Virtualization (React)

The main job of the FlexGrid is to convert JavaScript data objects into DOM elements that the user can interact with. In many cases, the data consists of large arrays with many thousands of items. Creating DOM elements for each of these items would make for large and slow pages. Virtualization is the process of keeping track of which portions of the data are visible and rendering only those parts. This reduces the number of DOM elements in the document tree and improves performance dramatically. The FlexGrid exposes the visible part of the data through the viewRange property. Whenever the user resizes the screen or scrolls the grid, the viewRange is updated and the grid updates its child DOM elements.

Learn about FlexGrid | FlexGrid API Reference

This example uses React.

import 'bootstrap.css'; import '@mescius/wijmo.styles/wijmo.css'; import ReactDOM from 'react-dom/client'; import React, { useState } from 'react'; import useEvent from 'react-use-event-hook'; import * as wjGrid from '@mescius/wijmo.react.grid'; import './app.css'; import { data, getData } from './data'; function App() { const [rowCount, setRowCount] = useState(''); const [cellCount, setCellCount] = useState(''); const flexInitialized = useEvent((flexgrid) => { setRowCount(flexgrid.rows.length.toString()); setCellCount(flexgrid.hostElement.querySelectorAll(".wj-cell").length.toString()); flexgrid.updatedView.addHandler(() => { setRowCount(flexgrid.rows.length.toString()); setCellCount(flexgrid.hostElement.querySelectorAll(".wj-cell").length.toString()); }); flexgrid.scrollPositionChanged.addHandler((s) => { // if we're close to the bottom, add 20 items if (s.viewRange.bottomRow >= s.rows.length - 1) { let view = s.collectionView; let index = view.currentPosition; // keep position in case the view is sorted addData(data, 20); view.refresh(); view.currentPosition = index; } }); }); const addData = useEvent((data, cnt) => { let more = getData(cnt, data.length); for (let i = 0; i < more.length; i++) { data.push(more[i]); } }); return (<div className="container-fluid"> <wjGrid.FlexGrid initialized={flexInitialized} itemsSource={data}/> <p> The grid now has <span id="rowCount">{rowCount}</span> {' '}rows and <span id="cellCount">{cellCount}</span> cell elements. </p> </div>); } const container = document.getElementById('app'); if (container) { const root = ReactDOM.createRoot(container); root.render(<App />); }
<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <title>MESCIUS Wijmo Wijmo FlexGrid Virtualization</title> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <!-- SystemJS --> <script src="https://cdnjs.cloudflare.com/ajax/libs/systemjs/0.19.40/system.src.js" integrity="sha512-G6mEj6h18+m3MvzdviSDfPle/TfH0//cXcB33AKlNR/Rha0yQsKefDZKRTkIZos97HEGq2JMV1RT5ybMoQ3WsQ==" crossorigin="anonymous"></script> <script src="systemjs.config.js"></script> <script> System.import('./src/app'); </script> </head> <body> <div id="app"></div> </body> </html>
.wj-flexgrid { height: 250px; margin: 6px 0px; } #rowCount, #cellCount { font-weight: bold; }
export function getData(cnt, start) { let data = []; let countries = "USA,Germany,UK,Japan,Italy,Greece".split(","); if (start == null) { start = 0; } for (let i = 0; i < cnt; i++) { data.push({ id: i + start, country: countries[i % countries.length], date: new Date(2014, i % 12, i % 28), amount: Math.random() * 10000, active: i % 4 === 0 }); } return data; } export const data = getData(100);
(function (global) { System.config({ transpiler: 'plugin-babel', babelOptions: { es2015: true, react: true }, meta: { '*.css': { loader: 'css' } }, paths: { // paths serve as alias 'npm:': 'node_modules/' }, // map tells the System loader where to look for things map: { 'jszip': 'npm:jszip/dist/jszip.js', '@mescius/wijmo': 'npm:@mescius/wijmo/index.js', '@mescius/wijmo.input': 'npm:@mescius/wijmo.input/index.js', '@mescius/wijmo.styles': 'npm:@mescius/wijmo.styles', '@mescius/wijmo.cultures': 'npm:@mescius/wijmo.cultures', '@mescius/wijmo.chart': 'npm:@mescius/wijmo.chart/index.js', '@mescius/wijmo.chart.analytics': 'npm:@mescius/wijmo.chart.analytics/index.js', '@mescius/wijmo.chart.animation': 'npm:@mescius/wijmo.chart.animation/index.js', '@mescius/wijmo.chart.annotation': 'npm:@mescius/wijmo.chart.annotation/index.js', '@mescius/wijmo.chart.finance': 'npm:@mescius/wijmo.chart.finance/index.js', '@mescius/wijmo.chart.finance.analytics': 'npm:@mescius/wijmo.chart.finance.analytics/index.js', '@mescius/wijmo.chart.hierarchical': 'npm:@mescius/wijmo.chart.hierarchical/index.js', '@mescius/wijmo.chart.interaction': 'npm:@mescius/wijmo.chart.interaction/index.js', '@mescius/wijmo.chart.radar': 'npm:@mescius/wijmo.chart.radar/index.js', '@mescius/wijmo.chart.render': 'npm:@mescius/wijmo.chart.render/index.js', '@mescius/wijmo.chart.webgl': 'npm:@mescius/wijmo.chart.webgl/index.js', '@mescius/wijmo.chart.map': 'npm:@mescius/wijmo.chart.map/index.js', '@mescius/wijmo.gauge': 'npm:@mescius/wijmo.gauge/index.js', '@mescius/wijmo.grid': 'npm:@mescius/wijmo.grid/index.js', '@mescius/wijmo.grid.detail': 'npm:@mescius/wijmo.grid.detail/index.js', '@mescius/wijmo.grid.filter': 'npm:@mescius/wijmo.grid.filter/index.js', '@mescius/wijmo.grid.search': 'npm:@mescius/wijmo.grid.search/index.js', '@mescius/wijmo.grid.grouppanel': 'npm:@mescius/wijmo.grid.grouppanel/index.js', '@mescius/wijmo.grid.multirow': 'npm:@mescius/wijmo.grid.multirow/index.js', '@mescius/wijmo.grid.transposed': 'npm:@mescius/wijmo.grid.transposed/index.js', '@mescius/wijmo.grid.transposedmultirow': 'npm:@mescius/wijmo.grid.transposedmultirow/index.js', '@mescius/wijmo.grid.pdf': 'npm:@mescius/wijmo.grid.pdf/index.js', '@mescius/wijmo.grid.sheet': 'npm:@mescius/wijmo.grid.sheet/index.js', '@mescius/wijmo.grid.xlsx': 'npm:@mescius/wijmo.grid.xlsx/index.js', '@mescius/wijmo.grid.selector': 'npm:@mescius/wijmo.grid.selector/index.js', '@mescius/wijmo.grid.cellmaker': 'npm:@mescius/wijmo.grid.cellmaker/index.js', '@mescius/wijmo.grid.immutable': 'npm:@mescius/wijmo.grid.immutable/index.js', '@mescius/wijmo.touch': 'npm:@mescius/wijmo.touch/index.js', '@mescius/wijmo.cloud': 'npm:@mescius/wijmo.cloud/index.js', '@mescius/wijmo.nav': 'npm:@mescius/wijmo.nav/index.js', '@mescius/wijmo.odata': 'npm:@mescius/wijmo.odata/index.js', '@mescius/wijmo.olap': 'npm:@mescius/wijmo.olap/index.js', '@mescius/wijmo.rest': 'npm:@mescius/wijmo.rest/index.js', '@mescius/wijmo.pdf': 'npm:@mescius/wijmo.pdf/index.js', '@mescius/wijmo.pdf.security': 'npm:@mescius/wijmo.pdf.security/index.js', '@mescius/wijmo.viewer': 'npm:@mescius/wijmo.viewer/index.js', '@mescius/wijmo.xlsx': 'npm:@mescius/wijmo.xlsx/index.js', '@mescius/wijmo.undo': 'npm:@mescius/wijmo.undo/index.js', '@mescius/wijmo.interop.grid': 'npm:@mescius/wijmo.interop.grid/index.js', '@mescius/wijmo.barcode': 'npm:@mescius/wijmo.barcode/index.js', '@mescius/wijmo.barcode.common': 'npm:@mescius/wijmo.barcode.common/index.js', '@mescius/wijmo.barcode.composite': 'npm:@mescius/wijmo.barcode.composite/index.js', '@mescius/wijmo.barcode.specialized': 'npm:@mescius/wijmo.barcode.specialized/index.js', "@mescius/wijmo.react.chart.analytics": "npm:@mescius/wijmo.react.chart.analytics/index.js", "@mescius/wijmo.react.chart.animation": "npm:@mescius/wijmo.react.chart.animation/index.js", "@mescius/wijmo.react.chart.annotation": "npm:@mescius/wijmo.react.chart.annotation/index.js", "@mescius/wijmo.react.chart.finance.analytics": "npm:@mescius/wijmo.react.chart.finance.analytics/index.js", "@mescius/wijmo.react.chart.finance": "npm:@mescius/wijmo.react.chart.finance/index.js", "@mescius/wijmo.react.chart.hierarchical": "npm:@mescius/wijmo.react.chart.hierarchical/index.js", "@mescius/wijmo.react.chart.interaction": "npm:@mescius/wijmo.react.chart.interaction/index.js", "@mescius/wijmo.react.chart.radar": "npm:@mescius/wijmo.react.chart.radar/index.js", "@mescius/wijmo.react.chart": "npm:@mescius/wijmo.react.chart/index.js", "@mescius/wijmo.react.core": "npm:@mescius/wijmo.react.core/index.js", '@mescius/wijmo.react.chart.map': 'npm:@mescius/wijmo.react.chart.map/index.js', "@mescius/wijmo.react.gauge": "npm:@mescius/wijmo.react.gauge/index.js", "@mescius/wijmo.react.grid.detail": "npm:@mescius/wijmo.react.grid.detail/index.js", "@mescius/wijmo.react.grid.filter": "npm:@mescius/wijmo.react.grid.filter/index.js", "@mescius/wijmo.react.grid.grouppanel": "npm:@mescius/wijmo.react.grid.grouppanel/index.js", '@mescius/wijmo.react.grid.search': 'npm:@mescius/wijmo.react.grid.search/index.js', "@mescius/wijmo.react.grid.multirow": "npm:@mescius/wijmo.react.grid.multirow/index.js", "@mescius/wijmo.react.grid.sheet": "npm:@mescius/wijmo.react.grid.sheet/index.js", '@mescius/wijmo.react.grid.transposed': 'npm:@mescius/wijmo.react.grid.transposed/index.js', '@mescius/wijmo.react.grid.transposedmultirow': 'npm:@mescius/wijmo.react.grid.transposedmultirow/index.js', '@mescius/wijmo.react.grid.immutable': 'npm:@mescius/wijmo.react.grid.immutable/index.js', "@mescius/wijmo.react.grid": "npm:@mescius/wijmo.react.grid/index.js", "@mescius/wijmo.react.input": "npm:@mescius/wijmo.react.input/index.js", "@mescius/wijmo.react.olap": "npm:@mescius/wijmo.react.olap/index.js", "@mescius/wijmo.react.viewer": "npm:@mescius/wijmo.react.viewer/index.js", "@mescius/wijmo.react.nav": "npm:@mescius/wijmo.react.nav/index.js", "@mescius/wijmo.react.base": "npm:@mescius/wijmo.react.base/index.js", '@mescius/wijmo.react.barcode.common': 'npm:@mescius/wijmo.react.barcode.common/index.js', '@mescius/wijmo.react.barcode.composite': 'npm:@mescius/wijmo.react.barcode.composite/index.js', '@mescius/wijmo.react.barcode.specialized': 'npm:@mescius/wijmo.react.barcode.specialized/index.js', 'jszip': 'npm:jszip/dist/jszip.js', 'react': 'npm:react/umd/react.production.min.js', 'react-dom': 'npm:react-dom/umd/react-dom.production.min.js', 'react-dom/client': 'npm:react-dom/umd/react-dom.production.min.js', 'redux': 'npm:redux/dist/redux.min.js', 'react-redux': 'npm:react-redux/dist/react-redux.min.js', 'bootstrap.css': 'npm:bootstrap/dist/css/bootstrap.min.css', 'css': 'npm:systemjs-plugin-css/css.js', 'plugin-babel': 'npm:systemjs-plugin-babel/plugin-babel.js', 'systemjs-babel-build':'npm:systemjs-plugin-babel/systemjs-babel-browser.js', "react-use-event-hook": "npm:react-use-event-hook/dist/esm/useEvent.js", }, // packages tells the System loader how to load when no filename and/or no extension packages: { src: { defaultExtension: 'jsx' }, "node_modules": { defaultExtension: 'js' }, } }); })(this);