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Virtual Scroll displays a virtual, "infinite" list. Supports multi-column. Based on angular2-virtual-scroll by @rintoj
This module displays a small subset of records just enough to fill the viewport and uses the same DOM elements as the user scrolls. This method is effective because the number of DOM elements are always constant and tiny irrespective of the size of the list. Thus virtual scroll can display infinitely growing list of items in an efficient way.
TBD
<virtual-scroll [items]="items" (update)="viewPortItems = $event">
<list-item *ngFor="let item of viewPortItems" [item]="item">
</list-item>
</virtual-scroll>alternatively
<virtual-scroll #scroll [items]="items">
<list-item *ngFor="let item of scroll.viewPortItems" [item]="item">
</list-item>
</virtual-scroll>alternatively
<div virtualScroll [items]="items" (update)="viewPortItems = $event">
<list-item *ngFor="let item of viewPortItems" [item]="item">
</list-item>
</div>Step 1: Install angular2-virtual-scroll
npm install @nomadreservations/virtual-scroll --saveStep 2: Import virtual scroll module into your app module
....
import { VirtualScrollModule } from '@nomadreservations/virtual-scroll';
....
@NgModule({
...
imports: [
....
VirtualScrollModule
],
....
})
export class AppModule { }Step 3: Wrap virtual-scroll tag around list items;
<virtual-scroll [items]="items" (update)="viewPortItems = $event">
<list-item *ngFor="let item of viewPortItems" [item]="item">
</list-item>
</virtual-scroll>You must also define width and height for the container and for it's children.
virtual-scroll {
display: block;
width: 350px;
height: 200px;
}
list-item {
display: block;
width: 100%;
height: 30px;
}Step 4: Create 'list-item' component.
'list-item' must a custom angular2 component, outside of this library. A sample list item is give below or check the demo app for list-item.component.ts.
import { Component, Input } from '@angular/core';
export interface ListItem {
index?: number;
name?: string;
gender?: string;
age?: number;
email?: string;
phone?: string;
address?: string;
}
@Component({
selector: 'list-item',
template: `
<div class="avatar">{{item.index}}</div>
<div class="item-content">
<div class="name">{{item.name}}</div>
<div>
<span class="badge">{{item.age}} / {{item.gender}}</span>
<span>{{item.email}} | {{item.phone}}</span>
</div>
<div>{{item.address}}</div>
</div>
`,
styleUrls: ['./list-item.scss']
})
export class ListItemComponent {
@Input()
item: ListItem;
}Child component is not a necessity if your item is simple enough. See below.
<virtual-scroll [items]="items" (update)="viewPortItems = $event">
<div *ngFor="let item of viewPortItems">{{item?.name}}</div>
</virtual-scroll>| Attribute | Type | Description |
|---|---|---|
| items | any[] | The data that builds the templates within the virtual scroll. This is the same data that you'd pass to ngFor. It's important to note that when this data has changed, then the entire virtual scroll is refreshed. |
| childWidth | number | The minimum width of the item template's cell. This dimension is used to help determine how many cells should be created when initialized, and to help calculate the height of the scrollable area. Note that the actual rendered size of the first cell is used by default if not specified. |
| childHeight | number | The minimum height of the item template's cell. This dimension is used to help determine how many cells should be created when initialized, and to help calculate the height of the scrollable area. Note that the actual rendered size of the first cell is used by default if not specified. |
| bufferAmount | number | The the number of elements to be rendered outside of the current container's viewport. Useful when not all elements are the same dimensions. |
| scrollAnimationTime | number | The time in milliseconds for the scroll animation to run for. Default value is 1500 |
| parentScroll | Element / Window | Element (or window), which will have scrollbar. This element must be one of the parents of virtual-scroll |
| update | Event | This event is fired every time start or end index change and emits list of items from start to end. The list emitted by this event must be used with *ngFor to render the actual list of items within <virtual-scroll> |
| change | Event | This event is fired every time start or end index change and emits ChangeEvent which of format: { start: number, end: number } |
If you are using AOT compilation (hope you do it) then in classic usage (with listening to update event) it is required to create field viewPortItems in your component.
There is a way how to avoid it.
<virtual-scroll #scroll [items]="items">
<list-item *ngFor="let item of scroll.viewPortItems" [item]="item">
</list-item>
</virtual-scroll>If inside of content of virtual scroll element you want to show also additional elements except list itself (e.g. search field), you need to specify block with list using id "container".
<virtual-scroll [items]="items"
(update)="viewPortItems = $event">
<input type="search">
<div #container>
<list-item *ngFor="let item of viewPortItems" [item]="item">
</list-item>
</div>
</virtual-scroll>If you want to use scrollbar of parent block, instead of scrolling block, set parentScroll.
<div #scrollingBlock>
<virtual-scroll [items]="items"
[parentScroll]="scrollingBlock.nativeElement"
(update)="viewPortItems = $event">
<input type="search">
<div #container>
<list-item *ngFor="let item of viewPortItems" [item]="item">
</list-item>
</div>
</virtual-scroll>
</div>If you want to use scrollbar of window, instead of scrolling block, set parentScroll.
<virtual-scroll
#scroll
[items]="items"
[parentScroll]="scroll.window">
<input type="search">
<div #container>
<list-item *ngFor="let item of scroll.viewPortItems" [item]="item">
</list-item>
</div>
</virtual-scroll>Items must have fixed height and width for this module to work perfectly. However if your list happen to have items with variable width and height, set inputs childWidth and childHeight to the smallest possible values to make this work.
<virtual-scroll [items]="items"
[childWidth]="80"
[childHeight]="30"
(update)="viewPortItems = $event">
<list-item *ngFor="let item of viewPortItems" [item]="item">
</list-item>
</virtual-scroll>The event end is fired every time scroll reaches at the end of the list. You could use this to load more items at the end of the scroll. See below.
import { ChangeEvent } from '@angular2-virtual-scroll';
...
@Component({
selector: 'list-with-api',
template: `
<virtual-scroll [items]="buffer" (update)="scrollItems = $event"
(end)="fetchMore($event)">
<list-item *ngFor="let item of scrollItems" [item]="item"> </list-item>
<div *ngIf="loading" class="loader">Loading...</div>
</virtual-scroll>
`
})
export class ListWithApiComponent implements OnChanges {
@Input()
items: ListItem[];
protected buffer: ListItem[] = [];
protected loading: boolean;
protected fetchMore(event: ChangeEvent) {
if (event.end !== this.buffer.length) return;
this.loading = true;
this.fetchNextChunk(this.buffer.length, 10).then(chunk => {
this.buffer = this.buffer.concat(chunk);
this.loading = false;
}, () => this.loading = false);
}
protected fetchNextChunk(skip: number, limit: number): Promise<ListItem[]> {
return new Promise((resolve, reject) => {
....
});
}
}If virtual scroll is used within a dropdown or collapsible menu, virtual scroll needs to know when the container size change. Use refresh() function after container is resized (include time for animation as well).
import { Component, ViewChild } from '@angular/core';
import { VirtualScrollComponent } from 'angular2-virtual-scroll';
@Component({
selector: 'rj-list',
template: `
<virtual-scroll [items]="items" (update)="scrollList = $event">
<div *ngFor="let item of scrollList; let i = index"> {{i}}: {{item}} </div>
</virtual-scroll>
`
})
export class ListComponent {
protected items = ['Item1', 'Item2', 'Item3'];
@ViewChild(VirtualScrollComponent)
private virtualScroll: VirtualScrollComponent;
// call this function after resize + animation end
afterResize() {
this.virtualScroll.refresh();
}
}You could use scrollInto(item) api to scroll into an item in the list. See below:
import { Component, ViewChild } from '@angular/core';
import { VirtualScrollComponent } from 'angular2-virtual-scroll';
@Component({
selector: 'rj-list',
template: `
<virtual-scroll [items]="items" (update)="scrollList = $event">
<div *ngFor="let item of scrollList; let i = index"> {{i}}: {{item}} </div>
</virtual-scroll>
`
})
export class ListComponent {
protected items = ['Item1', 'Item2', 'Item3'];
@ViewChild(VirtualScrollComponent)
private virtualScroll: VirtualScrollComponent;
// call this function whenever you have to focus on second item
focusOnAnItem() {
this.virtualScroll.scrollInto(items[1]);
}
}Always be sure to send an immutable copy of items to virtual scroll to avoid unintended behavior. You need to be careful when doing non-immutable operations such as sorting:
sort() {
this.items = [].concat(this.items || []).sort()
}This will be deprecated once Resize Observer is fully implemented.
Contributions are very welcome! Just send a pull request. Feel free to contact me or checkout my GitHub page.
Original Module:
The MIT License (MIT)
Copyright (c) 2016 Rinto Jose (rintoj)
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