Angular 我的新闻提要don'；单击链接两次后才会显示

我正在开发这个小应用程序，它可以显示Firebase数据库中的新闻，但当我突然转到新闻链接或提要时，它不会显示，直到我在导航栏中单击两次链接，我正在使用angular，请帮助

这是我的服务文件：

import {Injectable} from '@angular/core';
import {AngularFireDatabase} from 'angularfire2/database';


@Injectable({
  providedIn: 'root'
})
export class NewsService {
  list: any[];

  constructor(db: AngularFireDatabase) {
    db.list('/actu').valueChanges()
      .subscribe(list => {
        this.list = list;
        console.log(this.list);
      });
  }

  Getlist() {
    return this.list;
  }

  getnews(title: string) {
    return this.list.find(value => value.titre === title);
  }
}

---

最好不要在构造函数中完成调用，也不要订阅（）服务中的可观察对象。相反，在显示此数据的组件中返回并订阅它

新闻服务.ts

import {Injectable} from '@angular/core';
import {AngularFireDatabase} from 'angularfire2/database';


@Injectable({
  providedIn: 'root'
})
export class NewsService {

  constructor(private db: AngularFireDatabase) {
  }

  Getlist() {
    return db.list('/actu').valueChanges();
  }
}

import { NewsService } from './news.service';
//component declarations and imports ...
export class NewsComponent implements OnInit {
   list: any[];
   constructor(private newsService: NewsService){}

   buttonClicked(){
      this.newsService.Getlist().subscribe(list => {
        this.list = list;
        console.log(this.list);
      })
   }
}

news.component.ts

import {Injectable} from '@angular/core';
import {AngularFireDatabase} from 'angularfire2/database';


@Injectable({
  providedIn: 'root'
})
export class NewsService {

  constructor(private db: AngularFireDatabase) {
  }

  Getlist() {
    return db.list('/actu').valueChanges();
  }
}

import { NewsService } from './news.service';
//component declarations and imports ...
export class NewsComponent implements OnInit {
   list: any[];
   constructor(private newsService: NewsService){}

   buttonClicked(){
      this.newsService.Getlist().subscribe(list => {
        this.list = list;
        console.log(this.list);
      })
   }
}

news.component.html

<a (click)="buttonClicked()">nav button</a>

nav按钮

当然，这不是服务、组件或html中的唯一代码。。只是代码突出了您的问题