FlatList

FlatList

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>.

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 ids 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>, 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.

Props

ItemSeparatorComponent?: ?ReactClass<any>

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.

ListEmptyComponent?: ?ReactClass<any> | React.Element<any>

Rendered when the list is empty. Can be a React Component Class, a render function, or a rendered element.

ListFooterComponent?: ?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.

ListHeaderComponent?: ?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.

columnWrapperStyle?: StyleObj

Optional custom style for multi-item rows generated when numColumns > 1.

data: ?$ReadOnlyArray<ItemT>

For simplicity, data is just a plain array. If you want to use something else, like an immutable list, use the underlying VirtualizedList directly.

extraData?: any

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.

getItemLayout?: (data: ?Array<ItemT>, index: number) => {length: number, offset: number, index: number}

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.

horizontal?: ?boolean

If true, renders items next to each other horizontally instead of stacked vertically.

initialNumToRender: number

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.

initialScrollIndex?: ?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.

keyExtractor: (item: ItemT, index: number) => string

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.

legacyImplementation?: ?boolean

numColumns: number

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.

onEndReached?: ?(info: {distanceFromEnd: number}) => void

Called once when the scroll position gets within onEndReachedThreshold of the rendered content.

onEndReachedThreshold?: ?number

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.

onRefresh?: ?() => void

If provided, a standard RefreshControl will be added for "Pull to Refresh" functionality. Make sure to also set the refreshing prop correctly.

onViewableItemsChanged?: ?(info: { viewableItems: Array<ViewToken>, changed: Array<ViewToken>, }) => void

Called when the viewability of rows changes, as defined by the viewabilityConfig prop.

refreshing?: ?boolean

Set this true while waiting for new data from a refresh.

removeClippedSubviews?: boolean

Note: may have bugs (missing content) in some circumstances - use at your own risk.

This may improve scroll performance for large lists.

renderItem: (info: { item: ItemT, index: number, separators: { highlight: () => void, unhighlight: () => void, updateProps: (select: 'leading' | 'trailing', newProps: Object) => void, }, }) => ?React.Element<any>

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.

viewabilityConfig?: ViewabilityConfig

See ViewabilityHelper for flow type and further documentation.

Methods

scrollToEnd(params?: object)

Scrolls to the end of the content. May be janky without getItemLayout prop.

scrollToIndex(params: object)

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.

scrollToItem(params: object)

Requires linear scan through data - use scrollToIndex instead if possible.

Note: cannot scroll to locations outside the render window without specifying the getItemLayout prop.

scrollToOffset(params: object)

Scroll to a specific content pixel offset, like a normal ScrollView.

recordInteraction()

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.