VirtualScroll.md

VirtualScroll

This component renders a virtualized list of elements with either fixed or dynamic heights.

Prop Types

Property	Type	Required?	Description
className	String		Optional custom CSS class name to attach to root VirtualScroll element.
estimatedRowSize	Number		Used to estimate the total height of a VirtualScroll before all of its rows have actually been measured. The estimated total height is adjusted as rows are rendered.
height	Number	✓	Height constraint for list (determines how many actual rows are rendered)
noRowsRenderer	Function		Callback used to render placeholder content when rowCount is 0
onRowsRendered	Function		Callback invoked with information about the slice of rows that were just rendered: ({ overscanStartIndex: number, overscanStopIndex: number, startIndex: number, stopIndex: number }): void
onScroll	Function		Callback invoked whenever the scroll offset changes within the inner scrollable region: ({ clientHeight: number, scrollHeight: number, scrollTop: number }): void
overscanRowCount	Number		Number of rows to render above/below the visible bounds of the list. This can help reduce flickering during scrolling on certain browers/devices.
rowHeight	Number or Function	✓	Either a fixed row height (number) or a function that returns the height of a row given its index: ({ index: number }): number
rowRenderer	Function	✓	Responsible for rendering a row given an index. Signature should look like ({ index: number, isScrolling: boolean }): React.PropTypes.node
rowClassName	String or Function		Optional custom CSS class name to attach to Grid__cell element. If function given then signature should be look like: ({ index: number }): PropTypes.string
rowCount	Number	✓	Number of rows in list.
rowStyle	Object or Function		Optional custom inline style for individual row. If function given then signature should be look like: ({ index: number }): PropTypes.object
scrollToAlignment	String		Controls the alignment scrolled-to-rows. The default ("auto") scrolls the least amount possible to ensure that the specified row is fully visible. Use "start" to always align rows to the top of the list and "end" to align them bottom. Use "center" to align them in the middle of container.
scrollToIndex	Number		Row index to ensure visible (by forcefully scrolling if necessary)
scrollTop	Number		Forced vertical scroll offset; can be used to synchronize scrolling between components
style	Object		Optional custom inline style to attach to root VirtualScroll element.
tabIndex	Number		Optional override of tab index default; defaults to null.
width	Number	✓	Width of the list

Public Methods

forceUpdateGrid

Forcefull re-render the inner Grid component.

Calling forceUpdate on VirtualScroll may not re-render the inner Grid since it uses shallowCompare as a performance optimization. Use this method if you want to manually trigger a re-render. This may be appropriate if the underlying row data has changed but the row sizes themselves have not.

measureAllRows

Pre-measure all rows in a VirtualScroll.

Typically rows are only measured as needed and estimated heights are used for cells that have not yet been measured. This method ensures that the next call to getTotalSize() returns an exact size (as opposed to just an estimated one).

recomputeRowHeights (index: number)

Recompute row heights and offsets after the specified index (defaults to 0).

VirtualScroll has no way of knowing when its underlying list data has changed since it only receives a rowHeight property. If the rowHeight is a number it can compare before and after values but if it is a function that comparison is error prone. In the event that a dynamic rowHeight function is in use and the row heights have changed this function should be manually called by the "smart" container parent.

This method will also force a render cycle (via forceUpdate) to ensure that the updated measurements are reflected in the rendered list.

Class names

The VirtualScroll component supports the following static class names

Property	Description
VirtualScroll	Main (outer) element

Examples

Below is a simple VirtualScroll example. Each row in the virtualized list is rendered through the use of a rowRenderer function for performance reasons. This function must return an element with a unique key and must fit within the specified rowHeight.

Note that it is very important that rows do not have vertical overflow. It would make scrolling the list difficult (as individual items will intercept the scroll events). For this reason it is recommended that your rows use a style like overflow-y: hidden.)

import React from 'react';
import ReactDOM from 'react-dom';
import { VirtualScroll } from 'react-virtualized';
import 'react-virtualized/styles.css'; // only needs to be imported once

// List data as an array of strings
const list = [
  'Brian Vaughn'
  // And so on...
];

// Render your list
ReactDOM.render(
  <VirtualScroll
    width={300}
    height={300}
    rowCount={list.length}
    rowHeight={20}
    rowRenderer={
      ({ index, isScrolling }) => list[index] // Could also be a DOM element
    }
  />,
  document.getElementById('example')
);