// Same example using react-virtualized

import React from 'react';

import { AutoSizer, List, CellMeasurer, CellMeasurerCache } from 'react-virtualized';

export class DynamicVirtualScrollExample extends React.PureComponent
{
    useFixedHeader = true

    constructor()
    {
        super();
        const items = [];
        for (let i = 0; i < 1000; i++)
        {
            items[i] = 30 + Math.round(Math.random()*50);
        }
        this.state = { items };
        this.cache = new CellMeasurerCache({
            fixedWidth: true,
            defaultHeight: 55,
        });
    }

    renderItems(start, count)
    {
        return this.state.items.slice(start, start+count).map((item, index) => (<div
            key={'i'+(index+start)}
            ref={e => this.itemElements[index+start] = e}
            style={{height: item+'px', color: 'white', textAlign: 'center', lineHeight: item+'px', background: 'rgb('+Math.round(item*255/80)+',0,0)'}}>
            № {index+start}: {item}px
        </div>));
    }

    renderRow = ({ index, key, style, parent }) =>
    {
        const item = this.state.items[index];
        return (<CellMeasurer key={key} cache={this.cache} parent={parent} columnIndex={0} rowIndex={index}>
            <div
                key={'i'+index}
                ref={e => this.itemElements[index] = e}
                style={{...style, height: item+'px', color: 'white', textAlign: 'center', lineHeight: item+'px', background: 'rgb('+Math.round(item*255/80)+',0,0)'}}>
                № {index}: {item}px
            </div>
        </CellMeasurer>);
    }

    render()
    {
        this.itemElements = [];
        return (<div style={{position: 'relative', width: '400px', height: '400px'}}>
            <AutoSizer>
                {({ width, height }) => {
                    return <List
                        width={width}
                        height={height}
                        deferredMeasurementCache={this.cache}
                        rowHeight={this.cache.rowHeight}
                        rowRenderer={this.renderRow}
                        rowCount={this.state.items.length}
                        overscanRowCount={3}
                    />
                }}
            </AutoSizer>
            {this.useFixedHeader ? <div style={{
                position: 'absolute',
                top: 0,
                left: 0,
                right: '12px',
                height: '30px',
                background: '#0080c0',
                color: 'white',
                textAlign: 'center',
                lineHeight: '30px'}}>
                fixed header
            </div> : null}
        </div>);
    }
}