Class VirtualizedSectionList

VirtualizedSectionList.js:131–336

* Right now this just flattens everything into one list and uses VirtualizedList under the * hood. The only operation that might not scale well is concatting the data arrays of all the * sections when new props are received, which should be plenty fast for up to ~10,000 items.

 * sections when new props are received, which should be plenty fast for up to ~10,000 items.
 */
class VirtualizedSectionList<SectionT: SectionBase>
  extends React.PureComponent<DefaultProps, Props<SectionT>, State>
{
  props: Props<SectionT>;

  state: State;

  static defaultProps: DefaultProps = {
    ...VirtualizedList.defaultProps,
    data: [],
  };

  scrollToLocation(params: {
    animated?: ?boolean, itemIndex: number, sectionIndex: number, viewPosition?: number
  }) {
    let index = params.itemIndex + 1;
    for (let ii = 0; ii < params.sectionIndex; ii++) {
      index += this.props.sections[ii].data.length + 1;
    }
    const toIndexParams = {
      ...params,
      index,
    };
    this._listRef.scrollToIndex(toIndexParams);
  }

  getListRef(): VirtualizedList {
    return this._listRef;
  }

  _keyExtractor = (item: Item, index: number) => {
    const info = this._subExtractor(index);
    return (info && info.key) || String(index);
  };

  _subExtractor(
    index: number,
  ): ?{
    section: SectionT,
    key: string, // Key of the section or combined key for section + item
    index: ?number, // Relative index within the section
    leadingItem?: ?Item,
    leadingSection?: ?SectionT,
    trailingItem?: ?Item,
    trailingSection?: ?SectionT,
  } {
    let itemIndex = index;
    const defaultKeyExtractor = this.props.keyExtractor;
    for (let ii = 0; ii < this.props.sections.length; ii++) {
      const section = this.props.sections[ii];
      const key = section.key || String(ii);
      itemIndex -= 1; // The section itself is an item
      if (itemIndex >= section.data.length) {
        itemIndex -= section.data.length;
      } else if (itemIndex === -1) {
        return {section, key, index: null, trailingSection: this.props.sections[ii + 1]};
      } else {
        const keyExtractor = section.keyExtractor || defaultKeyExtractor;