VirtualizedList
Base implementation for the more convenient <FlatList> and <SectionList> components, which are also better documented. In general, this should only really be used if you need more flexibility than FlatList provides, e.g. for use with immutable data instead of plain arrays.
Virtualization massively improves memory consumption and performance of large lists by maintaining a finite render window of active items and replacing all items outside of the render window with appropriately sized blank space. The window adapts to scrolling behavior, and items are rendered incrementally with low-pri (after any running interactions) if they are far from the visible area, or with hi-pri otherwise to minimize the potential of seeing blank space.
Exampleโ
- TypeScript
- JavaScript
Some 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
PureComponentwhich means that it will not re-render ifpropsare shallow-equal. Make sure that everything yourrenderItemfunction 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 thedataprop 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 and 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
keyprop on each item and uses that for the React key. Alternatively, you can provide a customkeyExtractorprop.
Reference
Propsโ
ScrollView Propsโ
Inherits ScrollView Props.
dataโ
Opaque data type passed to getItem and getItemCount to retrieve items.
| Type |
|---|
| any |
Required getItemโ
(data: any, index: number) => any;
A generic accessor for extracting an item from any sort of data blob.
| Type |
|---|
| function |
Required getItemCountโ
(data: any) => number;
Determines how many items are in the data blob.
| Type |
|---|
| function |
Required renderItemโ
(info: any) => ?React.Element<any>
Takes an item from data and renders it into the list
| Type |
|---|
| function |
CellRendererComponentโ
CellRendererComponent allows customizing how cells rendered by renderItem/ListItemComponent are wrapped when placed into the underlying ScrollView. This component must accept event handlers which notify VirtualizedList of changes within the cell.
| Type |
|---|
React.ComponentType<CellRendererProps> |
ItemSeparatorComponentโ
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. Can be a React Component (e.g. SomeComponent), or a React element (e.g. <SomeComponent />).
| Type |
|---|
| component, function, element |
ListEmptyComponentโ
Rendered when the list is empty. Can be a React Component (e.g. SomeComponent), or a React element (e.g. <SomeComponent />).
| Type |
|---|
| component, element |
ListItemComponentโ
Each data item is rendered using this element. Can be a React Component Class, or a render function.
| Type |
|---|
| component, function |
ListFooterComponentโ
Rendered at the bottom of all the items. Can be a React Component (e.g. SomeComponent), or a React element (e.g. <SomeComponent />).
| Type |
|---|
| component, element |
ListFooterComponentStyleโ
Styling for internal View for ListFooterComponent.
| Type | Required |
|---|---|
| ViewStyleProp | No |
ListHeaderComponentโ
Rendered at the top of all the items. Can be a React Component (e.g. SomeComponent), or a React element (e.g. <SomeComponent />).
| Type |
|---|
| component, element |
ListHeaderComponentStyleโ
Styling for internal View for ListHeaderComponent.
| Type |
|---|
| View Style |
debugโ
debug will turn on extra logging and visual overlays to aid with debugging both usage and implementation, but with a significant perf hit.
| Type |
|---|
| boolean |
๐๏ธ disableVirtualizationโ
Virtualization provides significant performance and memory optimizations, but fully unmounts react instances that are outside of the render window. You should only need to disable this for debugging purposes.
| Type |
|---|
| boolean |
extraDataโ
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.
| Type |
|---|
| any |
getItemLayoutโ
(
data: any,
index: number,
) => {length: number, offset: number, index: number}
| Type |
|---|
| function |
horizontalโ
If true, renders items next to each other horizontally instead of stacked vertically.
| Type |
|---|
| boolean |
initialNumToRenderโ
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.
| Type | Default |
|---|---|
| number | 10 |
initialScrollIndexโ
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.
| Type |
|---|
| number |
invertedโ
Reverses the direction of scroll. Uses scale transforms of -1.
| Type |
|---|
| boolean |
keyExtractorโ
(item: any, 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 item.id, and then falls back to using the index, like React does.
| Type |
|---|
| function |
maxToRenderPerBatchโ
The maximum number of items to render in each incremental render batch. The more rendered at once, the better the fill rate, but responsiveness may suffer because rendering content may interfere with responding to button taps or other interactions.
| Type |
|---|
| number |
onEndReachedโ
Called once when the scroll position gets within onEndReachedThreshold from the logical end of the list.
| Type |
|---|
(info: {distanceFromEnd: number}) => void |
onEndReachedThresholdโ
How far from the end (in units of visible length of the list) the trailing 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.
| Type | Default |
|---|---|
| number | 2 |
onRefreshโ
() => void;
If provided, a standard RefreshControl will be added for "Pull to Refresh" functionality. Make sure to also set the refreshing prop correctly.
| Type |
|---|
| function |
onScrollToIndexFailedโ
(info: {
index: number,
highestMeasuredFrameIndex: number,
averageItemLength: number,
}) => void;
Used to handle failures when scrolling to an index that has not been measured yet. Recommended action is to either compute your own offset and scrollTo it, or scroll as far as possible and then try again after more items have been rendered.
| Type |
|---|
| function |
onStartReachedโ
Called once when the scroll position gets within onStartReachedThreshold from the logical start of the list.
| Type |
|---|