switchMap，startWith，switchMap？

Question

this.timeline$ = app.selectedSites$.pipe(
  debounceTime(2000),
  switchMap(sites => this.interval.pipe(map(() => sites))),
  switchMap(sites =>
    analytics.timeline(sites, 60 * 24 * 2, 60).pipe(
      map(result => {
        const colors = getColors(result);

        return {
          labels: result[0].datapoints.map(pair => pair[1]),
          datasets: (<any[]>result).map((target, i) => ({
            pointRadius: 0,
            label: target.target,
            fill: false,
            backgroundColor: colors[i % colors.length],
            borderColor: colors[i % colors.length],
            data: target.datapoints.map(pair => ({
              y: pair[0],
              x: pair[1]
            }))
          }))
        };
      })
    )
  ),
  share()
);

我希望this.timeline$在选择first $ changes (取消)时发出null，并开始为新列表加载第一个数据，然后每30秒刷新一次，但在刷新之前不发出null .我不知道该把startWith(空)放哪儿.

Answer 1

换句话说，您需要两个流:首先是所有运算符，另一个是发出null的流。

const source$ = app.selectedSites$
  .pipe(
    debounceTime(2000)
  )


this.timeline$ = source$.pipe(
  switchMap(sites => this.interval.pipe(map(() => sites))),
  switchMap(sites =>
    analytics.timeline(sites, 60 * 24 * 2, 60)
      .pipe(
        map(result => getField(result))
      )
  ),
  merge(source$.pipe(mapTo(null))),
  share()
);

Answer 2

这就是我最后的结果..。

toChartData(selector: (sites: string[]) => Observable<any>) {
    return this.app.selectedSites$.pipe(
      debounceTime(2000),
      switchMap(sites =>
        this.interval.pipe(
          switchMap(() => selector(sites)),
          startWith(null)
        )
      ),
      share()
    );
}