可觀察到的在angular2中沒有收到下一個值

Question

為了在angular2不同組件之間傳遞值，我使用了注入到不同組件中的不同服務。

在我的PagesService組件中，我定義了一個行為主題並希望傳遞一個值。

import { Injectable } from '@angular/core';
import { ApiService } from '../../apiService/api.service';
import { Playlists } from '../shared/playlists.model';
import { Subject, BehaviorSubject } from 'rxjs/Rx';


@Injectable()
export class PagesService {

  private currentPlaylists: Subject<Playlists> = new BehaviorSubject<Playlists>(new Playlists());

  constructor(private service: ApiService) {

  }

  getCurrentPlaylists() {
    return this.currentPlaylists.asObservable();
  }

  setCurrentPlaylists(playlists: Playlists) {
    console.log(playlists, 'i am here');
    this.currentPlaylists.next(playlists);
  }
}

我需要將播放列表傳遞給名為PagesComponent的組件

 import { Component, OnInit, Input, Output, OnChanges, EventEmitter, Injectable } from '@angular/core';
    import { Http, Response } from '@angular/http';
    import { Observable } from 'rxjs/Observable';
    import { PagesService } from './shared/pages.service';
    import { Subject,BehaviorSubject } from 'rxjs/Rx';
@Component({
  selector: 'pages',
  styleUrls: ['app/pages/pages.css'],
  templateUrl: 'app/pages/pages.html',
  providers: [PagesService]
})
            export class PagesComponent {

              playlists: Playlists;

              constructor(private service: PagesService, private playlistService: PlaylistService) {
                this.playlists = new Playlists();
                this.service.getCurrentPlaylists().subscribe((playlists) => {
                  console.log(playlists, 'new playlists coming');
                  this.playlists = playlists;
                }, error => {
                  console.log(error);
                });
              }
        }

這是控制台輸出：

更新播放列表后，您可以看到要傳遞到控制台的實際播放列表，但我沒有在頁面組件中收到它，

有任何想法嗎？

謝謝

Answer 1

哪個組件正在調用setCurrentPlaylists() ？

除PagesComponent之外的其他組件很可能正在調用此方法，而該其他組件可能具有providers: [PagesService]在其元數據中定義了providers: [PagesService] 。 這將導致創建兩個PagesService實例–一個由PagesComponent提供（和注入）的實例，另一個由某些其他組件提供（和注入）的實例。