如何基于另一个Observable重置RXJS扫描运算符

问题描述

我有一个在呈现虚拟列表中的最后一项时触发onScrollEnd事件的组件.此事件将发出一个新的API请求，以获取下一页，并使用scan运算符将它们与以前的结果合并.

此组件还具有一个触发onSearch事件的搜索字段.

触发搜索事件时，如何从scan运算符清除以前的累积结果?还是我需要在这里重构逻辑?

const loading$ = new BehaviorSubject(false);
const offset$ = new BehaviorSubject(0);
const search$ = new BehaviorSubject(null);

const options$: Observable<any[]> = merge(offset$, search$).pipe(
  // 1. Start the loading indicator.
  tap(() => loading$.next(true)),
  // 2. Fetch new items based on the offset.
  switchMap(([offset, searchterm]) => userService.getUsers(offset, searchterm)),
  // 3. Stop the loading indicator.
  tap(() => loading$.next(false)),
  // 4. Complete the Observable when there is no 'next' link.
  takeWhile((response) => response.links.next),
  // 5. Map the response.
  map(({ data }) =>
    data.map((user) => ({
      label: user.name,
      value: user.id
    }))
  ),
  // 6. Accumulate the new options with the previous options.
  scan((acc, curr) => {
    // TODO: Dont merge on search$.next
    return [...acc, ...curr]);
  }
);

// Fetch next page
onScrollEnd: (offset: number) => offset$.next(offset);
// Fetch search results
onSearch: (term) => {
  search$.next(term);
};

解决方案

找到了一个可行的解决方案:我在scan运算符之前使用withLatestFrom检查当前偏移量，并根据需要根据该值重置累加器./p>

Stackblitz演示

I have a component which triggers an onScrollEnd event when the last item in a virtual list is rendered. This event will do a new API request to fetch the next page and merge them with the previous results using the scan operator.

This component also has a search field which triggers an onSearch event.

How do I clear the previous accumulated results from the scan operator when a search event is triggered? Or do I need to refactor my logic here?

const loading$ = new BehaviorSubject(false);
const offset$ = new BehaviorSubject(0);
const search$ = new BehaviorSubject(null);

const options$: Observable<any[]> = merge(offset$, search$).pipe(
  // 1. Start the loading indicator.
  tap(() => loading$.next(true)),
  // 2. Fetch new items based on the offset.
  switchMap(([offset, searchterm]) => userService.getUsers(offset, searchterm)),
  // 3. Stop the loading indicator.
  tap(() => loading$.next(false)),
  // 4. Complete the Observable when there is no 'next' link.
  takeWhile((response) => response.links.next),
  // 5. Map the response.
  map(({ data }) =>
    data.map((user) => ({
      label: user.name,
      value: user.id
    }))
  ),
  // 6. Accumulate the new options with the previous options.
  scan((acc, curr) => {
    // TODO: Dont merge on search$.next
    return [...acc, ...curr]);
  }
);

// Fetch next page
onScrollEnd: (offset: number) => offset$.next(offset);
// Fetch search results
onSearch: (term) => {
  search$.next(term);
};

解决方案

Found a working solution: I check the current offset by using withLatestFrom before the scan operator and reset the accumulator if needed based on this value.

Stackblitz demo

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