Feature : Add virtual scroll on Tree Select Component

src/app/components/treeselect/treeselect.css

@@ -94,4 +94,12 @@
     .p-treeselect-clearable {
         position: relative;
     }
+
+    .p-treeselect-virtual-scroll .p-tree.p-component {
+      padding: 0;
+    }
+
+    .p-treeselect-virtual-scroll .p-tree-container.p-scroller-content {
+      padding: 1.25rem;
+    }
 }

src/app/components/treeselect/treeselect.ts

@@ -2,7 +2,7 @@ import { AnimationEvent } from '@angular/animations';
 import { CommonModule } from '@angular/common';
 import { AfterContentInit, ChangeDetectionStrategy, ChangeDetectorRef, Component, ContentChildren, ElementRef, EventEmitter, forwardRef, Input, NgModule, Output, QueryList, TemplateRef, ViewChild, ViewEncapsulation } from '@angular/core';
 import { NG_VALUE_ACCESSOR } from '@angular/forms';
-import { OverlayOptions, OverlayService, PrimeNGConfig, PrimeTemplate, SharedModule, TreeNode } from 'primeng/api';
+import { OverlayOptions, OverlayService, PrimeNGConfig, PrimeTemplate, ScrollerOptions, SharedModule, TreeNode } from 'primeng/api';
 import { DomHandler } from 'primeng/dom';
 import { ChevronDownIcon } from 'primeng/icons/chevrondown';
 import { SearchIcon } from 'primeng/icons/search';
@@ -113,7 +113,7 @@ export const TREESELECT_VALUE_ACCESSOR: any = {
                                 </span>
                             </button>
                         </div>
-                        <div class="p-treeselect-items-wrapper" [ngStyle]="{ 'max-height': scrollHeight }">
+                        <div class="p-treeselect-items-wrapper" [class.p-treeselect-virtual-scroll]="virtualScroll" [ngStyle]="{ 'max-height': scrollHeight }" >
                             <p-tree
                                 #tree
                                 [value]="options"
@@ -133,6 +133,9 @@ export const TREESELECT_VALUE_ACCESSOR: any = {
                                 [filterPlaceholder]="filterPlaceholder"
                                 [filterLocale]="filterLocale"
                                 [filteredNodes]="filteredNodes"
+                                [virtualScroll]="virtualScroll"
+                                [virtualScrollItemSize]="virtualScrollItemSize"
+                                [virtualScrollOptions]="virtualScrollOptions"
                                 [_templateMap]="templateMap"
                             >
                                 <ng-container *ngIf="emptyTemplate">
@@ -314,6 +317,21 @@ export class TreeSelect implements AfterContentInit {
      * @group Props
      */
     @Input() resetFilterOnHide: boolean = true;
+    /**
+     * Whether the data should be loaded on demand during scroll.
+     * @group Props
+     */
+    @Input() virtualScroll: boolean | undefined;
+    /**
+     * Height of an item in the list for VirtualScrolling.
+     * @group Props
+     */
+    @Input() virtualScrollItemSize: number | undefined;
+    /**
+     * Whether to use the scroller feature. The properties of scroller component can be used like an object in it.
+     * @group Props
+     */
+    @Input() virtualScrollOptions: ScrollerOptions | undefined;
     /**
      * An array of treenodes.
      * @defaultValue undefined

src/app/showcase/doc/treeselect/treeselectdoc.module.ts

@@ -16,10 +16,11 @@ import { InvalidDoc } from './invaliddoc';
 import { MultipleDoc } from './multipledoc';
 import { ReactiveFormsDoc } from './reactiveformsdoc';
 import { StyleDoc } from './styledoc';
+import { VirtualScrollDoc } from './virtualscrolldoc';
 
 @NgModule({
     imports: [CommonModule, AppCodeModule, AppDocModule, TreeSelectModule, FormsModule, ReactiveFormsModule, RouterModule],
     exports: [AppDocModule],
-    declarations: [ImportDoc, BasicDoc, MultipleDoc, CheckboxDoc, FilterDoc, FloatLabelDoc, InvalidDoc, DisabledDoc, StyleDoc, AccessibilityDoc, ReactiveFormsDoc]
+    declarations: [ImportDoc, BasicDoc, MultipleDoc, CheckboxDoc, VirtualScrollDoc, FilterDoc, FloatLabelDoc, InvalidDoc, DisabledDoc, StyleDoc, AccessibilityDoc, ReactiveFormsDoc]
 })
 export class TreeSelectDocModule {}

src/app/showcase/doc/treeselect/virtualscrolldoc.ts

@@ -0,0 +1,58 @@
+import { Component, Input } from '@angular/core';
+import { Code } from '../../domain/code';
+import { NodeService } from '../../service/nodeservice';
+
+@Component({
+    selector: 'virtual-scroll-doc',
+    template: ` <section class="py-3">
+        <app-docsectiontext [title]="title" [id]="id">
+            <p>VirtualScrolling is an efficient way of rendering the options by displaying a small subset of data in the viewport at any time. When dealing with huge number of options, it is suggested to enable VirtualScrolling to avoid performance
+                issues. Usage is simple as setting <i>virtualScroll</i> property to true and defining <i>virtualScrollItemSize</i> to specify the height of an item.</p>
+        </app-docsectiontext>
+        <div class="card flex justify-content-center">
+            <p-treeSelect class="w-full md:w-20rem" containerStyleClass="w-full" [(ngModel)]="selectedNodes" [options]="nodes" display="chip" [metaKeySelection]="false" selectionMode="checkbox" placeholder="Select Item"
+                          [virtualScroll]="true" [virtualScrollItemSize]="46" [virtualScrollOptions]="{ scrollHeight: '200px' }"></p-treeSelect>
+        </div>
+        <app-code [code]="code" selector="tree-select-virtual-scroll-demo"></app-code>
+    </section>`
+})
+export class VirtualScrollDoc {
+    @Input() id: string;
+
+    @Input() title: string;
+
+    nodes!: any[];
+
+    selectedNodes: any;
+
+    constructor(private nodeService: NodeService) {
+        this.nodeService.getLargeTreeNodes().then((files) => (this.nodes = files));
+    }
+
+    code: Code = {
+        basic: `<p-treeSelect class="w-full md:w-20rem" containerStyleClass="w-full" [(ngModel)]="selectedNodes" [options]="nodes" display="chip" [metaKeySelection]="false" selectionMode="checkbox" placeholder="Select Item" [virtualScroll]="true" [virtualScrollItemSize]="46" [virtualScrollOptions]="{scrollHeight: '200px'}"></p-treeSelect>`,
+        html: `
+<div class="card flex justify-content-center">
+    <p-treeSelect class="w-full md:w-20rem" containerStyleClass="w-full" [(ngModel)]="selectedNodes" [options]="nodes" display="chip" [metaKeySelection]="false" selectionMode="checkbox" placeholder="Select Item" [virtualScroll]="true" [virtualScrollItemSize]="46" [virtualScrollOptions]="{scrollHeight: '200px'}"></p-treeSelect>
+</div>`,
+        typescript: `
+import { Component } from '@angular/core';
+import { NodeService } from '../../service/nodeservice';
+
+@Component({
+    selector: 'tree-select-virtual-scroll-demo',
+    templateUrl: './tree-select-virtual-scroll-demo.html'
+})
+export class TreeSelectVirtualScrollDemo {
+    nodes!: any[];
+
+    selectedNodes: any;
+
+    constructor(private nodeService: NodeService) {
+        this.nodeService.getLargeTreeNodes().then((files) => (this.nodes = files));
+    }
+}`,
+
+        service: ['NodeService'],
+    };
+}

src/app/showcase/pages/treeselect/treeselectdemo.ts

@@ -10,6 +10,7 @@ import { ImportDoc } from '../../doc/treeselect/importdoc';
 import { InvalidDoc } from '../../doc/treeselect/invaliddoc';
 import { MultipleDoc } from '../../doc/treeselect/multipledoc';
 import { StyleDoc } from '../../doc/treeselect/styledoc';
+import { VirtualScrollDoc } from '../../doc/treeselect/virtualscrolldoc';
 
 @Component({
     templateUrl: './treeselectdemo.html'
@@ -41,6 +42,11 @@ export class TreeSelectDemo {
             label: 'Checkbox',
             component: CheckboxDoc
         },
+        {
+            id: 'virtual-scroll-doc',
+            label: 'Virtual Scroll',
+            component: VirtualScrollDoc
+        },
         {
             id: 'filter',
             label: 'Filter',

src/app/showcase/service/nodeservice.ts

@@ -1,4 +1,5 @@
 import { Injectable } from '@angular/core';
+import { TreeNode } from "../../components/api/treenode";
 
 @Injectable()
 export class NodeService {
@@ -763,6 +764,35 @@ export class NodeService {
         ];
     }
 
+    getDynamicTreeNodes(parentCount: number, childrenCount: number): TreeNode[] {
+        const nodes: TreeNode[] = [];
+
+        for (let parentIndex = 0; parentIndex < parentCount; parentIndex++) {
+            const children: TreeNode[] = [];
+
+            for (let childIndex = 0; childIndex < childrenCount; childIndex++) {
+                children.push({
+                    key: `${parentIndex}-${childIndex}`,
+                    label: `Child ${parentIndex}-${childIndex}`,
+                    selectable: true,
+                });
+            }
+
+            nodes.push({
+                key: parentIndex.toString(),
+                label: `Parent ${parentIndex}`,
+                selectable: true,
+                children: children,
+            });
+        }
+
+        return nodes;
+    }
+
+    getLargeTreeNodes() {
+        return Promise.resolve(this.getDynamicTreeNodes(10, 100));
+    }
+
     getTreeTableNodes() {
         return Promise.resolve(this.getTreeTableNodesData());
     }