import { Observable } from 'rxjs';
import * as i0 from "@angular/core";
/**
 * The visibilitychange event may not be trigger after a long period in background.
 * A setTimeout system is used in background to ensure the visibility event.
 */
export declare class AppVisibilityService {
    private timer;
    private visibility;
    private backgroundTimeout;
    private _hidden;
    get visible(): boolean;
    constructor(timer: number);
    get visibility$(): Observable<boolean>;
    private startBackgroundTimeout;
    private clearBackgroundTimeout;
    static ɵfac: i0.ɵɵFactoryDeclaration<AppVisibilityService, never>;
    static ɵprov: i0.ɵɵInjectableDeclaration<AppVisibilityService>;
}