Rocket.Chat.ReactNative/app/containers/EmojiPicker/EmojiCategory.tsx

import React from 'react';
import { FlatList, Text, TouchableOpacity } from 'react-native';

import shortnameToUnicode from '../../utils/shortnameToUnicode';
import styles from './styles';
import CustomEmoji from './CustomEmoji';
import scrollPersistTaps from '../../utils/scrollPersistTaps';
import { IEmoji, IEmojiCategory } from '../../definitions/IEmoji';

const EMOJI_SIZE = 50;

const renderEmoji = (emoji: IEmoji, size: number, baseUrl: string) => {
	if (emoji && emoji.isCustom) {
		return (
			<CustomEmoji
				style={[styles.customCategoryEmoji, { height: size - 16, width: size - 16 }]}
				emoji={emoji}
				baseUrl={baseUrl}
			/>
		);
	}
	return (
		<Text style={[styles.categoryEmoji, { height: size, width: size, fontSize: size - 14 }]}>
			{shortnameToUnicode(`:${emoji}:`)}
		</Text>
	);
};

class EmojiCategory extends React.Component<Partial<IEmojiCategory>> {
	renderItem(emoji: any) {
		const { baseUrl, onEmojiSelected } = this.props;
		return (
			<TouchableOpacity
				activeOpacity={0.7}
				key={emoji && emoji.isCustom ? emoji.content : emoji}
				onPress={() => onEmojiSelected!(emoji)}
				testID={`reaction-picker-${emoji && emoji.isCustom ? emoji.content : emoji}`}>
				{renderEmoji(emoji, EMOJI_SIZE, baseUrl!)}
			</TouchableOpacity>
		);
	}

	render() {
		const { emojis, width } = this.props;

		if (!width) {
			return null;
		}

		const numColumns = Math.trunc(width / EMOJI_SIZE);
		const marginHorizontal = (width - numColumns * EMOJI_SIZE) / 2;

		return (
			// @ts-ignore
			<FlatList
				contentContainerStyle={{ marginHorizontal }}
				// rerender FlatList in case of width changes
				key={`emoji-category-${width}`}
				keyExtractor={item => (item && item.isCustom && item.content) || item}
				data={emojis}
				extraData={this.props}
				renderItem={({ item }) => this.renderItem(item)}
				numColumns={numColumns}
				initialNumToRender={45}
				removeClippedSubviews
				{...scrollPersistTaps}
			/>
		);
	}
}

export default EmojiCategory;