当我想阅读Ionic 4中新闻列表的详细信息时遇到问题

Question

我编写了一个代码，该代码显示新闻列表，并将其存储在firestore中，并且一切正常，但是当我单击“详细信息”按钮以显示新闻的详细信息时，它在控制台上显示错误，但未显示页面上的详细信息 错误消息： DetailsPage_Host.ngfactory.js？ [sm]：1错误TypeError：无法读取未定义的属性“ doc”     在DetailsPage.push ../ src / app / details / details.page.ts.DetailsPage.getEventDetail（details.page.ts：57）处     在DetailsPage.push ../ src / app / details / details.page.ts.DetailsPage.ngOnInit（details.page.ts：33）

我的代码： news.page.html

<ion-content padding>
        <ion-item *ngFor=" let count of news | async">
          <h5>{{count?.title}}
            <button  routerLink="/details/{{count.id}} ">details</button>

            <img src="{{count?.image}}">
          </h5>

        </ion-item>
</ion-content>

news.page.ts

import { Component, OnInit } from '@angular/core';
import {AngularFirestore, AngularFirestoreDocument} from 'angularfire2/firestore';
import {Observable} from 'rxjs';
import { Router } from '@angular/router';
import 'rxjs/add/operator/map';
export class NewsPage implements OnInit {
  news: Observable<any[]>;
constructor(public db: AngularFirestore, private router: Router) { }

  ngOnInit() {
this.news = this.db.collection('123').snapshotChanges().map(actions => {
      return actions.map(a => {
        const data = a.payload.doc.data();
        const id = a.payload.doc.id;
        return { id, ...data };
      });
    });
}
}

details.page.html

<ion-content padding >
    ${{currentEvent?.content}}


</ion-content>

details.page.ts

import { Component, OnInit, ɵConsole } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { AngularFirestore, AngularFirestoreDocument } from 'angularfire2/firestore';
import {Observable} from 'rxjs';

export class DetailsPage implements OnInit {
  public eventListRef: firebase.firestore.CollectionReference;
  public currentEvent: any = {};
constructor(private router: ActivatedRoute, private afs: AngularFirestore) {

   }

  ngOnInit() {
     const newsId: string = this.router.snapshot.paramMap.get('id');
     console.log(newsId);
     this.getEventDetail(newsId).get().then(eventSnapshot => { //the error message 33 is Here
      this.currentEvent = eventSnapshot.data();
      this.currentEvent.id = eventSnapshot.id;
      });
  }
getEventDetail(newsId: string): firebase.firestore.DocumentReference {
  return this.eventListRef.doc(newsId);**//the error message 57 is Here**
  }
}

我该如何解决这个问题？