/
scroll-dispatcher.ts
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/
scroll-dispatcher.ts
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/**
* @license
* Copyright Google LLC All Rights Reserved.
*
* Use of this source code is governed by an MIT-style license that can be
* found in the LICENSE file at https://angular.io/license
*/
import {Platform} from '@angular/cdk/platform';
import {
ElementRef,
Injectable,
NgZone,
OnDestroy,
Optional,
SkipSelf,
} from '@angular/core';
import {fromEvent, of as observableOf, Subject, Subscription, Observable, Observer} from 'rxjs';
import {auditTime, filter} from 'rxjs/operators';
import {CdkScrollable} from './scrollable';
/** Time in ms to throttle the scrolling events by default. */
export const DEFAULT_SCROLL_TIME = 20;
/**
* Service contained all registered Scrollable references and emits an event when any one of the
* Scrollable references emit a scrolled event.
*/
@Injectable({providedIn: 'root'})
export class ScrollDispatcher implements OnDestroy {
constructor(private _ngZone: NgZone, private _platform: Platform) { }
/** Subject for notifying that a registered scrollable reference element has been scrolled. */
private _scrolled = new Subject<CdkScrollable|void>();
/** Keeps track of the global `scroll` and `resize` subscriptions. */
_globalSubscription: Subscription | null = null;
/** Keeps track of the amount of subscriptions to `scrolled`. Used for cleaning up afterwards. */
private _scrolledCount = 0;
/**
* Map of all the scrollable references that are registered with the service and their
* scroll event subscriptions.
*/
scrollContainers: Map<CdkScrollable, Subscription> = new Map();
/**
* Registers a scrollable instance with the service and listens for its scrolled events. When the
* scrollable is scrolled, the service emits the event to its scrolled observable.
* @param scrollable Scrollable instance to be registered.
*/
register(scrollable: CdkScrollable): void {
if (!this.scrollContainers.has(scrollable)) {
this.scrollContainers.set(scrollable, scrollable.elementScrolled()
.subscribe(() => this._scrolled.next(scrollable)));
}
}
/**
* Deregisters a Scrollable reference and unsubscribes from its scroll event observable.
* @param scrollable Scrollable instance to be deregistered.
*/
deregister(scrollable: CdkScrollable): void {
const scrollableReference = this.scrollContainers.get(scrollable);
if (scrollableReference) {
scrollableReference.unsubscribe();
this.scrollContainers.delete(scrollable);
}
}
/**
* Returns an observable that emits an event whenever any of the registered Scrollable
* references (or window, document, or body) fire a scrolled event. Can provide a time in ms
* to override the default "throttle" time.
*
* **Note:** in order to avoid hitting change detection for every scroll event,
* all of the events emitted from this stream will be run outside the Angular zone.
* If you need to update any data bindings as a result of a scroll event, you have
* to run the callback using `NgZone.run`.
*/
scrolled(auditTimeInMs: number = DEFAULT_SCROLL_TIME): Observable<CdkScrollable|void> {
if (!this._platform.isBrowser) {
return observableOf<void>();
}
return new Observable((observer: Observer<CdkScrollable|void>) => {
if (!this._globalSubscription) {
this._addGlobalListener();
}
// In the case of a 0ms delay, use an observable without auditTime
// since it does add a perceptible delay in processing overhead.
const subscription = auditTimeInMs > 0 ?
this._scrolled.pipe(auditTime(auditTimeInMs)).subscribe(observer) :
this._scrolled.subscribe(observer);
this._scrolledCount++;
return () => {
subscription.unsubscribe();
this._scrolledCount--;
if (!this._scrolledCount) {
this._removeGlobalListener();
}
};
});
}
ngOnDestroy() {
this._removeGlobalListener();
this.scrollContainers.forEach((_, container) => this.deregister(container));
this._scrolled.complete();
}
/**
* Returns an observable that emits whenever any of the
* scrollable ancestors of an element are scrolled.
* @param elementRef Element whose ancestors to listen for.
* @param auditTimeInMs Time to throttle the scroll events.
*/
ancestorScrolled(elementRef: ElementRef, auditTimeInMs?: number): Observable<CdkScrollable|void> {
const ancestors = this.getAncestorScrollContainers(elementRef);
return this.scrolled(auditTimeInMs).pipe(filter(target => {
return !target || ancestors.indexOf(target) > -1;
}));
}
/** Returns all registered Scrollables that contain the provided element. */
getAncestorScrollContainers(elementRef: ElementRef): CdkScrollable[] {
const scrollingContainers: CdkScrollable[] = [];
this.scrollContainers.forEach((_subscription: Subscription, scrollable: CdkScrollable) => {
if (this._scrollableContainsElement(scrollable, elementRef)) {
scrollingContainers.push(scrollable);
}
});
return scrollingContainers;
}
/** Returns true if the element is contained within the provided Scrollable. */
private _scrollableContainsElement(scrollable: CdkScrollable, elementRef: ElementRef): boolean {
let element: HTMLElement | null = elementRef.nativeElement;
let scrollableElement = scrollable.getElementRef().nativeElement;
// Traverse through the element parents until we reach null, checking if any of the elements
// are the scrollable's element.
do {
if (element == scrollableElement) { return true; }
} while (element = element!.parentElement);
return false;
}
/** Sets up the global scroll listeners. */
private _addGlobalListener() {
this._globalSubscription = this._ngZone.runOutsideAngular(() => {
return fromEvent(window.document, 'scroll').subscribe(() => this._scrolled.next());
});
}
/** Cleans up the global scroll listener. */
private _removeGlobalListener() {
if (this._globalSubscription) {
this._globalSubscription.unsubscribe();
this._globalSubscription = null;
}
}
}
/** @docs-private @deprecated @breaking-change 8.0.0 */
export function SCROLL_DISPATCHER_PROVIDER_FACTORY(
parentDispatcher: ScrollDispatcher, ngZone: NgZone, platform: Platform) {
return parentDispatcher || new ScrollDispatcher(ngZone, platform);
}
/** @docs-private @deprecated @breaking-change 8.0.0 */
export const SCROLL_DISPATCHER_PROVIDER = {
// If there is already a ScrollDispatcher available, use that. Otherwise, provide a new one.
provide: ScrollDispatcher,
deps: [[new Optional(), new SkipSelf(), ScrollDispatcher], NgZone, Platform],
useFactory: SCROLL_DISPATCHER_PROVIDER_FACTORY
};