Virtual Scroll displays a virtual, "infinite" list. Supports multi-column.
About
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 an infinitely growing list of items in an efficient way.
Angular 4+ compatible module
Supports multi-column
Easy to use apis
OpenSource and available in GitHub
Breaking Changes:
The value of ChangeEvent.end wasn't intuitive. This has been corrected. Both ChangeEvent.start and ChangeEvent.end are the 0-based array indexes of the items being rendered in the viewport. (Previously Change.End was the array index + 1)
New features:
Added ability to put other elements inside of scroll (Need to wrap list itself in @ContentChild('container'))
Added ability to use any parent with scrollbar instead of this element (@Input() parentScroll)
Added ability to use horizontal scrollbars
New feature is support of elements with different heights EXPERIMENTAL
If scroll container resizes, the items will auto-refresh. Can be disabled if it causes any performance issues by setting [checkResizeInterval]="0"
useMarginInsteadOfTranslate flag. Defaults to false. This can affect performance (better/worse depending on your circumstances), and also creates a workaround for the transform+position:fixed browser bug.
'my-custom-component' must be a custom angular2 component, outside of this library.
Child component is not necessary if your item is simple enough. See below.
<virtual-scroll [items]="items" (vsUpdate)="viewPortItems = $event"><div *ngFor="let item of viewPortItems">{{item?.name}}</div></virtual-scroll>
API
Attribute
Type
Description
enableUnequalChildrenSizes
boolean
If you want to use the "unequal size" children feature. This is not perfect, but hopefully "close-enough" for most situations. Defaults to false.
scrollThrottlingTime
number
Milliseconds to delay refreshing viewport if user is scrolling quickly (for performance reasons). Default is 0.
useMarginInsteadOfTranslate
boolean
Defaults to false. Translate is faster in many scenarios because it can use GPU acceleration, but it can be slower if your scroll container or child elements don't use any transitions or opacity. More importantly, translate creates a new "containing block" which breaks position:fixed because it'll be relative to the transform rather than the window. If you're experiencing issues with position:fixed on your child elements, turn this flag on.
scrollbarWidth
number
If you want to override the auto-calculated scrollbar width. This is used to determine the dimensions of the viewable area when calculating the number of items to render.
scrollbarHeight
number
If you want to override the auto-calculated scrollbar height. This is used to determine the dimensions of the viewable area when calculating the number of items to render.
horizontal
boolean
Whether the scrollbars should be vertical or horizontal. Defaults to false.
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 (DEPRECATED)
number
The minimum width of the item template's cell. Use this if enableUnequalChildrenSizes isn't working well enough. (The actual rendered size of the first cell is used by default if not specified.)
childHeight (DEPRECATED)
number
The minimum height of the item template's cell. Use this if enableUnequalChildrenSizes isn't working well enough. (The actual rendered size of the first cell is used by default if not specified.)
bufferAmount (DEPRECATED)
number
The the number of elements to be rendered above & below the current container's viewport. Use this if enableUnequalChildrenSizes isn't working well enough. (defaults to enableUnequalChildrenSizes ? 5 : 0)
scrollAnimationTime
number
The time in milliseconds for the scroll animation to run for. Default value is 750. 0 will completely disable the tween/animation.
parentScroll
Element / Window
Element (or window), which will have scrollbar. This element must be one of the parents of virtual-scroll
compareItems
Function
Predicate of syntax (item1:any, item2:any)=>boolean which is used when items array is modified to determine which items have been changed (determines if cached child size measurements need to be refreshed or not for enableUnequalChildrenSizes). Defaults to === comparison.
start (DEPRECATED) / vsStart
Event
This event is fired every time start index changes and emits ChangeEvent which is of format: { start: number, end: number }
end (DEPRECATED) / vsEnd
Event
This event is fired every time end index changes and emits ChangeEvent which is of format: { start: number, end: number }
update (DEPRECATED) / vsUpdate
Event
This event is fired every time the start or end indexes change and emits the list of items which should be visible based on the current scroll position 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 (DEPRECATED) / vsChange
Event
This event is fired every time the start or end indexes change and emits ChangeEvent which is of format: { start: number, end: number }
viewPortIndices
{ arrayStartIndex: number, arrayEndIndex: number }
Allows querying the visible item indexes in the viewport on-demand.
Note: The Events without the "vs" prefix have been deprecated because they might conflict with native DOM events due to their "bubbling" nature. See https://github.com/angular/angular/issues/13997
An example is if an element inside emits a "change" event which bubbles up to the (change) handler of virtual-scroll. Using the vs prefix will prevent this bubbling conflict because there are currently no official DOM events prefixed with vs.
Getting view port items without events
If you are using AOT compilation (I hope you are) then with classic usage (listening to update event) you are required to create a public field viewPortItems in your component.
Here's a way to avoid it:
<virtual-scroll #scroll [items]="items"><my-custom-component *ngFor="let item of scroll.viewPortItems"></my-custom-component></virtual-scroll>
Additional elements in scroll
If you want to nest additional elements inside virtual scroll besides the list itself (e.g. search field), you need to wrap those elements in a tag with an angular selector name of #container.
<virtual-scroll [items]="items"
(vsUpdate)="viewPortItems = $event"><inputtype="search"><div #container><my-custom-component *ngFor="let item of viewPortItems"></my-custom-component></div></virtual-scroll>
Use parent scrollbar
If you want to use the scrollbar of a parent element, set parentScroll to a native DOM element.
If the parentScroll is a custom angular component (instead of a native HTML element such as DIV), Angular will wrap the #scrollingBlock variable in an ElementRef https://angular.io/api/core/ElementRef in which case you'll need to use the .nativeElement property to get to the underlying javascript DOM element reference.
Note: The parent element should have a width and height defined.
Use scrollbar of window
If you want to use the window's scrollbar, set parentScroll.
<virtual-scroll
#scroll
[items]="items"
[parentScroll]="scroll.window"><inputtype="search"><div #container><my-custom-component *ngFor="let item of scroll.viewPortItems"></my-custom-component></div></virtual-scroll>
Items with variable size
Items must have fixed height and width for this module to work perfectly. If not, set [enableUnequalChildrenSizes]="true".
(DEPRECATED): If enableUnequalChildrenSizes isn't working, you can set inputs childWidth and childHeight to their smallest possible values. You can also modify bufferAmount which causes extra items to be rendered on the edges of the scrolling area.
<virtual-scroll [items]="items"
[enableUnequalChildrenSizes]="true"
(vsUpdate)="viewPortItems = $event"><my-custom-component *ngFor="let item of viewPortItems"></my-custom-component></virtual-scroll>
or
<virtual-scroll [items]="items"
[enableUnequalChildrenSizes]="true"
(vsUpdate)="viewPortItems = $event"><my-custom-component *ngFor="let item of viewPortItems"></my-custom-component></virtual-scroll>
Loading in chunks
The event end is fired every time the scrollbar reaches the end of the list. You could use this to dynamically load more items at the end of the scroll. See below.
Note: This should now be auto-detected, however the 'refresh' method can still force it if neeeded.
This was implemented using the setInterval method which may cause minor performance issues. It shouldn't be noticeable, but can be disabled via [checkResizeInterval]="0"
Performance will be improved once "Resize Observer" (https://wicg.github.io/ResizeObserver/) is fully implemented.
Refresh method (DEPRECATED)
If virtual scroll is used within a dropdown or collapsible menu, virtual scroll needs to know when the container size changes. 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" (vsUpdate)="scrollList = $event">
<div *ngFor="let item of scrollList; let i = index"> {{i}}: {{item}} </div>
</virtual-scroll>
`
})
exportclassListComponent {
protected items = ['Item1', 'Item2', 'Item3'];
@ViewChild(VirtualScrollComponent)
privatevirtualScroll: VirtualScrollComponent;
// call this function after resize + animation endafterResize() {
this.virtualScroll.refresh();
}
}
Focus an item
You can use the scrollInto(item, alignToBeginning?, additionalOffset?, animationMilliseconds?, animationCompletedCallback?) api to scroll into an item in the list.
You can also use the scrollToIndex(index, alignToBeginning?, additionalOffset?, animationMilliseconds?, animationCompletedCallback?) api for the same purpose.
See below:
import { Component, ViewChild } from'@angular/core';
import { VirtualScrollComponent } from'angular2-virtual-scroll';
@Component({
selector: 'rj-list',
template: `
<virtual-scroll [items]="items" (vsUpdate)="scrollList = $event">
<div *ngFor="let item of scrollList; let i = index"> {{i}}: {{item}} </div>
</virtual-scroll>
`
})
exportclassListComponent {
protected items = ['Item1', 'Item2', 'Item3'];
@ViewChild(VirtualScrollComponent)
privatevirtualScroll: VirtualScrollComponent;
// call this function whenever you have to focus on second itemfocusOnAnItem() {
this.virtualScroll.items = this.items;
this.virtualScroll.scrollInto(items[1]);
}
}
Sorting Items
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:
The MIT License (MIT)
Copyright (c) 2016 Rinto Jose (rintoj)
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
Angular 4+ module for virtual -infinite- list. Supports multi-column
We found that angular2-virtual-scroll demonstrated a not healthy version release cadence and project activity because the last version was released a year ago.It has 1 open source maintainer collaborating on the project.
Last updated on 30 Aug 2018
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