import { AfterViewInit, ElementRef, EventEmitter, OnDestroy, OnInit } from '@angular/core';
export declare class ObserveVisibilityDirective implements OnDestroy, OnInit, AfterViewInit {
    private _element;
    threshold: number;
    visibilityChange: EventEmitter<boolean>;
    visible: boolean;
    private _observer;
    constructor(_element: ElementRef);
    ngOnInit(): void;
    ngAfterViewInit(): void;
    ngOnDestroy(): void;
    private _createObserver;
    private _startObservingElements;
}
