javascript - 在 angular2 中使用与其他组件的可观察对话，没有收到即将到来的价值

Question

我有这个结构

app/
  --pages/
  ----pages.component.ts 
  --channel/
  ----shared/
  ------assignPlaylist.modal.ts

在 pages.component.ts 中，我有一个名为 playlist 的变量

export class PagesComponent {

  @Input() platform: Platform;

  @Output() onPlaylistsChange: EventEmitter<Playlists>;

  currentPageName: string;

  currentPage: Page;

  pages: Array<Page>;

  playlists: Playlists;
}

在 assignPlaylist.modal.ts 中，我创建了一个 http post 方法，它返回一个新的播放列表，我需要使用返回的播放列表来替换 pages.component.ts 中的播放列表

this.apiService.addPlaylistToPage(playlistId, stDate, etDate, this.apiService.getGlobalRegion(), callback)
          .subscribe(
            data => {
              if (this.apiService.g_platform == 'DESKTOP') {
                this.apiService.getPlaylist(this.apiService.getCurrentPage(), 'true' )
                .subscribe(
                  res => {                          this.pagesService.setCurrentPlaylists(res.playlists);
                  }
                );
            } else {
              this.apiService.getPlaylist(this.apiService.getCurrentPage(), 'false' )
              .subscribe(
                res => {           this.pagesService.setCurrentPlaylists(res.playlists);
                }
              );
            }
            }
          );

这是res，返回结果

这是播放列表的构造函数

export class Playlists {
  headerPlaylists: Array<Playlist>;
  bodyPlaylists: Array<Playlist>;
  wholePlaylists: Array<Playlist>;
}

-----更新--------------------- 正如答案中提到的，我做了以下更改.

@Injectable()
export class PagesService {

  private currentPlaylists: Subject<Playlists> = new BehaviorSubject<Playlists>(new Playlists());
  getCurrentPlaylists() {
    return this.currentPlaylists.asObservable();
  }

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

控制台显示“我在这里”，

我写在我的 pages.component.ts

 constructor(private service: PagesService, private playlistService: PlaylistService) {
    this.pages = [];
    this.currentPage = new Page();
    this.service.setCurrentPage(this.currentPage);
    this.playlists = new Playlists();
    this.onPlaylistsChange = new EventEmitter<Playlists>();
    this.service.getCurrentPlaylists().subscribe((playlists) => {
      console.log(playlists, 'new playlists coming');
      this.playlists = playlists;
    }, error => {
      console.log(error);
    });
  }

但是，我没有看到“新播放列表来了”的消息，是我用错了吗？

新更新：我检查了this.playlists，它的观察者是0，为什么？

Answer 1

一定要创建一个 PlaylistService 来公开 PagesComponent 可以订阅的 observable。

import { Injectable} from '@angular/core';
import { Subject,BehaviorSubject } from 'rxjs';
import {Playlists} from 'channel' /** Assumes this is where you have defined your Playlists interface **/

@Injectable()
export class PlaylistService {
    private _currentPlaylists$: Subject<Playlists> = new BehaviorSubject<Playlists>(null);
    constructor() {}

    currentPlaylists() {
      return this._currentPlaylists$.asObservable();
    }

    setCurrentPlaylists(playlists:Playlists){
      this._currentPlaylists$.next(playlists);
    }
}

然后将此服务导入您的页面组件并订阅播放列表，如下所示：-

this.playlistService.currentPlaylists().subscribe((playlists) => {
      this.playlists = playlists;
},error => {
    console.log(error);
});`

请记住，您还必须将此服务导入您的 assignPlaylistModal 并像这样使用它：-

   this.apiService.addPlaylistToPage(playlistId, stDate, etDate, this.apiService.getGlobalRegion(), callback)
      .subscribe(
        data => {
          if (this.apiService.g_platform == 'DESKTOP') {
            this.apiService.getPlaylist(this.apiService.getCurrentPage(), 'true' )
            .subscribe(
              res => {
                this.playListService.setCurrentPlaylists(res);
              }
            );
        } else {
          this.apiService.getPlaylist(this.apiService.getCurrentPage(), 'false' )
          .subscribe(
            res => {
              this.playListService.setCurrentPlaylists(res);
            }
          );
        }
        }
      ); 

请阅读有关可观察对象的更多信息，以了解为什么在此处使用 BehaviourSubject。http://reactivex.io/documentation/observable.html