Angular路由错误消息 - router-outlet is not a known element

/**
 * @description
 *
 * Acts as a placeholder that Angular dynamically fills based on the current router state.
 *
 * Each outlet can have a unique name, determined by the optional `name` attribute.
 * The name cannot be set or changed dynamically. If not set, default value is "primary".
 *
 * ```
 * <router-outlet></router-outlet>
 * <router-outlet name='left'></router-outlet>
 * <router-outlet name='right'></router-outlet>
 * ```
 *
 * A router outlet emits an activate event when a new component is instantiated,
 * and a deactivate event when a component is destroyed.
 *
 * ```
 * <router-outlet
 *   (activate)='onActivate($event)'
 *   (deactivate)='onDeactivate($event)'></router-outlet>
 * ```
 * @ngModule RouterModule
 *
 * @publicApi
 */
export declare class RouterOutlet implements OnDestroy, OnInit {
    private parentContexts;
    private location;
    private resolver;
    private changeDetector;
    private activated;
    private _activatedRoute;
    private name;
    activateEvents: EventEmitter<any>;
    deactivateEvents: EventEmitter<any>;
    constructor(parentContexts: ChildrenOutletContexts, location: ViewContainerRef, resolver: ComponentFactoryResolver, name: string, changeDetector: ChangeDetectorRef);
    ngOnDestroy(): void;
    ngOnInit(): void;
    get isActivated(): boolean;
    get component(): Object;
    get activatedRoute(): ActivatedRoute;
    get activatedRouteData(): Data;
    /**
     * Called when the `RouteReuseStrategy` instructs to detach the subtree
     */
    detach(): ComponentRef<any>;
    /**
     * Called when the `RouteReuseStrategy` instructs to re-attach a previously detached subtree
     */
    attach(ref: ComponentRef<any>, activatedRoute: ActivatedRoute): void;
    deactivate(): void;
    activateWith(activatedRoute: ActivatedRoute, resolver: ComponentFactoryResolver | null): void;
    static ɵfac: ɵngcc0.ɵɵFactoryDef<RouterOutlet, [null, null, null, { attribute: "name"; }, null]>;
    static ɵdir: ɵngcc0.ɵɵDirectiveDefWithMeta<RouterOutlet, "router-outlet", ["outlet"], {}, { "activateEvents": "activate"; "deactivateEvents": "deactivate"; }, never>;
}