I have a FlatList that receives (immutable) data of max. 50 elements and it renders in each list item Svg using react-native-svg.
Parts of the graphics are wrapped with a Pressable component for selecting the element.
Now the problem is, that I can't select any of the elements, until the FlatList went through all 50 items.
What I don't get is, that the offscreen items aren't even rendered, it's just the containers. Once it's all rendered, I can click the elements, the ripple effect shows and the event is fired.
Specs:
- Expo @ 46.0.0
- React Native @ 0.69.6
- React @ 18.0.0
- Running with android via
expo start --no-dev --minifythen open in Expo Go
Reproduction:
import React, { useEffect, useState } from 'react'
import { FlatList } from 'react-native'
import { Foo } from '/path/to/Foo'
import { Bar } from '/path/to/Bar'
export const Overview = props => {
const [data, setData] = useState(null)
// 1. fetching data
useEffect(() => {
// load data from api
const loaded = [{ id: 0, type: 'foo' }, { id: 1, type: 'bar' }] // make a list of ~50 here
setData(loaded)
}, [])
if (!data?.length) {
return null
}
// 2. render list item
const onPressed = () => console.debug('pressed')
const renderListItem = ({ index, item }) => {
if (item.type === 'foo') {
return (<Foo key={`foo-${index}`} onPressed={onPressed} />)
}
if (item.type === 'bar') {
return (<Foo key={`bar-${index}`} onPressed={onPressed} />)
}
return null
}
// at this point data exists but will not be changed anymore
// so theoretically there should be no re-render
return (
<FlatList
data={data}
renderItem={renderListItem}
inverted={true}
decelerationRate="fast"
disableIntervalMomentum={true}
removeClippedSubviews={true}
persistentScrollbar={true}
keyExtractor={flatListKeyExtractor}
initialNumToRender={10}
maxToRenderPerBatch={10}
updateCellsBatchingPeriod={100}
getItemLayout={flatListGetItemLayout}
/>
)
}
}
// optimized functions
const flatListKeyExtractor = (item) => item.id
const flatListGetItemLayout = (data, index) => {
const entry = data[index]
const length = entry && ['foo', 'bar'].includes(entry.type)
? 110
: 59
return { length, offset: length * index, index }
}
Svg component, only Foo is shown, since Bar is structurally similar and the issue affects both:
import React from 'react'
import Svg, { G, Circle } from 'react-native-svg'
const radius = 25
const size = radius * 2
// this is a very simplified example,
// rendering a pressable circle
const FooSvg = props => {
return (
<Pressable
android_ripple={rippleConfig}
pressRetentionOffset={0}
hitSlop={0}
onPress={props.onPress}
>
<Svg
style={props.style}
width={size}
height={size}
viewBox={`0 0 ${radius * 2} ${radius * 2}`}
>
<G>
<Circle
cx='50%'
cy='50%'
stroke='black'
strokeWidth='2'
r={radius}
fill='red'
/>
</G>
</Svg>
</Pressable>
)
}
const rippleConfig = {
radius: 50,
borderless: true,
color: '#00ff00'
}
// pure component
export const Foo = React.memo(FooSvg)
The rendering performance itself is quite good, however I can't understand, why I need to wait up to two seconds, until I can press the circles, allthough they have already been rendered.
Any help is greatly appreciated.
Edit
When scrolling the list very fast, I get:
VirtualizedList: You have a large list that is slow to update - make sure your renderItem function renders components that follow React performance best practices like PureComponent, shouldComponentUpdate, etc. {"contentLength": 4740, "dt": 4156, "prevDt": 5142}
However, the Components are already memoized (PureComponent) and not very complex. There must be another issue.
Hardware
I cross tested with an iPad and there is none if the issues described. It seems to only occur on Android.
