Angular 6 String Interpolation 不使用 .subscribe() 内的值更新

Question

我有一个组件可以显示特定视频的标题和艺术家。当我在我的服务中调用 playNext() 时，它应该用新数据更新标题和艺术家。我做了一个 console.log，我可以验证订阅是否有效。每次调用 playNext() 时我都会得到一个更新的值，但是模板中的值没有更新。它只在第一次正确显示。我错过了什么吗？

这是我的组件代码

@Component({
  selector: 'ntv-now-playing',
  templateUrl: './now-playing.component.html',
  styleUrls: ['./now-playing.component.css']
})
export class NowPlayingComponent implements OnInit {
  nowPlaying: Observable<Video>;
  video: Video;
  constructor(private videoService: VideoPlayerService) { }

  ngOnInit() {
    this.nowPlaying = this.videoService.getNowPlaying();
    console.log('nowPlayingComponent');
    this.nowPlaying.subscribe(v => {
      this.video = v;
      console.log('nowPlaying:', this.video);
    });
  }
}

在我的服务中，我这样做:为了简洁起见，我删除了一些工作代码。

@Injectable()
export class VideoPlayerService {
  ...
  nowPlayingChanged = new Subject<Video>();
  ...
  private nowPlaying: Video;

  constructor(private db: AngularFirestore) {}
  ...

  getNowPlaying(): Observable<Video> {
    return this.nowPlayingChanged;
  }

  playNext(vIdx: number, lastIdx: number) {
    console.log('playNext()');
    this.nowPlaying = this.videos[vIdx];
    console.log(this.nowPlaying);
    this.nowPlayingChanged.next(this.nowPlaying);

  }
}

我的模板有这个:

<div class="video-info">
  <h5>{{video?.title}} - {{video?.artist}}</h5>
  <div>Channel Info&nbsp;&nbsp;<button class="btn btn-secondary">+ Subscribe</button></div>
</div>

每次调用 playNext() 时，组件订阅函数内的控制台日志都会显示这一点，所以我知道它正在正确更改，只是 UI 没有更新。

nowPlaying: {artist: "Alan Walker", duration: "3:32", startTime: Timestamp, thumbnailPath: "https://i.ytimg.com/vi/60ItHLz5WEA/hqdefault.jpg", title: "Faded", …}
nowPlaying: {artist: "Deadmau5", duration: "3:37", thumbnailPath: "https://i.ytimg.com/vi/UG3sfZKtCQI/hqdefault.jpg", title: "Monophobia", videoId: "UG3sfZKtCQI"}
nowPlaying: {artist: "Steve Aoki", duration: "59:55", thumbnailPath: "https://i.ytimg.com/vi/sR3w1P2nPH8/hqdefault.jpg", title: "Tomorrowland", videoId: "x9ZkC3OgI78"}
video-player.component.ts:69 

任何建议表示赞赏。我见过一些人使用 ngZone，但我听说这可能不是最好的方法，老实说这感觉有点 hacky。

Answer 1

可能这可以帮助:

@Component({
  selector: 'ntv-now-playing',
  templateUrl: './now-playing.component.html',
  styleUrls: ['./now-playing.component.css']
})
export class NowPlayingComponent implements OnInit {
  nowPlaying: Observable<Video>;
  video: Video;
  constructor(
    private videoService: VideoPlayerService,
    private changeDetector: ChangeDetectorRef
   ) { }

  ngOnInit() {
    this.nowPlaying = this.videoService.getNowPlaying();
    console.log('nowPlayingComponent');
    this.nowPlaying.subscribe(v => {
      this.video = v;
      this.changeDetector.detectChanges();
      console.log('nowPlaying:', this.video);
    });
  }
}