Desired outcome: call method sendNotification() when a component first gets into view as the user scrolls down.

My solution (code follows):

1. Listen for window:scroll as learned reading this question
2. Doing some calculations to check if the element is in view
3. Calling the method

export class GalleryComponent implements OnInit {
  hintSent: boolean = false

  constructor(private _elementRef: ElementRef, private _notificationService: NotificationsService) { }

  ngOnInit(): void {
  }

  @HostListener("window:scroll", [])
  onWindowScroll() {
    let elem: Element = this._elementRef.nativeElement
    let top = elem.getBoundingClientRect().top
    let height = elem.getBoundingClientRect().height
    let noti = new Notification('Tocca le immagini','Scopri altri dettagli sul nostro prodotto interagendo con le immagini')
    if(top - window.innerHeight < 0 && top   height - window.innerHeight > 0)
      //this component is in view
      if(this.hintSent == false)
        this._notificationService.sendNotification(noti)
        this.hintSent = true
  }
}

The problem with my solution:

While angular renders the page the layout shift triggers the scroll event and calls the desired method before time since the user has not scrolled down yet. Now I could start listening for the scroll after a timeout or after the document.loaded event but is there a better solution?

CodePudding user response：

You should add your listener once you know your element has been created in view, hence in the lifecycle hook ngAfterViewInit. Your nativeelement may be wrong or not even exist before that.