React-native-gifted-chat with cloud firestore pagination

Question

I'm using Firestore to store messages. In order to optimize the mobile application performances, I would like to set a limit(50) in the firestore query. It works well and implemented the onLoadEarlier React-native-gifted-chat available in the props.

All is working fine.

But, when I send a new message in the chat, after scrolled up to see the earliers messages, only the 50 last messages with the new one, off course, are available.

So, each time I'm adding a message in the Firestore database, the onSnapshot (in the useeffect) is executed and apply the limit query.

Is there a way to avoid this ?

Thanks.

Here my useEffect :

useEffect(() => {
    const messagesListener = firestore()
    .collection('groups')
    .doc(group._id)
    .collection('messages')
    .orderBy('createdAt', 'desc')
    .limit(50)
    .onSnapshot(querySnapshot => {
        const newMessages = querySnapshot.docs.map(doc => {
            const firebaseData = doc.data();

            const data = {
                _id: doc.id,
                text: '',
                createdAt: new Date().getTime(),
                ...firebaseData
            };

            return data;
        });

        setMessages(previousMessages => {
            return GiftedChat.append(previousMessages, newMessages);
        });
    });

    return () => messagesListener();
}, []);

Answer 1

I am using FlatList in react-native to render chats and I had to paginate the chats list. Since Firestore query cursor is not supported in live listener, I created two list, recentChats & oldChats.

I populate recentChats using live listener query.onSnapshot & oldChats using cursor startAfter. FlatList data is combination of both list and I take care of merging logic.

const MESSAGE_LIMIT = 15;

const ChatWindow = props => {
  const { sessionId, postMessage, onSendTemplateButtonPress } = props;

  // Firestore cursor is not supported in query.onSnapshot so maintaining two chat list
  // oldChats -> chat list via cursor, recentChats -> chat list via live listener
  const [oldChats, setOldChats] = useState([]);
  const [recentChats, setRecentChats] = useState([]);

  // if true, show a loader at the top of chat list
  const [moreChatsAvailable, setMoreChatsAvailable] = useState(true);

  const [inputMessage, setInputMessage] = useState('');

  useEffect(() => {
    const query = getGuestChatMessagesQuery(sessionId)
      .limit(MESSAGE_LIMIT);
    const listener = query.onSnapshot(querySnapshot => {
      let chats = [];
      querySnapshot.forEach(snapshot => {
        chats.push(snapshot.data());
      });
      // merge recentChats & chats
      if (recentChats.length > 0) {
        const newRecentChats = [];
        for (let i = 0; i < chats.length; i++) {
          if (chats[i].sessionId === recentChats[0].sessionId) {
            break;
          }
          newRecentChats.push(chats[i]);
        }
        setRecentChats([...newRecentChats, ...recentChats]);
      } else {
        setRecentChats(chats);
        if (chats.length < MESSAGE_LIMIT) {
          setMoreChatsAvailable(false);
        }
      }
    });

    return () => {
      // unsubscribe listener
      listener();
    };
  }, []);

  const onMessageInputChange = text => {
    setInputMessage(text);
  };

  const onMessageSubmit = () => {
    postMessage(inputMessage);
    setInputMessage('');
  };

  const renderFlatListItem = ({ item }) => {
    return (<ChatBubble chat={item} />);
  };

  const onChatListEndReached = () => {
    if (!moreChatsAvailable) {
      return;
    }
    let startAfterTime;
    if (oldChats.length > 0) {
      startAfterTime = oldChats[oldChats.length - 1].time;
    } else if (recentChats.length > 0) {
      startAfterTime = recentChats[recentChats.length - 1].time;
    } else {
      setMoreChatsAvailable(false);
      return;
    }
    // query data using cursor
    getGuestChatMessagesQuery(sessionId)
      .startAfter(startAfterTime)
      .limit(MESSAGE_LIMIT)
      .get()
      .then(querySnapshot => {
        let chats = [];
        querySnapshot.forEach(snapshot => {
          chats.push(snapshot.data());
        });
        if (chats.length === 0) {
          setMoreChatsAvailable(false);
        } else {
          setOldChats([...oldChats, ...chats]);
        }
      });
  };

  return (
    <View style={[GenericStyles.fill, GenericStyles.p16]}>
      <FlatList
        inverted
        data={[...recentChats, ...oldChats]}
        renderItem={renderFlatListItem}
        keyExtractor={item => item.messageId}
        onEndReached={onChatListEndReached}
        onEndReachedThreshold={0.2}
        ListFooterComponent={moreChatsAvailable ? <ActivityIndicator /> : null}
      />
      {
        Singleton.isStaff ?
          null:
          <ChatInput
            onMessageInputChange={onMessageInputChange}
            onMessageSubmit={onMessageSubmit}
            inputMessage={inputMessage}
            style={GenericStyles.selfEnd}
            onSendTemplateButtonPress={onSendTemplateButtonPress}
          />
      }
    </View>
  );
};