Javascript Angular6轮询不返回数据

我有一个Angular应用程序，尝试每隔几秒钟检查外部数据服务的更改，并更新视图

我尝试从rxjs实现轮询，但无法访问对象，相反，轮询函数似乎不起作用，但假设这是因为返回的对象不可访问

app.component.ts

export class AppComponent {
  polledItems: Observable<Item>;
  items : Item[] = [];
  title = 'site';
  landing = true;
  tap = false;
  url:string;
  Math: any;

  getScreen(randomCode) {
    const items$: Observable<any> = this.dataService.get_screen(randomCode)
      .pipe(tap( () => {
      this.landing = false; 
      this.Math = Math
     }
    ));

    const polledItems$ = timer(0, 1000)
    .pipe(( () => items$))
    console.log(this.polledItems);
    console.log(items$);
  }

---

假设您需要一组项目，您可以使用类似的东西

// dont subscribe here but use the 
// observable directly or with async pipe
private readonly items$: Observable<Item[]> = this.dataService.get_screen(randomCode)
    // do your side effects in rxjs tap()
    // better move this to your polledItems$
    // observable after the switchMap
   .pipe(
     tap( () => { return {this.landing = false; this.Math = Math}; })
    );

// get new items periodicly
public readonly polledItems$ = timer(0, 1000)
   .pipe(
      concatMap( () => items$),
      tap( items => console.log(items))
   )

模板：

// pipe your observable through async and THEN access the member
<ng-container *ngFor="let polledItem of (polledItems$ | async)>
    <h3 class="item-name text-white">{{polledItem.item_name}}</h3>
</ng-container>

看看：

如果您正在等待的不是阵列而是单个，则不需要ngFor，而是访问您的项目名称，如：

<h3 class="item-name text-white">{{(polledItems$ | async).item_name}}</h3>

---

我已经更新了帖子，但是基本上收到了和以前一样的数据，我只是可以观察到{..在我的控制台中。抱歉，我错过了第二个可观察对象中的concatMap。allso将可观察对象添加为类成员不需要重新创建它们。polledItems应为可观察类型。控制台日志需要位于可观察对象内，否则数据到达时不会记录。导出类AppComponent{polledItems:Observable；..private readonly items$：Observable=..public readonly polledItems$=timer0，1000.pipe concatMap=>this.items$，点击polledItems=>console.logpolledItems；}

// pipe your observable through async and THEN access the member
<ng-container *ngFor="let polledItem of (polledItems$ | async)>
    <h3 class="item-name text-white">{{polledItem.item_name}}</h3>
</ng-container>

<h3 class="item-name text-white">{{(polledItems$ | async).item_name}}</h3>