[FlatList] Scrolling issues with FlatList when rows are variable height #13727
Description
I'm using a FlatList where each row can be of different height (and may contain a mix of both text and zero or more images from a remote server).
I cannot use getItemLayout because I don't know the height of each row (nor the previous ones) to be able to calculate.
The problem I'm facing is that I cannot scroll to the end of the list (it jumps back few rows when I try) and I'm having issues when trying to use scrollToIndex (I'm guessing due to the fact I'm missing getItemLayout).
I wrote a sample project to demonstrate the problem (simply try to scroll to the end with your finger - it won't allow you)
import React, { Component } from 'react';
import { AppRegistry, StyleSheet, Text, View, Image, FlatList } from 'react-native';
import autobind from 'autobind-decorator';
const items = count => [...Array(count)].map((v, i) => ({
key: i,
index: i,
image: 'https://dummyimage.com/600x' + (((i % 4) + 1) * 50) + '/000/fff',
}));
class RemoteImage extends Component {
constructor(props) {
super(props);
this.state = {
style: { flex: 1, height: 0 },
};
}
componentDidMount() {
Image.getSize(this.props.src, (width, height) => {
this.image = { width, height };
this.onLayout();
});
}
@autobind
onLayout(event) {
if (event) {
this.layout = {
width: event.nativeEvent.layout.width,
height: event.nativeEvent.layout.height,
};
}
if (!this.layout || !this.image || !this.image.width)
return;
this.setState({
style: {
flex: 1,
height: Math.min(this.image.height,
Math.floor(this.layout.width * this.image.height / this.image.width)),
},
});
}
render() {
return (
<Image
onLayout={this.onLayout}
source={{ uri: this.props.src }}
style={this.state.style}
resizeMode='contain'
/>
);
}
}
class Row extends Component {
@autobind
onLayout({ nativeEvent }) {
let { index, item, onItemLayout } = this.props;
let height = Math.max(nativeEvent.layout.height, item.height || 0);
if (height != item.height)
onItemLayout(index, { height });
}
render() {
let { index, image } = this.props.item;
return (
<View style={[styles.row, this.props.style]}>
<Text>Header {index}</Text>
<RemoteImage src = { image } />
<Text>Footer {index}</Text>
</View>
);
}
}
export default class FlatListTest extends Component {
constructor(props) {
super(props);
this.state = { items: items(50) };
}
@autobind
renderItem({ item, index }) {
return <Row
item={item}
style={index&1 && styles.row_alternate || null}
onItemLayout={this.onItemLayout}
/>;
}
@autobind
onItemLayout(index, props) {
let items = [...this.state.items];
let item = { ...items[index], ...props };
items[index] = { ...item, key: [item.height, item.index].join('_') };
this.setState({ items });
}
render() {
return (
<FlatList
ref={ref => this.list = ref}
data={this.state.items}
renderItem={this.renderItem}
/>
);
}
}
const styles = StyleSheet.create({
row: {
padding: 5,
},
row_alternate: {
backgroundColor: '#bbbbbb',
},
});
AppRegistry.registerComponent('FlatListTest', () => FlatListTest);