Virtualization (Angular)

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 Angular.

import 'bootstrap.css'; import '@mescius/wijmo.styles/wijmo.css'; import './styles.css'; // import '@angular/compiler'; import { Component, enableProdMode, NgModule } from '@angular/core'; import { platformBrowserDynamic } from '@angular/platform-browser-dynamic'; import { BrowserModule } from '@angular/platform-browser'; import * as wjcGrid from '@mescius/wijmo.grid'; import { WjGridModule } from '@mescius/wijmo.angular2.grid'; // @Component({ selector: 'app-component', templateUrl: 'src/app.component.html' }) export class AppComponent { data: any[]; rowCount: string; cellCount: string; // DataSvc will be passed by derived classes constructor() { this.data = this._getData(100); } flexInitialized(flexgrid: wjcGrid.FlexGrid) { this.rowCount = flexgrid.rows.length.toString(); this.cellCount = flexgrid.hostElement.querySelectorAll('.wj-cell').length.toString(); flexgrid.updatedView.addHandler((s, e) => { this.rowCount = s.rows.length.toString(); this.cellCount = s.hostElement.querySelectorAll('.wj-cell').length.toString(); }); flexgrid.scrollPositionChanged.addHandler((s, e) => { // 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 this._addData(this.data, 20); view.refresh(); view.currentPosition = index; } }); } private _getData(cnt: number, start?: number) { 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; } // add random data to an array private _addData(data: any, cnt: number) { let more = this._getData(cnt, data.length); for (let i = 0; i < more.length; i++) { data.push(more[i]) } } } // @NgModule({ imports: [WjGridModule, BrowserModule], declarations: [AppComponent], bootstrap: [AppComponent] }) export class AppModule { } // enableProdMode(); // Bootstrap application with hash style navigation and global services. platformBrowserDynamic().bootstrapModule(AppModule);
<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <title>MESCIUS Wijmo FlexGrid Arrays and CollectionViews Binding</title> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <!-- Polyfills --> <script src="node_modules/core-js/client/shim.min.js"></script> <script src="node_modules/zone.js/fesm2015/zone.min.js"></script> <!-- SystemJS --> <script src="https://cdnjs.cloudflare.com/ajax/libs/systemjs/0.21.5/system.src.js" integrity="sha512-skZbMyvYdNoZfLmiGn5ii6KmklM82rYX2uWctBhzaXPxJgiv4XBwJnFGr5k8s+6tE1pcR1nuTKghozJHyzMcoA==" crossorigin="anonymous"></script> <script src="systemjs.config.js"></script> <script> // workaround to load 'rxjs/operators' from the rxjs bundle System.import('rxjs').then(function (m) { System.set(SystemJS.resolveSync('rxjs/operators'), System.newModule(m.operators)); System.import('./src/app.component'); }); </script> </head> <body> <app-component></app-component> </body> </html>
<div class="container-fluid"> <!-- the grid --> <wj-flex-grid #flex [(itemsSource)]="data" (initialized)="flexInitialized(flex)"> </wj-flex-grid> <p> The grid now has <span id="rowCount">{{rowCount}}</span> rows and <span id="cellCount">{{cellCount}}</span> cell elements. </p> </div>
.wj-flexgrid { height: 250px; margin: 6px 0px; } #rowCount, #cellCount { font-weight: bold; } body { margin-bottom: 24pt; }
(function (global) { SystemJS.config({ transpiler: './plugin-typescript.js', typescriptOptions: { "target": "ES2022", "module": "system", "emitDecoratorMetadata": true, "experimentalDecorators": true, }, baseURL: 'node_modules/', meta: { 'typescript': { "exports": "ts" }, '*.css': { loader: 'systemjs-plugin-css' } }, paths: { // paths serve as alias 'npm:': '' }, packageConfigPaths: [ '/node_modules/*/package.json', "/node_modules/@angular/*/package.json", "/node_modules/@mescius/*/package.json" ], map: { 'core-js': 'https://cdn.jsdelivr.net/npm/core-js@2.6.12/client/shim.min.js', 'typescript': 'https://cdnjs.cloudflare.com/ajax/libs/typescript/5.2.2/typescript.min.js', "rxjs": "https://cdnjs.cloudflare.com/ajax/libs/rxjs/7.8.1/rxjs.umd.min.js", 'systemjs-plugin-css': 'https://cdn.jsdelivr.net/npm/systemjs-plugin-css@0.1.37/css.js', '@mescius/wijmo': 'npm:@mescius/wijmo/index.js', '@mescius/wijmo.input': 'npm:@mescius/wijmo.input/index.js', '@mescius/wijmo.styles': 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'https://cdnjs.cloudflare.com/ajax/libs/jszip/3.10.1/jszip.min.js', "@angular/common/http": "https://cdn.jsdelivr.net/npm/@angular/common@16.2.6/fesm2022/http.mjs", "@angular/core": "https://cdn.jsdelivr.net/npm/@angular/core@16.2.6/fesm2022/core.mjs", "@angular/platform-browser": "https://cdn.jsdelivr.net/npm/@angular/platform-browser@16.2.6/fesm2022/platform-browser.mjs", "@angular/common": "https://cdn.jsdelivr.net/npm/@angular/common@16.2.6/fesm2022/common.mjs", "@angular/compiler": "https://cdn.jsdelivr.net/npm/@angular/compiler@16.2.6/fesm2022/compiler.mjs", "@angular/forms": "https://cdn.jsdelivr.net/npm/@angular/forms@16.2.6/fesm2022/forms.mjs", "@angular/localize": "https://cdn.jsdelivr.net/npm/@angular/localize@16.2.6/fesm2022/localize.mjs", "@angular/platform-browser-dynamic": "https://cdn.jsdelivr.net/npm/@angular/platform-browser-dynamic@16.2.6/fesm2022/platform-browser-dynamic.mjs", }, // packages tells the System loader how to load when no filename and/or no extension packages: { "./src": { defaultExtension: 'ts' }, "node_modules": { defaultExtension: 'js' }, wijmo: { defaultExtension: 'js', } } }); })(this);