A fast and lightweight virtual scrolling solution for Angular that supports single column lists, grid lists and view caching.
@lithiumjs/ngx-virtual-scroll requires @lithiumjs/angular. Both can be installed from npm:
npm install @lithiumjs/angular @lithiumjs/ngx-virtual-scroll
Import NgxVirtualScrollModule
. Use the li-virtual-scroll
component to declare a list with virtual scrolling:
<li-virtual-scroll [items]="items">
<!-- liVirtualItem defines a list item element for each item -->
<div *liVirtualItem="let item">
{{ item.name }}
</div>
</li-virtual-scroll>
Note: The li-virtual-scroll
element is a scroll container and needs to have a defined maximum size to ensure scrolling occurs.
The size of the list item elements can either be explicitly passed in, or calculated automatically. Width is only required for grid lists.
[!IMPORTANT] All item elements in the list must be the same size. For best results, make sure that the elements have a constant size that does not change. If the element size is not constant and changes based on the number of elements in the container (i.e. flexbox), then the item size must be declared explicitly.
If itemWidth
or itemHeight
are not explicitly passed, they will be automatically calculated by rendering the first item in the list and recording its size. This method only works for list items that have a constant size.
Use the itemWidth
and itemHeight
inputs to explicitly declare the width/height (in pixels) of the list item elements:
<li-virtual-scroll [items]="items" [itemWidth]="128" [itemHeight]="128">
<div *liVirtualItem="let item">
{{ item.name }}
</div>
</li-virtual-scroll>
[!NOTE] Include the element's margins as part of the width/height.
If the list being rendered is a grid list with multiple items per row, make sure to set gridList
to true
:
<li-virtual-scroll [items]="items" [gridList]="true">
<div *liVirtualItem="let item">
{{ item.name }}
</div>
</li-virtual-scroll>
Asynchronous view rendering can be used to improve scrolling responsiveness for items with complex views. When enabled, a placeholder element will be temporarily be shown while the item is rendered asynchronously. The placeholder element can be customized using the liVirtualPlaceholder
directive:
<li-virtual-scroll [items]="items" [asyncRendering]="true">
<!-- Items contain complex components: -->
<div *liVirtualItem="let item">
{{ item.name }}
<app-complex-component>...</app-complex-component>
</div>
<!-- Placeholder only prints the item name: -->
<div *liVirtualPlaceholder="let item">
{{ item.name }}
</div>
</li-virtual-scroll>
Note that the placeholder should be lightweight so that it can be rendered quickly.
View caching can be enabled to improve scrolling performance by caching views that are not being rendered for later re-use. View caching can be toggled on or off, or enabled with a maximum cache size (recommended for very large lists or complex views, as these could cause high memory usage):
<!-- Up to 256 views will be cached -->
<li-virtual-scroll [items]="items" [viewCache]="256">
<div *liVirtualItem="let item">
{{ item.name }}
</div>
</li-virtual-scroll>
The scroll debounce controls how often the virtual scroll should respond to scroll position changes. The default is 50 milliseconds.
<!-- Virtual scroll will render on scroll changes every 100ms -->
<li-virtual-scroll [items]="items" [scrollDebounceMs]="100">
<div *liVirtualItem="let item">
{{ item.name }}
</div>
</li-virtual-scroll>
Increasing the scroll buffer length will render more items outside of the viewport, which can reduce view pop-in when scrolling quickly. The buffer length is expressed in multiples of the list container's client height:
<li-virtual-scroll [items]="items" [bufferLength]="3">
<div *liVirtualItem="let item">
{{ item.name }}
</div>
</li-virtual-scroll>
The default virtual scroll strategy can be overriden by providing a custom VirtualScrollStrategy
service implementation using the LI_VIRTUAL_SCROLL_STRATEGY
injection token:
@NgModule({
providers: [
{
provide: LI_VIRTUAL_SCROLL_STRATEGY,
useClass: AppFooVirtualScrollStrategy
}
]
})
export class AppFooModule {}
The default virtual scroll strategy can also be overriden using NgxVirtualScrollModule.withOptions
:
@NgModule({
imports: [
NgxVirtualScrollModule.withOptions({
scrollStrategy: AppFooVirtualScrollStrategy
})
]
})
export class AppModule {}
This can happen when your list element has an unlimited height. The li-virtual-scroll
component is a scroll container that needs a maximum height for virtual scrolling to work. You must apply a maximum height to the list element for virtual scrolling to work.
This usually happens when your list item elements do not have a constant size and you have not explicitly declared itemWidth
/itemHeight
.
If your list container uses a layout that dynamically resizes elements (i.e. flexbox), you must ensure that the items have a constant size for the automatic width/height calculation to work correctly. If this is not possible, you must instead explicitly declare the item size using the itemWidth
/itemHeight
inputs. See this section for more information.
This can happen when incorrect itemWidth
/itemHeight
values are given. Make sure that you have calculated the size of your elements correctly (this should also include margins). See this section for more information.
VirtualScroll
(li-virtual-scroll
)Component used to create a virtual scrolling container.
items
- The list of items to render.asyncRendering
- (Optional) Whether or not to enable asynchronous rendering of views, which loads in placeholder elements while rendering items. Defaults to false
.bufferLength
- (Optional) How much extra list content should be rendered, measured in multiples of the list container's client height. This helps improve scrolling responsiveness for fast scrolling. Defaults to 1
.eventCapture
- (Optional) Whether or not to use event capture mode for capturing scroll events from scrollContainer
. Defaults to false
.gridList
- (Optional) Whether or not the list is a grid list with multiple items per row. Defaults to false
.itemWidth
- (Optional) The width of each item being rendered, in pixels. Calculated automatically based on the width of the first item if not given.itemHeight
- (Optional) The height of each item being rendered, in pixels. Calculated automatically based on the height of the first item if not given.scrollDebounceMs
- (Optional) How often to respond to scroll position changes, in milliseconds. Defaults to 50
.trackBy
- (Optional) A TrackByFunction
used to compute the identity of items. Defaults to a function returning the item reference.viewCache
- (Optional) Whether views can be cached. Can be a boolean or a number representing the maximum number of views to cache at a given time. Defaults to false
.VirtualItem
([liVirtualItem]
)Structural directive used to render items inside a li-virtual-scroll
component.
VirtualPlaceholder
([liVirtualPlaceholder]
)Structural directive used to render placeholder elements inside a li-virtual-scroll
component.
NgxVirtualScrollModule
The Angular module for this library.
NgxVirtualScrollModule.Options
The options to configure the module with.
export interface Options {
scrollStrategy?: Type<VirtualScrollStrategy<unknown>>;
}
scrollStrategy
- The custom VirtualScrollStrategy
service implementation to use.NgxVirtualScrollModule.withOptions
Allows configuration of the module with custom options.
export class NgxVirtualScrollModule {
public static withOptions(
options: NgxVirtualScrollModule.Options
): ModuleWithProviders<NgxVirtualScrollModule>;
}
options
- The options to configure the module with.VirtualScrollStrategy
Interface for defining a custom virtual scroll strategy.
export interface VirtualScrollStrategy<T> {
destroyViewRef(
scrollState: VirtualScrollState<T>,
viewRef: EmbeddedViewRef<VirtualItem.ViewContext<T>>
): void;
destroyView(
scrollState: VirtualScrollState<T>,
view: VirtualScrollState.ViewInfo<T>
): void;
cacheView(
scrollState: VirtualScrollState<T>,
view: VirtualScrollState.ViewInfo<T>
): void;
renderViewForItem(
scrollState: VirtualScrollState<T>,
item: T,
globalIndex: number,
deferViewCreation?: boolean
): Observable<VirtualScrollState.ViewInfo<T>>;
unrenderView(
scrollState: VirtualScrollState<T>,
view: VirtualScrollState.ViewInfo<T>
): void;
purgeViewCache(scrollState: VirtualScrollState<T>): void;
}
DefaultVirtualScrollStrategy
The default VirtualScrollStrategy
service implementation.