react-native-reversed-flat-list

A reversed React Native FlatList, useful for creating performant bottom-anchored lists for chats and whatnot

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Documentation

Use exactly like you would use FlatList.

- import {FlatList} from 'react-native';
+ import ReversedFlatList from 'react-native-reversed-flat-list';
 
const MessageList = ({ messages, renderMessage }) => (
-  <FlatList
+  <ReversedFlatList
    data={messages}
    renderItem={renderMessage}
  />
);

This component has not been tested with all the different options, bells and whistles of FlatList. If you hit a use case that doesn't work, please submit a Pull Request!

How does it work

aka. The One Weird Trick They Don't Want You To Know About Making Performant Reverse Lists in React Native

I learned the basic mechanism from expo/react-native-invertible-scroll-view. The trick is to scale transform the FlatList's backing ScrollView to -1 in order to flip it on it's horizontal vertical axis, causing the list to look upside-down-mirrored. We then perform the same flip for each row within the list to turn them back the right way around. (To make it more natural to use the component with time-ordered datasets (oldest first), we also reverse the dataset.)

const styles = StyleSheet.create({
  flip: {
    transform: [{ scaleY: -1 }]
  }
});

Surprisingly, this works well, fast and reliably.

Attribution

The flip transform trick as far as I know, by @Satya164.
Initial FlatList implementation prototyped by @joshyhargreaves.

License

MIT licensed