react-native/Libraries/Lists/FlatList.js

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule FlatList
 * @flow
 */
'use strict';

const MetroListView = require('MetroListView'); // Used as a fallback legacy option
const React = require('React');
const View = require('View');
const VirtualizedList = require('VirtualizedList');

const invariant = require('fbjs/lib/invariant');

import type {StyleObj} from 'StyleSheetTypes';
import type {ViewabilityConfig, ViewToken} from 'ViewabilityHelper';
import type {Props as VirtualizedListProps} from 'VirtualizedList';

type RequiredProps<ItemT> = {
  /**
   * Takes an item from `data` and renders it into the list. Example usage:
   *
   *     <FlatList
   *       ItemSeparatorComponent={Platform.OS !== 'android' && ({highlighted}) => (
   *         <View style={[style.separator, highlighted && {marginLeft: 0}]} />
   *       )}
   *       data={[{title: 'Title Text', key: 'item1'}]}
   *       renderItem={({item, separators}) => (
   *         <TouchableHighlight
   *           onPress={() => this._onPress(item)}
   *           onShowUnderlay={separators.highlight}
   *           onHideUnderlay={separators.unhighlight}>
   *           <View style={{backgroundColor: 'white'}}>
   *             <Text>{item.title}}</Text>
   *           </View>
   *         </TouchableHighlight>
   *       )}
   *     />
   *
   * Provides additional metadata like `index` if you need it, as well as a more generic
   * `separators.updateProps` function which let's you set whatever props you want to change the
   * rendering of either the leading separator or trailing separator in case the more common
   * `highlight` and `unhighlight` (which set the `highlighted: boolean` prop) are insufficient for
   * your use-case.
   */
  renderItem: (info: {
    item: ItemT,
    index: number,
    separators: {
      highlight: () => void,
      unhighlight: () => void,
      updateProps: (select: 'leading' | 'trailing', newProps: Object) => void,
    },
  }) => ?React.Element<any>,
  /**
   * For simplicity, data is just a plain array. If you want to use something else, like an
   * immutable list, use the underlying `VirtualizedList` directly.
   */
  data: ?$ReadOnlyArray<ItemT>,
};
type OptionalProps<ItemT> = {
  /**
   * Rendered in between each item, but not at the top or bottom. By default, `highlighted` and
   * `leadingItem` props are provided. `renderItem` provides `separators.highlight`/`unhighlight`
   * which will update the `highlighted` prop, but you can also add custom props with
   * `separators.updateProps`.
   */
  ItemSeparatorComponent?: ?ReactClass<any>,
  /**
   * Rendered when the list is empty. Can be a React Component Class, a render function, or
   * a rendered element.
   */
  ListEmptyComponent?: ?(ReactClass<any> | React.Element<any>),
  /**
   * Rendered at the bottom of all the items. Can be a React Component Class, a render function, or
   * a rendered element.
   */
  ListFooterComponent?: ?(ReactClass<any> | React.Element<any>),
  /**
   * Rendered at the top of all the items. Can be a React Component Class, a render function, or
   * a rendered element.
   */
  ListHeaderComponent?: ?(ReactClass<any> | React.Element<any>),
  /**
   * Optional custom style for multi-item rows generated when numColumns > 1.
   */
  columnWrapperStyle?: StyleObj,
  /**
   * A marker property for telling the list to re-render (since it implements `PureComponent`). If
   * any of your `renderItem`, Header, Footer, etc. functions depend on anything outside of the
   * `data` prop, stick it here and treat it immutably.
   */
  extraData?: any,
  /**
   * `getItemLayout` is an optional optimizations that let us skip measurement of dynamic content if
   * you know the height of items a priori. `getItemLayout` is the most efficient, and is easy to
   * use if you have fixed height items, for example:
   *
   *     getItemLayout={(data, index) => (
   *       {length: ITEM_HEIGHT, offset: ITEM_HEIGHT * index, index}
   *     )}
   *
   * Remember to include separator length (height or width) in your offset calculation if you
   * specify `ItemSeparatorComponent`.
   */
  getItemLayout?: (data: ?Array<ItemT>, index: number) =>
    {length: number, offset: number, index: number},
  /**
   * If true, renders items next to each other horizontally instead of stacked vertically.
   */
  horizontal?: ?boolean,
  /**
   * How many items to render in the initial batch. This should be enough to fill the screen but not
   * much more. Note these items will never be unmounted as part of the windowed rendering in order
   * to improve perceived performance of scroll-to-top actions.
   */
  initialNumToRender: number,
  /**
   * Instead of starting at the top with the first item, start at `initialScrollIndex`. This
   * disables the "scroll to top" optimization that keeps the first `initialNumToRender` items
   * always rendered and immediately renders the items starting at this initial index. Requires
   * `getItemLayout` to be implemented.
   */
  initialScrollIndex?: ?number,
  /**
   * Used to extract a unique key for a given item at the specified index. Key is used for caching
   * and as the react key to track item re-ordering. The default extractor checks `item.key`, then
   * falls back to using the index, like React does.
   */
  keyExtractor: (item: ItemT, index: number) => string,
  /**
   * Multiple columns can only be rendered with `horizontal={false}` and will zig-zag like a
   * `flexWrap` layout. Items should all be the same height - masonry layouts are not supported.
   */
  numColumns: number,
  /**
   * Called once when the scroll position gets within `onEndReachedThreshold` of the rendered
   * content.
   */
  onEndReached?: ?(info: {distanceFromEnd: number}) => void,
  /**
   * How far from the end (in units of visible length of the list) the bottom edge of the
   * list must be from the end of the content to trigger the `onEndReached` callback.
   * Thus a value of 0.5 will trigger `onEndReached` when the end of the content is
   * within half the visible length of the list.
   */
  onEndReachedThreshold?: ?number,
  /**
   * If provided, a standard RefreshControl will be added for "Pull to Refresh" functionality. Make
   * sure to also set the `refreshing` prop correctly.
   */
  onRefresh?: ?() => void,
  /**
   * Called when the viewability of rows changes, as defined by the `viewabilityConfig` prop.
   */
  onViewableItemsChanged?: ?(info: {
    viewableItems: Array<ViewToken>,
    changed: Array<ViewToken>,
  }) => void,
  legacyImplementation?: ?boolean,
  /**
   * Set this true while waiting for new data from a refresh.
   */
  refreshing?: ?boolean,
  /**
   * Note: may have bugs (missing content) in some circumstances - use at your own risk.
   *
   * This may improve scroll performance for large lists.
   */
  removeClippedSubviews?: boolean,
  /**
   * See `ViewabilityHelper` for flow type and further documentation.
   */
  viewabilityConfig?: ViewabilityConfig,
};
type Props<ItemT> = RequiredProps<ItemT> & OptionalProps<ItemT> & VirtualizedListProps;

const defaultProps = {
  ...VirtualizedList.defaultProps,
  numColumns: 1,
};
type DefaultProps = typeof defaultProps;

/**
 * A performant interface for rendering simple, flat lists, supporting the most handy features:
 *
 *  - Fully cross-platform.
 *  - Optional horizontal mode.
 *  - Configurable viewability callbacks.
 *  - Header support.
 *  - Footer support.
 *  - Separator support.
 *  - Pull to Refresh.
 *  - Scroll loading.
 *  - ScrollToIndex support.
 *
 * If you need section support, use [`<SectionList>`](docs/sectionlist.html).
 *
 * Minimal Example:
 *
 *     <FlatList
 *       data={[{key: 'a'}, {key: 'b'}]}
 *       renderItem={({item}) => <Text>{item.key}</Text>}
 *     />
 *
 * More complex example demonstrating `PureComponent` usage for perf optimization and avoiding bugs.
 *
 * - By binding the `onPressItem` handler, the props will remain `===` and `PureComponent` will
 *   prevent wasteful re-renders unless the actual `id`, `selected`, or `title` props change, even
 *   if the inner `SomeOtherWidget` has no such optimizations.
 * - By passing `extraData={this.state}` to `FlatList` we make sure `FlatList` itself will re-render
 *   when the `state.selected` changes. Without setting this prop, `FlatList` would not know it
 *   needs to re-render any items because it is also a `PureComponent` and the prop comparison will
 *   not show any changes.
 * - `keyExtractor` tells the list to use the `id`s for the react keys.
 *
 *
 *     class MyListItem extends React.PureComponent {
 *       _onPress = () => {
 *         this.props.onPressItem(this.props.id);
 *       };
 *
 *       render() {
 *         return (
 *           <SomeOtherWidget
 *             {...this.props}
 *             onPress={this._onPress}
 *           />
 *         )
 *       }
 *     }
 *
 *     class MyList extends React.PureComponent {
 *       state = {selected: (new Map(): Map<string, boolean>)};
 *
 *       _keyExtractor = (item, index) => item.id;
 *
 *       _onPressItem = (id: string) => {
 *         // updater functions are preferred for transactional updates
 *         this.setState((state) => {
 *           // copy the map rather than modifying state.
 *           const selected = new Map(state.selected);
 *           selected.set(id, !selected.get(id)); // toggle
 *           return {selected};
 *         });
 *       };
 *
 *       _renderItem = ({item}) => (
 *         <MyListItem
 *           id={item.id}
 *           onPressItem={this._onPressItem}
 *           selected={!!this.state.selected.get(item.id)}
 *           title={item.title}
 *         />
 *       );
 *
 *       render() {
 *         return (
 *           <FlatList
 *             data={this.props.data}
 *             extraData={this.state}
 *             keyExtractor={this._keyExtractor}
 *             renderItem={this._renderItem}
 *           />
 *         );
 *       }
 *     }
 *
 * This is a convenience wrapper around [`<VirtualizedList>`](docs/virtualizedlist.html),
 * and thus inherits it's props (as well as those of `ScrollView`) that aren't explicitly listed
 * here, along with the following caveats:
 *
 * - Internal state is not preserved when content scrolls out of the render window. Make sure all
 *   your data is captured in the item data or external stores like Flux, Redux, or Relay.
 * - This is a `PureComponent` which means that it will not re-render if `props` remain shallow-
 *   equal. Make sure that everything your `renderItem` function depends on is passed as a prop
 *   (e.g. `extraData`) that is not `===` after updates, otherwise your UI may not update on
 *   changes. This includes the `data` prop and parent component state.
 * - In order to constrain memory and enable smooth scrolling, content is rendered asynchronously
 *   offscreen. This means it's possible to scroll faster than the fill rate ands momentarily see
 *   blank content. This is a tradeoff that can be adjusted to suit the needs of each application,
 *   and we are working on improving it behind the scenes.
 * - By default, the list looks for a `key` prop on each item and uses that for the React key.
 *   Alternatively, you can provide a custom `keyExtractor` prop.
 *
 */
class FlatList<ItemT> extends React.PureComponent<DefaultProps, Props<ItemT>, void> {
  static defaultProps: DefaultProps = defaultProps;
  props: Props<ItemT>;
  /**
   * Scrolls to the end of the content. May be janky without `getItemLayout` prop.
   */
  scrollToEnd(params?: ?{animated?: ?boolean}) {
    this._listRef.scrollToEnd(params);
  }

  /**
   * Scrolls to the item at a the specified index such that it is positioned in the viewable area
   * such that `viewPosition` 0 places it at the top, 1 at the bottom, and 0.5 centered in the
   * middle. `viewOffset` is a fixed number of pixels to offset the final target position.
   *
   * Note: cannot scroll to locations outside the render window without specifying the
   * `getItemLayout` prop.
   */
  scrollToIndex(params: {
    animated?: ?boolean, index: number, viewOffset?: number, viewPosition?: number,
  }) {
    this._listRef.scrollToIndex(params);
  }

  /**
   * Requires linear scan through data - use `scrollToIndex` instead if possible.
   *
   * Note: cannot scroll to locations outside the render window without specifying the
   * `getItemLayout` prop.
   */
  scrollToItem(params: {animated?: ?boolean, item: ItemT, viewPosition?: number}) {
    this._listRef.scrollToItem(params);
  }

  /**
   * Scroll to a specific content pixel offset in the list.
   * 
   * Check out [scrollToOffset](docs/virtualizedlist.html#scrolltooffset) of VirtualizedList
   */
  scrollToOffset(params: {animated?: ?boolean, offset: number}) {
    this._listRef.scrollToOffset(params);
  }

  /**
   * Tells the list an interaction has occured, which should trigger viewability calculations, e.g.
   * if `waitForInteractions` is true and the user has not scrolled. This is typically called by
   * taps on items or by navigation actions.
   */
  recordInteraction() {
    this._listRef.recordInteraction();
  }

  /**
   * Provides a handle to the underlying scroll responder.
   */
  getScrollResponder() {
    if (this._listRef) {
      return this._listRef.getScrollResponder();
    }
  }

  getScrollableNode() {
    if (this._listRef) {
      return this._listRef.getScrollableNode();
    }
  }

  componentWillMount() {
    this._checkProps(this.props);
  }

  componentWillReceiveProps(nextProps: Props<ItemT>) {
    invariant(
      nextProps.numColumns === this.props.numColumns,
      'Changing numColumns on the fly is not supported. Change the key prop on FlatList when ' +
      'changing the number of columns to force a fresh render of the component.'
    );
    this._checkProps(nextProps);
  }

  _hasWarnedLegacy = false;
  _listRef: VirtualizedList;

  _captureRef = (ref) => { this._listRef = ref; };

  _checkProps(props: Props<ItemT>) {
    const {
      getItem,
      getItemCount,
      horizontal,
      legacyImplementation,
      numColumns,
      columnWrapperStyle,
    } = props;
    invariant(!getItem && !getItemCount, 'FlatList does not support custom data formats.');
    if (numColumns > 1) {
      invariant(!horizontal, 'numColumns does not support horizontal.');
    } else {
      invariant(!columnWrapperStyle, 'columnWrapperStyle not supported for single column lists');
    }
    if (legacyImplementation) {
      invariant(numColumns === 1, 'Legacy list does not support multiple columns.');
      // Warning: may not have full feature parity and is meant more for debugging and performance
      // comparison.
      if (!this._hasWarnedLegacy) {
        console.warn(
          'FlatList: Using legacyImplementation - some features not supported and performance ' +
          'may suffer'
        );
        this._hasWarnedLegacy = true;
      }
    }
  }

  _getItem = (data: Array<ItemT>, index: number) => {
    const {numColumns} = this.props;
    if (numColumns > 1) {
      const ret = [];
      for (let kk = 0; kk < numColumns; kk++) {
        const item = data[index * numColumns + kk];
        item && ret.push(item);
      }
      return ret;
    } else {
      return data[index];
    }
  };

  _getItemCount = (data: ?Array<ItemT>): number => {
    return data ? Math.ceil(data.length / this.props.numColumns) : 0;
  };

  _keyExtractor = (items: ItemT | Array<ItemT>, index: number) => {
    const {keyExtractor, numColumns} = this.props;
    if (numColumns > 1) {
      invariant(
        Array.isArray(items),
        'FlatList: Encountered internal consistency error, expected each item to consist of an ' +
        'array with 1-%s columns; instead, received a single item.',
        numColumns,
      );
      return items.map((it, kk) => keyExtractor(it, index * numColumns + kk)).join(':');
    } else {
      return keyExtractor(items, index);
    }
  };

  _pushMultiColumnViewable(arr: Array<ViewToken>, v: ViewToken): void {
    const {numColumns, keyExtractor} = this.props;
    v.item.forEach((item, ii) => {
      invariant(v.index != null, 'Missing index!');
      const index = v.index * numColumns + ii;
      arr.push({...v, item, key: keyExtractor(item, index), index});
    });
  }

  _onViewableItemsChanged = (info) => {
    const {numColumns, onViewableItemsChanged} = this.props;
    if (!onViewableItemsChanged) {
      return;
    }
    if (numColumns > 1) {
      const changed = [];
      const viewableItems = [];
      info.viewableItems.forEach((v) => this._pushMultiColumnViewable(viewableItems, v));
      info.changed.forEach((v) => this._pushMultiColumnViewable(changed, v));
      onViewableItemsChanged({viewableItems, changed});
    } else {
      onViewableItemsChanged(info);
    }
  };

  _renderItem = (info: Object) => {
    const {renderItem, numColumns, columnWrapperStyle} = this.props;
    if (numColumns > 1) {
      const {item, index} = info;
      invariant(Array.isArray(item), 'Expected array of items with numColumns > 1');
      return (
        <View style={[{flexDirection: 'row'}, columnWrapperStyle]}>
          {item.map((it, kk) => {
            const element = renderItem({
              item: it,
              index: index * numColumns + kk,
              separators: info.separators,
            });
            return element && React.cloneElement(element, {key: kk});
          })}
        </View>
      );
    } else {
      return renderItem(info);
    }
  };

  render() {
    if (this.props.legacyImplementation) {
      return <MetroListView {...this.props} items={this.props.data} ref={this._captureRef} />;
    } else {
      return (
        <VirtualizedList
          {...this.props}
          renderItem={this._renderItem}
          getItem={this._getItem}
          getItemCount={this._getItemCount}
          keyExtractor={this._keyExtractor}
          ref={this._captureRef}
          onViewableItemsChanged={this.props.onViewableItemsChanged && this._onViewableItemsChanged}
        />
      );
    }
  }
}

module.exports = FlatList;