rnbis-Step2.js

import React, {useEffect, useState} from 'react';
import {SafeAreaView, StyleSheet, Text, View} from 'react-native';

import {FlatList} from 'react-native-bidirectional-infinite-scroll';
import {MessageBubble} from './MessageBubble';
import {queryMoreMessages} from './utils';

const App = () => {
  const [messages, setMessages] = useState();

  useEffect(() => {
    // When app is opened, we are going to render 50 messages on screen.
    // Generally this is where you connect to chat server and query first batch of messages.
    const initChat = async () => {
      const initialMessages = await queryMoreMessages(50, 0);
      setMessages(initialMessages);
    };

    initChat();
  }, []);

  // Add 10 more messages to end of the list.
  // In real chat application, this is where you have your pagination logic.
  const loadMoreOlderMessages = async () => {
    const newMessages = await queryMoreMessages(10);
    setMessages((m) => {
      return m.concat(newMessages);
    });
  };

  // Add 10 more messages to beginning of the list.
  // In real chat application, this is where you have your pagination logic.
  const loadMoreRecentMessages = async () => {
    const newMessages = await queryMoreMessages(10);
    setMessages((m) => {
      return newMessages.concat(m);
    });
  };

  if (!messages) {
    // If the messages are not ready, lets not show anything.
    // Generally you can render some kind of loading indicator in this case.
    return null;
  }

  /**
   * NOTE:
   * 
   * - You can also control the scroll offset, at which `onEndReached` and `onStartReached`
   *   should be called, using props - onEndReachedThreshold and onStartReachedThrehols
   * - We are using `inverted` FlatList, since thats a common UX for Chat applications.
   */
  return (
    <SafeAreaView style={styles.safeArea}>
      <View style={styles.header}>
        <Text style={styles.headerTitle}>Chat between two users</Text>
      </View>
      <FlatList
        data={messages}
        inverted
        onEndReached={loadMoreOlderMessages}
        onStartReached={loadMoreRecentMessages}
        renderItem={MessageBubble}
      />
    </SafeAreaView>
  );
};

const styles = StyleSheet.create({
  header: {
    alignItems: 'center',
    paddingVertical: 10,
    borderBottomColor: '#BEBEBE',
    borderBottomWidth: 1,
  },
  headerTitle: {fontSize: 20, fontWeight: 'bold'},
  safeArea: {
    flex: 1,
  },
});

export default App;