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.
Example
- 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
PureComponent
which means that it will not re-render ifprops
are shallow-equal. Make sure that everything yourrenderItem
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 thedata
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 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
key
prop on each item and uses that for the React key. Alternatively, you can provide a customkeyExtractor
prop.
Reference
Props
ScrollView Props
Inherits ScrollView Props.
data
Opaque data type passed to getItem
and getItemCount
to retrieve items.
Type |
---|
any |
Required getItem
(data: any, index: number) => any;
A generic accessor for extracting an item from any sort of data blob.
Type |
---|
function |
Required getItemCount
(data: any) => number;
Determines how many items are in the data blob.
Type |
---|
function |
Required renderItem
(info: any) => ?React.Element<any>
Takes an item from data
and renders it into the list
Type |
---|
function |
CellRendererComponent
Each cell is rendered using this element. Can be a React Component Class, or a render function. Defaults to using View
.
Type |
---|
component, function |
ItemSeparatorComponent
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 |
ListEmptyComponent
Rendered when the list is empty. Can be a React Component (e.g. SomeComponent
), or a React element (e.g. <SomeComponent />
).
Type |
---|
component, element |
ListItemComponent
Each data item is rendered using this element. Can be a React Component Class, or a render function.
Type |
---|
component, function |
ListFooterComponent
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 |
ListFooterComponentStyle
Styling for internal View for ListFooterComponent
.
Type | Required |
---|---|
ViewStyleProp | No |
ListHeaderComponent
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 |
ListHeaderComponentStyle
Styling for internal View for ListHeaderComponent
.
Type |
---|
View Style |
debug
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 |
disableVirtualization
Deprecated. 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 |
extraData
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 |
getItemLayout
(
data: any,
index: number,
) => {length: number, offset: number, index: number}
Type |
---|
function |
horizontal
If true
, renders items next to each other horizontally instead of stacked vertically.
Type |
---|
boolean |
initialNumToRender
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 |
initialScrollIndex
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 |
inverted
Reverses the direction of scroll. Uses scale transforms of -1
.
Type |
---|
boolean |
keyExtractor
(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 |
maxToRenderPerBatch
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 |
onEndReached
(info: {distanceFromEnd: number}) => void;
Called once when the scroll position gets within onEndReachedThreshold
of the rendered content.
Type |
---|
function |
onEndReachedThreshold
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.
Type |
---|
number |
onRefresh
() => 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 |
onScrollToIndexFailed
(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 |
onViewableItemsChanged
Called when the viewability of rows changes, as defined by the viewabilityConfig
prop.
Type |
---|
(callback: {changed: ViewToken[], viewableItems: ViewToken[]}) => void |
persistentScrollbar
Type |
---|
bool |
progressViewOffset
Set this when offset is needed for the loading indicator to show correctly.
Type |
---|
number |
refreshControl
A custom refresh control element. When set, it overrides the default <RefreshControl>
component built internally. The onRefresh and refreshing props are also ignored. Only works for vertical VirtualizedList.
Type |
---|
element |
refreshing
Set this true while waiting for new data from a refresh.
Type |
---|
boolean |
removeClippedSubviews
This may improve scroll performance for large lists.
Note: May have bugs (missing content) in some circumstances - use at your own risk.
Type |
---|
boolean |
renderScrollComponent
(props: object) => element;
Render a custom scroll component, e.g. with a differently styled RefreshControl
.
Type |
---|
function |
viewabilityConfig
See ViewabilityHelper.js
for flow type and further documentation.
Type |
---|
ViewabilityConfig |
viewabilityConfigCallbackPairs
List of ViewabilityConfig
/onViewableItemsChanged
pairs. A specific onViewableItemsChanged
will be called when its corresponding ViewabilityConfig
's conditions are met. See ViewabilityHelper.js
for flow type and further documentation.
Type |
---|
array of ViewabilityConfigCallbackPair |
updateCellsBatchingPeriod
Amount of time between low-pri item render batches, e.g. for rendering items quite a ways off screen. Similar fill rate/responsiveness tradeoff as maxToRenderPerBatch
.
Type |
---|
number |
windowSize
Determines the maximum number of items rendered outside of the visible area, in units of visible lengths. So if your list fills the screen, then windowSize={21}
(the default) will render the visible screen area plus up to 10 screens above and 10 below the viewport. Reducing this number will reduce memory consumption and may improve performance, but will increase the chance that fast scrolling may reveal momentary blank areas of unrendered content.
Type |
---|
number |
Methods
flashScrollIndicators()
flashScrollIndicators();
getScrollableNode()
getScrollableNode(): any;
getScrollRef()
getScrollRef():
| React.ElementRef<typeof ScrollView>
| React.ElementRef<typeof View>
| null;
getScrollResponder()
getScrollResponder () => ScrollResponderMixin | null;
Provides a handle to the underlying scroll responder. Note that this._scrollRef
might not be a ScrollView
, so we need to check that it responds to getScrollResponder
before calling it.
scrollToEnd()
scrollToEnd(params?: {animated?: boolean});
Scrolls to the end of the content. May be janky without getItemLayout
prop.
Parameters:
Name | Type |
---|---|
params | object |
Valid params
keys are:
'animated'
(boolean) - Whether the list should do an animation while scrolling. Defaults totrue
.
scrollToIndex()
scrollToIndex(params: {
index: number;
animated?: boolean;
viewOffset?: number;
viewPosition?: number;
});
Valid params
consist of:
- 'index' (number). Required.
- 'animated' (boolean). Optional.
- 'viewOffset' (number). Optional.
- 'viewPosition' (number). Optional.
scrollToItem()
scrollToItem(params: {
item: ItemT;
animated?: boolean;
viewOffset?: number;
viewPosition?: number;
);
Valid params
consist of:
- 'item' (Item). Required.
- 'animated' (boolean). Optional.
- 'viewOffset' (number). Optional.
- 'viewPosition' (number). Optional.
scrollToOffset()
scrollToOffset(arams: {
offset: number;
animated?: boolean;
});
Scroll to a specific content pixel offset in the list.
Param offset
expects the offset to scroll to. In case of horizontal
is true, the offset is the x-value, in any other case the offset is the y-value.
Param animated
(true
by default) defines whether the list should do an animation while scrolling.