import { TemplateRef, ViewContainerRef } from '@angular/core';
import { Observable } from 'rxjs';
/**
 * @internal
 */
export interface _RxVirtualViewContent {
    viewContainerRef: ViewContainerRef;
    templateRef: TemplateRef<unknown>;
}
/**
 * @internal
 */
export interface _RxVirtualViewPlaceholder {
    templateRef: TemplateRef<unknown>;
}
/**
 * @internal
 */
export declare abstract class _RxVirtualViewObserver {
    abstract observeElementVisibility(virtualView: HTMLElement): Observable<boolean>;
    abstract observeElementSize(element: Element, options?: ResizeObserverOptions): Observable<ResizeObserverEntry>;
}
/**
 * @internal
 */
export declare abstract class _RxVirtualView {
    abstract registerContent(content: _RxVirtualViewContent): void;
    abstract registerPlaceholder(placeholder: _RxVirtualViewPlaceholder): void;
}