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VirtualScroller.js
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VirtualScroller.js
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import React, { Component } from 'react'
const setInitialState = (settings) => {
const { itemHeight, amount, tolerance, minIndex, maxIndex, startIndex } = settings
const viewportHeight = amount * itemHeight
const totalHeight = (maxIndex - minIndex + 1) * itemHeight
const toleranceHeight = tolerance * itemHeight
const bufferHeight = viewportHeight + 2 * toleranceHeight
const bufferedItems = amount + 2 * tolerance
const itemsAbove = startIndex - tolerance - minIndex
const topPaddingHeight = itemsAbove * itemHeight
const bottomPaddingHeight = totalHeight - topPaddingHeight
const initialPosition = topPaddingHeight + toleranceHeight
return {
settings,
viewportHeight,
totalHeight,
toleranceHeight,
bufferHeight,
bufferedItems,
topPaddingHeight,
bottomPaddingHeight,
initialPosition,
data: []
}
}
class Scroller extends Component {
constructor(props) {
super(props)
this.state = setInitialState(props.settings)
this.viewportElement = React.createRef()
}
componentDidMount() {
this.viewportElement.current.scrollTop = this.state.initialPosition
if (!this.state.initialPosition) {
this.runScroller({ target: { scrollTop: 0 } })
}
}
runScroller = ({ target: { scrollTop } }) => {
const { totalHeight, toleranceHeight, bufferedItems, settings: { itemHeight, minIndex }} = this.state
const index = minIndex + Math.floor((scrollTop - toleranceHeight) / itemHeight)
const data = this.props.get(index, bufferedItems)
const topPaddingHeight = Math.max((index - minIndex) * itemHeight, 0)
const bottomPaddingHeight = Math.max(totalHeight - topPaddingHeight - data.length * itemHeight, 0)
this.setState({
topPaddingHeight,
bottomPaddingHeight,
data
})
}
render() {
const { viewportHeight, topPaddingHeight, bottomPaddingHeight, data } = this.state
return (
<div
className="viewport"
ref={this.viewportElement}
onScroll={this.runScroller}
style={{ height: viewportHeight }}
>
<div style={{ height: topPaddingHeight }}></div>
{
data.map(this.props.row)
}
<div style={{ height: bottomPaddingHeight }}></div>
</div>
)
}
}
export default Scroller