0.49

Edit

FlatList

A performant interface for rendering basic, 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 its 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.

Also inherets ScrollView Props, unless it is nested in another FlatList of same orientation.

Props

Methods

Reference

Props

numColumns

TypeRequired
No

Methods

scrollToEnd()

scrollToEnd(([params]: object));

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

scrollToIndex()

scrollToIndex((params: object));

Scrolls to the item at 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()

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()

scrollToOffset((params: object));

Scroll to a specific content pixel offset in the list.

Check out scrollToOffset of VirtualizedList

recordInteraction()

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.

flashScrollIndicators()

flashScrollIndicators();

Displays the scroll indicators momentarily.

← DrawerLayoutAndroidImage →