Method componentDidUpdate

native/chat/chat-list.react.js:136–221

(prevProps: Props)

  }

  componentDidUpdate(prevProps: Props) {
    const { flatList } = this;
    if (!flatList || this.props.data === prevProps.data) {
      return;
    }

    if (this.props.data.length < prevProps.data.length) {
      // This should only happen due to MessageStorePruner,
      // which will only prune a thread when it is off-screen
      flatList.scrollToOffset({ offset: 0, animated: false });
      return;
    }

    const { scrollPos } = this;
    const { viewerID } = this.props;

    let curDataIndex = 0,
      prevDataIndex = 0,
      heightSoFar = 0;
    let adjustScrollPos = 0,
      newLocalMessage = false,
      newRemoteMessageCount = 0;
    while (prevDataIndex < prevProps.data.length && heightSoFar <= scrollPos) {
      const prevItem = prevProps.data[prevDataIndex];
      invariant(prevItem, 'prevItem should exist');
      const prevItemKey = chatMessageItemKey(prevItem);
      const prevItemHeight = chatMessageItemHeight(prevItem);

      let curItem = this.props.data[curDataIndex];
      while (curItem) {
        const curItemKey = chatMessageItemKey(curItem);
        if (curItemKey === prevItemKey) {
          break;
        }

        if (curItemKey.startsWith(localIDPrefix)) {
          newLocalMessage = true;
        } else if (chatMessageItemHasNonViewerMessage(curItem, viewerID)) {
          newRemoteMessageCount++;
        }
        adjustScrollPos += chatMessageItemHeight(curItem);

        curDataIndex++;
        curItem = this.props.data[curDataIndex];
      }
      if (!curItem) {
        // The only case in which we would expect the length of data to
        // decrease, but find that an item was removed, is if the start
        // of the chat is reached. In that case, the spinner at the top
        // will no longer be rendered. We break here as we expect the
        // spinner to be the last item.
        if (prevItemKey === 'loader') {
          break;
        }
        console.log(
          `items not removed from ChatList, but ${prevItemKey} now missing`,
        );
        return;