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Load Data on Demand

You can use the createChildren function to specify custom logic to load data. This function is called each time a user expands a node that was not expanded before. The node's identifier is passed to the function as an argument. Send this identifier to the data service that should return data for child nodes.

As an alternative, you can enable virtual mode to use the default load logic.

Backend API
<dx-tree-view id="simple-treeview" [createChildren]="createChildren" dataStructure="plain" rootValue="" [expandNodesRecursive]="false" [height]="500" > </dx-tree-view>
import { NgModule, Component, enableProdMode } from '@angular/core'; import { BrowserModule } from '@angular/platform-browser'; import { platformBrowserDynamic } from '@angular/platform-browser-dynamic'; import { HttpClient, HttpClientModule } from '@angular/common/http'; import { lastValueFrom } from 'rxjs'; import { DxTreeViewComponent, DxTreeViewModule } from 'devextreme-angular'; if (!/localhost/.test(document.location.host)) { enableProdMode(); } @Component({ styleUrls: [`app/app.component.css`], selector: 'demo-app', templateUrl: `app/app.component.html`, providers: [], }) export class AppComponent { createChildren: DxTreeViewComponent['createChildren']; constructor(http: HttpClient) { this.createChildren = (parent: Record<string, { id: unknown }>) => { const parentId = parent ? parent.itemData.id : ''; return lastValueFrom( http.get(`https://js.devexpress.com/Demos/Mvc/api/TreeViewData?parentId=${parentId}`), ); }; } } @NgModule({ imports: [ BrowserModule, DxTreeViewModule, HttpClientModule, ], declarations: [AppComponent], bootstrap: [AppComponent], }) export class AppModule { } platformBrowserDynamic().bootstrapModule(AppModule);
// In real applications, you should not transpile code in the browser. // You can see how to create your own application with Angular and DevExtreme here: // https://js.devexpress.com/Documentation/Guide/Angular_Components/Getting_Started/Create_a_DevExtreme_Application/ const componentNames = [ 'accordion', 'action-sheet', 'autocomplete', 'bar-gauge', 'box', 'bullet', 'button-group', 'button', 'calendar', 'chart', 'check-box', 'circular-gauge', 'color-box', 'context-menu', 'data-grid', 'date-box', 'date-range-box', 'defer-rendering', 'diagram', 'draggable', 'drawer', 'drop-down-box', 'drop-down-button', 'file-manager', 'file-uploader', 'filter-builder', 'form', 'funnel', 'gallery', 'gantt', 'html-editor', 'linear-gauge', 'list', 'load-indicator', 'load-panel', 'lookup', 'map', 'menu', 'multi-view', 'nested', 'number-box', 'pie-chart', 'pivot-grid-field-chooser', 'pivot-grid', 'polar-chart', 'popover', 'popup', 'progress-bar', 'radio-group', 'range-selector', 'range-slider', 'recurrence-editor', 'resizable', 'responsive-box', 'sankey', 'scheduler', 'scroll-view', 'select-box', 'slider', 'sortable', 'sparkline', 'speed-dial-action', 'splitter', 'switch', 'tab-panel', 'tabs', 'tag-box', 'text-area', 'text-box', 'tile-view', 'toast', 'toolbar', 'tooltip', 'tree-list', 'tree-map', 'tree-view', 'validation-group', 'validation-summary', 'validator', 'vector-map', ]; window.exports = window.exports || {}; window.config = { transpiler: 'ts', typescriptOptions: { module: 'system', emitDecoratorMetadata: true, experimentalDecorators: true, }, meta: { 'typescript': { 'exports': 'ts', }, 'devextreme/time_zone_utils.js': { 'esModule': true, }, 'devextreme/localization.js': { 'esModule': true, }, 'devextreme/viz/palette.js': { 'esModule': true, }, '@angular/platform-browser-dynamic': { 'esModule': true, }, '@angular/platform-browser': { 'esModule': true, }, '@angular/core': { 'esModule': true, }, '@angular/common': { 'esModule': true, }, '@angular/common/http': { 'esModule': true, }, '@angular/compiler': { 'esModule': true, }, '@angular/animations': { 'esModule': true, }, '@angular/forms': { 'esModule': true, }, }, paths: { 'npm:': 'https://unpkg.com/', 'bundles:': '../../../../bundles/', }, map: { 'ts': 'npm:plugin-typescript@4.2.4/lib/plugin.js', 'typescript': 'npm:typescript@4.2.4/lib/typescript.js', /* @angular */ '@angular/compiler': 'bundles:@angular/compiler.umd.js', '@angular/platform-browser-dynamic': 'bundles:@angular/platform-browser-dynamic.umd.js', '@angular/core': 'bundles:@angular/core.umd.js', '@angular/core/primitives/signals': 'bundles:@angular/core.primitives.signals.umd.js', '@angular/common': 'bundles:@angular/common.umd.js', '@angular/common/http': 'bundles:@angular/common-http.umd.js', '@angular/platform-browser': 'bundles:@angular/platform-browser.umd.js', '@angular/platform-browser/animations': 'bundles:@angular/platform-browser.umd.js', '@angular/forms': 'bundles:@angular/forms.umd.js', /* devextreme */ 'devextreme': 'npm:devextreme@24.1.4/cjs', '@devextreme/runtime': 'npm:@devextreme/runtime@3.0.13', 'devextreme/bundles/dx.all': 'npm:devextreme@24.1.4/bundles/dx.all.js', 'devextreme-quill': 'npm:devextreme-quill@1.7.1/dist/dx-quill.min.js', 'devexpress-diagram': 'npm:devexpress-diagram@2.2.10', 'devexpress-gantt': 'npm:devexpress-gantt@4.1.56', /* devextreme-angular umd maps */ 'devextreme-angular': 'bundles:devextreme-angular/devextreme-angular.umd.js', 'devextreme-angular/core': 'bundles:devextreme-angular/devextreme-angular-core.umd.js', ...componentNames.reduce((acc, name) => { acc[`devextreme-angular/ui/${name}`] = `bundles:devextreme-angular/devextreme-angular-ui-${name}.umd.js`; return acc; }, {}), 'jszip': 'npm:jszip@3.10.1/dist/jszip.min.js', 'tslib': 'npm:tslib@2.6.1/tslib.js', 'rxjs': 'npm:rxjs@7.5.3/dist/bundles/rxjs.umd.js', 'rxjs/operators': 'npm:rxjs@7.5.3/dist/cjs/operators/index.js', 'rrule': 'npm:rrule@2.6.4/dist/es5/rrule.js', 'luxon': 'npm:luxon@1.28.1/build/global/luxon.min.js', 'es6-object-assign': 'npm:es6-object-assign@1.1.0', 'inferno': 'npm:inferno@7.4.11/dist/inferno.min.js', 'inferno-compat': 'npm:inferno-compat/dist/inferno-compat.min.js', 'inferno-create-element': 'npm:inferno-create-element@7.4.11/dist/inferno-create-element.min.js', 'inferno-dom': 'npm:inferno-dom/dist/inferno-dom.min.js', 'inferno-hydrate': 'npm:inferno-hydrate@7.4.11/dist/inferno-hydrate.min.js', 'inferno-clone-vnode': 'npm:inferno-clone-vnode/dist/inferno-clone-vnode.min.js', 'inferno-create-class': 'npm:inferno-create-class/dist/inferno-create-class.min.js', 'inferno-extras': 'npm:inferno-extras/dist/inferno-extras.min.js', // Prettier 'prettier/standalone': 'npm:prettier@2.8.8/standalone.js', 'prettier/parser-html': 'npm:prettier@2.8.8/parser-html.js', }, packages: { 'app': { main: './app.component.ts', defaultExtension: 'ts', }, 'devextreme': { defaultExtension: 'js', }, 'devextreme/events/utils': { main: 'index', }, 'devextreme/events': { main: 'index', }, 'es6-object-assign': { main: './index.js', defaultExtension: 'js', }, 'rxjs': { defaultExtension: 'js', }, 'rxjs/operators': { defaultExtension: 'js', }, }, packageConfigPaths: [ 'npm:@devextreme/*/package.json', 'npm:@devextreme/runtime@3.0.13/inferno/package.json', 'npm:rxjs@7.5.3/package.json', 'npm:rxjs@7.5.3/operators/package.json', 'npm:devexpress-diagram@2.2.10/package.json', 'npm:devexpress-gantt@4.1.56/package.json', ], }; System.config(window.config); // System.import('@angular/compiler').catch(console.error.bind(console));
<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml" lang="en"> <head> <title>DevExtreme Demo</title> <meta http-equiv="X-UA-Compatible" content="IE=edge" /> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=5.0" /> <link rel="stylesheet" type="text/css" href="https://cdn3.devexpress.com/jslib/24.1.4/css/dx.light.css" /> <script src="https://unpkg.com/core-js@2.6.12/client/shim.min.js"></script> <script src="https://unpkg.com/zone.js@0.13.0/dist/zone.js"></script> <script src="https://unpkg.com/reflect-metadata@0.1.13/Reflect.js"></script> <script src="https://unpkg.com/systemjs@0.21.3/dist/system.js"></script> <script src="config.js"></script> <script> System.import("app").catch(console.error.bind(console)); </script> </head> <body class="dx-viewport"> <div class="demo-container"> <demo-app>Loading...</demo-app> </div> </body> </html>