Lazy-Loaded Trees

In the tree grid below, collapsed nodes have a single dummy child. When a node is expanded, more nodes are loaded on demand. This is a common pattern known as 'lazy-loading'.

import 'bootstrap.css'; import '@grapecity/wijmo.styles/wijmo.css'; import './styles.css'; import * as wjGrid from '@grapecity/wijmo.grid'; import * as wjCore from '@grapecity/wijmo'; // document.readyState === 'complete' ? init() : window.onload = init; // function init() { // // create the grid var theGrid = new wjGrid.FlexGrid('#theGrid', { childItemsPath: 'children', headersVisibility: 'Column', groupCollapsedChanged: groupCollapsedChanged, autoGenerateColumns: false, columns: [ { binding: 'name', header: 'Customer Name', width: '*' }, { binding: 'id', header: 'ID', align: 'center', cssClass: 'id-column' } ], itemsSource: getData(), }); // // start collapsed theGrid.collapseGroupsToLevel(0); // // update row when items are loaded function updateRowCount(grid) { document.getElementById('rowCount').textContent = wjCore.Globalize.format(grid.rows.length, 'n0'); } updateRowCount(theGrid); // // load data when collapse node is expanded function groupCollapsedChanged(s, e) { var row = s.rows[e.row], item = row.dataItem; // // did we just expand a node with a dummy child? if (!row.isCollapsed && item.children.length == 1 && item.children[0].name == '') { // // can't lazy load while updating rows if (s.rows.isUpdating) { row.isCollapsed = true; return; } // // replace the dummy child with actual nodes item.children.length = 0; var cnt = Math.round(Math.random() * 5) + 1; for (var i = 0; i < cnt; i++) { var node = createNode(); item.children.push(node); } // // refresh the view s.collectionView.refresh(); // // collapse the new item's child items for (var i = row.index + 1; i < s.rows.length; i++) { var childRow = s.rows[i]; if (childRow.level <= row.level) { break; } childRow.isCollapsed = true; } // // update row count updateRowCount(s); } } var nodeId; function createNode(dummy) { var first = 'Al,Bob,Cal,Dan,Ed,Fred,Greg,Hal,Ian,Jack,Karl,Lou,Moe,Nate,Oleg,Paul,Quincy,Rod,Sue,Uwe,Vic,Walt,Xiu,Yuri,Zack'.split(','), last = 'Adams,Baum,Cole,Dell,Evans,Fell,Green,Hill,Isman,Jones,Krup,Lee,Monk,Nye,Opus,Pitt,Quaid,Riems,Stark,Trell,Unger,Voss,Wang,Xie,Zalm'.split(','), name = dummy ? '' : getOneOf(first) + ' ' + getOneOf(last), children = []; if (!dummy) { children.push(createNode(true)); } if (nodeId == null) nodeId = 0; return { id: nodeId++, name: name, children: children }; } function getOneOf(arr) { return arr[Math.floor(Math.random() * arr.length)]; } // create/retrieve data function getData() { var tree = []; tree.push(createNode()); tree.push(createNode()); return tree; } }
<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <title>GrapeCity Wijmo FlexGrid Lazy Loading Tree Grid</title> <meta name="viewport" content="width=device-width, initial-scale=1.0"> <!-- SystemJS --> <script src="node_modules/systemjs/dist/system.src.js"></script> <script src="systemjs.config.js"></script> <script> System.import('./src/app'); </script> </head> <body> <div class="container-fluid"> <div id="theGrid"> </div> <p> The grid currently has <b id="rowCount"></b> rows. </p> </div> </body> </html>
.wj-flexgrid { max-height: 300px; margin: 12px; } .wj-flexgrid .wj-cell { padding: 8px; } .wj-flexgrid .wj-group:not(.wj-state-selected):not(.wj-state-multi-selected) { background-color: white; } .id-column { font-style: italic; } document { margin-bottom: 48pt; }
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