Angular 8在导航后未更改标题

import { Component, OnInit } from '@angular/core';
import { Router, NavigationEnd } from '@angular/router';

@Component({
  selector: 'app-root',
  template: `
    <router-outlet></router-outlet>
  `,
})
export class AppComponent implements OnInit {
  constructor(private router: Router) {}

  ngOnInit() {
    this.router.events.subscribe(event => {
      if (event instanceof NavigationEnd) {
        const currentRoute = this.router.routerState.snapshot.root;
        const title = this.getPageTitle(currentRoute);
        this.updatePageTitle(title);
      }
    });
  }

  getPageTitle(route: any): string {
    let title = '';
    while (route.firstChild) {
      route = route.firstChild;
      if (route.data && route.data.title) {
        title = route.data.title;
      }
    }
    return title;
  }

  updatePageTitle(title: string) {
    document.title = title;
  }
}