1} data={this.props.articles} sliderWidth={this.props.screenWidth} itemWidth={this.props.screenWidth} itemHeight={this.props.screenHeight} keyExtractor={(item, index) => item.article+ '-' + index} scrollEnabled={this.isListMode() && this.state.isArticleLoaded} onSnapToItem={this.onItemSnap} renderItem={(params) => renderCorrectArticleDetail(params)} />

Even with initialNumToRender={1} and maxToRenderPerBatch={1} it still triggers renderItem 12 times. This is causing big performance issues for me. Any ideas?

[Cactiw]

I moved whole renderItem function to the new PureComponent (I use functional components, so I use React.memo)

import React from "react";

export default React.memo(() =>
    const daysToRender = [0, 1, 2, 3]
    return(
            <Carousel data={daysToRender} renderItem={
                     (props) => <ScrollPaneView item={props.item} index={props.index}/>
))

ScrollPaneView.js:

export default React.memo(({item, index} => {
    console.log("Rendering", index)
    return (
        <View><Text>Rendered</Text></View>
    )
}

And now renderItem is called only once for each item.