多次发出 RxJS http 请求

Question

我已将open() 方法附加到我的ng-select 元素，以便使用来自外部API 的数据填充它。

我遇到的问题：如果我打开下拉列表 5 次然后我输入一个字母，它将向服务器发出 5 个 http 请求以填充数据。当我使用虚拟滚动功能时，同样的问题。

component.html

<ng-select [items]="filterValuesBuffer"
         [typeahead]="filterValuesInput$[filter.name]"
         [virtualScroll]="true"
         [multiple]="true"
         [closeOnSelect]="false"
         [loading]="filterValuesLoading[filter.name]"
         [(ngModel)]="filter.filter_values"
         (scrollToEnd)="onScrollToEnd(filter.name)"
         (open)="onFilterOpen(filter.name)"
         typeToSearchText="No values found"
         bindLabel="name">
</ng-select>

component.ts

filterValuesInput$: Map<string, Subject<string>[]> = new Map();

onFilterOpen(filterName) {
    this.filterValuesLoading[filterName] = true;

    this.getFilterValues(filterName, '')
      .subscribe(res => {
        this.afterKey = res.after_key;
        this.filterValuesLoading[filterName] = false;
        this.filterValuesBuffer = res.filter_values;
      });
}


getFilterValues(filterName, afterKey) {
    return this.filterValuesInput$[filterName].pipe(
      tap(() => this.filterValuesLoading[filterName] = true),
      startWith(''),
      distinctUntilChanged(),
      switchMap(term  => this.search.getFilterValues(filterName, '' + term, '' + afterKey)),
    )
}

如何防止这种行为？

编辑虚拟卷轴：

(scrollToEnd)="fetchMore(filter.name)"

fetchMore(filterName) {
    this.filterValuesLoading[filterName] = true;

    this.getFilterValues(filterName, this.afterKey)
      .subscribe(res => {
        this.afterKey = res.after_key;
        this.filterValuesLoading[filterName] = false;
        this.filterValuesBuffer = this.filterValuesBuffer.concat(res.filter_values);
      })
  }

Answer 1

尝试改变你的方法，如下所示：-

public openedFiterName = {};
onFilterOpen(filterName) {
    this.filterValuesLoading[filterName] = true;
    if(this.openedFilterName[filterName]) {
      this.filterValuesLoading[filterName] = false;
      this.filterValuesBuffer = this.openedFilterName[filterName];
      return;
    }
    this.getFilterValues(filterName, '')
      .subscribe(res => {
        this.openedFiterName[filterName] = res.filter_values; 
        this.afterKey = res.after_key;
        this.filterValuesLoading[filterName] = false;
        this.filterValuesBuffer = res.filter_values;
      });
}

fetchMore(filterName) {
    this.filterValuesLoading[filterName] = true;

    this.getFilterValues(filterName, this.afterKey)
      .pipe(take(1)).subscribe(res => {
        this.afterKey = res.after_key;
        this.filterValuesLoading[filterName] = false;
        this.filterValuesBuffer = this.filterValuesBuffer.concat(res.filter_values);
      })
  }

Answer 2

那是因为您从不退订 getFilterValues()。您应该绑定到(close) 并在那里取消订阅：

onFilterOpen(filterName) {
  this.subscription = this.getFilterValues(filterName, '')
    .subscribe(res => ...);
}

onFilterClose() {
  this.subscription.unsubscribe();
}

您最终可以使用takeWhile() 运算符。见Angular/RxJs When should I unsubscribe from `Subscription`