Method _subExtractor

VirtualizedSectionList.js:166–200

(
    index: number,
  )

  };

  _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;
        return {
          section,
          key: key + ':' + keyExtractor(section.data[itemIndex], itemIndex),
          index: itemIndex,
          leadingItem: section.data[itemIndex - 1],
          leadingSection: this.props.sections[ii - 1],
          trailingItem: section.data[itemIndex + 1],
          trailingSection: this.props.sections[ii + 1],
        };
      }
    }
  }

  _convertViewable = (viewable: ViewToken): ?ViewToken => {
    invariant(viewable.index != null, 'Received a broken ViewToken');